This is one of 126 contributing papers to the World Commission on Dams. It reflects solely the views of its authors. The views, conclusions, and recommendations are not intended to represent the views of the Commission. The views of the Commission are laid out in the Commission's final report "Dams and Development: A New Framework for Decision-Making".

Contributing Paper

Molluscan Biodiversity and the Impact of Large Dams

Mary Seddon National Museum and Galleries of Wales, UK

Co-chair IUCN Mollusc Specialist Group

Prepared for Thematic Review II.1: Dams, ecosystem functions and environmental restoration

For further information see http://www.dams.org/

Report to IUCN Species Survival Commission

Molluscan Biodiversity

and the impact of large dams

Prepared by Dr Mary.B. Seddon

National Museum & Galleries of Wales, Cardiff, UK

Co-Chair of IUCN SSC Mollusc Specialist Group

The following have provided data and helpful comments on the

status of the freshwater faunas.

This includes access to unpublished manuscripts which are in press

or in preparation.

Arthur Bogan (North Carolina State Museum), Philippe Bouchet

(Museum d’Histoire Naturelles, Paris), David Brown (Natural

History Museum, London), Kevin Cumings (Illinois Natural History

Survey), Olivier Gargimony (Museum d’Histoire Naturelles, Paris),

Dai Herbert (Natal Museum, South Africa), Cristian Ituarte (Museo

de la Plata, Argentina), Thomas Kristiansen (Danish Bilharzia

Laboratory, Copenhagen), Richard Neves (US Fish & Wildlife

Service), Winston Ponder (Australian National Museum) Willem

Sirgel (University, South Africa), K. Walker.

Introduction

The phylum Mollusca is currently the second most diverse animal group, with origins which datebefore the Cambrian. The phylum includes Snails (Order Gastropoda), clams and mussels(Order Bivalvia), but also less obvious animals such as slugs and sea-slugs (which have aninternal shell), and octopus and squid (Order Cephalapoda), as well as some smaller orderswhich not known to the general public.

1.0. GEOGRAPHIC DISPOSITION OF BIODIVERSITY

A. HOW MANY MOLLUSCS ARE THERE?There are various estimates of the number of species, with Boss (1973) estimating the number ofspecies as 80,000, whereas van Bruggen (1995) estimated that the total number of species willreach 135,000 species. The variation relates to the interpretation and extrapolation of the level ofundescribed species that are currently being published each year.

Table A1 Summary Statistics on Molluscan Biodiversity

Sources: Boss (1973), van Bruggen (1995)

Species Notes

Marine 31,000 - 100,000 Boss (1973), van Bruggen (1995)

Terrestrial 14,000-35,000 Boss (1973), van Bruggen (1995)

Freshwater 5,000-5,000 Boss (1973), van Bruggen (1995)

Riverine 4000 (Excluding Spring-snails)

Importance of Molluscs to Ecosystem

The biomass of the Mollusca is very important to ecosystems (Summary in van Bruggen, 1995).In marine environments, molluscs may form the dominant group, especially in their larval stage,but also on soft substrates (bivalves), and on hard substrates, where some molluscs such as Pearloysters (Pinctada) and mussels may be more important in terms of their biomass than corals(Salvat, 1970). In freshwater environments biomass of molluscs is significant in someenviroments: for example in temperate countries lake bottoms maybe covered with the smallbivalves from families Sphaeriidae and Pisidiidae. Berrie & Boize (19xx) estimate that 80% of thebiomass of benthic invertebrates at River Thames (at Reading) is composed of freshwater Unioidmussels.

In tropical areas, the same can be true. Brown (1994) summarises much of the data available oncontribution of molluscs to the biomass of freshwater systems in Africa, and shows thatprosobranchs contribute the major part in Lakes, such as Chad, Malawi, Tanganyika and Victoria.He cites examples such as Hart (1979; table 6) observations that the species from twoprosobranch genera Bellamya (e.g. Bellamya capillata 0.40 g/m-2) and Melanoides (e.g. Melanoidestuberculata 1.74 g/m-2) provide a major part of the biomass of Lake Sibaya.

Molluscs in the man-made Lake Kariba made up nearly the entire biomass of the benthic animals(Prosobranchs 4.1 % and Bivalves 95.8%) (Machena & Kautsky, 1988) and Brown uses their datato calculate figures of two prosobranch genera Bellamya (e.g. Bellamya capillata 0.28 g/m-2) andMelanoides (e.g. Melanoides tuberculata 4.08 g/m-2). The latter species, Melanoides tuberculata, isadapted to maintaining large populations in stable environments with a long mean generationtime and a low intrinsic rate of natural increase (see Pointer et al. 1991; Brown, 1994).

SPECIES AND GENETIC DIVERSITY Molluscs are characterised by a soft body, usually with an exoskeleton in the form of a shell,consisting of a body, a single muscular foot, a dorsal mass with a visceral sac, fleshy skin fold (themantle, which is contains the glands which form the external shell). The alimentary canalcontains a “scraping tongue”, the radula, which can be used as a character in identification. Thefreshwater fauna can be divided into three main groups:

Freshwater Gastropods (Prosobranchia)Freshwater Gastropods (Pulmonata)Freshwater Bivalves (Bivalvia).

The greatest freshwater species diversity and endemism is found within the Prosobranchia andthe Bivalvia groups.

Freshwater prosobranchsThese range in size from large prosobranchs such as the apple-snails of the Ampullaridae (up to40 mm in size) to the small springs-snails (1-8 mm).The Afrotropical fauna differs from that of India and SE Asia in its greater richness of species inthe families Ampullaridae, Bithyniidae, Thiaridae and Planorbidae (Brown 1994). Brown notesthe lack of any Hydrobioid radiation in the Afrotropical region, contrasting it with the radiationsreported for the Mekang River (Brandt, 1974; Davis, 1982). Davies (1982) suggests that this is dueto the lack of limestone regions, but Brown (1984) notes that there are suitable perenical riversystems, but the water tends to be low.The origins of these fauna evolved when the area was part of Pangaea (which broke up 150million years ago) and then Gondwanland which Davis (1982) suggests accounts for the presenceof some snail groups in Africa, as well as South America and SE Asia.

These groups can be summarised as :

1) South America, Africa, India/Asia. Family Pomatiopsidae Ampullariidae Thiaridae (Genera Potadoma, Pachychilae and Brota) 2) Africa – India – SE Asia.

Family Viviparidae (especially Genus Bellamya)Thiaridae (Genus Thiara, Melanoidea)Planorbidae (Subfamily Bulininae)

Brown (1994) attributes the success of families such as the Ampullaridae to their liking forhabitats such as swamps and muddy slow flowing rivers. The genus endemic to Africa, Lanistes,shows that some adaptations may be related to their predators (fish), the sandy substrate forfeeding and life in deep water (Brown 1994).

The Hydrobiidae are a diverse group of prosobranchs, occuring in lakes, springs, seeps, marshesand lotic waters. These species are often found in very high densities, and thus can provide ahigh component of the benthic epifauna. Some of the genera (e.g. Fontigens) exist in subterraneanwaters and springs (Hersler et al 1990), and those species which have highly isolated and

geographically separated populations are currently being studied to determine their phylogenticrelationships.

Freshwater pulmonatesFreshwater pulmonates can be found in all microhabitats in freshwater systems. The groupexhibits the least levels of diversity in most freshwater systems. The freshwater pulmonates arethought to be less diverse in Africa due to their need to fill the lung with atmospheric air,reducing their ability to invade deep-water biotypes in lakes (Brown, 1994). These taxa areexcellent colonists, as they are often able to live at high densities in shallow, even seasonal, waterbodies, and as self-fertilising hermaphrodites they are able to disperse and colonise new waterbodies.

In terms of the life-cycle, the species are usually are oviparous, laying eggs capsules of differenttypes according to family. The number of eggs per capsule varies from one (e.g. the limpetgroups Ferrissia) to over one hundred (e.g. Lymanea natalensis) (Brown, 1994). Water temperatureis generally an important influence on growth rate, although other factors, such as changes inbiotope, or food shortages can also have an impact on pulmonate growth rates (Brown, 1994).

Freshwater bivalvesIn order to understand the potential impacts that river channels changes and impoundments haveon bivalves it is useful to know more about the life cycle strategies of these groups. Bivalves,other then freshwater mussels, typically produce either free-swimming larva (trochophere orveliger) or have direct development releasing juveniles. The freshwater mussels (Unionoidea)have reproductive strategy involving a larval stage (called the Glochidia), which is retained in thefemale brood pouch or gills and released for their intermediate stage as a parasite of a host fishbefore being transformed to bottom dwelling juveniles (or in one case in the USA an aquaticsalamander: the mudpuppy, Necturus sp. ; Bogan, 1998; Watters, 1994). A few US speciesdeviate from this system, for example Obliquaria reflexa, which can bypass the parasitic phase(Howells et al., 1996). Most freshwater mussels have separate sexes, although some species areknown to be hermaphrodite.

Spawning, egg deposition and incubation.Male discharge sperm direct into the water. Females inhale waterborne sperm during normalfeeding and respiration, and egg fertilisation takes place. The fertilised eggs and developingglochidia are retained in brood pouches in the gills (not all gills have brood pouches, this variesfrom species to species).In the US mussels, long term (Bradytictic) breeders spawn and fertilise eggs in late spring,summer or early fall producing mature glochidia by late fall or winter, however, the glochidiamay not be released until spring or early summer of the following year. In contrast short term(Tachyticitic) breeders spawn, fertilise eggs, develop and release glochidia from late spring toearly fall.

Glochidia may be released singly or in groups. Some species discharge conglutinates which“mimic” warm, grubs or fish; and thus are consumed by the host fish. The glochidia cannot swimbut must drift with water currents. If they do not find a suitable host fish within a few days theywill die. Similarly if they attach to a none-host species or are incorrectly on a host species, againwithin a few days they will die (Howells et al., 1996).

The infection on the host-fish is usually light, and encysted glochidia row little during theparasitic stage, hence the impact on the fish is minimal. Released juveniles are often similar in sizeto the glochidia. Consequently, on release, if they do not become lodged in a suitable substratethey will not survive.

FeedingFreshwater mussels are filter feeders requiring a rich and plentiful supply of diatoms, desmids,filamentous algae and other algal species.

Factors influencing vulnerabilityFreshwater mussels are especially vulnerable to habitat disturbance. The mussels of Unionoideawith their obligate parasitic state, requiring host fish are especially threatened. As at present, onlyabout 25% of the host fish for the mussels in the USA have been correctly identified, it is moredifficult to predict the impact on damming, as clearly the movement of fish within the riversystems will affect the reproductive success of these mollusc species.

Many species in USA and Europe have extended life cycles, some of which span over 100 years,where maturity is delayed until 6 – 15 years (Bauer, 1993; Chesney & Oliver 1998). Some speciesalso have reduced powers of dispersal, high juvenile mortality and long turnover times.

