fw400 terr aquat linkages magazine 2008

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Terrestrial-Aquatic Linkages:

Understanding the Flow of Energy and

Nutrients across Ecosystem Boundaries

Artwork by USFS

Adam Hansen, Justin Peterson, Jeremy Ellis,Ginny Sednek, and Ben Wilson

Department of Fish, Wildlife, and Conservation Biology

Colorado State University

Fort Collins, Colorado 80526

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Abstract. The importance of aquatic-

terrestrial linkages has been well establishedin a variety of ecosystems. Marine subsidies

support high primary consumer production,

which sustains dense supralittoral secondary

consumers. Terrestrial invertebrate inputsplay important roles in streams. Depending

on the season, invertebrates falling into a

stream can make up as much as 50% of theannual consumption in some fish species.

Similarly, emerging aquatic insects can

comprise up to 90% of a riparian predatorsdiet. The timing of both aquatic and

terrestrial emergence can be crucial for food

web sustainability. Anadromous salmon actas a vector for the transport of marine

derived nutrients inland. Finally, subsidiescan promote sustainable populations in low

productivity terrestrial systems, or even betransported by migratory birds thousands of

miles to the detriment of various lakes,

ponds, and rivers, if overabundant.

Adjacent ecosystems rarely function

independently of each other, even those thatappear to have discrete boundaries (Barret et

al. 2005). For example, terrestrial andaquatic habitats interact extensively, with

each system being inherently linked by the

cross-habitat transfer of energy or nutrients(Ince et al. 2007). This flux of organic

matter or nutrients from a donor habitat to

a recipient habitat is known as an

ecological subsidy (Polis et al. 2004; Ince etal. 2007). These subsidies typically have

high temporal and spatial variation, can

enter recipient habitats at any trophic level,can have dramatic influences on food web

dynamics (e.g., competition), and can be

transported through the movement oforganisms (Polis et al. 2004). The goal of

this paper is to review the current state of

knowledge about the specific mechanisms

driving the flow of energy and nutrientsbetween different aquatic and terrestrial

systems.

Trophic interactions at the land-sea

interface: importance of food web

linkages

By Adam G. Hansen

The land-sea interface or coastalecotone (e.g., estuaries) is a major

ecosystem encompassing 8% of the earths

surface along an estimated 594,000 km ofshoreline (Polis and Hurd 1996; Polis et al.

2004). Carbon and nutrients flow

extensively across this ecotone boundary(i.e., subsidies), forming a complex food

web (Vernberg and Vernberg 2001; Polis et

al. 2004). Coastal zones are sites ofsignificant human degradation (Kappel

2005), and conservation requires scientiststo understand trophic interactions between

these ecosystems (Pasquaud et al. 2007).The goal of this paper is to describe the

primary mechanisms through which marine

and adjacent terrestrial habitats receivesubsidies, and their importance.

Marine subsidies enter terrestrial

systems through shoreline drift of animalcarrion and detrital algae, the import of

carcasses, food scraps, reproductive by-products, and waste products (e.g., guano)

from ocean foraging seabirds (e.g.,

cormorants and gulls), sea turtles, andpinnipeds (e.g., sea lions), and from wind-

blown sea foam and spray (Polis

et al. 2004; Ellis et al. 2006).

Detrital algae. Photo by Joseph Dougherty.

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For example, Polis and Hurd (1996)

estimated the ocean to contribute 2,720 2,810 g dry massm

-2yr

-1and 110 530 g

dry massm-2

yr-1

of shoreline plant detritus

and animal carrion (e.g., seabirds, fish, and

crabs) to small, unproductive (< 100 g drymassm-2

yr-1

),desert islands in the Gulf of

California, respectively. These subsidies

support high primary consumer production(e.g., detritivorous arthropods), which

sustains dense populations of supralittoral,

arthropodivorous consumers (e.g., spiders,scorpions, and lizards) on small islands (low

perimeter/area ratio) and in coastal areas

worldwide (Polis and Hurd 1996; Andersonand Polis 1998). Polis and Hurd (1995)

describe how supralittoral spiders achievedensities six times greater than inland

counterparts, and increase further (4 5times) on islands with seabird colonies due

to the addition of avian parasites and

scavengers to the food web (Figure 1).

