Polar Biology

, Volume 28, Issue 5, pp 402–421

Southeastern Chukchi Sea (Alaska) epibenthos

Authors

    • Institute of Marine ScienceUniversity of Alaska Fairbanks
  • Stephen C. Jewett
    • Institute of Marine ScienceUniversity of Alaska Fairbanks
  • Arny Blanchard
    • Institute of Marine ScienceUniversity of Alaska Fairbanks
Original Paper

DOI: 10.1007/s00300-004-0683-4

Cite this article as:
Feder, H.M., Jewett, S.C. & Blanchard, A. Polar Biol (2005) 28: 402. doi:10.1007/s00300-004-0683-4

Abstract

Epibenthos of the southeastern Chukchi Sea, inclusive of Kotzebue Sound, was sampled in 1976. Crustaceans dominated abundance while echinoderms, mainly sea stars, dominated biomass. Spatial distribution of fauna was determined by cluster analysis. Scavenger-predators were dominant trophic groups, although suspension feeders dominated some regions. Unexpected high abundance and biomass under Alaska Coastal Water and factors related to presence and distribution of fauna are discussed. Dissimilarities between the benthic systems of the southeastern and northeastern Chukchi Seas are attributed to more complex water mass and flow patterns in the southern system. Entrained particulate organic carbon disperses through the area to support an abundant and apparently highly productive benthic fauna, which sustains resident and transient populations of demersal fishes and marine mammals. Epibenthos was sampled again in 1998 and, although little change was apparent in community composition, many taxa had higher abundance and biomass than 22 years earlier, a trend similar to findings observed in the northeastern Bering Sea.

Introduction

Arctic marine environments are typically characterized by: low water temperatures, prolonged ice cover, extreme seasonal variation in irradiance regime, and a single pulse of low water-column primary productivity (Heimdal 1989). Despite such environmental constraints, benthic fauna in some Arctic waters are abundant and biomass values high, which is explained by increased efficiency of energy transfer from the water column to the sea bed (Petersen and Curtis 1980; Grebmeier and Barry 1991). This is supported for the northern Bering and southeastern Chukchi Seas, where almost 70% of water-column primary production escapes zooplankton grazing and settles to the sea floor (Grebmeier et al.1988; Grebmeier and McRoy 1989). Carbon flux to the bottom is supplemented by carbon derived from ice algae (Horner 1976), as also noted by Carey (1987) in the Beaufort Sea. Dunton et al. (1989) suggest close coupling of primary production to coastal benthic fauna in the contiguous northeastern Chukchi Sea. Effectiveness of this coupling in the northeastern Bering and Chukchi Seas is evidenced by the presence of numerous benthic-feeding marine mammals (Lowry et al. 1980; Fay 1982; Frost and Lowry 1988; Moore and Clarke 1986; Highsmith and Coyle 1992).

The eastern Chukchi Sea infauna is the subject of numerous studies that document the diversity and richness of this benthic component (Stoker 1981; Grebmeier et al. 1988, 1989; Feder et al. 1994a, b). These studies used grabs, which are inadequate for sampling epifauna (Piepenburg et al. 1996). Further, epifaunal organisms mostly occur in low numbers, and are underestimated or missed using grabs. Epibenthic species are particularly important in benthic systems in higher latitudes because of their high biomass (Schwinghamer 1981), bioturbation activity (Grebmeier and McRoy 1989; Graf 1992), trophic interactions with infauna, demersal fishes and marine mammals (Jewett and Feder 1980, 1981; Feder and Jewett 1981) and contribution to total benthic energy turnover (Piepenburg et al. 1996). Despite the importance of epibenthos in high-latitude ecosystems, few papers address this faunal component quantitatively in the Chukchi Sea. MacGinitie (1955) lists epifaunal species off Barrow in the northeastern Chukchi Sea and includes ecological and reproductive information. Pettibone (1954) describes epibenthic polychaetes, Shoemaker (1955) amphipods, MacGinitie (1959) mollusks and Abbott (1966) ascidians. Sparks and Pereyra (1966) present a qualitative account of epifauna in the southeastern Chukchi Sea. Quantitative assessments of epifaunal mollusks (Feder et al. 1994b) and snow crab (Paul et al. 1997) were conducted in the northeastern Chukchi Sea.