The prolonged lifecycle of the freshwater mussels does mean that populations may appearsecure, when in fact no active recruitment is taking place, and as such these populations may wellend up being functionally extinct. For those species which have few extant populations, it resultsin species (e.g. ) which are “Functionally extinct”. Chesney & Oliver (1998) have a figure whichillustrates this point well (Figure x.x)

Figure xx Hypothetical size distributions for recruiting and senescent

populations of Margaritifera margaritifera

TABLE XXEnvironmental and biotic factors influencing the various stages of the life cycle of UnioidMussels (amended from Chesney & Oliver, 1998). Items highlighted in bold are directlyimpacted after impoundment; in italics, indirect impacts of impoundments.

FACTOR LIFE CYCLE STAGES AFFECTEDExploitation (pearl fishing, shells forbuttons/seeding)

Adults

Fish host population size GlochidiumMussel population size Fertilisation, glochidium numbersRiver Bed Adults, juvenilesFlow regime Fertilisation, glochidial infection, settlement,

juvenile and adultSuspended solids Adults, feeding and broodingEutrophication Adults, juvenilesNitrogen Adults, juvenilesPhosphate Adults, juvenilesDissolved Oxygen All stagesConductivity Adults, juvenilesCalcium Adults, juvenilesPH Adults, juvenilesInterstitial particulates JuvenilesInterstitial water chemistry JuvenilesIndustrial pollutants All stagesPesticides All stages

Chesney & Oliver (1998) point out that it is important to understand the life cycle of Europeanfreshwater pearl mussel species and to adopt survey, monitoring and management protocols forall phases. Table 1 has been adapted from Chesney & Oliver (1998) who illustrated the wideranging interactions of life cycle stages to environmental parameters for M. margaritifera. In muchof the early survey work in the 1970’s in Europe the impact surveys tended focus on the adultstage which, in pearl mussels, is the most resistant phase to environmental change.Again, in most handbooks, the habitat preferences are often simplified and for example Chesney& Oliver (1998) cited the preferences for the Freshwater Pearl Mussel which is often quoted ‘ingravel patches behind rocks in riffles, mostly in oligotrophic upland rivers’. They noted that thisis a gross simplification of where M. margaritifera actually lives, as the species can be found in fastflowing lowland rivers and in uniform gravel beds in water depths of over a metre and issometimes tolerant of calcium rich water ( e.g. Ireland and the Lake District).In many Unionid bivalves, failure to recruit viable juveniles to populations appears to be themajor obstacle to species recovery (Chesney & Oliver 1998). These authors list several problemareas for recovery, and all these conditions may exist in the post-impoundment phase:

• eutrophication effects are crucial for post-glochidial juveniles, especially on theirinterstitial environment requirements.

• nutrification, especially raised nitrate and phosphate levels, may have a moredeleterious effect on juveniles.

• clogging of the interstitial spaces by organic debris may reduce oxygen as wellpreventing access to the sediment.

Correcting these problems will involve:• Catchment management and river restoration• Reviewing and changing agricultural practices to reduce eutrophication.• These will involve raising ‘public’ (=involved organisations) awareness.

Tackling these problems requires some degree of total river management which is bothcontentious and problematic as it conflicts with current practice in agriculture, forestry and wastemanagement. Should environmental problems prove impractical to correct in the short term, then many riverswill lose their remaining senescent populations before recruitment can be restarted. At a futuredate such rivers may once again be suitable, but can only be stocked by translocation, a procedurewhich is currently not successful. Alternatively if we could captive breed the remaining stockthrough to the post juvenile stage we could maintain the adult population and create a largertime period in which the juvenile environment could be re-established. Currently it is a simpleprocess to infect young salmonids with glochidia but the subsequent growth through to five yearsof age has never been completed with any great success. It must be borne in mind that in-situ conservation which preserves genetic identity and leads torecognition of local adaptations is preferable to conservation through translocation as this affectsthe gene pool and should only be used in extreme circumstances. Liu, Mitton & Herrmann (1996)concluded this when evaluating the restocking of the giant floater (Pyganodon grandis) in theColorado basin; they concluded that the dgreee of differentiation among drainages was so greatas to require new populations to be founded with individuals from the natuiraql populationswithin the same drainage basin. Key notes •Environment recovery will be complex and may take many years. •Species recovery may rely on re-introduction and captive breeding. •Considerable research and funding needs to be directed at the problems of

translocation and captive breeding. An overview of Threatened Species Seddon (1998) gave an overview of the Molluscs included in the 1996 Red List of ThreatenedAnimals (Baillie & Groombridge, 1996). The first review of threatened invertebrates was carried out by Collins et al. (1983) and thishighlighted the threatened molluscs of specific regions such as islands e.g. Hawaii, FrenchPolynesia and Madeira, freshwater species from USA and Lake Baikal as well as the exploitedspecies such as Giant Clams (Tridacnidae). Global lists have given the status of endangeredmolluscs since 1984 through the work of the IUCN Species Survival Commission MolluscSpecialist Group (IUCN 1987). Evaluation of freshwater Molluscs in river systems has been a problem using the new criteria as itcan be difficult to establish the range data for linear river systems. Estimating status of rifflespecies, for example, as it is extremely difficult to estimate area of occupancy where species occurin small riffles all the way along the river. As the data on extent of occurrence (i.e. river) are oftendifficult to obtain and populations are difficult to assess, a problem which applies to many USand European freshwater species, some species which were listed in 1994 were not listed in 1996,except as Data Deficient. Molluscan extinctions is a significant problem, as the diagram below shows:

Figure 2 Diagram showing the proportion of molluscan extinctions as a total of

all animal extinctions since 1600 AD.

Freshwater Species which are Threatened Many of the US freshwater species were evaluated on the basis of population decline rather thanrange data. Range data provide evidence for assessment of the spring-snails as CriticallyEndangered; where there are molluscs with populations in only one known locality (B1). Thespring snails of Austria, Australia and the USA fall into this CE category when there is a threat ofover-abstraction of water from the wells or pollution of the water source (B2a, c). It is likely thatas more endemic spring snails are properly assessed a high proportion of these taxa are likely tobe threatened, given the degree of exploitation of their habitats. Some of these spring snails arealso subject to natural fluctuations (B3) in their populations (Lepitki 1997) consequently acatastrophic event at a low point in their population cycle increases the possibility of extinction. Many African freshwater molluscs were included in the 1996 Red List for the first time, asinformation on their status is becoming more accessible. These species are threatened by declinein quality of water, pollution, damming and increased sediment load. Given the generation timeof these species they are accessed at the category Vulnerable B1 and 2c. Freshwater spring snailsfrequently fall into the Vulnerable D2 class on the basis of small range. 1.1. RIVER ORIGIN TO MOUTH

Freshwater ecosystems have a range of molluscan habitats within rivers, as well as adjacenthabitats where species rely on the flow of water through the catchment. In general a river is aone-way system, as many species of mollusc can only move downstream by drifting or beingdislodged by flood events and moved downstream. In some stages of their life cycle thosespecies which have a larval form can move significant distances upstream with the aid of a thirdparty (e.g. host fish during a larval stage). Gregarious migrations upstream have been reportedrarely for molluscs, however, Schneider & Frost (1986) did observe that the freshwater neritidsnail Neritina (Clypeolum) latissima was capable of moving upstream by crawling along the bedof Rio Claro in Costa Rica in groups when dislodged by flood waters (although the water levelswhen this was observed were low).

Hynes (1976) showed that in a short clean river there is an increase in invertebrate speciesdiversity downstream, with increasing numbers of microhabitats, increased eutropificationenhancing productivity and increased sediment imput. More recently specific work on molluscandiveristy downstream has been attempted. Mouthan (1999) presents the results of a survey of 272stations in rivers of Franche Centé, France. He found that there were nine different“malacotypes”, which could be identified, from the total of 52 species recorded in the survey. Herecognises that there were taxonomic insufficiencies in this work, especially in the spring snailfamily Hydrobiidae. He found that there was a general increase in the number of taxa along the river system, with fewspecies at the headwaters (Hydrobiidae spp. – not separated) to 48 species in the lower reaches ofthe river. It must be noted though that there is a decline in the number of species (39) at thelowest point on the river system. Mouthan (1999) discusses the reasons for this, suggesting thatthis may not be a true reflection of the original levels of diversity, but may be related to thesampling sites. One of the rivers sampled in this study has a series of locks and conurbationsalong the course. Six of the species which are not present at this level on the river system aresusceptible to pollution. The lower levels of dissolved oxygen during the summer may also limitthese six species, as well as Pisidium obtusale; thus Mouthan (1999) concludes that the decline inthe lower levels is due to anthrogenic activity including hydropower developments. Mouthonalso noted that the in the areas of highest species richness, a significant number of species alsohad their highest abundance in this malacozone. Mouthan (1999) noted that gastropods (such as the Planorbidae) which favour lentic habitatswith rich vegetation, reach their maximum species diversity and abundance at malacozone 6 onthis hypothetical river, which he again attributes to declining quality of habitats in the lowerreaches of the river. Valovirta (1998) shows that the density and distribution of mussels along a river can change,especially on old log floating rivers in Finland. This pattern is also reflected for most otherfreshwater species, and as such bed formation and sediments are very important for the largeUnioinid mussels.

Molluscs can be divided into different groups on the basis of their habitat requirements:

• Species which are generalists, found in all sizes of water bodies, in all types of waterconditions. • Specialist species requiring permanent water, with specialised microhabitats and/orspecific water conditions • Specialist species requiring temporary water bodies; these species are moreopportunists and tend to be good colonists. • Species that live in the riparian habitats besides large water bodies, requiring aconstant input of water into the habitat. Such species may be marsh dwelling species(e.g. Vertigo moulinsiana), gallery forest species adjacent to the river. • Species that are spring specialists fed by underground aquifers. These include thefamily Hydrobiidae.