Figure 1. Food web of small, desert islands in the

Gulf of California. Arrows denote carbon andnutrient flow from one ecosystem component to

another. The horizontal dotted line represents the

land-sea interface (from Polis and Hurd 1995).

Lastly, Anderson and Polis (1998) providedirect evidence (stable isotopes) for coastal

consumers exhibiting greater marine-based

diets than inland individuals, with coastal

(Gulf of California) spider and scorpion

tissue having significantly greater levels ofmarine-derived

13C and

15N.

Marine subsidies are important for

carnivorous mammals (Polis and Hurd

1996). For example, Rose and Polis (1998)measured coyote Canis latrans density to be

2.4 13.7 times greater along the Gulf of

California coast than in adjacent inlandhabitats receiving no marine input. Carlton

and Hodder (2003) describe how mammals

(e.g., raccoons, minks, and black bears) havebeen observed, worldwide, intentionally

entering intertidal communities to prey on

exposed marine organisms (e.g., gastropodmollusks, crabs, and fish). These mammals

ultimately act as vectors for the transport ofmarine-derived nutrients inland (Carlton and

Hodder 2003).Conversely, coastal marine systems

receive terrestrial subsidies (nutrients,

particulate and dissolved organic carbon)indirectly from river discharge and directly

from supralittoral vegetation (Polis et al.

2004). Terrestrially-derived carbon,nitrogen, and phosphorus, delivered by

rivers, stimulate in situ phytoplankton andbenthic microalgal production, both being

important drivers of coastal marine food

webs and fish production (Loneragan andBunn 1999).

Lower estuary of Columbia River. Photo by Jim

Wark.

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Loneragan and Bunn (1999) found there to

be strong, positive relationships betweencommercial fisheries catch (prawns, mud

crabs, and mullet) and summer discharge

from the Logan River, southeast

Queensland, Australia, strengthening theargument for conserving natural flow

regimes. Dunton et al. (2006) describe how

nutrient and terrestrial detritus accumulationfrom arctic river input (e.g., Mackenzie

River) can comprise 54 69% of the total

particulate carbon available to consumers, inlagoon-barrier island systems, along the

Alaskan Beaufort Sea coast (Figure 2).

Based on stable isotopes, arctic codinhabiting these lagoon systems were found

to derive 52 85% of their carbon fromterrestrial sources (Dunton et al. 2006).

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Figure 2. Major factors accounting for the high

productivity and biomass of estuarine inhabitants in

northern Alaskan coastal ecosystems (from Dunton et

al. 2006).

Supralittoral vegetation is animportant source of carbon (terrestrial

insects and leaf litter) for coastal marine fish

(Polis et al. 2004). Fish species richness andarthropod addition are both positively

associated with supralittoral vegetation

(Romanuk and Levings 2003; Romanuk and

Levings 2006). Based on stable isotopes,Romanuk and Levings (2005) estimated

juvenile Pacific salmon (Chinook, chum,

and pink) to derive 5.5 39.7% of theircarbon from supralittoral vegetation sources

along the coast of British Columbia. Results

provided evidence for the juvenile salmon

forming a trophic hierarchy, partitioningmarine and terrestrial-derived resources. It

was concluded that subsidies derived from

supralittoral vegetation may allow

coexistence in resource limited marinehabitats (Romanuk and Levings 2005).

Carbon and nutrient flow between

the land and sea occurs in both directions.Input of material from sea to land increases

primary consumer production, allowing

secondary consumers to achieve densitiesthat would otherwise be unattainable

without such subsidies (Polis and Hurd

1996). Terrestrial-derived subsidiescontribute large amounts of carbon and

nutrients to the sea, making coastal marinesystems the most productive ocean habitats

(Polis et al. 2004). Each system is greatlyinfluenced by the other, and conservation

efforts must recognize that coastal marine

and terrestrial habitats are integrated, notdiscrete biological communities.