The investigation presented here represents one component of a study of the benthic system of the eastern Chukchi Sea (Fig. 1). Results from the northeastern Chukchi are presented in Feder et al. (1994a, b). Preliminary assessment of data from the southeastern Chukchi is included in Wolotira et al. (1977), Feder and Jewett (1978), Jewett and Feder (1981) and Feder et al. (1991a). Most data reported here were obtained in 1976. Limited qualitative epifaunal data are available for the area from 1986–1987 (Feder et al. 1991a). Surveys in 1998 and 1999 addressed the fisheries potential for the area, and resulted in information for the distribution of dominant epifaunal invertebrates present (Fair and Nelson 1999; Nelson et al. 2000). These surveys were carried out approximately 24 km south of the village of Kivalina near the DeLong Mountains Terminal (DMT), where zinc concentrate is shipped to world markets. Quantitative accounts of epifauna adjacent to the DMT are included in Dames and Moore (1983a, b) and RWJ Consulting (2001). Heightened interest in fisheries potential, shipping activity, presence of substantial marine-mammal populations, and increased worldwide interest in ice-covered, marine systems (Dunton et al. 1989; Hobson et al. 1995; Smith and Grebmeier 1995; Piepenburg et al. 1997; Weslawski et al. 1997; Ambrose et al. 1995, 2001) suggest that information about the benthic environment within the study area has broad interest, particularly in light of the current concerns about global warming.
Fig. 1

Station locations in the southeastern Chukchi Sea, Alaska where biological trawl samples were collected in 1976. The dashed line represents the approximate location of the hydrographic front. Inset in upper right corner shows the general current patterns in the study area.

The objectives were to (1) generate a faunistic inventory of epifauna, (2) identify dominant species and their distributions, abundance and biomass, (3) evaluate taxon assemblages and relate these assemblages to environmental features, (4) examine trophic interactions related to faunal distribution and water-current delivery of particulate organic carbon (POC), and (5) compare fauna between 1976 and 1998.

Materials and methods

Study area

The southeastern Chukchi Sea, including the Chukchi Bight (an embayed area between the Lisburne and Seward Peninsulas) and Kotzebue Sound (Fig. 1), lies within the continental shelf in water, generally ≤60 m depth. Kotzebue Sound is 10–21 m deep with a depth of 27 m at its entrance. The area is characterized by long, severely cold winters and short, cool summers. Presence of sea ice for 7–8 months is a dominant feature with duration of a maximum ice-free period of 4–5 months (McRoy and Goering 1974).

Bering Strait, mouth of the Sound and inshore adjacent to coastal regions, except the central Sound, comprise gravelly to sandy substrates. The Sound has a muddy-sand to sandy-mud substrate with sandy substrate dominant along the coast. Coasts within the Bight are subject to severe storms that impact the shoreline and the shallow subtidal (Allen and Weedfall 1966). Wave erosion of cliffs and barrier islands between Kivalina and Cape Thompson supplies coarse sediment and gravel to the near-shore region (Creager 1963). The central Bight and Sound are less affected by ice gouging than adjacent near-shore waters (Hunter and Reiss 1985).

Water masses in the southeastern Chukchi Sea, during the open-water season, reflect a combination of advective and in situ processes, with the most important of these being the northward advection of water through the Bering Strait (Coachman et al. 1975). Water masses flowing through the Bering Strait are the Bering Shelf water (BSW), the Anadyr water (AW) and the Alaska Coastal water (ACW). Just north of the Bering Strait, BSW and AW mix to form the Bering Shelf–Anadyr water (BSAW). A horizontal gradient between more saline, colder BSAW and less saline, warmer ACW maintains a hydrographic front of variable strength (Coachman et al. 1975; Grebmeier et al. 1988). BSAW is a major source of POC in the study area. ACW, reinforced by fluvial flux, is characterized by high terrigenous POC (Naidu et al. 1993). Major sources of POC are phytoplankton, zooplankton, under-ice algae and eelgrass (McRoy 1968; Horner 1976). Water-column productivity is probably increased locally within a seasonal polynya adjacent to the coast between Kivalina and Point Hope (Stringer and Groves 1991; Smith et al. 1990).