In addition the different lifestyle and reproductive strategies that these species adopt influencethe diversity along the river system from origin to mouth. 1.2. Latitudinal gradients Van Bruggen (1995) demonstrated that latitudinal variability exists in freshwater molluscs inAfrica. Using data from Brown (1980) he shows that the highest numbers of species being foundin the tropics (105 species at 0 - 5°S) and lower numbers found in the freshwater systems of northAfrica (5-20 species from desert to mediterranean systems) and southern Africa (38-40 species) (see Figure 1.2.1). However, overlying this trend there are some notable deviations at “hotspots of endemism anddiversity”, where some temperate areas with specialist “species swarms” have much higherlevels of diversity. [insert diagram Figure 1.2.1

Picture of Africa, with species diversity across Africa] 1.3. Continent The highest levels of diversity and endemism within the freshwater molluscan fauna, as presentlyrecognised, lie in North America (USA: 945 species; Bogan, 1998). Other notable centres ofendemism are found in the rivers of Indo-China, such as the Mekong River and in freshwaterlakes where there have been speciose radiations, such as Lake Baikal (Siberia), Lake Tanganyika(Africa) and Lake Biwa (Japan) (See below section 1.4). However, these comments reflect thepresent state of knowledge, which may well change as our levels of knowledge aboutdistributions and the taxonomic insufficiency for molluscs in riverine systems in S. America andSE Asia is improved. In north America much of the speciation lies in the families Pleuroceridae (Gastropoda) andUnionidae (Bivalvia). A high proportion of small range endemism lies within the specialist springsnail groups (Family Hydrobiidae) in Europe, USA (c. 20% of mollusc fauna: see below) andAustralia , and the initial survey work in Sulawesi has shown there are a large number ofundescribed species within this group (Bouchet, 1995; Haas pers. comm). Undoubtly furtherwork in the less surveyed areas will reveal other areas of high diversity and endemism withinthese spring snails. 1.4. Global species hotspots and endemism (based on “Hotspots of freshwater molluscan diversity” prepared by Olivier Gargominy, Arthur Bogan,Philippe Bouchet, Winston Ponder: draft discussion paper from Mollusc Specialist Group) 1.4.1 USA The current enumeration of about 601 taxa of freshwater gastropods (table 1) and 300 taxa ofunionoid bivalves (Table 2) is based on Turgeon et al. (1988) and their subsequently revisedversion (Turgeon et al ,1999?). In the USA freshwater ecosystems are disproportionatelyendangered relative to other groups (Master, 1990) with molluscs being the most highlythreatened group within the freshwater organisms. Table 1 Freshwater molluscan diversity in North America (after Bogan, 1998)

Gastropoda Bivalvia Total No. of Families 14 5 19 No. of Genera 88 57 145 No. of Species 601 344 945

Table 2 North American freshwater bivalve diversity (After Bogan, 1998) Family Genera Species Margaritiferidae 2 5 Unionidae 48 295 Dreissenidae 2 3 Corbiculidae 1 2

Sphaeriidae 4 39 Total 57 344

Table 3

Table 3 North American gastropod diversity (after Bogan, 1998) Family Genera Species Acroloxidae 1 1 Ampulariidae 2 4 Ancylidae 4 13 Bithyniidae 1 1 Hydrobiidae 37 228 Lymnaeidae 10 58 Neritidae 1 1 Physidae 4 43 Planorbidae 12 47 Pleuroceridae 7 156 Pomatiopsidae 1 6 Thiaridae 2 3 Valvatidae 1 11 Viviparidae 5 29 Total 88 601

1.4.1.1 USA- RIVERS The extinction crisis for the US freshwater mussels was recognised last century. Higgins (1858)observed declines in the Unionoid species which he suggested related to deforestation. Rhoads(1899) remarked on the decimation of freshwater bivalves in the lower Monongahela River abovePittsburgh which he believed was due to pollution. Ortmann (1909) reported declines on theTennessee River systems due to papermill effluents. However documentation of the extinctioncrisis did not really gain momentum until the 1970’s (Athhearn, 1970; Heard, 1970; Stansberry,1970; Taylor, 1970). Bogan (1998) summarises the state of knowledge on the extinctions of thefreshwater molluscan fauna in the USA.

Table 4 Threatened Status of North America Unionoid Bivalves (after Bogan 1998) Total Percent No. of Taxa 300 No. of Candidate taxa 61 20.33 No. of Threatened taxa 5 1.66 No. of Endangered taxa 57 19.00 No. of Extinct taxa 35 11.66

Table 5 Threatened Status of North American freshwater gastropods (after Bogan ,1998) Total Percent No. of Taxa 601 No. of Candidate taxa 173 28.8 No. of Threatened taxa 0 0 No. of Endangered taxa 9 1.5 No. of Extinct taxa 42 6.99

The greatest diversity in the regional freshwater faunas are reported for Mobile Bay in Alabamaand the Tennessee River Basin and these are also some of the most threatened faunas. Forexample with 7 % of total taxa of prosobranch gastropod fauna found in the Mobile Bay Riverbasin, and the Tennessee River Basin, now extinct (Bogan, 1998). Most of the extinctions in thisgroup (38 out of 42 taxa) in the Mobile Bay fauna, occurred when the big river shoal fauna wasimpounded and covered by deep standing water and subsequent increased siltation. Ohio-Tennessee River Basin In the Tennessee River Basin species are under threat following the construction of dams and thesubsequent regulation of flow. A number of gastropods from the family Pleuroceridae are underthreat, as they persist on clean swept shoal areas below dams on the river (Bogan, 1998), andthree other species have been extirpated from the river Haag & Thorp, J.H. (1991). These authorsalso reported drop of 50% in number of freshwater mussels from c.100 species that were presentprior to the multiple impoundments, but noted that the presence of the. Asian Freshwater Clam(Corbicula fluminalis) had also had an impact reducing the density of native mussels in the areaswhere they remained. In terms of the general molluscan community, Haag & Thorp observedlateral channel changes and seasonal changes in the gastropod and bivalve abundances, whichthey believed reflected differences in breeding cycle and reproductive behaviour. These lateralchanges across the channel, relate to the bed type and water depth, for example, typical densitiesof the Pleurocids ranged from 947 m2 (4.7m water depth) to 1011.8 m2 (7.6m water depth). The Cumberland River, in the upper part of the Ohio-Tennessee River basin had a series ofimpoundments and locks establised between 1916 and 1923 (Blaock & Sieckel, 1996). Over 85freshwater mussel species were known on this river system, prior to impoundment. In the reachof the river directly under Lake Barkely there were 45 species, and in the reach under Kentucky25 species known. Blaock & Sieckel (1996) point out that these esimates are minumum’s for eachreach of river, as mussel distributions are very patchy, and sampling few sites (7 – 19) may meanspecies were not recorded. Blaock & Sieckel (1996) describe changes in species diversity andspecies abundance. For example although mussel abundance shown a loss of 50% between 1911and 1994, over 65% of the shells were a single species Quadrula quadrula. Table below shows thenumber of species lost in the the Kentucky portion of the lower Cumberland river, which wassinudated by Lake Barkeley. Most of these species were ones that were recorded at low % of thetotal fauna ( 1.28 – 3.12%), but species such as Plethobasus cordatum comprised 40.7% of the faunain 1911, declining to 7.2% by 1981 and is now not recorded in the reservoir and has declinedmarkedly in the riverine sections. 1911 1981 1994 Original Fauna 25 15 4 New Species - 6 5 (2 new) Local extinctions 10 11

The Mississippi River system is expected to lose as much as 50% of the current species over thenext decade, directly related to the invasion of the zebra mussel (Master, 1996). Stein & (1996)points out that the decline of freshwater mussels this will have a detrimental role to the entireecosystem, as the freshwater mussels play an imprtant role in sediment mixing and nutrientrecycling, and given their dominance in terms of biomass, the removal could have long-termrecupercussions, as yet unknown. Summary Statistics area R1: Ohio-Tennessee rivers (Mississippi), USA (see WCMC report) richness of which: endemic extinct or threatened Gastropods 99 Bivalves 120 16 EX

area R2: Mobile Bay basin (Tombigbee-Alabama rivers), USA Within the Mobile Bay system there are 6 endemic genera ; greatest species diversity in thePleuroceridae (76 spp.) richness of which: endemic extinct or threatened Gastropods 118 110 * 38 presumed extinct

* 1 Endangered * 70 Candidate

Bivalves 74 40 25 EX * US Federal List of Threatened and Endangered Wildlife 1.4.1.2. USA- SPRING SYSTEMS The endemic spring-snails are one of the highly endangered groups in the USA and Mexico.These species are very restricted in their ranges, are typically very abundant within in their smallranges, and have a generation time of under a year. Summary Statistics Springs: area 1: arid/semi-arid Western USA richness of which: endemic extinct or threatened Gastropoda (only Family Hydrobiidae;espcially the genus Pyrgulopsis) *

ca. 100 >58 3 EX Others candidates on Federal List of Threatened andEndangered Wildlife

area S2: Florida, USA richness of which: endemic extinct or threatened Gastropods (mainly Family Hydrobiidae)

84 ca. 43

Bivalves

1.4.2.1. SE ASIA: MEKONG RIVER The Lower Mekong river was investigated by Davis (1970), and there is a high radiation withintwo groups in the Prosobranchs; the faunal assemblage contains over 120 species, mainly thepomatiopsid family Triculinae (92 endemic species, 11 endemic genera) and the Stenothyridae (19endemic species). However, there remains more to survey, as only about 500 km of the lowerMekong main course (with the tributary Mun River) has been well-studied. Summary Statistics: area R3: Mekong River (lower Mekong), Thailand-Laos-Cambodia

of which: richness endemic extinct or threatened Gastropods 121 111 Unknown Bivalves 39 5 Unknown

1.4.3. S. ASIA: 1.4.3.1 NORTHERN WESTERN GHATS, INDIA The main literature from this region is given in Subbao Rao (1979). There are some distinctivetaxa within the region: 2 endemic genera Turbinicola, Cremnoconchus. The highly localised genusCremnoconchus is of phylogenetic significance, as it is the only member of the familyLittorinidinidae known living in a freshwater/terrestrial environment. Members of this groupare typically found in Mangrove or marine shore environments. The succineid genus Lithotis is known from two species: L. tumida not collected since itsdescription in 1870, and L. rupicola only known from a single locality. At present there are no species listed as Endangered on the Red List (Baillie & Groombridge,1996), but a recent submission for a species of Unionid Pseudomulleria daleyti Smith, 1898 from thefamily Etheriidae has just been evaluated as Endangered B1, B2c. This freshwater specieslives in rivers attached to rocks, in clusters of 3 to 10 individuals, only occasionally exposedusually submerged. This species is currently threatened by the construction of a dam, and itis anticipated that if construction goes ahead the range will decline, with the possibility of localextinction. It is only known from one other site, and at present the current status of this otherpopulation is unknown. Summary Statistics: area R4: Northern Western Ghats, India of which: richness endemic extinct or threatened Gastropods ca. 60 ca. 10 Unknown Bivalves 11 3 1 : see note above 1.4.3.1 Japan area L2: Lake Biwa, Japan At present no species for this region has been listed, which is a reflection of the non evaluationrather than the status of the fauna. Again many of these probably qualify as Vulnerable D2, if nothigher. richness of which: endemic extinct or threatened