Terrestrial-aquatic linkages: terrestrial

invertebrate inputs into stream systems

By Justin Peterson

Stream systems have been studiedhistorically by examining the organisms and

processes that are restricted to the stream.Terrestrial inputs supplement streams that

have low autochthonous production

(Vannote et al. 1980), and influence carbonpathways in the system (Rosenfield and Roff

1992). More recent developments show the

importance of terrestrial inputs into streams

in terms of food webs within and outside ofthe stream (Nakano et al. 1999), as well as

research applications (Nakano andMurakami 2001; Saunders and Fausch2007). Terrestrial stream inputs are crucial

links that provide fish forage (Kawaguchi

and Nakano 2001), and can control thedistribution of fishes in the stream

(Kawaguchi et al. 2003). The following

discusses terrestrial inputs into stream


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systems, highlighting the importance of the

riparian area, as well as invertebrate inputs.Fish are dependent on terrestrial

inputs in various settings, and the

importance of terrestrial inputs into streams

has been well established. Drifting andfalling invertebrates make up a large portion

of salmonid diets and may determine their

distributions in a stream system (Kawaguchiand Nakano 2001). Overall, invertebrates

made 51% of the total annual prey

consumption in forested streams, and 35%of total annual prey consumption in a

grassland reach (Romanisyn et al. 2007).

Differences are also observed in terms ofriparian type and terrestrial input in a variety

of streams (table 1 from Baxter et al. 2005).

The highest inputs are observed in closed

canopy rivers and can make upapproximately 50% of salmonid diets in

those stream sections (Kawaguchi et al.

2003; Baxter et al. 2005). Differences in

invertebrate input as a result of differingriparian vegetation and cover were observed

in several studies (Dineen et al. 2007;

Romanisyn et al. 2007). Terrestrialinvertebrate supply can be influenced by

riparian type. Drifting terrestrial

invertebrates were highest in open-canopystreams (Dineen et al. 2007), and falling

invertebrates highest in forested closed

canopy streams (Romanisyn et al. 2007).Carbon pathways are also linked to

terrestrial inputs.

Table 1. The differences of stream order, riparian type, and terrestrial input in a variety of streams in the spring,

summer, fall, and winter (from Baxter et al. 2005). Values for terrestrial invertebrate input represent mean dry mass

(mg m-2 day-1). Starred values represent fields with no data.

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Rosenfield and Roff (1992) examined the

carbon pathways in forested and unforestedstream systems using carbon isotopes that

differ based on origin in a terrestrial setting

or in the stream. Results showed fish derive

higher amounts of carbon from terrestrialinputs in forested stream sections (Rosenfield

and Roff 1992).

Food web dynamics can also bedependent on terrestrial subsidies. Terrestrial

invertebrate inputs can have cascading

impacts for the entire ecosystem food web ina headwater stream (Nakano et al. 1999).

When terrestrial inputs were blocked from

the channel, certain fish species shifted toforage on aquatic invertebrates, and the

reduced grazing from those invertebrates ledto an increase in benthic periphyton.

Maintaining overhanging riparian vegetationand banks is crucial for invertebrate input for

foraging fish species (Nakano and Murakami

2001; Romanisyn et al. 2007). Nakano et al.(figure 1 1999) relates the importance of

terrestrial invertebrates in a forest stream

system showing darker bars for those speciesthat rely on terrestrial inputs.

Figure 1. Food web illustration of a forest streamshowing allochthonous invertebrate subsidies

(modified from Nakano and Murakami 2001). Bar

thickness is indicative of annual resource budgets of

each fish species from terrestrial prey.

Knowing the importance of terrestrial

inputs helps can help identify streams thatmight be negatively affected as a result of

reduced terrestrial linkages. Land use

practices can negatively affect potential

terrestrial inputs by interfering or changingriparian vegetation structure (Edwards and

Huryn 1996). Saunders and Fausch (2007)

examined the consequences of removedriparian vegetation by cattle grazing and

showed that prolonged grazing reduces

riparian vegetation, invertebrate input, andtrout biomass. Ungrazed areas inside

exclosures had higher numbers of juvenile

Oncorhynchus mykiss, and relate theimportance of intact riparian vegetation

(Bayley and Li 2007).

Barrier used by Nakano and Murakami 2001.

Seasonality can affect the timing of

invertebrate input into streams, and affects

forage availability (Edwards and Huryn

1996; Nakano and Murakami 2001; Baxter et

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al. 2005; Romanisyn et al. 2007). Seasonality

is important for terrestrial insect inputs in theform of drift, or fall into the stream system.

Terrestrial input is highest in the summer

months, (table 1 from Baxter et al. 2005), and

seasonal differences in invertebrate inputscan also be seen (figure 2 modified from

Nakano and Murakami 2001).