The main stream of BSAW flows into the Chukchi with ACW passing along the eastern near shore. Cross-frontal mixing between BSAW and ACW is promoted by the presence of eddy-like fluctuations of the northward flow of BSAW just north of Bering Strait and the variable winds in the area that generate up- and down-welling events (Feder et al. 1991a; T. Weingartner, personal communication). Anticyclonic eddies east of Cape Prince of Wales further mix BSAW and ACW (Fleming and Heggarty 1966; Coachman et al. 1975). One branch of these mixed waters follows the depth contours northward to the coast between Kivalina and Point Hope, where it is deflected to the northwest at current speeds of 15–75 cm s−1. Another branch of these waters flows along the northern coast of the Seward Peninsula (Fleming and Heggarty 1966; Coachman et al. 1975; Winsor and Chapman 2004). Prevalence of a strong eastward-moving littoral current along the Seward Peninsula coast is indicated by the presence of extensive barrier islands, sandy substrate inshore and the Cape Espenberg spit (Naidu 1988). This current slows within an eddy behind Cape Espenberg in Kotzebue Sound, and water movement in the Sound is generally sluggish. Near-bottom water in summer, and cold, high-salinity bottom water formed following sea-ice formation in fall and winter flows out of the Sound along the deepest channel and northwestward along the coast from Kivalina to Point Hope (Fleming and Heggarty 1966; Coachman et al. 1975; Feder et al. 1991a). Runoff from river systems within the Sound in summer reinforces the coastal current between Cape Krusenstern and Point Hope. A localized region of central Kotzebue Sound occasionally becomes anoxic under heavy ice cover in winter (Feder et al. 1991a).

Data collection and analysis

Data were collected from the NOAA ship Miller Freeman 5–16 September 1976, using a modified Eastern otter trawl with a 17-m horizontal opening (Wolotira et al. 1977). Calculations from these data were previously reported in Feder and Jewett (1978) using a 12.2-m horizontal trawl opening rather than 17 m. The latter trawl opening was applied to most calculations in this paper. Tows were 30 min in duration at an average speed of 6.5 km h−1. A total of 70 stations were occupied (Fig. 1; Appendix S1). Sampling depths ranged from 15 m to 64 m. Typically, one tow was made at each station.

Catches were sorted on shipboard, given tentative identifications, enumerated, weighed, and fixed in 10% buffered formalin. Organisms mainly comprised epifauna, although some infauna was collected. Epifauna that could not be quantified and infauna were included in the taxa count, but not included in abundance, biomass calculations and multivariate analysis. Abundance and biomass were converted to individuals km−2 and kg km−2, respectively. All species of the gastropod Buccinum are included as Buccinum spp. and hermit crabs as Paguridae in distribution maps. General comments on distribution of epifauna were not collected quantitatively and some infaunal taxa are included in the Results. A group-average agglomerative hierarchical cluster analysis was applied to a dissimilarity matrix of quantifiable epifaunal taxon abundance data to identify community relationships (Clifford and Stephenson 1975). A dissimilarity matrix was calculated utilizing the Bray–Curtis coefficient (Bray and Curtis 1957) on ln(x+1) transformed abundance data.

In August 1998 the Bering Sea Fisherman’s Association conducted test fishing in the same area using similar collection methods as the 1976 study to update the small-boat fishery resources potential (Fair and Nelson 1999). Comparison of dominant taxa between the two periods is presented by percent frequency of taxon occurrence, mean abundance (ind. km−1), and mean biomass (kg km−1) (note: this abundance and biomass is per km, not per km−2). Since the 1998 values were presented as individuals and kg per km, we also present our 1976 values in the comparison table using the same units. Values for mean abundance and biomass of dominant taxa from 1976 are adjusted to the same trawl opening width (12.2 m) used in 1998.

