Ecology of North American Arctic continental shelf benthos: a review

Continental Shelf Research, Vol. 11, Nos 8-10, pp. 865-883. 1991.

0278--4343/91 $3.00 + 0.00 © 1991 Pergamon Press plc

Printed in Great Britain.

E c o l o g y o f N o r t h A m e r i c a n Arctic c o n t i n e n t a l s h e l f b e n t h o s : a review ANDREW G . CAREY, J r

(Received 22 January 1990; in revised form 2 May 1990; accepted 10 October 1990) Abstract--The zoogeography, ecology, and biology of continental shelf invertebrate benthos along the arctic coast of North America from Alaska to western Greenland are reviewed. Environmental influences are noted and the life histories as well as the food sources of the fauna are summarized. The existence of regionally associated, characteristic community structures, centred upon the northern Bering Sea and the eastern Chukchi Sea, the Beaufort Sea, the Canadian Archipelago, the eastern Canadian Arctic, and western Greenland, is indicated. Early field research was exploratory and fragmented. Since 1940 more extensive studies oriented toward surveys and environmental baselines have been conducted. Over the last few decades physiological ecology studies of selected species have been undertaken to better understand adaptations to polar conditions. Recent Canadian research has included long-term field experiments on the effects of oil spillage in arctic waters as well as quantitative studies of benthos across the Archipelago and within fiords and other specialized environments. This research has suggested the need for basic biological and ecological research from the level of species through complete ecosystems in arctic waters. Additional studies on the long-term effects of pollution should be undertaken in the colder regions where it is likely that biological processes are slower and the effects of pollution are more long-lasting. Specifically, the ability to define pelagic-benthic coupling in Canadian arctic waters would provide insight into the role of the benthos in low productivity arctic ecosystems. In summary co-operative international research programmes on continental shelf benthos throughout the Arctic Basin and its surrounding seas should be undertaken. Knowledge of the range of shelf environments will provide insight into the controlling physical and biological features of the environment as well as the role of the seafloor within the arctic environment.

INTRODUCTION

IN addition to the existence of common benthic fauna and the similarity of arctic environmental conditions the entire North American region is influenced by the development of resources and accompanying problems of pollution that are regional rather than territorial in scope. Since the quantity and taxonomic composition of fauna have not been adequately described arctic benthic research (previously reviewed by CURTIS,1975) is in an initial stage of development. This has placed limits upon our ability to accurately determine broad-scale patterns of distribution, numerical density, and biomass across the North American Arctic. The acquisition of standardized quantitative data would yield vital basic and applied information on ecologically important species and communities. * College of Oceanography, Oregon State University, Corvallis, OR 97331-5503, U.S.A. 865

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180*

l ~

ARCTICOCEAN GREENLAND

BEAUFORT ALASKA

.

,

30*

150"

CANADA QUEBEC

i 20 °

90 °

60 °

Fig. 1. Location map illustrating the continental shelf regions in the North American Arctic where benthic ecological research has been undertaken. (1) Bering/Chukchi seas, (2) Beaufort Sea, Mackenzie River delta, (3) Melville Sound, Melville Island, Bathurst Island, (4) Jones Sound, Lancaster Sound, Ellesmere Island, (5) Thule, Greenland, (6) Northern Baffin Island, BaffinBay, (7) Godhaven, Greenland, (8) Godthaab, Greenland, (9) Southern Baffin Island, Southern Davis Strait, and (10) Labrador Sea, Ungava Bay.

This review discusses the state of current knowledge of invertebrate benthos on the arctic shelf of north America and provides specific suggestions for the research undertakings required to answer the most basic questions concerning the biology and ecology of the arctic benthos. For review purposes the North American marine arctic region (Fig. 1) can be considered as extending from the northeastern Bering Sea southward to Nunivak Island (NEIMAN, 1963) and then eastward to the Strait of Belle Isle (BRicCs, 1974; STEELE, 1975). In addition within this region marine zoogeographers have recognized high-arctic, lowarctic, and subarctic zones (e.g. EKMAN, 1953; NEIMAN, 1963) the precise geographic boundaries of which remain unclear (BRIGGS, 1974). The continental shelves in the western North American Arctic are shallow and range from the broad continental platforms of the Bering and Chukchi seas to the narrow western Beaufort Sea Shelf (HERMAN,1974). The Canadian Archipelago contains two physiographic provinces: (1) an inner, narrow segment of submerged coastal zone; and (2) a broader, uniform outer portion with the shelf break at 80-150 km offshore. The Archipelago is dissected by numerous channels ranging in width from 10 to 120 km and in some areas extending to over 700 m in depth.