Gastropods 38 19 Bivalves 16 9 area L9: Chilka Lake [brackish water], India of which: richness endemic extinct or threatened Gastropods 28 ca. 11 Unknown Bivalves 43 25 Unknown area L10: Inl_ Lake, Myanmar richness of which: endemic extinct or threatened Gastropods 25 9 Unknown Bivalves 4 2 Unknown 1.4.4. SOUTH AMERICA Much of the faunal knowledge in this region is still at the checklist stage, and there is still a needto carry out investigations of the headwaters, and make inter darinage systems comparisons toestablish the taxonomic status of some of the nominal taxa for the region. 1.4.4.1 SOUTH AMERICA: PARANA RIVER The surveys prior to the construction of the Parana Dam on the Parana river showed that therewere endemic species present in the rapids. These species were threatened with extinctionresulted from changes in the flow regime at Yacréta-Apipe rapids on the Parana River after theParana Dam was constructed (Bertonatti, 1999). These species were taken into a captive breedingprogramme, and three taxa (Aylacostoma guaraniticum (Hylton-Scot, 1953) Aylacostoma chloroticum(Hylton-Scot, 1953) Aylacostoma stigmaticum (Hylton-Scot, 1953) are now extinct in the wild(Darrigan pers. comm; see Quintana, 1999; pers. Comm. For Action Plan). Downstream from the now disappeared Guayri Falls (flooded when Brazil and Paraguay builtthe Itaipú hydroelectric plant), the Upper Paraná river runs along the Paraguay/Argentinaborder confined between vertical walls up to 100 m high, deeply eroding the stony Serra Geralplateau. Around 56°W, during a remote geologic time, the Paraná was temporarily delayed by abasaltic mantle that obstructed its way to the southwest. An amygdaloid rock called spilite,showing a vacuolar appearance due to steam bubbles, was originated in contact with freshwater.Finally, the Paraná surpassed this bed, divided in multiple branches that then anastomosed toform a large and complex system with more than 300 islands (Ibicuí, Yacyretá, Talavera, ApipéGrande, and lesser islands), many rapids such as Apipé, and deeper passages such as Mbaracayá. This portion of the Paraná, having a flat bed and serious obstacles for navigation, becameradically different from the preceding river, which was deep and carved between high gullies.Downstream was also completely different, where the water runs towards the confluence withthe Paraguay River, and also in its last sections, which developed a wide floodplain and finallyreach their end in the Plata estuary. Such a limnic singularity brought about endemic forms of lifein this particular section, which were not able to expand their distribution to other parts of thebasin. Instead, they developed a remarkable “ecological fidelity” to the river bottom in the rapidsarea. This is the case of the prosobranch snails belonging to the genus Aylacostoma, a group ofparticular scientific interest within the mollusk fauna of Argentina and Paraguay. These molluskshave a unique reproductive system characterized by parthenogenesis (reproduction withoutmales) and simultaneous development of up to three embryos inside a marsupium, or

adventitious pouch, located within the parent's neck. These young snails are “born” when theyhave attained a surprisingly big size, and are thus able to withstand the violence of the rapids.They feed while protected within a thicket of diatoms, green and red algae growing upon theadult's shell. Aylacostoma belongs to a group of mollusks of cenozoic origin, which invaded South Americafrom the northern hemisphere in late Cretaceous or early Tertiary periods, when both continentsbecame connected for the first time, some 65 million years ago. An abundant fossil record instrata from the Paleocene ranging to the southern tip of Patagonia evidences its early andsuccessful adaptive radiation. Climatic and hydrographic changes, however, restricted itsdistribution towards the north. Nowadays, the group is limited to fluvial systems in northernSouth America. Just one relict area from its former southern distribution persisted outside thetropics, in the Plata basin until three years ago: the Yacyretá-Apipé rapids, now flooded by themain Yacyretá reservoir (1,600 km2). Those rapids represented the unique habitat of a group of endemic species from Argentina andParaguay (Aylacostoma guaraniticum, A. chloroticum, A. stigmaticum, A. cingulatum), where theywere discovered and described as late as the 1950s. This discovery was a late and surprisingaddition of a tropical family (Thiaridae) to the faunistic inventory of these temperate countries.Their populations were abundant but had a very limited range, and were made up completely offemales. Due to their particular mode of reproduction, all individuals are essentially identicalwithin each population or micro-deme (diversity only shows up as a few mutant or senilespecimens) whereas differences appear only between demes. These populations could beregarded as clones, since the offspring are not produced by the mating of males and females withdifferent features, but are exact replicas of a single parent. In cases such as the present one, thelow genetic variability leads to a very low adaptive potential to withstand environmentalchanges. Moreover, due to their viviparity and low mobility, these snails do not disperse fromtheir birth place. Even if reproduction without mating is the rule in these species, this may beperiodically compensated by gene recombination by a still unknown mechanism. The cytologicalstructure of the individuals (haploid, diploid or polyploid), as well as many biological features ofthe Argentine-Paraguayan forms, are still completely unknown. Although their 4 cm long shell makes them conspicuous to a keen observer, and severalthousands were present in a limited area, these snails were totally unknown to the local people.However, plentiful shell collections were gathered by occasional visitors during the lowest watersof this century. This evidences the secret life of these animals and their fidelity to the bottom ofthe Paraná river in the rapids area, characterized by its difficult access and risky navigation. Since the Yacyretá area was the only place where they were found, their total extinction wasexpected on flooding of the reservoir, which would lead to the disappearance of the rapids andall the organisms so strictly adapted to life in this habitat. Indeed, the former rapids becamecovered by more than 10 m of still water. Thus, the rocky, well-illuminated bottom bathed byclear and oxygen-rich waters promoting a dense layer of algae, changed to its presentappearance: a dark and muddy bottom in which algae were unable to survive. Given thisscenario, in August 1993 a team of biologists from the Argentine Museum of Natural Sciences(MACN) were permitted by the Entidad Binacional Yacyretá, in charge of the dam, to survey thetypical locations of the snails in this portion of the river. Many sites were surveyed, including thefew rapids still existing, since most of them (such as the renowned Apipé rapids) were lost duringthe early flooding of the dam. A dense Aylacostoma population consisting of five differentmorphotypes was found along a 150 m stretch of shore in the rapids area. Of these, three could beidentified as known species, but the other two might be new varieties that, unfortunately, were tobe discovered scarcely before their inclusion in the long list of casualties due to human activities

Summary Statistics: area R5: Parana River, Argentina-Paraguay richness of which: endemic extinct or threatened Gastropods Thiaridae

>7 7 3 EW

1.4.4.2 SOUTH AMERICA: URUGUAY & LA PLATA RIVER One species of terrestrial gastropod (Anthinus albolabiatus) which was formerly endemic to GalleryForest adjacent to Uruguay River has been proposed as Extinct following construction of the SaltoGrande Dam (Mansur, 1999; pers. comm.). The La Plata River malacofauna is also suffering declines relating to the spread of the SoutheastAsian Freshwater mussel (Limonoperna fortunei (Dunker, 1857), which is colonising new areasmoving upstream in the estuarine river system; the species has expanded upsteam north to theconfluence of the Paraguay River and the Parana River, a distance of over 1,100 km since 1991(Darrigan, 1998). Summary Statistics: area R11: Lower Uruguay River and Rio de la Plata, Argentina-Uruguay-Brazil Number richness endemic extinct or threatened Gastropods 54 26 Unknown Bivalves 39 8 Unknown This lake is one of the notable hotspots in terms of other species endemism and as such figures onthe Molluscan endemicity have been established. Again the spring-snails for the region have yetto be investigated. No estimates of threat to the fauna have been established. area L8: Lake Titicaca, Bolivia-Peru of which: richness endemic extinct or threatened Gastropods 24 15 1.4.5.1 AFRICA: SOUTH OF THE SAHARA The level of molluscan diversity is not as high as the drainage systems in North America or theMekong, but the richest river systems are listed here. There are four main basin drainage systemsin africa, south of the sahara, the Niger, the Nile, Zaire and Zambezi (see Figure xx). The endemic threatened species are nearly all specialised for rapids in river systems. Thesespecies are often only known from small stretches of the river system.

LAKE VOLTA Area: 8800 Km2

Maximum Depth: 80m Year of closure: 1964

The construction of the dam, and the subsequent colonisation of the lake by Bulinus truneatus, afreshwater pulmonate, lead to an increase in the level of urinary schistomiasis reported in theregion (See list of publications in Brown, 1994). Prior to the construction of the dam, this specieswas rare, other species from the same genus such as Bulinus globosus, were more common.However, the latter species was unable to exploit the new habitat, as it cannot tolerate the lake-level fluctuations. Bulinus truneatus, on the other hand, uses the equatic vegetation such asCeratophyllum demersum, and dense populations survive in these stands. In contrast a smaller lakecreated by a dam 20 Km downstream on the Volta River, sustains Biomphalaria pfeifferi. Thus therehas been a change in the species assemblages found pre-impoundment and post-impoundment,and with the additional consequences of increase in human diseases, associated with thecolonising molluscan species. The Niger, despite its length does not have any endemic species, although the headwaters havenot been properly explored. Brown (1994) speculates that the lack of endemism maybe due to theimpact of Pleistocene climatic change, leading to fluctuations in river level. The majority ofendemism is found in the Volta basin (six endemic species of the prosobranch family Thiaridae(Potadoma togoiensis, P. bicarinata, Pseudocleopatra voltana, P. togoensis). Other notable species in the area include 4 species of the genus Sierraia which are known to livein rivers that are practically devoid of dissolved chemical content in some seasons. Summary Statistics for region. area R6: Western lowland forest and the Volta basin, Ghana-Cote d'Ivoire-Sierra Leone-Liberia-Guinea richness of which: endemic extinct or threatened Gastropods >=28 19 (plus 9 'near endemic') 2 CR Central-Southern Africa Zambezi River System. Upper and Middle Zambezi. (Brown, 1994)

Dam No. ofSpecies

No. of Endemics

Prosobranchia 3 22 2 Pulmonates 4 3 Bivalves

Lake Kariba: Zambezi River. (Brown, 1994) Area: 4300Km; Length, 300Km; Maximum Depth, 125m Year of closure 1958 (filled 1963) Brown (1994) lists the known gastropod fauna from the Upper and Middle Zambezi Riversystem. He notes that two species are endemic to the area, Gabbiella balovalensis and Gabiellazambica; both are from the family Hydrobiidae, and are found in very few localities. He notes thatthe headwaters and low tributaries are insufficiently known. Some species became established inthe lake soon after damming, due to the rapid expansion of the plant Salvinia.

