Indian Journal of Marine SciencesVol. 19, September 1990, pp. 159-164

Macro and meiofaunal abundance in six sandy beaches ofLakshadweep islands

Z A Ansari. Prita Ramani, C U Rivonker & A H ParulekarNational Institute of Oceanography. Dona Paula, Goa 403004, India

1_ Received 28 September 1989. revised II June 1990

L The macro and meiofauna were investigated quantitatively. Of the 8 macrofaunal taxa recorded. thepolychaetes and crustaceans made up the bulk of the population and biomass on all beaches. Total macrofau-nal density varied from 71 to 3 I57.m -2 and biomass from 5.22 to 325.1 g.m - 2. High meiofaunal density(2620-6555.10 cm -2) was recorded at most of the beaches and these were made up mainly of nematodes(46.7%) and benthic copepodes (23.7%). On all beaches the meiofauna tended to be concentrated at thosetide levels where no high degree of desiccation of the sand occurred. Macrofauna and meiofa una biomasswere extrapolated to I III transect of beach giving macrofaunal values of26.12 to 975 g. ( I III transect) - I andmeiofaunal values of295.7 to 794.5 g. (I m transect) - I. Based on biomass, meiofauna contributed more than50% to the total production on all the beaches. The macrofauna/meiofauna ratio gave low values indicatingthe dominance of meiofauna on all beaches.

I

I

Sandy shores provide an environment of high physi-cal stress to marine fauna, as a result of which relativ-ely few species inhabit this zone. Different authorsstudying the intertidal macro and meiofauna. havereported Impoverished macrofauna but abundantand diverse meiofauna I -4. Quantitative studies onthe intertidal coralline sandy sediment ofIndo-Paci-fie coral atolls in general and Lakshadweep in partic-ular. are very few. Some studies have been carried outon macro and meiofauna of Polynesian atolls'. PromLakshadweep archipelago reports?" H on molluscanand benthic faunal distribution in the intertidal sandofKavaratti atoll and other beaches are available. Inthe present study an attempt was made to give compa-rative account of intertidal macro and mciobcnthos,on quantitative basis. of the 6 beaches. namely Agani,Kalpeni, Bingararn, Kavaratti . Minicoy and Kad-mat atoll of Lakshadweep.

Lakshadweep archipelago consists of 12 atolls and5 submerged banks. Except Minicoy. the Agaui. Kal-peni, Bingaram, Kavaratti and Kadmat arc locatedwithin the geographical limits of 100_12°N and71 °40' -74°E. The Minicoy atoll (8° 18'N and 73°E) isthe southernmost atoll and the largest in the Laksha-dweep archipelago. The shore of the lagoon side of theatolls are characterized with sandy beach having 111e-di um to coarse coralline sand and beach rocks expo-sed during low tide. The beaches are of scmicn closedtype witl; varying exposure and with minimum waveaction.

The Lakshadwcep Archipelago has a tropical clim-ate where the year may be divided into three seasonse.g, the southwest monsoon (June-September). post-

monsoon (October-January) and prcmonsoon (Fe-bruary-May). During monsoon period heavy rainf-all is reported in this region which terminates in lateSeptember or early October after which the weather isless varying. The air temperature fluctuates around30°C except during monsoon time when it is helow25T. The tides are of mixed type with a strong sernidi-urnal influence. The beaches arc fairly stable exceptduring the monsoon season when changes in beachprofile take place due to erosion. The width of in terti-dal areas ranges from 7 to 15 m with gentle slope andlittle wave action.

Materials and MethodsData presented here are hased on 108 samples coll-

ected during different seasons and different years(1985-1987) during 3 cruises of R. V. Gaveshani. Theresults therefore do not necessarily pertain to the sea-sonal cycle. The comparisons depict a broad basedpicture of changes in macro and meiofauna of the 6beaches. of 6 atolls studied. The sampling stationswere located along. a transect from high water mark(HW) to the low water mark (LW) and three transectswere selected on each island. For macrofauna a quad-rant (0.25 m ' area) was forced into the sediment andthe sand of the enclosed area was dug out to a depth of15 cm and sieved (0.5 mm screen). The material remai-ning on the screen was fixed in a 5% buffered formalinRose Bengal solution. Duplicate samples were takenat each level. Mciofauna was collected at each tidelevel in 3 replica tc series of I0 ern- area to a depth of 10ern. Each core sample was sliced into 2 sub samples or5 em layer and preserved in Y~'oformalin Rose Bengal

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INDIAN J MARSCI, VOL. 19. SEPTEMBER 1990

solution. All macrofauna were grouped, counted andwet weight mass was determined. Similarly all meiof-auna were counted and average wet weight of the ma-jor taxa recorded. Th.e biomass of macrofauna andmeiofauna were extrapolated to get biomass valuesfor I m wide transect". The total biomass was thenconverted to production estimates by multiplying fa-ctor 8 for meiofauna'? and 2.5 formacrofaunall. Me-chanical properties of the sediment were ana lysed bythe method of Folk 11. Organic content of the sedim-ent was determined by the titration method':'.