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The shallow Bering Strait is the only connection between the Arctic seas and the Pacific Ocean. Northerly moving currents transport Bering and Chukchi seawaters at depth across the Arctic Basin and thereafter eastward into the Canada Basin (AAGAARD, 1984). The clockwise, wind-driven Beaufort Gyre is the predominant surface current in the Beaufort Sea. A southerly net current flows from the Arctic Basin through the passes of the Archipelago into northern Baffin Bay through Smith, Jones, and Lancaster sounds (COACHMANand AA6AARD, 1974). Arctic conditions are intensified in the Labrador Sea by cold water moving southward from the Arctic Basin via the Davis Strait and the westward component of the East Greenland Current (COACHMANand AAGAARD,1974; BRIGGS, 1974). Sea ice predominates most of the year along the continental shelf of the Beaufort Sea and the ,majority of the Canadian Archipelago (KAMeHUIS, this issue). Open water is present for longer periods of time in the southwestern regions of the Chukchi and northern Bering seas and eastward in Davis Strait and the Labrador Sea. Sea ice has a significant effect upon arctic ecosystems and its impact upon the logistics of northern polar waters has been a major reason for the slow development of marine benthic ecological research in the North American Arctic. In addition CURTIS (1975) concluded that a lack of commercial interest as well as the slow development of scientific interest in the North American Arctic have resulted in inertia in the field of benthic research in northern waters. METHODS AND DATA COMPATIBILITY The colder temperatures and multi-age ice cover of the Arctic Ocean require the modification of existing techniques for the retrieval and processing of standard benthic samples. During winter months sea ice presents special problems. Fast ice on the inner shelf often reaches thicknesses of 1.8 m and requires a specialized approach to the problem of cutting holes sufficiently large to deploy sampling equipment (HARGV.AVEet al., 1989). Most of the reported North American arctic benthic data have been acquired from depths up to 200 m on the continental shelves drawn from projects using a variety of sampling gear and techniques to collect benthic fauna. In this review comparisons of faunal biomass, numerical density, and species diversity have been made with the use of data acquired by similar field and laboratory techniques. As reviewed methodologically by HOLMEand MCINTVRE(1984) the sediment depth to which a sampler digs and the area of its coverage are influenced by the size and type of sampler used as well as the substrate type. The use of different types of infaunal sampling gear or sieve aperture sizes (for concentrating animal samples) can lead to discrepancies in the data particularly in numerical density data and thus prevent rigorous trend analysis (THOMSONet al., 1986). The published data have not been consistently comparable for reason of the application of different measures of biomass. Most standing stock data have been reported as preserved wet weights although some of the biomass data are reported as organic carbon; a more meaningful biological term (PERCY, 1979; WACASEYand ATKINSON,1987b; GREBMEIERet al., 1989; KORCZYNSKI,1989). ZOOGEOGRAPHY CLARKE(1963) suggested that arctic fauna comprises a few endemic species plus Atlantic and Pacific fauna that have migrated northward, and is relatively young. It is likely that the

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polychaete and bivalve fauna of the arctic continental shelf were destroyed during each major period of glaciation (BERNARD, 1979; BILYARDand CAREY, 1980). These fauna are dominant members of the benthos and are those used as key arctic indicator species. The polychaete worm fauna in the western Beaufort Sea (to a depth of 300 m) reflects very few endemics, the dominance of amphiboreal-arctic species, and a low number of total species (BxLVARDand CAnEr, 1980). In contrast the deeper bathyal fauna has more endemic species and is related to the Atlantic fauna, suggesting that it is older and has been isolated from the Pacific fauna by the shallow Bering Strait. Adjacent to Point Barrow the fauna reflects close affinities to the Bering Sea Polychaeta while in Canadian waters the benthos has affinities to Atlantic fauna from the Mackenzie River region and eastward (WACASEY, 1975; WAGNER, 1977). The Canadian bivalve fauna is arctic-circumpolar with few Atlantic and Pacific species while the fauna from western Greenland is a mixture of Atlantic subarctic and arctic species (LtraiNSgY, 1980). Other molluscan groups, including gastropods and amphineurans, have extensive geographic ranges and close zoogeographic relationships to Atlantic fauna (GILKINSONet al., 1986). It would appear that the Hudson Strait is a boundary between polar and mixed fauna zones. There have been no identified recent immigrations of Pacific bivalve fauna into the Canadian Arctic. QUANTITATIVE ECOLOGY

The initial phases of benthic ecological research are descriptive and focus on the taxonomic composition of fauna and quantitative bio-indices of numerical density, biomass, and species diversity. For this review quantitative information is separated into five regions from the west to the east across the North American Arctic and is based primarily upon different geographic, hydrographic and geological environments. Biomass and numerical density data are divided into macrofauna living within the sediments (infauna >1.0 mm in length), macrofauna living on the substrate surface (epifauna), and meiofauna (from 0.62 to 0.5 mm in length). The largest standing stocks of benthos are found in the northern Bering Sea while the smallest stocks are located in the Beaufort Sea. The waters of the Canadian Archipelago and the Labrador Sea are characterized by intermediate abundances. Northeastern Bering and eastern Chukchi seas