Zaire Basin The lower Zaire Basin is one of the richer areas in central Africa, including the largest expanse oftropical lowland forest (Guineao-Congo). There are some classic accounts of the fauna of theregion given in Pilsbry & Bequeart (1927) and Mandahl-Barth (1968). The basin changes along itslength, with mountain torrents in the east, leveling to a sluggish stream, descending abruptly tothe central basin, where on the stretch between Kisangani to Kinshasa there is a drop of 100mover 200 km. The section beyond Kinshasa have series of rapids to Matadi, a distance of 350 km,and in these rapids there are species representing 5 endemic 'rheophilous' genera, belonging tothe prosobranch families Bithyniidae (Congodoma, Liminitesta) and Assimineidae (Pseudogibbula,Septariellina, Valvatorbis). These species adhere to bare rock, resisting fast currents and toleratinga wide range of water levels (Brown, 1994). Brown (1994) notes the uniqueness of the genusSeptariellina that resemble the freshwater limpets Ancylidae. area R7: Lower Zaire Basin (downstream of Kinshasa), Congo-Democratic Republic of Congo richness of which: endemic extinct or threatened Gastropods 96 24 1 EN

2 VU area R9: Madagascar richness of which: endemic extinct or threatened Gastropods 30 12 1 EN Endemic genus Melanatria. area L4: Lake Tanganyika, Burundi-Democratic Republic of Congo-Tanzania-Zambia richness of which: endemic extinct or threatened Gastropods 68 45 32 EN Bivalves 15 8 area L5: Lake Malawi, Malawi-Mozambique-Tanzanie richness of which: endemic extinct or threatened Gastropods 28 16 7 EN

1 VU Bivalves 9 1 area L6: Lake Victoria, Kenya-Tanzania-Uganda richness of which: endemic extinct or threatened Gastropods 28 13 5 EN

1 VU Bivalves 18 9

1.4.6. EUROPE (INCLUDING FORMER SOVIET UNION) area R10: Zrmanja River, former Yugoslavia Number richness endemic extinct or threatened Gastropods * 11 * 5 * Unknown * only hydrobioid snails area S4: Balkans region, former Yugoslavia-Austria-Bulgaria-Greece of which: richness endemic extinct or threatened Gastropods ca. 190 ca. 180 3 EX

9 CR 10 EN 3 VU

area L1: Lake Baikal, Russia Nearly180 species are known from Lake Baikal (Sitnikova, 1995), of which about 2/3rds areendemic to the lake system. The radiations include the hydrobid group, which are largely lakedwelling in Baikal, with the endemic genus Kobeltocochlea. Many of these species are currentlyincluded in the Russian Red List, but as they have not been evaluated in terms of the new IUCNcriteria, although in all liklihood, many of them will qualify under Vulnerable D2. Slugina et al (1994) noted that the bivalves, whilst not so numerous provide an important part ofthe biomass in the lake system. With endemic species of the family Sphaeriidae dominating thebenthic macrofauna on the bottom near shore area. richness of which: endemic extinct or threatened Gastropods Prosobranchs Pulmonates

147 64 83

114

Bivalves 31 14 area L7: Lake Ohrid and Ohrid basin, Albania-Former Yugoslavia richness of which: endemic extinct or threatened Gastropods 72 55 1 EX 1.4.7. AUSTRALIAN FRESHWATER MOLLUSCS Recent accounts of the freshwater molluscs of Australia are described in Mollusca: a southernsynthesis (Beesley, Ross & Wells, 1998), and the data is here is drawn from there, and otherreferenced sources. The main diversity of the Australian freshwater fauna lies in the family Hydrobiidae (springsnails), although endemic species are known within the Assimidae, Pomatiopsidae and theBithyinidae. Within the bivalves, the largest species are the freshwater mussels, such as thefamily Hyriidae (which is also present in South America), and this group was used by McMichael& Hisock (1958) to draw up biogeographical patterns for freshwater molluscs in Australia. Other

important families are the Corbulidae and the Sphaeriidae. The most cosmopolitan group is inthe pulmonates, similar to patterns of endemism seen in the USA. There has been a decline in freshwater biodiversity in river systems in Australia, where some ofthese groups were well adapted to the strong seasonality of the flow regimes (successive seasonswith flash flooding) are now reducing in abundance and diversity since control of river systems(Walker, 1985; Ponder, 1998). The best documented cases lie in the Murray-Darling RiverSystems. There the freshwater gastropods and bivalves in the system have dramatically declinedin recent decades. There are three reasons given for these declines: a. predation by the freshwater fish, especially the common carp (Cyprinus carpio) which becamewidespread in the 1960's. These fish also disturb the sediments on the river bed, leading todegradation of the habitats (Fletcher, Morison & Hume, 1985) b. changes in the flow patterns through intensive flow regulation after impoundments and weirconstruction c. possible changes in the biofilms of algae, bacteria and fungi which are a potential food sourcefor molluscs (Sheldon, 1994) area S5: Great Artesian basin, Australia richness of which: endemic extinct or threatened Gastropods area S6: Western Tasmania, Australia of which: richness endemic extinct or threatened Gastropods 4 EX 1.4.8. SE ASIA: NEW CALEDONIA & SULAWESI Much work is still being done in this region. Sulawesi & Indonesia Bouchet has already recognised the presence of 3 endemic freshwater genera: Tylomelania,Miratesta and Protanoylus. But there are many species still undescribed. In Lake Poso Bogan &Bouchet (1998) noted that all ten species currently recorded are endemic, but there are significantnew species such as Posotrea anomiodies which is a member of a new genus of the freshwater clamCorbiculidae. The new species was found cemented to a hard substrate, showing characterswhich are unique, for the region and the family, and as such places a higher conservation valueon the fauna of Lake Poso. Summary Statistics: area L3: Sulawesi (Lake Poso and the Malili lakes system), Indonesia richness of which: endemic extinct or threatened Gastropods ca.50 ca.40 1 EX Bivalves 5 2 1 EX area S7: New Caledonia of which: richness endemic extinct or threatened Gastropods 81 65 40 VU

3 EN 1 EX

LAKES area L2: Lake Biwa, Japan At present no species for this region has been list, which is a reflection of the non evaluationrather than the status of the fauna. Again many of these probably qualify as Vulnerable D2, if nothigher. richness of which: endemic extinct or threatened Gastropods 38 19 Bivalves 16 9 area L4: Lake Tanganyika, Burundi-Democratic Republic of Congo-Tanzania-Zambia richness of which: endemic extinct or threatened Gastropods 68 45 32 EN Bivalves 15 8 area L8: Lake Titicaca, Bolivia-Peru of which: richness endemic extinct or threatened Gastropods 24 15 area L9: Chilka Lake [brackish water], India of which: richness endemic extinct or threatened Gastropods 28 ca. 11 Unknown Bivalves 43 25 Unknown area L10: Inl_ Lake, Myanmar richness of which: endemic extinct or threatened Gastropods 25 9 Unknown Bivalves 4 2 Unknown The extinction crisis for the US freshwater mussels was recognised last century, where Higgins(1858) observed declines related to deforestation. Rhoads (1899) remarked on the decimation offreshwater bivalves in the lower Monongahela River above Pittsburgh due to pollution andOrtmann (1909) reported declines on the Tennessee River systems due to paper mill effluents.However documentation of the extinction crisis did not really gain momentum until the 1970’s(Athhearn, 1970; Heard, 1970; Stansberry, 1970; Taylor, 1970). Freshwater mussels (Bivalvia) areespecially vulnerable to habitat disturbance. These species have extended life cycles, some ofwhich span over 100 years, where maturity is delayed until 6 – 15 years (Bauer, 1993; Chesney &Oliver 1998). Some species also have reduced powers of dispersal, high juvenile mortality andlong turnover times. In the USA these mussels are most successful where water velocities are low

enough to allow substrate stability, but high enough to prevent excessive siltation. Similarconditions occur in Europe, although some species are adapted to surviving in silty/muddyenvironments. In the USA most rivers show a patchy distribution of mussels, with some areascontaining densely packed “beds”, which may be composed of many species, with other patchesof river bed being devoid of any species (Neves & Widlak, 1987)

2.0. UPSTREAM IMPACTS Frequently the data available for pre/post impoundment is assembled by the provision ofchecklists. These often do not indicate the absolute impact of impounments upstream of the site. It is clear that to some extent the impact depends on the type of flow into the reservoir and thenature of the channels. Direct reduction of species upstream relating to changes in river channel Molluscan survey was undertaken on a braided river that enters a reservoir on the River Inn inAustria; the river is currently dammed by weirs for hydroelectric production (Foeckler,Diepodder & Diechner, 1991). The data shows that there has been a decline upstream of thereservoir lossing 10 species (Table xx) and a drastic decline downstream of 38 species. Theupstream decline is due to changes in the flow regime, as since the braided system has beenmanaged by channelisation there has been an increase in river gradient of 1.3% deepening, thebed and consequently reducing the active floodplain area, with some marginal areas only beinginundated once every ten years. This has reduced biotype diversity with consequent loss ofspecies. Table xx. Decline in Freshwater Molluscan species within the Inn catchment since 1971 (dataabstracted from Foeckler, Diepodder & Diechner, 1991)

No. of species New species Species lost Current survey River Salzach

36 1 10

River Inn below reservoir.

7 ?38

Surveys by Seidel (1971-3)

45

They recognise the loss of species typical of temporary habitats (Segmentina nitida, Viviparuscontectus), the more demanding species of permanent water (Acroloxus lacustris, Radix ampla,Gyraulus crista, Anodonta anatina) and species requiring non-polluted water (Unio crassus, Pisidiumterinilineatum). Interesting they attribute some of these absences to the indirect effects of changed flow relating topresence of the reservoir downstream. They predict that the temporary habitat species such as the endangered species Segmentina nitidawill become extinct quickly in the region but most significant impacts are on their alpine specialspecies, which are not present in all rivers, such as Gyraulus acronicus.

2.1. Movement of species upstream Dam building activity which blocks migratory fish or changes fish communities can also impacton the freshwater mussel communities which depend on the fish as glochidial hosts. Dam construction at Lake Pepin on the Mississippi River lead to the demise of mussels upstreamof the dam, as the runs of skipjack herring, their host species, were blocked (Eddy & Underhill,1974). 2.2. Movement of nutrients upstream

3.0. LATERAL IMPACTS The major impact on molluscan biodiveristy is on the terrestrial areas adjacent to the currentriver system. Maintenance of areas of contiguous undisturbed land within this system is animportant consideration for molluscan conservation. For example In the steepsided valleys of theKwaZulu Natal province, dam construction, or any development that results in the loss orfragmentation of relatively pristine or untransformed habitat is likely to impact upon molluscpopulations. The reservoirs will not only eliminate terrestrial molluscs in the areas to be flooded,they will also transform the habitat in their immediate neighbourhood. This could also result inthe formation of an in-valley barrier, separating up-stream and down-stream populations(depending on the width of the valley and the height of the dam). This would obviously impactupon gene flow and population dynamics in low vagility invertebrates such as molluscs. Rogers (1995) examined riparian wetlands (including riverine forests and thicket) and concludedthat in southern Africa these habitats were under severe threat, especially from alien biotas. In South America there are possible species extinctions related to loss of gallery forest adjacent torivers which are now submerged following construction of the Salto Grande Dam. The land-snailAnthinus albolabiatus (Jaeckel, 1927) (Mollusca; Gastropoda:Strophcheilidae) was formerlyendemic to Gallery Forest of Uruguay River and has been submitted for inclusion in the IUCNRed List of Threatened Animals. 3.1. Movement of species laterally 3.2. Movement of nutrients laterally 3.3. Water table changes A high number of endemic Spring-snails (Family Hydrobiidae) live in small geographicallyrestricted habitats located in the headwater of the main channels and tributaries within the watercatchments. This group of species is second most endangered groups within freshwater molluscs.In Europe, Australia and the USA, this species group usually comprises c. 20% of the totalfreshwater fauna. The species are already under pressure from water abstraction at the springs and from habitatalteration to facilitate abstraction, although a more indirect threat is from reduction ofgroundwater levels. Such changes can result from impoundment and the consequent impact onthe flow regime and groundwater recharge within the catchment.