Results

Faunal composition and distribution of taxa

A total of 165 taxa in 11 phyla were collected (Table 1; Appendix S2). The number of taxa per trawl varied between 6 (station A55 northeast of Cape Prince of Wales at 17 m) and 53 (station A3 adjacent to Point Hope at 38 m) with an average of 26 taxa for all stations. A disjunct distribution was apparent for dominant taxa (Fig. 2). Mollusks dominated taxon representation with 69 taxa, and arthropod crustaceans and echinoderms comprised 33 and 21 taxa, respectively. Echinoderms made up the bulk of epifaunal biomass with 59.7%; mollusks and crustaceans contributed 14.1% and 13.6%, respectively (Table 2). Crustaceans dominated abundance with 35.5%, followed by echinoderms, tunicates, and mollusks with 31.9%, 19.9%, and 7.7%, respectively.
Table 1

Number and percent of benthic invertebrate taxa by phylum and class from trawls in the southeastern Chukchi Sea–Kotzebue Sound, 5–16 September 1976 (modified from Feder and Jewett 1978)

Phylum

Class

Number of taxa

% of taxa

Porifera

Demospongia

4

2.50

Cnidaria

Hydrozoa

1

0.61

Anthozoa

5

3.03

Totals

6

3.64

Rhynchocoela

Unidentified

1

0.61

Annelida

Polychaeta

13

7.88

Mollusca

Polyplacophora

1

0.61

Bivalvia

27

16.36

Gastropoda

40

24.24

Cephalopoda

1

0.61

Totals

69

41.82

Arthropoda

Crustacea

33

20.00

Sipunculida

1

0.61

Echiurida

Echiuroidea

1

0.61

Ectoprocta

Cheilostomata

3

1.82

Cyclostomata

2

1.21

Ctenostomata

3

1.82

Totals

8

4.85

Echinodermata

Asteroidea

11

6.67

Echinoidea

2

1.21

Ophiuroidea

5

3.03

Holothuroidea

3

1.82

Totals

21

12.73

Chordata

Ascidiacea

8

4.85

Grand Totals

165

100.00

Fig. 2

Distribution of 16 dominant epifaunal taxa in the study area in 1976. Abundance (ind. km−2) of taxa is represented by size of circles.

Table 2

Percent composition by abundance (ind. km−2) and wet weight (kg km−2) of dominant epifaunal invertebrates

Phylum

% Abundance of all phyla

% Weight of all phyla

Dominant taxa

% Abundance of phylum

% Abundance of all phyla

% Weight of phylum

% Weight of all phyla

Arthropoda

35.52

13.63

Chionoecetes opilio

33.50

11.90

47.23

6.44

Pagurus trigonocheirus

16.23

5.76

14.95

2.04

Argis lar

13.08

4.65

4.43

0.60

Sclerocrangon boreas

11.02

3.91

3.76

0.51

Pagurus capillatus

10.17

3.61

6.69

0.91

Hyas coarctatus alutaceus

8.08

2.87

11.75

1.60

Labidocheirus splendescens

3.67

1.30

2.56

0.35

Pandalus goniurus

1.60

0.57

0.09

0.01

Pagurus rathbuni

1.10

0.39

0.69

0.09

Telmessus cheiragonus

1.00

0.36

7.29

0.99

Echinodermata

31.86

59.72

Ophiura sarsi

34.74

11.07

1.52

0.91

Leptasterias polaris acervata

22.50

7.17

23.42

13.99

Asterias amurensis

20.14

6.42

42.08

25.13

Strongylocentrotus droebachiensis

12.50

3.98

9.79

5.84

Lethasterias nanimensis

2.98

0.95

9.73

5.81

Gorgonocephalus caryi

2.04

0.65

5.75

3.43

Henricia sp.

1.60

0.51

0.14

0.09

Leptasterias sp.

1.14

0.36

0.15

0.09

Evasterias echinosoma

0.87

0.28

6.01

3.59

Crossaster papposus

0.73

0.23

0.23

0.14

Mollusca

7.65

14.06

Neptunea heros

72.40

5.54

82.75

11.63

Neptunea ventricosa

13.31

1.02

10.85

1.53

Beringius beringi

2.18

0.17

2.07

0.29

Buccinum scalariforme

1.59

0.12

0.29

0.04

Buccinum polare

1.52

0.12

0.25

0.03

Buccinum angulosum

1.45

0.11

0.35

0.05

Neptunea communis borealis

1.31

0.10

0.25

0.03

Volutopsius castaneus

1.25

0.10

0.80

0.11

Serripes groenlandicus

1.25

0.10

0.52

0.07

Pyrulofusus deformis

1.05

0.08

0.70

0.10

Urochordata

19.88

9.42

Boltenia echinata

42.92

8.53

3.78

0.36

Chelyosoma orientale

19.57

3.89

2.87

0.27

Chelyosoma spp.