Large standing stocks of detrital-feeding benthic macrofauna as high as 500 g m -z at water depths from 50 to 150 m in muddy sand have been reported to the south of St Lawrence Island in the northern Bering Sea (Fig. 1) (NEYMAN, 1960; NEIMAN, 1963; FILATOVA and BARSANOVA, 1964). The primary productivity data to explain these high values were not available when reported but NEWMAN(1960) suggested that the high standing stocks of benthic invertebrates were due to low bottom temperatures that served to exclude demersal fish predators. In waters less than 50 m in depth the mean standing stocks were 8-50 g m -2 in sand and 20-30 g m -2 at depths greater than 50 m in muddy sediment. Recent studies have included winter and summer surveys of the macrobenthos (STOKER, 1978, 1981) and a co-ordinated multi-disciplinary effort to study organic material and nutrient fluxes between the pelagic and benthic environments; that is pelagic-benthic

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coupling (Gva~BMEmRet al., 1989). Beneath the very productive Bering Sea--Anadyr Water (BSAW) faunal densities ranged from 1684 to 6940 ind. m -2, and biomass ranged from 118 to 2377 g m -2 (Table 1) (GR~BMEmRetal., 1988). The Bering and Chukchi Sea shelves are shallow and range from 19 to 55 m in depth with central shallow basins in which the macrobenthic standing stock was largest. Stoker (1978) suggested that Chukchi Sea benthos utilize detrital organic materials exported from the northern Bering Sea; amphipods and bivalves being the dominant taxa. Under the less productive Alaskan coastal waters macrofauna at other station groups were less abundant; 641--4193 ind. m -2 and a biomass of 2.0-15.4 g m -2 (GREBMEIERet al., 1988).

Beaufoet Sea The numerical density and biomass (i.e. wet preserved weight) of macrofauna in the southwestern Beaufort Sea are greatest at the shelf edge and upper slopes at depths of 140--700 m (CAGEYet al., 1974; CAGEYand RUFF, 1977). Low numbers and biomass, as a result of active ice scouring, have been recorded at depths of 15-25 m (BRAUN, 1985; BARNES et al., 1984). Macrofaunal biomass is lower than other regions in the North American Arctic and numerical densities on the shelf are also lower in comparison to other regions of the Alaskan and Canadian Arctic or to boreal shelves (Table 1). In the eastern Beaufort Sea the Mackenzie River outflow significantly lowers bottom water salinity to the northwest decreasing benthic standing stocks and diversity (WACASEY, 1974, 1975; WACASEYet al., 1977). The benthos are more abundant on the Mackenzie Shelf to the northwest, perhaps as a result of particulate transport by river outflow. At a depth of 5 m in the lagoon enviroment of Stefansson Sound (Fig. 1) benthic meiofaunal densities averaged 58 ind. cm -2 (CAGEYand MONTAGNA,1982). In the months of March and May nematode worms accounted for 90% of this population with harpacticoid copepods at 3-4% and polychaetes at 3%. Seaward of the barrier islands in the nearshore Beaufort Sea at 9 m depth, average meiofaunal densities from April to June were 15 +_ 5 ind. cm -2 (CAGEY, unpublished data). Compared to data from a more

Table 1.

Mean macrobenthic biomass (wet preserved wt) in the North American Arctic. Depth 5--63 m

Location Bering Sea Bering-Anadyr Alaska Coastal Beaufort Sea Melville Island Boothia Peninsula Lancaster Sound Northern Baffin Island West Greenland Labrador

Biomass (gm -E)

643 248 77 94 188 319 200-438 48-320 346

Reference

GREBMEIERet al. (1989) GR~aMEIERet al. (1989) CAREV(1977) BUCHANANet al. (1977) THOMSONet al. (1978) THOMSONand CRoss (1980) ELLIS (1960) ELLIS (1960) BARRIEet al. (1980)

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eastward environment in the North American Arctic standing stocks of benthic meiofauna were low at this location (Table 1).

Canadian Arctic archipelago

From 1976 to 1979 the multi-disciplinary Eastern Arctic Environmental Studies Program (EAMES) conducted quantitative benthic ecological studies from northern Baffin Island to the Hudson Strait and the northern Labrador Sea (Fig. 1) (WACASEYet al., 1980; THOMSON, 1982; STEWART, 1983; STEWARTet al., 1985; WACASEYand ATKINSON, 1987a). The application of similar field and laboratory techniques yielded comparable data and demonstrated quantitative trends in community structures at given latitudes and depths. Data from additional samples in the Northwest Passage of the central Canadian Arctic have been compiled from a number of studies utilizing various techniques (THOMSONet al., 1986). Beyond a barren zone down to 5 m in depth the numerical density of macro-infauna to depths of 50 m off Melville and Bathurst islands in the western and central Arctic Archipelago were generally similar (THOMSON et al., 1986). In Lancaster Sound off northern Baffin Bay standing stocks varied with depth and location (THOMSON, 1982) but were higher than those reported in the Beaufort Sea (Table 1). The highest levels were between 15 and 105 m ranging from 3560 to 4564 ind. m -2 and a biomass of 787 to 1094 g m -2. Amphipods accounted for about 76% of the total biomass at 5 m depth, and bivalves for about 52-78% at 10-100 m depth. At depths between 5 and 10 m biomass was usually low and caused by the presence of fast ice during the winter and by low salinity and ice scour during the summer open water season (Table 2). This appears to be a widespread phenomenon across the Arctic nearshore zone. Beyond a depth of 106 m the biomass decreased with depth. For example the standing stock of benthic macrofauna ranged from 19.8 to 479.9 g m -2 southeast of Baffin Island in an area which included Ungava Bay (STEWART, 1983; STEWARTet aI., 1985). In the nearshore environment off Cape Hatt, northern Baffin Island, total meiofaunal densities averaged 583 ind. cm-2 that is greater than the densities reported in the Beaufort Sea and for average boreal environments (Table 3; Fig, 1) (MARTINand CROSS,1986; SNOW et al., 1987). The meiofaunal community was comprised of 68.4% nematodes, 10.1% foraminiferans, 7.7% copepods and 13.8% miscellaneous fauna.