Figure 2. The allochthonous prey consumption of a

fish assemblage from a forested stream for a 12-monthperiod (modified from Nakano and Masashi Murakami

2001).

Increased allochthonous prey reliance occursin the spring, peaks during the summer, and

declines to the lowest occurrence in the

winter. Input timing is also important due tothe reduced occurrence of aquatic

invertebrate availability during the times of

high terrestrial input (Nakano and MasashiMurakami 2001).

Pan trap. Photo by Carl Saunders.

Terrestrial inputs are a crucial link for

food webs, and maintaining naturalecosystem processes in streams. Overhanging

riparian vegetation also ensures invertebrate

inputs. Depending on the fish assemblage,

disruption of inputs will alter food webs, andmay result in a trophic cascade. Interrupting

the input can disrupt entire food webs,

forcing fish to focus on aquatic prey, leadingto shifts in stream production. Sources that

disrupt riparian vegetation alter these inputs,

and threaten natural stream ecosystemfunctions.

Emerging Insects: Trophic Interactions of

Terrestrial and Aquatic Systems

By Jeremy Ellis

Emergent insects are an importantfood source for riparian predators (Lynch et

al. 2002). Characteristics of these insects

make them susceptible to high predation atcertain times of the year. In some instances

emerging insects can make up to 90% of a

predators diet (Kato et al. 2004). Emergentinsects are an important subsidy to birds,

lizard and spiders (Burdon and Harding2008). This paper will show how emerging

insects disperse and how predation of these

insects is an important subsidy to terrestrialpredators like birds, lizards and spiders.

Emerging aquatic insects have life

history traits that make them susceptible to

predation all year or at certain times of theyear. These insects spend most of their life

underwater and emerge as adults to breed and

lay eggs back into the water. Ephemeroptera(mayflies), Plecoptera (stoneflies) and

Trichoptera (caddisflies) (EPT) usually

emerge in May-June in temperate regions.Diptera (true-flies) mostly emerge in the

warmer months. In tropical regions

emergence can be year round (Baxter el al.

2005). Emerging insects can average about10,000-20,000 insects per meter (m) per

year. These insects disperse above and

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around the stream in order to feed, rest,

breed, and disperse eggs.

Adult mayflyEphemeroptera. (Phil Myers).

Lateral dispersal for emerging insects

is important to understand how predators will

react to their dispersal. This dispersal isusually to feed or is a mechanism to colonize

new habitats (Malmqvist 2002). Somespecies of stoneflies marked with stable

isotope15N flew up to 1 km from their natal

stream. But most emerging insects are found

within 11 m of the stream (Winterbourn et al.

2007). Using Malaise traps, Winterbourn elal. (2007) found that about 7% of

Ephemeroptera and 43% of Trichoptera

migrated away from the stream into the entire

valley or the surrounding hillsides (Table 1).

Table 1. Abundance (%) of insects Ephemeroptera,

Plecoptera and Trichoptera trapped in forest, valley

and hillside. Forests are closest to streams and

hillsides are farthest from streams (from Winterbourn

et al. 2007).

Forest Valley Hillside

Ephemeroptera 90.2 2 7.8

Plecoptera 91.9 6.2 1.9

Trichoptera 56.7 36.3 7Likewise Lynch et al (2002) found

that emerging insect abundance decreases

exponentially farther from the waters edge.But this study shows that about 50 insects per

m per day were moving into the riparian

zone 15 m from stream center. This

movement is important to understand because

when the insects leave the relative safety of

the water they encounter new predators in theriparian areas.

Aquatic insects are very important to

spiders because the insects can provide a bulk

of a spiders diet. Spiders, both web-buildingand ground dwelling, have been shown to

have a higher biomass near a stream edge,

and web densities increase near a streamwhere aquatic insect biomass is high, and

decrease with distance from the stream

(Baxter et al. 2005, Burdon and Harding2008, and Sanzone et al. 2002) (Figure 2).