18.59

3.69

47.62

4.48

Styela macrenteron

14.50

2.88

21.31

2.01

Halocynthia aurantium

2.81

0.56

16.55

1.56

Boltenia ovifera

1.20

0.24

3.05

0.29

Styelidae

0.24

0.05

0.45

0.04

Urochordata

0.18

0.04

4.36

0.41

Dominant echinoderms were the sea stars Asterias amurensis at 54 (77%) stations, Leptasterias polaris acervata at 57 (81%) stations, Lethasterias nanimensis at 41 (59%) stations and Evasterias echinosoma at 30 (43%) stations. Other important echinoderms were the sea urchin Strongylocentrotus droebachiensis at 47 (67%) stations, brittle star Ophiura sarsi at 40 (57%) stations, and basket star Gorgonocephalus caryi at 35 (50%) stations. Highest abundance for Asterias occurred at the entrance to and immediately outside Kotzebue Sound, extending northwestward along the coast off Kivalina (Fig. 2). Several high-abundance stations were also present at the western edge of the Chukchi Bight and along the Seward Peninsula. Leptasterias spp. (mainly L. polaris acervata) occurred throughout the area with highest abundance at the northwestern end of the study area. It was relatively common in the eastern Sound. Distribution of the common sea stars Lethasterias and Evasterias was similar to that of Asterias, with the highest abundance at the entrance and immediately outside the Sound and along the coast to Point Hope. Strongylocentrotus occurred in low numbers east of the hydrographic front and with highest abundances off Cape Prince of Wales and Point Hope. Urchins near Point Hope (70.3 mm±0.67 SE) were significantly larger (t=1.65, P=<0.001, df=196) than those near Cape Prince of Wales (44.4 mm±0.64). Ophiura occurred within the Sound, mid-Chukchi Bight and outer shelf, with highest abundance in the Bight and western edge of the area. Gorgonocephalus occurred with relatively high abundance from the outer Sound and along the coast to Point Hope. Highest abundance for the basket star was at A14 off Kivalina, A2 and A3 near Point Hope and several stations southwest of Point Hope.

Of the 69 molluscan taxa, the large gastropod Neptunea heros dominated, occurred at 42 (60%) stations, and represented 83% of the molluscan biomass and 72% of abundance. Highest abundance and biomass occurred within the southwestern region with high abundance also off Point Hope (station A3) and several stations in eastern Kotzebue Sound. The gastropods N. ventricosa (37: 53% of the stations), Beringius beringi (34: 49% stations) and six species of Buccinum (29: 41% stations) were also important. Buccinum mainly occurred in the northwestern portion of the area and inner Kotzebue Sound. The drilling snails Natica and Polinices occurred in most areas where bivalves were common. Bivalves were widely dispersed throughout the area (Feder et al 1991a). The cockle Serripes groenlandicus was common at the mouth of the Sound and along the coast north of Cape Krusenstern. Other bivalves taken qualitatively by trawl throughout the study area were Nuculana, Nucula, Macoma, Hiatella, Astarte, Clinocardium and Thyasira (Feder et al. 1991a). The scallop Chlamys was only present adjacent to Point Hope (A1, A2, A3).

The snow crab Chionoecetes opilio occurred at 62 (89%) stations, contributed 47% of crustacean biomass and 33% of abundance, but only represented 6% of total biomass of all taxa. Highest abundance occurred at the entrance of Kotzebue Sound. Relatively high values were also recorded on the western edge of the study area. The composition of this crab comprised sublegal males and immature females. The crabs Paguridae, Hyas coarctatus alutaceus and Telmessus cheiragonus and the crangonid shrimps Argis lar and Sclerocrangon boreas were also important. Highest abundance for Paguridae was within and adjacent to Kotzebue Sound and extending out of the Sound along the coast to Point Hope but they were also abundant at the western edge of the area. Hyas occurred at 63 (90%) stations and was common within and at the entrance to the Sound, and along the coast to Point Hope. The helmet crab Telmessus was present along the coasts of the Seward and Lisburne Peninsulas, and Kotzebue Sound, occurring at 21 (30%) stations, with the highest abundance along the coast near Kivalina. Argis was present at 59 (84%) stations, and was most abundant from the outer Sound, extending along the coast to Point Hope. Sclerocrangon occurred at 19 (27%) stations, but was only abundant along the coast between Kivalina and Point Hope. The shrimp Pandalus goniurus was found at 16 (23%) stations, generally in low numbers with highest abundance adjacent to Point Hope, along the coast adjacent to Kivalina (A15, A21, A22), B19 adjacent to Cape Espenberg and A28 within the Chukchi Bight with low numbers in the Sound. The king crab Paralithodes camtschaticus occurred in low numbers at three stations and P. platypus at two stations.