Results and DiscussionSediment characteristics= The median particle di-

ameter of all the beaches (Table I) ranged from 0.27 to0.55 mm indicating the dominance of median corall-ine sand particles. Narayanan and Sivadas 7 reportedmedian particle size of 0.38 to 0.43 mm at Kavaratti.The low phi quartile deviation (Qdo) and very lowvalues of skewness (SKcp) indicate that at all the beac-hes a high proportion of sand particles fall in narrowrange around the median and the particles of bothlarger and smaller sizes were equally sorted. Harkant-ra 14 working in a high energy beach reported stronglyfine skewed to strongly coarse skewed sediment. The

differences in the sediment characteristics may be dueto the differences in exposures between these beach-es IS. However it may be mentioned here that all thebeaches are protected by reef which are several hund-red meters away from the shore and therefore thewave action on these beaches is minimum. This wasfurther confirmed by the fact that no significant relati-onship exists between the degree of exposure and be-ach slope.

The sediment organic carbon, as expected, was mo-derate. The values were highest (0.47%) at Kalpeniand lowest (0.24%) at Kavaratti. On these oceanicbeaches the sources of organic input are limited. Themain contribution of organic carbon are the dead anddecaying seagrasses and seaweeds. Thomassin and Vit-iello 16 also reported low value of organic carbon inthe cora1\ine sediment of Tulear reef Madagascar.

Macrofauna-Total macrofaunal density(no.m - 2) was highest at Agatti (3157) and lowest atKadmat (71) (Table 2). Of the 8 groups, polychaeteswere the most dominant group at all the beaches, con-tributing from 55 to 92% of the total population.Next in abundance were crustaceans and bivalves.Miscellaneous groups constituted of hydrozoans, ec-hiroid worms. sea anemones. etc. formed a substant-

Island

Table I-Summary of abiotic factors at Lakshadweep

Tidal Md (mm) Qd(q,) Sk(4)) Mean Mean organic Salinity oflevel Md (mm) carbon (%) interstitial water

(xlO-3)

HW 0.45 0.59 -0.05 34MW 0.54 0.60 -0.03 0.55 0.39 30LW 0.66 0.67 -0.04 32

HW 0.28 0.34 +0.04 32MW 0.31 0.29 +0.05 0.32 0.47 33lW 0.37 0.33 +0.05 30

HW 0.28 0.53 -0.02 33MW 0:35 0.51 -0.02 0.37 0.37 -'LW 0.48 0.52 -0.02 33

HW 0.22 0.47 -0.05 36MW 0.24 0.52 -0.02 0.27 0.24 .-6LW 0.35 0.50 -0.04 34

HW 0.29 0.43 +0.07 34MW 0.34 0.49 +0.03 0.35 0.25 3~LW 0.42 0.44 +0.05 .':'HW 0.36 0.55 +0.03 3.'MW 0.42 0.50 +0.03 0.40 0.28 .'3lW 0.42 0.54 +0.04 30

Agatti

Kalpeni

Bingaram

Kavaratti

Minicoy

Kadmat

160

ANSARI et al: MACRO & MEIOFAUNAL ABUNDANCE

JI

ial portion of the population in the present study.Narayanan and Sivadas? also reported polychaetesand crustaceans as the major macrobenthic compon-ents in the intertidal sand ofKavaratti. Ansell et 1I1.9

found polychaetes and bivalves as the major group onthe south Indian beaches. However, Mclachlan II hasreported the dominance of bivalves in the intertidalmacrofauna of South African beaches. Among otherstudies Thomassin et al. 5, reported the dominance ofmolluscs in the coral sediments of Polynesian atolls.Thus the intertidal macrofauna population at Laksh-adweep atolls show wide variation from extremelypoor at Kadmat to extremely high density at Agatti.These extreme range of macrofaunal density could bethe result of differing food supply and the sedimentcharacteristics. Beach exposure also plays importantrole in the distribution of intertidal fauna 15.

There was a distinct zone of faunal distributionalong the tidal gradients and several faunistic assem-blages could be identified. While the polychaetes occ-urred consistently at all tidal levels, the upper zonewas characterized by the presence of crustaceans suchas Eurydice sp. and Talorchesia sp. The mid waterlevel was characterized by the presence of pelecyp-ods, ghost crab and mole crab tHippa sp.). Amongtwo species of pelecypods Mesodesma glabratum wasrecorded at all the beaches excepting Kadmat whileDonax sp. was found only at Minicoy. The neap tidewas unproductive in terms of macrofaunal densityexcept at places of seagrass beds. The distribution ofmajor taxa also varied along the exposure gradient.Similar observations have been made at Kavaratti".Studies on intertidal fauna of South African beachesalso revealed the pattern in the distribution offaunaalong tidal gradient II.