Likewise, when the number of emerging

insects was experimentally decreased, spiderdensity near the stream declined (Burdon and

Harding 2008). Using stable isotopes tomeasure the amount of carbon from aquatic

origin, Kato et al. (2004) found that in June,the peak of emergence,

13C was most

depleted, similar to aquatic prey. When

emergence declined in July,13

C in spidersbecame more similar to terrestrial prey. Prey

in orb-webs was 50-90% aquatic insects in

May-June in the same area (Kato et al. 2003).This information shows that spiders can be

dependent on emergent insect subsidies andrespond to the densities of emerging insects,

comparable to birds.

Iwata et al. (2003) showed thatabundance of flycatchers and gleaners was

positively correlated to aquatic insect

abundance in the riparian area. This was also

observed in a prairie stream by Gray (1993).Gray (1993) also observed that when the

stream dried and there was no emergence

during a drought in 1989 densities offlycatchers and gleaners was greatly reduced.

When the stream was flowing there were 11

birds/ha, and when the stream was dry therewas about 2 birds/ha. This could be due to

multiple factors but lack of asubsidy fromthe stream is one of them. Flycatchers fed

above the stream or within 5 m of the stream.Dry mass of flycatchers diets is 82% aquatic

insects due to this behavior (Iwata et al.

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2003). Gleaners also show this behavior and

had 67% of their diets composed of aquaticinsects (Iwata et al. 2003). For these birds,

emerging aquatic insects are a large part of

their diet making emergence a very important

factor for their food web.

Overall emerging insects have a large

effect on the surrounding system. Theyinfluence predator movement and cause shifts

in feeding habits during emergence. These

subsidies cannot be overlooked because so

many species depend on them to survive.Emerging insects connect terrestrial and

aquatic environments by moving energy from

streams to land.

The impact of anadromous salmon on

aquatic and terrestrial ecosystems

By Ginny Sednek

Anadromous salmon and trout

(Oncorhynchus spp. and Salmo spp.)

transport large magnitudes of nutrients toaquatic and terrestrial habitats. Ninety-five

percent of the biomass of ocean migrating

salmon is marine derived nutrients, (MDN),

including carbon, nitrogen, and phosphorous(Naiman et al. 2002). The organic subsidy

brought to freshwater habitats positively

impacts food webs (Schindler et al. 2003)

Figure 2. Linear relationship between spider densities

(no. webs*m3

) and emerging insect biomass (g*m2

of stream) (From Burdon and Harding 2008).

Emergent insects provide a subsidy

for riparian lizards as well as birds and

spiders. Sabo and Power (2002) show thatwhen the aquatic insect subsidy is

experimentally blocked from lizards, the

lizards growth is lower when compared tounblocked lizards. The aquatic insects hadeffects on lower trophic levels as well. When

emergence occurs, lizards tend to shift from

terrestrial prey to emerging aquatics. Thisreduces pressures on terrestrial insects for a

short time (Sabo and Power 2002).

and biological productivity (Figure 1).

The nutrients salmon provide to aquatic

ecosystems are beneficial to fish, aquatic

invertebrates, salmon eggs, and riparianhabitats. Migrating salmon have an immense

value to adjacent terrestrial ecosystems;transferring energy to the land which sustains

wildlife and forests. Over the past century,

salmon returning to spawn in their native

freshwater habitats has decreased to 6-7% oftheir historic abundance (Gresh et al. 2000).

Conservation of salmon are important to

consider for biological productivity becauseof the ecological cascade that follows. Here,

I review the importance of anadromoussalmon in freshwater aquatic and terrestrialecosystems.

The benefit of salmon extends across

habitat boundaries. Terrestrial ecosystems

increase fish survival (cover, shade, nutrients,etc.) and anadromous salmon return to thesame forested areas to reproduce and depositWestern fence lizard Sceloporus occidentalis. (Jim

Boone Photo).

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Figure 1. The effects of anadromous salmon, containing marine derived nutrients (MDN), on biological productivity in

aquatic and terrestrial ecosystems (From Cederholm et al. 1999).

rich nutrients (Cederholm et al. 1999). Theenergy salmon transfer to oligotrophic

systems consists of carbon, nitrogen, andphosphorous, positively impacting the

biological communities (Gende et al. 2002).

This nutrient subsidy enters the trophicsystem directly (consumption of flesh, eggs)

and indirectly (dissolved nutrients) (Naiman

et al. 2002). Energy from salmon becomes apart of different trophic levels, starting in

riverine habitats and proceeding to inland

forests.Salmon play important roles in

riverine ecosystems. When salmon return totheir natal streams they spawn, die, and

create an abundant source of nutrients for fish

and aquatic invertebrates (Cederholm et al.