Table 2.

Distributional zones for macrofauna: the inner North American Arctic continental shelf. Modified from WACASeY (1974)

Zone Nearshore Inshore Transition Continental shelf Upper slope

Depth (m) 0-2 2-20 15-30 30-100 > 100

Comments Barren zone at 1-2 m. Annually depopulated by freezing and ice scouring. Strongly influenced by freshwater run-off. Intensely scoured by ice keels. Biomass higher at shelf edge. Biomass begins to decrease.

Depth (m)

5-6 9 3-12

Location

Beaufort Sea (OCSEAP) Stefansson Sound Nearshore Beaufort N. Baffin Island (BIOS) Clayey silt Clayey sand Sand

Substrate

54.6 12.2 398.6

Nematoda

2.0 1.8 44.7

Copepoda

1.8 0.8 139.2

Misc.

Density (no. cm -2)

58.4 142.0 582.5

Total

Table 3. Summary of North American Arctic meiofauna densities

CAREVand MONTAGNA(1982) CAREY(unpublished data) MARTIN and Cnoss (1986)

Reference

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Western Greenland

Some benthic communities on the west Greenland Shelf (Fig. 1) are dominated by bivalve species with biomass standing stocks ranging from 160 to 1482 g m -2 (VINE, 1939). The highest biomass figures represent a shallow community dominated by the clam species Cardium groenlandicum. In Disko Bugt at depths from 28 to 179 m there were 749565 ind. m -2 numerical density and 46-59 g m-2 biomass. On the inner shelf off Godthaab benthos macrofauna averaged 1729 ind. m -2 and 133 g m-2 (wet wt) at 10 m depth (Table 1) (ELLIS, 1960). Inland seas and fiords

During the SAFE (Sedimentology of Arctic Fiords Experiment) Project, initiated by the Geological Survey of Canada in 1981, benthic fauna were sampled in 10 Baffin Island fiords (Fig. 1). Characteristic benthic macrofaunal species groups associated with sediment types were distributed down the axes of the fiords (DALEet al., 1989; SYvrrsKi et al., 1989). Fine glacial sediments were found at the heads of fiords and decreased with distance from the source. Firm sediments mixed with gravel and shell (i.e. 'firm ground') supported the most abundant and diverse communities including encrusting fauna as well as ophiuroids, errante motile polychaetes, bivalves, and sea urchins. At shallow depths low salinity surface water formed during summer ice melt appeared to alter the polychaete distributions at depths of less than 10 m (CURTIS, 1972). The benthos of inland seas is not well known. Virtually no information is available on Hudson Bay benthos (ROFF AND LEGENDRE, 1986). ENVIRONMENTAL EFFECTS

Environmental and biological interactions control the structure and functions of benthic communities. However the relative effect of environmental factors changes from one arctic shelf region to another dependent upon the intensity of gradients and disturbances. Differences in water mass, sediment characteristics, and ice gouging are the primary environmental factors affecting the structure and function of benthic communities. Water masses

In the southeastern Beaufort Sea, WAGNER (1977) reported that distributions of molluscan species to a depth of 200 m were associated with depth rather than sediment type. Four water masses delineated by temperature were present in the area but the narrow temperature range did not appear to affect species distributions. The higher standing stocks of macroinfauna (of >1.0 mm) associated with the shelf edge and upper slope are probably caused by the transport of particulate organic carbon around Point Barrow from the productive Bering and Chukchi seas by the Beaufort Undercurrent (CAREY and RUFF, 1977; AAGAARD, 1984). An analysis of station similarities for the southeastern Baffin Island and northern Labrador shelves, based upon numerical abundance, separated the fauna into two major groups of stations, those shallower than 300 m and those deeper than 300 m (STEWARTet al., 1985). Subgroups within each depth range on cluster tended to be associated with water masses rather than sediment types. For example shallow stations were associated with cold bottom water. One shallow station subgroup occurred under the Hudson Strait