Macrobenthic biomass was highest at Agatti andlowest at Kadmat (Table 2). Biomass values followedthe trend of population density in the distributionfrom high water to low water. High to very high biom-ass values have been reported from Indian beaches?which are attributed to high density of bivalves.

Meiofauna·-Nematodes are generally the domin-ant taxon in marine meiofauna 17, although the prop-ortion ofharpacticoid copepods increases in coarsersand on exposed beaches. The meiofaunal density(Table 3) was highest at Agatti and lowest at kavarat-ti. Total density (no. 10 em -2) varied between 2620and 6555. In an other study from Andaman islands,Ansari and Ingole!" reported meiofaunal density ra-nging from 2270 to 6 I 16.10ern - 2 in the fine intertidalsand which coincidentally is similar to the values obs-erved in the present study. The meiofauna was mainlyrepresented by nematodes, harpacticoids, turbellari-ans and polychaetes. Among other groups the gastro-

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INDIAN J MAR SCI, VOL. 19, SEPTEMBER 1990

trich, kinorhynchs, tardigrada, archiannelida andnauplii were present. On all the beaches except Agattinematodes form numerically the most dominantgroup followed by harpacticoids and turbellarians(Fig. 1). At Agatti harpacticoids were dominant, foll-owed by nematodes and turbellarians. Averaging theproportion (percentage wise) for the six beaches. it isobserved that nematodes contribute 46.7%, harpacti-coids 23.7%, turbellarians 12.3% and polychaetes5.17%. Other groups also-made significant contribut-ion of 12.2%. While the distribution ofmciofauna islargely determined by sediment particles. oxygen, te-mperature and food supply on the exposed beach-es9.11.19. meiofaunal densities in the present studyand their variations were due to exposure, grain sizeand organic matter. Semiexposcd beaches are repor-ted to have large number of taxa than exposed beach-es 15. Thomassin et al. 5 reported that meiofaunal dist-ribution was more related to thc grain size, organicmatter and degree of oxygenation in the coral sands ofthe reef flat in Polynesia. Unlike macrofauna therewas no correlation between mciofaunal density andtidal exposure but the fauna was generally concentra-ted at mid and high water mark.

Total meiofaunal biomass (wet weight, mg.IOcm - 2) for each beach and tidal level was calculatedand presented in Table 3. These beaches have highlyvariable mciofaunal biomass like their larger coun te-rpart and do not show consistency with tidal exposu-re.

mi POLYCHAfT A IUlII TUR8EllARIA• OTHERS

oFig. I--Taxonomic composition of the rneiofauna of the six beac-

hes studied

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ANSARI et af.: MACRO & MEIOFAUNAL ABUNDANCE

From Table 4 it appears that the fauna at all tidelevels was aggregated mainly in the top 0-5 em layerexcept at Kavaratti which may be due to changes insampling time. Because of a better drainage (coarsesand) and high atmospheric temperature and exposu-re, the fauna seems to migrate downward in the sandcolumn?". This emphasizes the importance of drain-age on oceanic sandy beaches. The meiofauna of thepresent study appears to be concentrated more atthose levels where desiccation is not too severe andoxygen is available. Others have also reported conce-ntration of meiofauna in the upper layer of sandybeaches+t+>'. Due to varying degrees of exposureand flooding different tidal level will experience diffe-rent temperature and oxygen regime, depending onthe width of the beach. This accounts for the differen-ces in faunal density at various tidal levels.

Comparison of meiofauna-An attempt has beenmade in the present study to compare the density ofmeiofauna with other areas (Table 5). Total densityrecorded in the present study area is comparablewith other areas except that of Malaya, Porto Novoand Stockhlom where densities were comparativelylow. One of the reasons for differences in meiofaunadensities recorded by other is the methodology usedby different workers. It may be noted that in the coralsand at Malaya the dominant group was copepoda-".In the coarse sand of 0.55 mm median diameter Janss-on25 also observed dominance of benthic copepodaand so did McLachlan I 3 in the median grain size of0.27 mm diameter. In the present study only Agattishowed dominance of copepoda in the sediment of0.55 mm diameter. It reemphasizes that benthic cope-'pod increases in coarser sand on exposed sandy beac-hesI3•19. In the medium and fine sand the copepodswere second most important group.