4.0. RESERVOIR IMPACTS A. Construction impacts

4.1. Site impacts (effects on river environment & biota at site) Stresses associated with site disturbance, such as dam contruction resulting in physicaldisturbance of the river bed may cause species from the bivalve groups superfamily Unionidea toprematurely empty their brood pouches of glochidia resulting in reproductive decline (Howells etal., 1996). 4.2. Off-site impacts (materials for dam, access roads, etc.) Riparian habitats, such as gallery forest and marsh also hold unique species, which are sensitiveto disturbance during the construction phase. The destruction of habitats for temporary roadsleads to loss of species, which maybe permanent or temporary, depending on the degree ofdegradation and the amount of habitat fragmentation. Increased traffic of heavy lorries on the access roads leads to the increased dust which coats thelocal vegetation degrading the adjacent habitats. However, data on such losses are rarelyreported, and hence it is difficult to quantify such claims. B. Post-construction impacts of reservoir 4.3. Running to still water impacts - reduces lotic, increases lentic biota There are several sections in this report which observe the extinctions or threats to molluscspecies from rapids on the rivers systems, notably in Africa, North and South America. Such data is also available for decline in local species richness for Europe, for example Fruget(1991) found that partitioning with a series of dams on the lower Rhone, had an influence on theresultant macroinvertebrate community structure and distribution, especially due to changes inflow velocity. The Lower Rhône has a significant number of low level dams for hydroelectricproduction and irrigation schemes. Most were constructed between 1957 and 1985, althoughchannel management was an ongoing process in the industrialisation period in France. Only 19species of Mollusc were recorded, although this was the most taxonomically diverse group ofmacroinvertebrate in the sampling sites along the river. In terms of relative abundance, molluscsformed 7% of total fauna, significantly less than the Chironomids (61%), as as such thesignificance in this case is the loss of diveristy, rather an impact on the biomass, as is the case withthe Chironomids. However, the creation of the dam can also reduce lentic taxa, through channel management afterconstruction. For example, river regulation on the lower Murray River in Australia has altered thenormal flooding regime leading to alienation of the billabongs (low Ox-bow lakes) from the mainchannel. These lentic macrohabitats (billabongs and backwaters) are characterised by a highdensity of scrapers, especially freshwater gastropods. Since regulation was introduced someMollusc species have become extinct (Boulton & Lloyd , 1991). 4.4. Creates new sublittoral and profundal zones The construction of the dam on the Lake Volta in West Africa, and the subsequent colonisation ofthe lake by Bulinus truneatus, a freshwater pulmonate, lead to an increase in the level of urinaryschistomiasis reported in the region (See list of publications in Brown, 1994). Prior to theconstruction of the dam, this species was rare, other species from the same genus such as Bulinusglobosus, were more common. However, the latter species was unable to exploit the new habitat inthe littoral zone, as it cannot tolerate the lake-level fluctuations. Bulinus truneatus, on the otherhand, uses the aquatic vegetation such as Ceratophyllum demersum, and dense populations survivein these stands. Thus there has been a change in the species assemblages found pre-impoundment and post-impoundment resulting from changes in the littoral zone, and with the

additional consequences of increase in human diseases, associated with the colonising molluscanspecies. 4.5. Water level fluctuation impacts Brown (1994) describes the gastropod diversity of some of the man made lakes in Africa whichare comparable in size to the larger natural lakes. These lakes are the result of dam constructionfor economic reasons; usually hydroelectric power generation. The outflow from these lakesdiffers from the natural lakes, with most man made lakes suffering seasonal draw-down as flowout from the lakes is regulated to ensure that the large inflow during the rainy season can becontained. This gives a very unstable littoral zone, which in itself will place special stresses onaquatic life at the margins; a factor which will restrict the number of mollusc species which cansurvive in the lake. 4.6. Chemistry changes (mercury, humic acids, etc.) Reservoir construction may alter water chemistry which may in turn impact on successfulspawning of mussels (Isom, 1971). Bivlave species are very sensitive to water chemistry, as thetranslocation experiments on endangered mussel species in Europe has shown, as changes inweater chemistry can lead to stress triggering release of glochoidea during unsuitable flow/waterconditions. In Africa, Brown (1994) notes that the salinity of the man made lakes remains quite low, despitethe degree of evaporation, partly related to the annual flow regime (and high in flow). In contrast the contruction of dams on the Murray-Darling rivers in Australia has led to increasesalinities in the reservoir water, but there is no evidence to suggest that these increases have hadany impact on the freshwater mussels in the system (Vickery 1978; Walker 1981). However thesalinity levels of water in the evaporation basins used to store irrigation return water in theMurray-Darling system, is listed as having an impact on molluscs (Walker, 1998). Dissolved oxygen levels below 20% saturation can cause stress to freshwater mussels (Ellis 1937,Ingram 1957), although some species can withstand brief periods of low oxygen levels. 4.7. Physical changes to the fluvial system 4.7.1.Physical disturbance Stresses associated with site disturbance, through harvesting, artificial disturbance of bed forfishing purposes or navigation may cause species from the bivalve groups superfamily Unionideato prematurely empty their brood pouches resulting in reproductive decline (Howells et al.,(1996). 4.7.2. Increased siltation The greatest diversity in the prosobranch gastropod fauna in the USA is found in the Mobile BayRiver basin, and the Tennessee River Basin, with 7 % of total taxa now extinct (Bogan, 1998).Most of the extinctions in this group (38 out of 42 taxa) are in the Mobile Bay fauna, when the bigriver shoal fauna was impounded and covered by deep standing water and subsequent siltation. Fuller (1974) considered siltation to be a major factor impacting mussel communities in the US.Howells et al (1996) suggest that some freshwater mussel species may be unable to survive siltoverlays greater than 0.6cm, in contrast, other species may emerge from silt overlays of 18cm,although some species need to emerge within a few hours of overlay or they will die. Howells etal. (1996) also noted that the presence of silt in suspended load may reduce the feeding efficiencyof filter-feeding bivalves.

In Texas Neck (1982) noted that reservoir construction was probably the most significant factorinfluencing mussel populations. In Texas only one natural lake existed prior to the constructionof reservoir dams. He gives one possible reason for a reduction in the number of mussel speciesin the state as inability to colonise areas which were newly formed silt beds, as the species locallyavailable were not adapted to living within silt beds. 4.7.3. Temperature Early work in the US, when the demise of large Unionid bivalves was becoming apparent, ledIsom (1971) to conclude that reservoir construction may alter water temperature which may inturn impact on successful spawning of mussels. More recent work on freshwater musselsconfirms these findings, where temperature affects growth and the duration of the growingseason (Tevesz & Carter, 1980). 4.7.4 Dissolved oxygen Dissolved oxygen levels below 20% saturation can cause stress to freshwater mussels (Ellis 1937,Ingram 1957), although some species can withstand brief periods of low oxygen levels. 4.12 SITE SHADING, AND ADJACENT VEGETATION Whilst freshwater mussels can survive, in the sort term, removal of the shading trees adjacent to achannel, will lead, in the long term, to a decline as growth rates are potential controlling agents ofunionid distribution (Morris & Corkum, 1999). Species that grow in rivers dominated withforested riparian vegetation show slow growth through life, whereas species which dominate ingrassy rivers have rapid early growth, and achieve a smaller maximum size at a younger age.(Morris & Corkum, 1999). This shading thus effects the species which can in the long termsurvive in the channel, and some mussel species are known to attempt to relocate to morefavourable habitats downstream. 4.13 GENETIC VARIABILITY IN RESERVOIR POPULATIONS OF PROSOBRNACH MOLLUSCS IN ISRAEL The freshwater prosobranch genus Melanopsis is a key group in many studies concerningsystematics, parasitology, ecology, palaeontology and evolution (Heller et al. in press). TheJordan Valley has highly variable populations of Melanopsis and in fossil sediments (in whichMelanopsis is very abundant). Heller (in press) describes the shell morpometrics sites within this region. Within Melanopsiscostata Heller et al (in press) distinguish three groups, and tentatively suggest that they may besubspecies. Shells from the upper Jordan River are elongate (M. c. costata); those from LakeKinneret are stout (M. c. jordanica); and in those of the Yarmouk each rib consists of a pronouncedupper tubercule, fused to a pronounced, straight lower ridge (M. c. noetlingi). Heller et al. (in press) describes the former environment where the water level of Lake Kinneretused to fluctuate annually at an average of 0.80–1.00 m (maximum 1.50 m). In 1932 the Kinneretwas dammed and its outlet deepened to construct a hydro-electrical plant, and from that yearonwards annual fluctuations in the water level increased to 3 m. In 1964, when the lake becameIsrael’s major reservoir, its level was increased by 1 m; and was left at peak levels for much longerperiods than in its natural condition (Nun, 1977). The small, stout shell of M. c. jordanicacorrelates with a stormy habitat. A stout, globose shell could accommodate more foot muscle andthus enable a stronger adherence to rocks and boulders during severe storms. Melamposis c.jordanica is found in Lake Kinneret (170 km2), which differs from the Jordan in its frequentstorms. Daily from April to October, a western breeze from the Mediterranean Sea reaches theKinneret at about noon. This breeze causes the lake to become wavy, choppy or stormy until latein the evening. From December to mid-March there is no western breeze, but strong easternwinds from the Syrian desert (the ‘Sharkiyeh”) then frequently reach the lake causing similareffects (Heller, 1979a). Two snail-predating fish, Barbus longiceps and Blennius fluviatilis, are found

in Israel mainly in Lake Kinneret (Heller, 1979a); they may perhaps exert some selection on shellcolours. M. c. jordanica occurs only along rocky shores of the Kinneret, consisting of gravel,cobble, stones and boulders; and is not found on muddy shores consisting of muds, sands andsilts. It occurs down to a depth of 5 m (Tchernov, 1975a; Raanan, 1986). Further, in its naturalcondition the lake’s salinity was almost 400 mg/l (chlorinity). Recent diverting of haline springsfrom the lake has decreased its salinity to about 200 mg/l (Nun, 1977). Today’s major habitat ofM. c. jordanica is thus very disturbed. Beyond Lake Kinneret, M. c. jordanica occurs in the upperreaches of the lower Jordan River, from the exit of Lake Kinneret another 2 km downstream, toDeganiya (beyond which the Jordan is polluted and no Melanopsis are found for quite adistance). Specimens in the National Mollusc collection record itspresence also 30 kmdownstream (Dalhamya, Shifa). Raanan (1986) suggested that the black and banded morphs of M. costata of Lake Kinneret maybelong to two separate species, with incomplete reproductive isolation. However conchiometricand electrophoretic studies do not support this suggestion (Marko, 1984; Altman & Ritte, 1996). In the small, 1 km-long section of the north-eastern shores of Lake Kinneret, from the UpperJordan outlet to the Nahal Meshoshim outlet, shells intermediate between M. c. jordanica and M.c.costata were found. This small stretch has undergone considerable changes since the draining ofthe Hula in 1958: large quantities of sediment that once used to be deposited in the Hula todayreach the Kinneret where they have created a rapidly expanding delta, into which the river bed ofthe Jordan now extends about 1 km eastwards, towards the Nahal Meshoshim outlet (Nun, 1977).Heller et al (op cit) point out that it is noteworthy that among 35 samples of Lake Kinneret whoseisozymes were examined by Altman & Ritte (1996), their two samples from Nahal Meshoshimoutlet had the lowest average genotypic similarity. Their evidence (based upon electrophoresis)supports Heller et al. (op cit) suggestion (based on conchiometrics) that the Meshoshim outletpopulation differs from other populations of Lake Kinneret (which are jordanica) in that it isintermediate between M.c. jordanica and M.c. costata. In the lower reaches of the lower Jordananother shell occurs, M. c. noetlingi. In zones of contact the three species largely remain distinct. Hybrids are found in overlappingzones of no more than a few hundred m, and at low frequencies. This suggests that the speciesmaintain their distinct genetic integrities, and that the narrow hybrid zones act as substantial, butnot absolute barriers to gene flow. Tchernov (1975b) notes that the smooth and costatedMelanopsis interbreed, at sites where small water bodies reach the shore of Lake Kinneret.Situations comparable to Melanopsis, where taxa maintain their integrity yet hybridize at the edgeof their geographical or ecological distributions, have been found in a variety of animals,including mammals, birds, amphibians, reptiles, orthopterans and butterflies (Grant & Grant,1992; Harrison, 1993; Werner & Watson, 1996; Jiggins et al. 1996). Among gastropods however,only few cases of hybrid zones have been reported. Heller et al. (op cit.) do not comment on the possible role that damming has played in thechanging genetic composotion of these populations, howver, given the nature of this freshwatergenus, it is extremely likely that envionmental changes within the Lake resulting from changesafter damming in 1930’s may well have played a part.