1999). Other salmonids and fish species gain

an ample supply of nutrients when salmonspawn, by consuming carcasses, eggs, and fry

(Gende et al. 2004). Aquatic invertebratesare also attracted to the vast amount of

organic matter. Winder et al. (2005)

discovered that the lifecycle of certaincaddisfly species in southwest Alaska

coincided with salmon runs. These aquatic

invertebrate larvae also become a food sourcefor other fish and wildlife (Cederholm et al.

1999). The habitat that surrounds riverine

systems, the riparian areas, also benefits bythe energy subsidy. Ben-David et al. (1998)studied the effects of salmon carcassesfertilizing riparian vegetation in southeast

Alaska; their findings show how flooding and

predator activity moves nitrogen-rich

nutrients into the riparian zone.

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Spawning salmon help the

development of their eggs and fry, allowingtheir species to thrive. According to

Schindler et al. (2003), when female salmon

build redds (nests), the sediment composition

is altered, increasing water and oxygen flow(benefits developing eggs), while removing

fine sediments. Dead adult salmon also

provide nutrients for salmon fry, increasinggrowth rates and survival (Cederholm et al.

1999). The nutrients adult salmon provide

enter a feedback loop, helping the survival ofits own species.

Wildlife communities adjacent to

salmon run systems are heavily dependent onthe abundance and availability of salmon.

The nutrients salmon provide help thesurvival and reproduction of a variety of

wildlife (e.g., bears, eagles, mink, otters,deer; Willson and Halupka 1995). Ben-

David (1997) found that the timing of

reproduction in mink (Mustela vison)coincides with salmon spawning so that the

female has adequate nutrients for lactation.

Female bears with cubs alter feeding habitswhen salmon are abundant, avoiding salmon

streams to reduce infanticide by other bears(Ben-David et al. 2004).

Photo from Schindler et al. 2003.

In fall, salmon carcasses are an essential part

of mink diets, aiding preparation for winter(Ben-David et al. 1997).

Helfield and Naiman (2006) describe

how bears and salmon are mutually

dependent. Bears benefit from salmonnutrients and fertilize riparian areas (i.e.

dragging up carcasses, defecation) which in

turn improves riparian habitat for juvenilesalmon. Bears can kill 50% of the salmon in

small streams, carrying most of the carcasses

to the riparian forest, and leaving the remainswhich enhance wildlife and vegetation

(Gende et al. 2004).

Salmon are an important resource thatmove nutrients across habitat boundaries.

Conservation of these fishes is imperative forbiological communities that rely on salmon

rich in MDN. Reduced numbers of salmonhas created a nutrient deficit, affecting

salmon dependent ecosystems (Gresh et al.

2000). Salmon need to be considered askeystone species because of the extensive

effect on many organisms. Understanding

the effects salmon have on aquatic andterrestrial communities will allow biologists

conserve habitats across physical boundaries.

Aquatic subsidies promote viable

populations in low productive terrestrial

systems

By Ben Wilson

Typically systems with large amountsof primary production can produce a large

amount of available food, which in turn can

support greater populations (Odum et al.1984). Ecologists have long recognized that

the dynamics of one system are closely

linked to processes occurring in adjacent oreven distant environments (Odum et al.

1971). Energy being transported across

habitat boundaries from an aquatic area of

high primary production to a terrestrialhabitat of lower primary production is crucial

for an organisms sustainability (Huxel and

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McCann 1998). Here I will discuss the

connection of various terrestrial organismspreferred habitats and the aquatic systems

within those habitats. I will do this by

focusing on terrestrial carnivore and

omnivore behaviors in very low productiveterrestrial habitats that are adjacent to highly

productive aquatic habitats. Furthermore, I

will also investigate negative subsidyinteractions of overpopulated terrestrial

organisms on adjacent aquatic systems.

Rose and Polis (1998) found whilestudying desert coyotes (Canis latrans) that

aquatic primary production plays a crucial

role in the coyotes chosen terrestrial habitat.Primary production from coastal areas was

found to be on average 33 times higher thanprimary production of nearby arid desert

habitats. Coyotes also frequented the coastalregions 4.7 times more often.