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outflow from the Canadian Arctic archipelago, while another benthic group was found beneath the cold Baffin Island current. It was suggested that the contrast in arctic and temperate water masses may be related to the increase in benthic species diversity. Two congeneric amphipod species (Pontoporeia affinis and P. femorata) live in the nearshore southwestern Beaufort Sea but occur at overlapping depth ranges. Based upon discriminant statistical analysis the environmental features that appear to be important determinants of small-scale distributions are temperature, depth, and salinity (Bosrmosa et al., 1982). PERCY(1983, 1985) reported that the salinity tolerances of species can be correlated with their distributions in nearshore environments. Mesidotea entomon, an effective osmoregulator, lives in low salinity coastal waters in depths of less than 10 m while M. sabini, a less effective osmoregulator, can be found in the most saline environments from depths of 10 to 441 m. M. sabirica, living at depths of 5-25 m, is intermediate in both low salinity tolerance and capabilities and in situ salinity range. The hydrographic regime is also a determinant of the level of primary productivity within a region, in turn affecting carbon/nitrogen input to the seafloor and the organic content of sediments. GREBMEIERet al. (1989) have demonstrated these influences upon benthic community structures, abundance and energetics. Those of greater biomass may be found under nutrient-rich, productive waters with detritus/suspension-feeding amphipods in coarser sediments and deposit-feeding polychaetes in sediments with silt and clay. Sediments

Where sediments are heterogeneous and patchy as on the southwestern Beaufort Sea Shelf (CAREYand RUFF, 1977) the animal-sediment relationships for bivalve molluscs are either weak or difficult to demonstrate. As delineated by canonical analysis other taxa (e.g. polychaete species) appear to be affected by sediment type (BILVARDand CAGEY, 1979). In contrast statistical groups of polychaete species in the western Beaufort Sea are distributed by depth. When the silt-clay composition surpasses a threshold level the composition of infaunal species changes from suspension- to deposit-feeding forms (GREBMEmR et al., 1989). Bivalve molluscan fauna appear to be distributed across the inner shelf (at 5-25 m depth) according to functional groupings of deposit and suspension feeders (CAREYet al., 1984). Deposit-feeding bivalves are generally associated with fine sediment found at a depth of 25 m. The high species richness of bivalve fauna in the nearshore zone may be caused by the decreased wave action and lower constant environmental disturbance resulting from ice damping effects. Macro-infaunal species are generally associated with certain sediment types. Transitional fauna such as fiord benthos occur within zones of sediment change (DALE et al., 1989). High sediment heterogeneity (measured by sorting coefficients) appears to encourage higher species diversity (GREBMEIERe t al., 1989). For example a diverse and selective detritus/suspension-feeding community occurs in a heterogeneous sediment structure in the central Chukchi Sea. Ice gouging

Across the North American Arctic sea ice reduces the abundance of coastal and nearshore benthos by freezing, gouging, and decreased salinity resulting from ice melt

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(PETERSEN, 1977; THOMSONet al., 1986). On the inner continental shelf of the Beaufort Sea the keels of pack-ice pressure ridges plough through the bottom disrupting sediment (BARNES et al., 1984). During the ice-covered months the transition zone from fast ice to moving pack ice is a zone of disturbance. During summer months shoal areas are also impacted by individual pressure ridge remnants. Ice gouging significantly disturbs benthic communities altering community structures by changing the sedimentary environment for at least 3 years (BRAUN, 1985). Though the density of benthos decreases within gouges, at the same time species diversity increases. Comparison of the taxonomic composition within scours and surrounding sediments suggests there is a strong correlation between species distributions and sediment characteristics. In the eastern Canadian Arctic Archipelago icebergs originating from Ellesmere Island and Greenland significantly scour, compact, and transport sediments on the continental shelf and slope of Baffin Island and Newfoundland (PEREIRA e t al., 1988; WOODWORTHLYNAS et al., this issue). The massive disruption of sediments, with subsequent effects on sedimentation, results in patchy sedimentary distributions. It is likely that gouging in deeper water has long-term effects on benthic communities but this is caused by sedimentation effects that are similar to those of moving pack ice on the inner shelf. POLLUTION ECOLOGY

Laboratory toxicity studies of individual species and field experimentation of total biota have been undertaken to measure the potential effects of oil and gas exploration in the cold, ice-covered waters of the Arctic. Recent research has been summarized by the NATIONAL RESEARCH COUNCIL (1985), WELLS and PERCY, (1985) and REY and ALEXANDER (1989). Laboratory investigation Laboratory studies on individual species were undertaken by the Outer Continental Shelf Environmental Assessment Program (OCSEAP) in Alaskan waters and by the Beaufort Sea Project in Canadian waters (NA~ONAL RESEARCh COUNCIL, 1985, Table 5-13). However cumulative information on the sublethal effects of oil on arctic benthic invertebrates is taxonomically, biologically, and behaviourally incomplete (WELLS and PERCY, 1985). Invertebrate exposure to oiled sediments causes distinct behavioural reactions, ranging from attraction to the sediment to prevention of colonization by polychaetes and mortality (ATLAS et al., 1978; Busnoosrl, 1981). Many of the responses appear to be similar to those of temperate animals. Infaunal species such as bivalve molluscs (Macoma baltica) often move out of oiled sediments (TAYLOR and KARINEN, 1977). Amphipods (Crustacea: Amphipoda) appear to be more sensitive to petroleum contamination than other taxa including isopods (Crustacea: Isopoda). The scavenging and burrowing amphipod Onisimus affinis consistently avoids oil-tainted fish, whereas the scavenging isopod Mesidotea entomon does not (PERCY, 1976). O. affinis can readily detect and avoid lightly contaminated sediments but apparently loses sensory capability at high oil concentrations (PERCY, 1977). Other crustaceans including the burrowing amphipod Corophium clarencense and the isopods Mesidotea entomon and M. sabirica do not distinguish between oil-