5.0. DOWNSTREAM IMPACTS Neves (1999, pers. comm) is his recent review of impact construction of impoundments onmolluscan species richness provides the data in Table 5.0.1. This shows that there has been adecline of between 40% and 80% loss from the original diversity levels of these rivers, over a

period of 50 years. The figures in post dam richness also indicate the stretches downstream ofthe dam where the bed is devoid of mussels. Table 5.0.1 Impact of Dam contruction and impoundments on Molluscan biodiversity in the USA (Neves,1999; conference presentation)

Dam/Date

Pre-Dam Richness

Post-Dam Richness

Center Hill, Caney Fork

(1948)

39 species (pre-1940)

7 species (>12 km)

Demopolis, Tombigbee R.

(1954)

50 species (1933-35)

29 species (1992)

Wolf Creek, Cumberland R.

(1952)

39 species (1947-49)

11 species (1984) 4 species (1993)

(>18 km) Table 5.0.2 Mollusca Species present within reservoir region, USA Source: Neves, 1999.

Reservoir Date

Preimpoundment Richness

Postimpoundment Richness

Norris, Clinch R.

(1937)

40 species (1935-37)

12 species (1990’s)

Center Hill, Caney Fork

(1948)

39 species (pre-1940)

2 species (1993)

Cumberland, Cumberland R.

(1952)

59 species (1947-49)

16 species (1961)

Wheeler,

Tennessee R. (1936)

>60 species (pre-1935)

38 species (1960-69) 18 species

(1991) Demopolis,

Tombigbee R. (1954)

50 species (1933-35)

8 species

Demopolis/Warrior, WarriorR.

(1954/57)

48 species (pre-1950)

13 species (1972-75)

Vaughan & Taylor (1999) looked at molluscan distributions along a 240 km stretch of the LittleRiver in Oklahoma finding that there was a mussel extinction gradient downstream from largeimpoundments, where with increasing distance from the dam there was a relative increase inmussel species richness and species abundance. The general distribution of mussels was nestedreflecting the distance from the dam on the river and its tributaries, with only those stretchesfurthest from the dam containing the relatively rare species. After the next dam downstream, thesame trends were apparent, but apparently weaker, with reduced mussel abundance overall.

5.1. Seasonality of flow 5.2. Change in flow regime Australian freshwater mussels Alathyria jacksoni and Velesunio ambiguus have different habitatpreferences in the Murray-Darling river system, the former being a large river species, which isless tolerant of environmental changes, and is particularly vulnerable to dehydration (Walker,1998). Velesunio ambiguus occurs in temporary pools, lakes and minor streams and can survive outof water for up to a year (Walker, 1998). The flow regime in Murray-Darling basin is influencedby dams and weirs with the consequence that the habitats occupied by these species are lessdistinct. However, below the Darling confluence the dams have been replaced by weirs, which isa habitat which is more favourable for Velesunio ambiguus and Walker (1981) found fromarchaeological studies that Alathyria jacksoni has declined in abundance, whereas Velesunioambiguus has increased in abundance. 5.2.1. Increase in flow High water velocities can displace the setting of juvenile mussels in freshwater systems beforethey have an opportunity to settle on the bed (Layzer & Madison, 1993; Chesney & Oliver, 1998). It may also have indirect effects, causing:

• more bedload movement damaging molluscs ( juvenile mussels are especiallyvulnerable; Young & Williams, 1983).

• increased bed erosion moving material (and contained mussels downstream)• decreasing habitat complexity through closing oxbow type channels ( see above

sections)Williams et al (1993) suggest that sediment stability might be one of the most critical habitatrequirments for freshwater mussels.5.2.1. Decreases in flowLong periods of low flow below dams, can result in stranding of mussels (Fisher and Lavoy, 1972;Chesney & Oliver, 1998). Mussels are unable to repond quickly to changes in water flow, asalthough they are able to relocate if conditions become poor, they move slowly. If the musslkesurvive the stranding, the stresses will have lead to a loss of the glochidia, and may lead to alonger term reproductive decline ( McMahon, 1991; Chesney & Oliver 1998).

5.3. Physical changes (temperature, oxygen, & other water quality measures)

5.3.1 Water temperatures downstream of damWater releases downstream during summer months in US river systems are colder than the waterentering the reservoir. In some river systems this has been shown to reduce, or even eliminatemussel populations (Ahlstedt, 1983; Miller et. Al. 1984 Lydeard & Mayden, 1995). This is due tothe suppression of the mussel metabolic rates at a rtime when growth should be high, which inturn leads to a suppression of reproduction (Vaughn & Taylor, 1999).

There are other indirect results of water temperature changes relating to the changing fishdistributions. Vaughn and Taylor (1999) described the replacement of warm-water fish withmore tolerant species and introuduced coldwater species such as Rainbow (Oncorhyncus mykiss)and Brown trout (Salmo trutta) as porviding a potential permanent colonisation barrier tomussels, given the fact mussels species require specific host species, and to a large extent most ofhost fish species are unknown.

5.3.3. Salinisation

In Australia, there has been dam construction and weirs in the Murray-Darling basin, changingthe flow regimes, there is less distinction between the occupied habitats of two mussel species,but below the Darling confluence the dams have been replaced by*****File corrupted….get the back up version from Desktop NMGW

mussel species Hyridella glenelgensis ( Bivalve: Unionidae) which lives in the Glenelg River systemof south-west Victoria, is cited as being at risk through water diversions and salinisation (Walker,1998).Not all salinisation is the direct effect of dam construction, but additional factors such as landclearence is given as a possible reason for the decline of the species Westralunio carteri from theAvon river system in western Australia (Kendrick 1976).

5.4. Turbidity and sedimentIn the Tennessee River Basin a number of Pleurocerid gastropod species are under threat, as theypersist on clean swept shoal areas below dams on the river (Bogan, 1998). These areas are at riskfrom increased sedimentation and changes in flow regime.

5.5. Water velocity

5.6. Downstream lakes

5.7. Changes to food chain

The gastropod fauna of the River Murray has declined from 18 species (recorded from varioussources: Museum collections, Publications and Archaeological middens) to a single abundantnative species , a limpet from the genus Ferrissia and an introduced species Physa acuta (Sheldon& Walker, 1993). The survival of this limpet is attributed to shape of the radula, and the smallsize of the animal, which Botting (1995) believed would allow the species to exploit the minuteparticles associated with the biofilms, and that most of the larger species would not have accessto this food source. Sheldon (1994) believes that there have been changes in the biofilms of algae,bacteria and fungi in the Murray River which are a potential food source for molluscs, and thatthis factor, along with predation and flow regulation accounts for the decline of species in thesystem.Most of these species are still present elsewhere in the Murray-Darling basin, but one species forthe family Viviparidae Notopala hanleyi, is believed to be extinct in its natural habitat, remainingas an abundant species in three irrigation pipelines in South Australia, where it is regarded as apest species, which requires control to allow water flow for irrigation.

8.2. Agriculture, forestry, industry and municipal effects

The reservoirs created by dams are often used for recreational activities such as fishing andboating. New species can be introduced by these activities into the catchment area. In the case ofMollusca, fish stocking by species outside their native catchment areas can introduce newfreshwater mussels, where juveniles, which had their glochidial stage on the fish are released inthe reservoir, and conditions there are suitable for the survival of the species. Howells et al (1996)cite two cases in Texas, where ponds and reservoirs have new distribution records of the “floater”freshwater mussel groups.

8.3. Medical implications of changing molluscan species in riversHydropower and irrigation projects carry the risk of increasing the local prevalence of snail-transmitted diseases in both humans and livestock. These diseases are caused by two main types

of parasitic helminthes: flukes (Trematoda) and roundworms (Nematoda). Both these groups oforganisms have complex life cycles that involve periods in larval hosts, such as snails and anadult phase in birds or mammals. These hosts are usually very specific, and the increase indisease results from decline of the native species, and increase in abundance of the host species,sometimes replacing the natives as there were “alien” to that specific catchment area.Burch & Upatham (1989) list those snail species which are known to be intermediate hosts, andindicates their distributions and parasites in the Meokng River basin. Although there are over 50species of Pomatiopsidae recognised in the Mekong basin, only two are though to beintermediate hosts for human parasites (Neotricula species).

Schistomiasis:In the Mekong river Schneider et al. (1984) believed that these was an increase in parasitetransmission resulting from proposed impoundments which change river habitat and ecology.This is because the species which can act as hosts become more prolific as they are adapted to thenew environments whereas other similar species which are not vectors, (usually in the samegenus or closely related species) decline in abundance, and maybe lost to the river system(Woodruff & Upatham, 1992). In Thailand in 1992 the Pak Mun hydropower and irrigationproject caused controversy as to whether the blood flukes which pass on Schistomiasis wouldbecome established from the nearest known source in Laos (Usher, 1991).

Paragonimiasis:The knowledge in 1992, suggested that molluscs were not the source of this disease in theMekong basin, as the creation of new habitats has not yet led to the expansion of the known snailvectors into Thailand. However, there remains a chance that the snails may become establishedand impact on the local species of the genus Brotia.

Opisthorchiasis:There are 12 species of the freshwater prosobranch Bithynia recognised in Thailand, but only thethree species in the subgenus Digniostoma transmit Opisthorchis viverrini. These species can live atvery high densities and are usually found in rice fields, canals, ponds and lakes. Riverimpoundment has led to an increase in the abundance of these three species, and diseaseoutbreaks were noted at the time of construction of the Ubolratana (or Nam Pong) Dam in NEThailand (Woodruff & Upatham, 1992).

Echinostomatiasis:Schneider et al. (1984) predicted that proposed impoundments would lead to an increase in theincidence of infections and increasing disease severity.