Tunicates (Urochordata: Boltenia, Styela, Chelyosoma, Halocynthia) were present at 83% of the stations. Where tunicates were present, they were in large numbers, representing 20% of total abundance but only 9% of the biomass. Highest numbers were outside the Sound, extending along the coast from Kivalina to Point Hope (stations A2, A3, A13, A14, A15). Boltenia spp. was present at 50%, Styela spp. at 51%, Chelyosoma at 23% and Halocynthia at 9% of stations. Localized high abundance of Chelyosoma occurred at stations A13, A14, and A15 along the Lisburne Peninsula.

Three other taxon groups were relatively abundant in some areas—sea anemones (Actiniidae), the soft coral Eunephthya rubiformis, and bryozoans. Anemones were at 44% of the stations but only represented 4% of the total epifaunal biomass. Highest abundance was at the mouth of the Sound. Eunephthya, present at 33% of stations, occurred in low numbers in the Sound but with high abundance off Kivalina and the northwestern region of the area. Although bryozoans were not included in the abundance and biomass calculations, this group occurred at 44% of stations, mainly in Kotzebue Sound and along the coast to Point Hope. Numerous sponges occurred at one station (A54) north of Bering Strait.

Multivariate analysis

Ten station groups were defined by cluster analysis with two stations not joining a group (Figs. 3, 4; Table 3; Appendix). Station A-54, west of Cape Prince of Wales close to the Bering Strait, was dominated in abundance and biomass by the sea urchin Strongylocentrotus droebachiensis with nearly 75,000 ind. km−2 and 4,100 kg km−2. The sea cucumber Psolus japonicus and Chionoecetes opilio were also important. Station A-55, north of Cape Prince of Wales close to the coast, was distinguished by low number of taxa, abundance and biomass.
Fig. 3

Dendrogram showing station groups formed by cluster analysis of epifaunal abundance data from 1976. DNJ did not joined group

Fig. 4

Distribution of epifaunal groups based on cluster analysis of abundance data from 1976.

Table 3

Average abundance (ind. km−2) and biomass (kg km−2) for station groups and dominant epifaunal taxa

Group

Abundance

Biomass

Number of taxa

Abundance

Biomass

A54

86,057

5,004

21

Strongylocentrotus droebachiensis

74,550

Strongylocentrotus droebachiensis

4,111

Hyas coarctatus alutaceus

6,744

Psolus japonicus

412

Psolus japonicus

1,316

Hyas coarctatus alutaceus

216

Chionoecetes opilio

907

Lethasterias nanimensis

55

Pagurus trigonocheirus

378

Paralithodes platypus

48

A55

509

61

5

Asterias amurensis

270

Asterias amurensis

58

Argis lar

143

Labidocheirus splendescens

2

Labidocheirus splendescens

64

Argis lar

1

Actiniidae

16

Actiniidae

<1

Crangon dalli

16

Crangon dalli

<1

I

2,555

417

9

Asterias amurensis

1,733

Asterias amurensis

381

Chionoecetes opilio

309

Telmessus cheiragonus

8

Pagurus capillatus

95

Urochordata

5

Labidocheirus splendescens

76

Gorgonocephalus caryi

5

Telmessus cheiragonus

73

Chionoecetes opilio

4

II

53,285

2,330

17

Ophiura sarsi

18,799

Leptasterias polaris acervata

1,576

Leptasterias polaris acervata

16,440

Neptunea heros

181

Chionoecetes opilio

3,432

Asterias amurensis

172

Pagurus trigonocheirus

2,376

Gorgonocephalus caryi

80

Argis lar

2,304

Ophiura sarsi

75

III

216,268

7,637

28

Boltenia echinata

47,585

Chelyosoma spp.