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contaminated and clean sediments. Weathered oil contains fewer volatile hydrocarbons thus decreasing the avoidance response by animals and detrimental effects on their growth (PERCY, 1977, 1978). The differing hydrocarbon compositions of crude oils and the amount of weathering are probable explanations for some of the differences in laboratory experimental results.

Field investigation From 1980 to 1985, SNow et al. (1987), SERGYand BLACKALL(1987) and CROSS and HUMPHREY(1987), as well as others, undertook field experiments on the fate and effects of a moderate-sized oil spill. Since the shoreline and coastal waters are the environments most likely to be heavily impacted by nearshore oil spills (SANDERSel al., 1980) four similar bays at Cape Hatt on northern Baffin Island were selected for study, the Baffin Island Oil Spill Project (BIOS) treated two bays with 15 m 3 of crude oil and a third with 15 m3 of crude oil chemically dispersed with 1.5 m 3 of Corexant. A fourth nearby bay was used as a reference for documenting 'normal' environmental and faunal changes. The addition of untreated crude oil incurred no short-term effects on the macro-infauna but within 24 h of release the dispersed oil treatment caused acute effects upon the fauna of the treated bay and a neighbouring bay (CRoss and THOMSON, 1987; CROSSet al., 1987). A large number of infauna and epifauna, particularly the bivalve Serripes groenlandicus, emerged from the sediment the first day. After the initial and major impact of the dispersed oil on the benthic fauna, the oil largely disappeared (CROSS and HUMPHREY, 1987). However the untreated oil became stranded on the beach and during ensuing years was washed down into the subtidal zone to reach levels of 119 ppm. Over the following 2year period hydrocarbon concentrations in the environment and biota returned to near background levels. For the probable reason that the exposure was short and because oil concentrations in all bays remained at relatively low levels neither the treated oils nor the untreated oil incorporated in the sediments appeared to cause large-scale mortality among the benthos. There were indications that some motile, epibenthic species avoided contaminated sediments by migration to deeper water (CROSSet al., 1987). Four years after the oil spills hydrocarbon concentrations in the sediments of the experimental bays had stabilized (CRoss and HUMPHREY, 1987). Three species of benthos (the bivalves Serripes groenlandicus and Macoma calcarea, and the sea urchin Strongylocentrotus droebachiencsis) had increased levels of oil in their tissues. Statistical interaction terms suggested this was the possible effect of oil contamination. However no definite conclusions were drawn from this study since changes in population structures, abundance, distributions, and size-weight relationships were in the range of natural variability. In addition small-scale field experiments with oiled sediments, water, and ice have been undertaken. The effects on the benthic macrofauna were most often unclear due probably to the small size of the experimental containers (ATLAS et al., 1978; ATLAS, 1985). However slow oil degradation by bacteria has indicated that hydrocarbons may remain in the Arctic environment over long periods of time. In temperate waters when oil becomes mixed with intertidal sediments-it may be added to the nearshore benthic environment over a period of years by the reworking of sediments through wave action (SANDERSet al., 1980). The same local reservoir effect may be caused by the inclusion of a large oil spill in multi-year pack ice.