Table 8.3.1Human diseases, where Molluscs act as intermediate hosts, which may be increasing as the resultof impoundation in Thailand(Data abstracted from Woodruff & Upatham, 1992)

Disease Intermediate hosts Source of InformationSchistomiasisBlood-Fluke:

Schistoma japonicum

Molluscs:Oncomelania spp.Neotricula spp.

Woodruff & Upatham (1992)

ParagonimiasisParagonimia heterotremus

( N.B. P. westamani has not

Molluscs:

Brotia asperata

Woodruff & Upatham (1992)

been recorded from humans inthe Mekong basin yet) Melanoides tuberculata

Tarebia graniferaOpisthorchiasis:

Opisthorchis viverrini

Molluscs:

Bithynia funiculata

Bithynia siamensis

Bithynia goniomphalos

Woodruff & Upatham (1992)

EchinostomatiasisNumerous Echinostomespecies

Molluscs:Various hosts including Pilaampullacea, P. polita, Radixrubiginosa, Indoplanorbisexustus, Filopaludina spp.

Woodruff & Upatham (1992)

9.0. PRIORITY OF IMPACTS

9.1.3 Loss of keystone speciesStein & Flack (1996) points out that the current decline of freshwater mussels in the MississippiBasin will have a detrimental role to the entire ecosystem. They point out that the freshwatermussels play an important role in sediment mixing and nutrient recycling, and given theirdominance in terms of biomass, their removal could have long-term recupercussions, as yetunknown.

9.1.4 Loss of stocks of economic speciesMany of the declining mussel species were traditionally used in the button industry, andincreasingly for the use as seeding material for pearl production. Thus ultimately there will be aeconomic loss to the region.In terms of the economic losses, Bowen et al. (1994) estimated that the annual value of unionidshell exports to Japan exceed $40 million, and the Zebra mussel, which will continue to exist inthe river systems, is not a suitable substitute.

9.2. Highest priority impactsThese can be ordered in terms as those that are not reversible; that is the direct loss of habitat, asmitigation and habitat creation rarely recreates the existing habitat, in terms of it’s original speciescomposition.

9.2.1 Loss of habitat under areas of impoundmenta. Extinctions in Mollusca directly associated with dam construction occur with the loss of“rapid” habitats within river systems, as frequently these contain endemic species.b. Local extirpation of species in the adjacent riparian forests, which can with localised specieslead to fragmentation of populations ultimately threatening the species.Care should be taken during Environmental Impact Assessments to make sufficient provision forinvertebrate surveys of these habitats.

9.2.2. Preventation of migratory routes for fish hosts

After dam construction and impoundment, unless sufficient provision is made for migratoryspecies, another severe impact is the preventation of fish movments leading to decline in themussels that utilise the fish as a host during the life cycle.Care should be taken during design phase to design suitable fish passes which will not stress thefish, which may impact on the mussel species.

9.2.3 Changing bed characteristicsSiltation after the impoundment leads to loss both of species within the reservoir area, and on thesteam bed downstream of the dam.

10.0. CUMULATIVE EFFECTS

10.1. Are there other dams on the river or drainage basin?

Some of the river systems here have more than one dam, which has in itself contributed to localextinctions.

If several large dams are required on a single river system, this could have severe impacts onmolluscan diversity and abundance, and considerable lengths of undisturbed beds are requiredto overcome the effect of a single impoundment. To prevent extinctions where large dams areessential, preference should be given to designs that favour long lengths of undisturbed streambed.

10.2 What are additive or synergistic effects of the planned dam in combination?

10.2.1 Extinctions and Decline in Biodiversity

The impact of dam contruction on biodiversity is a combined function with other factorsincluding:

Pollution:in the USA and Europe water pollution, especially in large river systems has been a serious factorcausing decline in mollusc biodiversity since the beginnings of large-scale industry. Theseindustries used river systems to abstract water for power, dispose of liquid waste and dischargeused water. In more recent decades industrialisation has had a similar impact on rivers in SEAsia, India and Australia.

Exploitation:Direct harvesting of freshwater bivalves providing shell for the button industry has been a majorfactor contributing to the decline of mussels in the USA (Bogan, 1998) and India (Subbao Rao,1978). In addition shell in both of these regions is now used for seeding pearl oysters, and thefishing of mussels for their own pearls has been an on-going industry for over 2000 years, asRoman exploitation is known.

Alien Species:In the USA and South America a new factor, alien species is causing extinctions of an alreadydepleted fauna. The combination of the Zebra mussel (Dreissena polymorpha) and the AsianFreshwater clam (Corbibula fulminalis) is causing decline of many native freshwater species (Stein& Flack, 1996).

In recent years, the spread of the Zebra mussel in particular has had the most profound impact interms of threatening US freshwater mussels. The Zebra mussel has a different life cycle, partly

due to the lack of a need for a host fish, and partly as it can anchor. The native mussels are largeenough to be used as a anchoring point for Zebra mussels and thus they become smothered byhigh densities of the non-native species.

Ricciardi, Neves & Rasmussen (1998) estimated the decline period for various lakes and rivers inNorth America. They show that after colonisation of Dreissena polymorpha to Lake Erie, LakeOneida and Lake Wawasee decline of the native mussels happened within 4 years, whereas inLake St Clair and Detroit River decline took eight years. They noted that most of the GreatLake/St Lawrence and Hudson River species were not endemic, thus the losses do not representglobal extinctions. However, as already noted the Mississippi river system, could lose 60endemic species. Of these species c. 65% only exist in large channels and mainstem channels (38species) which are those parts of the river system which are most vulnerable to invasions ofDreissena polymorpha. However, although the smaller channels may not be as vulnerable to theinvasion of D. polymorpha, Ricciardi et al (1998) point out that the fragmentation of thesepopulations in these channels may increase the likelihood of extinction from other anthropogeniceffects such as regulation of flow after impoundment’s.

Ricciardi et al (1998) also point out that as survivorship of the glochidia is already low and thatthe larval dispersal is restricted by dams (Williams et al. 1992), the recovery potential througheither immigration or recolonisation for the large Unioids is reduced.

Based on the known losses of freshwater mollusc species, Ricciardi et al. (1998) provide estimatesof projected extinction curves, one extrapolating that without the Zebra Mussel the species losswould have equated to 1.2% per decade, but with the Zebra Mussel the rate reaches 12% perdecade. However, when the number of functionally extinct species are taken into account thepredicted species loss, without the Zebra Mussel increases to 4.2% per decade. This led Ricciardiet al. (1998) to conclude that the estimates of 12% per decade, are in fact conservative, as otherfactors such river regulation are not diminishing, thus unless major river restoration programmesare undertaken, these species are in grave danger of extinction.

[Insert Figure 1 from Ricciardi ?]

10.2.2. Increase in Medical problems

Recommendations

1) Use stabilisation methods for the riverbed which do not impact on the invertebratecommunities.

2) Protect water supplies including ground water.3) Protect adjacent riparian forests, preventing development of monocultures, especially those

of alien species.4) Preserve fish fauna, allowing free movement beyond impoundments.5) Chesney & Oliver (1998) point out that in-situ conservation which preserves genetic identity

and leads to recognition of local adaptations is preferable to conservation throughtranslocation as this affects the gene pool and should only be used in extreme circumstances.

Put more funding and effort into at the problems of translocation and captive breeding.

MBS: Material to incorporate, then dump

Thailand has 170 species, with 96 brackish water species recognised, however few of these speciestransmit human diseases at present.

Number Pest speciesOrder 6Families 23Genera 75Freshwater species 170 + < 20Brackish water species 96

Burch & Upatham (1989) list those species which are known to be intermediate hosts, andindicates their distributions and parasites.Although there are over 50 species of Pomatiopsidae recognised in the Mekong basin, only twoare though to be intermediate hosts for human parasites (Neotricula species).

MBS: Material to incorporate, then dump

Woodruff D.S. & Upatham E. Suchart (1992) Snail transmitted diseases of medical and vetinaryimportance in Thailand & the Mekong Valley Journal of Medical and Applied Malacology, 4: 1 –12Burch, J.B. & Upatham E. Suchart (1989) Medically important mollusks of Thailand Journal ofMedical and Applied Malacology, 1: 1 –9.

Hydropower and irrigation projects carry the risk of increasing the local prevalence of snail-transmitted diseases in both humans and livestock. These diseases are caused by two main typesof parasitic helminthes: flukes (Trematoda) and roundworms (Nematoda). Both these groups oforganisms have complex life cycles that involve periods in larval hosts, such as snails and anadult phase in birds or mammals. These hosts are usually very specific, and the increase indisease results from decline of the native species, and increase in abundance of the host species,sometimes replacing the natives as there were “alien” to that specific catchment area.

Schistomiasis: Schneider et al. (1984) believed that these was an increase in parasite transmissionresulting from proposed impoundments which cahgne river habitat and ecology. This is becausethe species which can act as hosts become more prolific as they are adapted to the newenvironments whereas other similar species which are not vectors, (usually in the same genus orclosely related species) decline in abundance, and maybe lost to the river system. In Thailand in1992 the Pak Mun hydropower and irrigation project caused controversy as to whether the bloodflukes which pass on Schistomiasis would become established from the nearest known source inLaos (Usher, 1991).

Paragonimiasis: The knowledge in 1992, suggested that molluscs were not the source of thisdisease in the Mekong basin, as the creation of new habitats has not yet led to the expansion ofthe known snail vectors into Thailand. However, there remains a chance that the snails maybecome established and impact on the local species of the genus Brotia.

Opisthorchiasis: There are 12 species of the freshwater prosobranch Bithynia recognised inThailand, but only the three species in the subgenus Digniostoma transmit Opisthorchis viverrini.These species can live at very high densities and are usually found in rice fields, canals, pondsand lakes. River impoundment has led to an increase in the abundance of these three species, anddisease outbreaks were noted at the time of construction of the Ubolratana (or Nam Pong) Dam inNE Thailand Woodruff & Upatham, 1992).

Echinostomatiasis: Schneider et al. (1984) predicted that proposed impoundments would lead toan increase in the incidence of infections and increasing disease severity.

Table XXHuman diseases, where Molluscs act as intermediate hosts, which may be increasing as the resultof impoundation in Thailand (Data abstracted from Woodruff & Upatham, 1992)

Disease Intermediate hosts Source of InformationSchistomiasisBlood-Fluke:

Schistoma japonicum

Molluscs:Oncomelania spp.Neotricula spp.

Woodruff & Upatham (1992)

ParagonimiasisParagonimia heterotremus

( N.B. P. westamani has notbeen recorded from humans inthe Mekong basin yet)

Molluscs:

Brotia asperata

Melanoides tuberculata

Tarebia granifera

Woodruff & Upatham (1992)

Opisthorchiasis:

Opisthorchis viverrini

Molluscs:

Bithynia funiculata

Bithynia siamensis

Bithynia goniomphalos

Woodruff & Upatham (1992)

EchinostomatiasisNumerous Echinostomespecies

Molluscs:Various hosts including Pilaampullacea, P. polita, Radixrubiginosa, Indoplanorbisexustus, Filopaludina spp.

Woodruff & Upatham (1992)