Fig. 1. The food web shows the Baja California coyote

at the center, receiving energy from terrestrial and

marine subsidies. The width of the line indicates thepercentage of input the coyote receive from each

source. (From Rose and Polis 1998)

The scat from these coyotes contained 47.8%

of its mass from aquatic subsidies (mostly

protein rich animal carrion). Predatory habitsof the coyote allows for the highly productive

aquatic systems to transfer allochthonous

energy to low primary production systems(Polis 2004).

Predators benefit directly from aquatic

systems by feeding on coastline animalcarrion. Do omnivores also capitalize on an

increase in productivity? Stapp and Polis

(2003) observed higher population densities

of mice in the supra-littoral zone, and thatcapture rates declined the further from the

coast the traps were set on islands with no

predators. They also suggested that micewere poor conduits for transporting energy

inland and spent most of their time close to

the coastline. Predators might choose tospend a majority of their time near coastlines

not only for aquatic subsidies but also

because of an increase in prey populationsdue to available aquatic subsidies.

Both large and small terrestrialorganisms have similar chosen habitats not

only because of their trophic relationshipwith each other but also because of the

availability of aquatic subsidies. In return

both predator and prey benefit from eachothers presence. The input of marine

allochthonous energy is likely to occur

around the worlds 594000 km of coastline(Polis and Hurd 1996) (Hammond 1990).

Considering that much of the worldcoastlines actually receive one or two orders

of magnitude more marine biomass than that

of coastal site in Baja California where thesestudies took place (Polis and Hurd 1996) we

can infer that healthy productive aquatic

systems are a key component for the viability

of the worlds terrestrial populations.Therefore, protecting marine and freshwater

systems should be considered when

protecting all terrestrial species.In recent decades lesser snow geese

populations have skyrocketed (7% per year)

largely because of more food availability viaagriculture and a decrease in hunting pressure

(Jefferies et al. 2002). The increase in

population has proven to be detrimental to

their nesting grounds. Instead of typicalfeeding on above ground forage, the geese

are also destructively feeding on roots and

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rhizomes. This has converted the Arctic flats

into Arctic marshes which have difficultysustaining secondary invertebrate production

(Power et al. 2004). An indirect effect would

be the degradation of water quality in nearby

aquatic systems. Loss of vegetation wouldcause an increase in nutrients draining into

local lakes, ponds, and rivers. Geese have

also been found to directly affect aquaticsystems by transporting subsides from other

areas. Up to 40,000 geese each year spend

their winter in the Bosque del ApacheNational Wildlife Refuge in central New

Mexico. It was estimated that 45%-75% of

annual nitrogen and phosphorous for the areacame from geese translocation from

agricultural fields (Post et al. 1998).

Fig. 2 Daily ratios of nitrogen:phosphorous excreted

and loaded in the winter and spring of 1994-1995 by

lesser snow geese in the Bosque del Apache NationalWildlife Refuge in central New Mexico. The average

annual nitrogen:phosphorous ratio is shown for

comparison (From Stapp and Polis 1998).

Increase of nutrients in an aquatic system can

promote blue-green algae blooms. Thedensity of the algae blooms can be lethally

toxic to fish and invertebrates and natural

restoration is difficult. Degraded waterquality paired with eutrophication increases

the chance of contagious cholera and type Cbotulism outbreaks that can threaten the

entire ecosystem (Power et al. 2004).In conclusion, terrestrial organisms

take advantage of increased productivity

flowing as subsides from aquatic systems.Predator and prey populations are also found

to increase. This allows for low productive

terrestrial environments that are adjacent to

highly productive aquatic systems to sustainviable populations. However, if the terrestrial

organisms population becomes too large

then the aquatic system suffers through

negative subsidy exchanges. Thereforeterrestrial populations surrounding aquatic

systems are sensitive to the dynamics of both

terrestrial and aquatic systems.

Conclusion

Conservation and management

requires scientists to understand the trophic

interactions between aquatic and terrestrialsystems. Marine environments, freshwater

environments, and associated terrestrialhabitats are directly intertwined by the flux of

material. These subsidies can have dramaticinfluences on population dynamics and food

web processes. The greatest impact from

subsidies is observed when they flow fromproductive to unproductive systems.

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