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In the shallow and rich waters of the northern Bering and eastern Chukchi seas selective detritus/suspension-feeding fauna (amphipods and bivalves) are dominant (Gl~BMEIER et al., 1989). Deposit-feeding polychaetes and bivalves occur where the silt and clay content range from 16 to 52%. The majority of the continental shelf benthic macro-infauna in the less productive Beaufort Sea are deposit/detritus-feeding forms (CAREYand RUFF, 1977). In the inshore zone the scavenging gammarid amphipod, Pseudalibrotus (= Onisimus) litoralis, migrates to the ice undersurface to feed on sympagic meiofauna in the early spring and ice diatoms during late May and early June (CAREYand BOUDmAS, 1987). Pseudalibrotus litoralis usually lives on the bottom and is most abundant from depths of 15-20 m. The early primary production of ice algae provides a small, early source of energy for the benthos below as well as sympagic animals associated with the ice (HoRNERand SCHRADER, 1982; HORNER, 1985; CAREY,1987). Benthic fishes tend to occur in lagoonal and nearshore waters where they can feed on abundant epibenthic crustaceans (CRAICand MCCART, 1976). Nearshore fish species from Resolute Bay (Cornwallis Island, N.W.T.) feed on benthic invertebrates, particularly polychaetes, amphipods, and mysid shrimps (GREEN, 1979). The most abundant offshore fish, the Arctic cod (Boreogadus saida), feeds on a broad range of mostly pelagic or epibenthic fauna: sympagic amphipods and copepods in offshore waters and mysids, amphipods and copepods in nearshore waters (LowRY and FROST,1981; CRAI~et al., 1985). Fish predation on benthic invertebrates in Arctic offshore waters is probably greatly reduced owing to the low bottom temperatures that exclude demersal, predaceous fishes from more southern environments (Vra~, 1939; NEIMAN, 1963; JEWETTand FEDER, 1981). Species association analyses have suggested that it is probable that predation by invertebrates on other benthic species is not significant (STOKER, 1981). In the northern Bering and Chukchi seas, diving marine mammals are the major predators of benthos on the inner shelf. The walrus, Odobenus rosmarus, feeds on benthic bivalve molluscs to depths of 60 m (OLIVERet al., 1983). Walrus feeding activities represent a significant physical disturbance to the bottom environment since the dominant infaunal invertebrates are reduced in number within walrus feeding pits. In the northern Canadian Archipelago bearded seals (Erignathus barbatus) feed on benthic fauna, whelks, and epibenthic shrimp (FINLEYand EVANS, 1983). In the Bering and Chukchi seas, and occasionally in the Beaufort Sea, the gray whale (Eschrichtius robustus) feeds on benthic macrofauna, particularly amphipod crustaceans, by sucking up benthos along with portions of surface sediment (NERINI and OLIVER, 1983). Gray whales may radically disturb from 9 to 14% of the benthos annually in the northern Bering Sea (NERINI, 1984).

FAUNA Because the arctic marine environment exhibits marked primary production seasonality benthic animals may store reserves of protein and lipid before the onset of winter (KoRczYNSKI, 1989). A benthic amphipod species, Onisimus affinis, increases its lipid content before spawning but does not increase lipid and caloric reserves for the winter (PERCY, 1979). In general caloric values for a broad range of benthic invertebrates indicate that mean caloric values for arctic fauna are not significantly different from those of boreal animals (WACASEYand Aa~:INSON, 1987b).

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Arctic fauna generally grow and reproduce slowly (THORSON, 1936; MACGINITIE, 1955; DUNBAR, 1968; CHIA, 1970; CLARKE, 1979), producing fewer energy-rich eggs directly developed in the benthic environment rather than indirectly developed as members of the meroplankton. Some of the more abundant forms, such as the filter-feeding bivalve Mytilis edulis of Disko Bugt (Greenland) ingest energy-rich and seasonally abundant phytoplankton in shallow exposed environments and reproduce large quantities of planktonic larvae (PETERSEN, 1978). The deeper-living and deposit-feeding benthos (such as polychaetes) exist in food-poor environments. They mature slowly and reproduce with fewer directly developed, energy-rich eggs (CURTIS, 1977; PETERSEN, 1978). For the North American arctic environment, life history data including information on recruitment, growth, reproduction and development, are scant.

BENTHIC--PELAGIC COUPLING The quality and quantity of organic carbon that reaches the seafloor has a direct effect upon benthic biomass (GREBMEIERet al., 1988). Under the productive BSAW in the Northern Bering Sea, stable carbon isotope and C/N data suggest that nitrogen-rich marine carbon reach the benthos. High standing stocks of benthos (20.2 g C m -2) occur under the BSAW in comparison to the lower biomass (6.3 g C m-2) under less productive Alaskan Coastal Water (ACW). Total sediment-oxygen uptake rates decrease from 19.2 mmol 02 m -2 day -1 under the BSAW to 8.7 mmol 02 m -2 day -1 under the ACW (GREBMEIER et al., 1989). Lower organic carbon input rates to the benthos decrease respiration rates despite higher temperatures (GREBMEIERand McRoY, 1989). Macrofauna respiration and the effects of bioturbation are major components in bottom carbon cycling and greater food input to the bottom increases benthic biomass (GREBMEIERet al., 1989). Increased primary production in overlying waters with increased carbon flux to the bottom affect sedimentary organic content. In turn feeding strategies and standing stocks of the benthos are influenced by the carbon flux. A comparison Of energy fluxes in arctic (Disko Bugt, West Greenland), temperate and tropical regions suggests that energy fluxes in arctic ecosystems are dominated by the seafloor and by the water column in the more southern ecosystems of the temperate North Sea and the tropical seas off Thailand'(PETERSEN and CURTIS, 1980).