Comparison of macrofauna and meiofauna- Themacrobenthos and meiobenthos of the six beachesunder investigation are compared on the basis of theirdensity, biomass values and production estimates for

I m transect of beach (Table 6). For macrofauna, totaldensity per Im transect was highest at Agatti andlowest at Kadmat. Similarly the biomass was highestat Agatti and lowest at Kadmat. Total macrofaunalbiomass (g per 1 m transect) of all the beaches variedfrom 26.12 to 975. Narayanan and Sivadas? reportedan average value of90.47 g.(1 m transect) -1 from Kavar-atti beach, while Ansell et al? found maximum wetweight biomass value of 500 g.(l m transect) -1 from thesouth Indian beaches. Wide range of biomass valuesbetween 7.04 and 6600 are reported from south Afri-can beaches I I which was attributed to the presence orabsence of bivalves and gastropods. A noticeable fea-ture of the beaches under investigation is the very lownumber of bivalves and the absence of gastropods.This is probably due to the textural properties of thesediment and beach exposure. Namboodiri and Siva-das" reported only one species of bivalve in the sandybeach and 19 species in the lagoonal floor of Kavarat-ti. They reported that poor representation of mollu-sea was due to increased exposure of the beach. Gana-pati and Lakshaman Ra024 found paucity of the fa-

Table 5-Summary of the data on intertidal meiofauna

Locality Type of Total DominantReference deposit meiofauna group

(no. 10 cm-2)

Malaya-" Coral sand 244 CopepodaPorto Novo ' Sand 969-1960 NematodaGoal4 Medium sand 24-3525 NematodaAndamans!" Fine sand 2323-6116 NematodaKakiriada-" Fine sand 680-4095 NematodaStockholm+' Coarse sand 391-1529 CopepodaSardinia Bay" Medium sand 3710 Copepoda

Present study

Agatti Coarse sand 6555 CopepodaKa1pani Medium sand 5240 NematodaKadmat Medium sand 4716 Nematoda

Table 4-Vertical distribution of meiofauna (no. 10 em -2)

High water Mid water Low water

0-5 cm 5-10 em 0-5 em 5-10 em 0-5 em 5-10 em

1954 335 1944 914 1416 921627 276 1152 578 1365 3421282 278 682 641 1062 322480 484 283 318 632 425513 530 589 432 730 400

1197 1052 450 570 587 756

Islands

AgattiKalpeniBingarainKavarattiMinieoyKadmat

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INDIAN J MAR SCI, VOL. 19, SEPTEMBER 1990

Table ~Density (no. 1 m transect.":'), biomass (g. 1 in transect-I) and production estimates (g. 1 m transect-I) for macro andmeiofauna and percentage contribution of the total macro and meiofaunal production at 6 coralline beaches of Lakshadweep

Islands Macrofauna Meiofauna

Density Biomass Production %P Density Biomass Production %P

9471 975.00 2437.50 42.93 1966 x \03 405.08 3240.00 57.066163 635.04 1587.60 23.65 1397 x \03 640.20 5121.60 76.348987 925.65 2314.13 37.04 1509 x \03 491.57 3932.56 62.952211 157.88 394.70 13.58 959 x \03 313.83 25\0.64 86.41

2511 201.11 502.78 17.52 745 x \03 295.71 2365.68 82.47-300 26.12 65.29 1.01 2358 x \03 794.50 6356.00 98.98

AgattiKalpeniBingararnKavarattiMinicoyKadmat

P = Production

una in the intertidal sand having poor organic matter.The organic matter coming from the sea is mainly inthe fonn of washed up algae and seagrasses. The qua-ntity of organic matter lying on and in the sediment isof great importance to the deposit feeding molluscs-".The meiofaunal component showed less variation inboth density and biomass. The density (no. x 103 per1 m transect) varied between 745 and 2358 and biom-ass (g. I m transect - I) between 295.71 to 794.50. Thisreemphasizes the fact that small metazoans can mai-ntain more stable population on sandy beaches thantheir larger counterparts I. The macrobenthos/rneio-benthos ratio in terms of their density varied from1/626 to 1/167 among the six beaches. Low ratios ag-ain indicate the dominance of meiofauna on sandybeaches. Thomassin et al:" have estimated ratio betw-een 1/190 and 1/12 in the coral sediment of Tiahurareef of Polynesia.

The production estimates indicate that the meiofa-una are quantitatively more important than the macr-ofauna on these oceanic sandy beaches and contrib-ute> 50% to the secondary production on these bea-ches. McLachlan 11 has estimated macro and meiofa-una production from EL WS to a height of 2 m atsandy beaches of South Africa. He reported a macrof-aunal contribution of 53% and meiofauna contribut-ion of 47% in the secondary production of these beac-hes. He, however, emphasized that, had estimates ofproduction for transect been extended to a height of> 2 m above the EL WS, as in the present study, themeiofaunal contribution would have been greaterthan macrofauna. The high contribution ofmeiofa-una in the secondary production of intertidal sandyareas of Lakshadweep atolls is therefore justified.

AcknowledgementAuthors are grateful to Dr B.N. Dessai, Director,

164

for encouragement. Thanks are also due to the collea-gues for their help in collection of samples.

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