DISCUSSION AND CONCLUSIONS Research on the benthos of the North American arctic continent remains in its initial stages of development and fundamental knowledge of the fauna is scarce and fragmented in space and time. The baseline data required for improved comprehension of the benthic ecology of the re#on include the taxonomic composition and abundances of the fauna. Acquisition of additional data, including patterns of distribution, numerical density, and biomass form the foundation for the formulation of basic and applied research questions concerning the ecological importance of species and communities. The process of accumulating comparable patterns of distribution, abundance, diversity, feeding type, and community energetics has been initiated. These scientific efforts provide insight into the patterns of adaptation of benthic animals to colder, often ice-covered, waters. Benthicpelagic coupling studies have added to our understanding of how the energy fixed by

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primary production is divided and utilized by pelagic and benthic organisms. Ultimately benthic ecologists will be able to determine the energetic and biogeochemical roles of individual species populations in arctic ecosystems as well as the role of the total habitat of the shallow seafloor and its biotic components. From the viewpoint of applied research the BIOS Project has been a unique experiment iri measurement of the effects of moderate-sized oil spills in the environment of the North American Arctic. The results of this well-planned field experiment, however ambiguous, have added to our understanding of both the immediate and short-term effects of oil on nearshore benthic organisms and have demonstrated the need to undertake similar experiments or experiments of opportunity to measure the long-term effects of oil spills in the Arctic coastal environment. Research literature

During the last two decades studies of the Beaufort Sea benthos of the Alaskan, Yukon, and Northwest Territories continental shelves have been primarily undertaken with the sponsorship of the petroleum industry and government service agencies. Thus spurred by the development of the petroleum industry and by increased scientific interest in the nature and integrity of the polar environment research efforts have been oriented toward the potential impacts of gas and oil exploration and production. As a consequence benthic ecological research has been in a rapid growth phase since the 1970s. A recent search of the ASTIS (Arctic Science and Technology Information System, Arctic Institute of North America) database yielded the following Canadian references: 92 reports, 33 journal articles, and 18 chapters of the proceedings of meetings (CAREV,unpublished data). Research methodology

Similar to efforts in other regions of the world, quantitative surveys of benthic megafauna, macrofauna and meiofauna have been undertaken only for localized areas, and frequently with the use of different sampling techniques, methods of sample processing, and levels of taxonomic work-up. Broad-scale benthic surveys utilizing standardized techniques accompanied by complementary environmental studies have only been infrequently undertaken in the Canadian Arctic. Benthic community pollution ecology has long been criticized for its labour-intensive character (WAXWlCX, 1988). While the study of critical biological, ecological, and pollution effects must be undertaken on ecologically important'species useful information may be derived from fundamental ecological studies that deal with broader-scale taxonomic categories (GREBMEmRet al., 1989). General trends

It appears from the data available that a trend exists in benthic numerical density and biomass which may be strongly correlated with the hydrography and primary productivity of given regions. Benthos occurs in the greatest quantities in the northeastern Bering Sea through the shallow Chukchi Sea, while the lower primary productivity of the Beaufort Sea is reflected in the lower quantity of benthic invertebrates. However this observation is subject to the qualification that by virtue of the Beaufort Sea Undercurrent there is an

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apparent influence of Bering--Chukchi seawaters on the western Beaufort Sea outer-shelf, upper-slope fauna. Toward the east (beyond the stratified water column of the Arctic Basin) the abundance of benthos increases in the waters of the Canadian Archipelago. Primary production is larger in these areas presumably caused by the thorough mixing of water masses in the passages and channels of this topographically complex region. Water masses, by their gradients in salinity and temperature, affect the distribution and abundance of arctic benthos and have particularly important effects on primary production. For example there is a strong correlation between primary production and sedimentary organic carbon and in the abundance of benthic macrofauna in the northern Bering and southern Chukchi seas. Research needs

Numerous and basic scientific questions about the biology and ecology of arctic benthos remain unanswered including the following: how are animals adapted to the cold and highly seasonal polar environment? What are the processes controlling the distribution, abundance, and production of arctic benthos? What are the roles of benthic communities and the seafloor in the arctic ecosystem? To answer these fundamental questions as well as those oriented toward pollution effects extensive and consistent research efforts should be undertaken. Recommentations include the following proposals: (1) large-scale, standardized surveys of benthic communities including time-series studies to determine broad-scale patterns of distribution, abundance, and limits of natural variability; (2) basic biological studies including life histories, population dynamics, biochemistry, physiological ecology, and food webs of ecologically important benthic species; (3) measurement of the long-term effects of oil spills on the biology of benthic fauna, including spills under ice-covered conditions, to determine if there are subtle but detrimental effects from major oil spills or from continuous, low-level inputs of hydrocarbons; (4) time-series studies of secondary production and the energetics of benthic communities to define the dynamics of benthos under arctic conditions; and (5) integrated multi-disciplinary studies on year-round benthic-pelagic coupling to determine the processes that control the abundance of benthic fauna, the structure of benthic communities, and the role of the seafloor in the arctic ecosystem. Based upon this review of recent benthic ecology in the North American and Canadian Arctic it may be observed that this field is on the threshold of exciting research that will synthesize our fundamental understanding of the structure, functions, and controlling environmental factors and processes of the arctic environment. A broad overview is needed to mold benthic ecological projects into a programme producing comparable results in the Arctic Basic and surrounding seas. Benthic ecologists should undertake research within the framework of the arctic ecosystem. Long-term co-operative research programmes should be undertaken by the nations bordering the Arctic Ocean. An international advisory committee on benthic research particularly for applied projects would encourage integated, multi-disciplinary approaches based upon the use of standardized research.

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