1,347

Chelyosoma orientale

28,161

Strongylocentrotus droebachiensis

1,169

Sclerocrangon boreas

27,380

Gorgonocephalus caryi

830

Chelyosoma spp.

25,106

Leptasterias polaris acervata

584

Strongylocentrotus droebachiensis

12,717

Evasterias echinosoma

557

IV

31,460

2,317

15

Neptunea heros

14,312

Neptunea heros

1,635

Chionoecetes opilio

5,191

Neptunea ventricosa

167

Argis lar

2,545

Asterias amurensis

147

Pagurus trigonocheirus

2,186

Chionoecetes opilio

147

Neptunea ventricosa

1,968

Leptasterias polaris acervata

58

V

9,065

1,226

17

Asterias amurensis

3,843

Asterias amurensis

847

Actiniidae

2,047

Lethasterias nanimensis

133

Ophiura sarsi

759

Telmessus cheiragonus

83

Telmessus cheiragonus

640

Actiniidae

68

Lethasterias nanimensis

465

Evasterias echinosoma

46

VI

28,676

1,357

22

Chionoecetes opilio

5,873

Neptunea heros

366

Pagurus trigonocheirus

4,515

Asterias amurensis

294

Neptunea heros

4,387

Lethasterias nanimensis

177

Ophiura sarsi

2,803

Chionoecetes opilio

151

Argis lar

1,948

Leptasterias polaris acervata

95

VII

29,756

2,274

23

Pagurus trigonocheirus

5,982

Asterias amurensis

1,092

Asterias amurensis

4,964

Evasterias echinosoma

219

Pagurus capillatus

4,546

Neptunea heros

194

Actiniidae

3,034

Pagurus trigonocheirus

144

Neptunea heros

2,046

Actiniidae

100

VIII

43,428

2,217

24

Chionoecetes opilio

16,916

Asterias amurensis

1,158

Pagurus capillatus

10,132

Neptunea heros

335

Asterias amurensis

5,260

Chionoecetes opilio

271

Neptunea heros

5,222

Pagurus capillatus

101

Pagurus trigonocheirus

1,181

Lethasterias nanimensis

101

IX

51,184

2,865

22

Chionoecetes opilio

12,848

Asterias amurensis

1,464

Asterias amurensis

6,654

Chionoecetes opilio

361

Ophiura sarsi

6,644

Lethasterias nanimensis

315

Actiniidae

5,194

Actiniidae

172

Pagurus trigonocheirus

3,569

Evasterias echinosoma

120

X

29,314

999

23

Asterias amurensis

5,484

Leptasterias polaris acervata

256

Hyas coarctatus alutaceus

5,082

Asterias amurensis

147

Ophiura sarsi

3,395

Neptunea heros

145

Leptasterias polaris acervata

2,832

Gorgonocephalus caryi

92

Pagurus trigonocheirus

2,711

Chionoecetes opilio

53

Group I

Three stations along the Seward Peninsula north of Shishmaref, with an abundance of 2,555 ind. km−2 and biomass of 417 kg km−2. Asterias amurensis characterized the group in abundance and biomass.

Group II

Twelve stations along the northwestern region, with an abundance of 53,285 ind. km−2 and biomass of 2,330 kg km−2. The two dominant taxa in abundance were the brittle star Ophiura sarsi and the sea star Leptasterias polaris acervata. Leptasterias dominated biomass with considerably lower values for other taxa.

Group III

Five stations along the coast from Kivalina to west of Point Hope, with the most taxa (28) and highest abundance (216,268 ind. km−2) and biomass (7,637 kg km−2) of all groups. The group was dominated by tunicates, although crangonid shrimps (Sclerocrangon boreas, Argis lar) were abundant. The tunicates Chelyosoma spp. dominated biomass with relatively high values for Strongylocentrotus, the basket star Gorgonocephalus caryi, and the sea stars L. polaris acervata and Evasterias echinosoma.

Group IV

Eight stations at the southwestern edge of the area, with an abundance of 31,460 ind. km−2 and biomass of 2,317 kg km−2. Neptunea heros dominated abundance and biomass.

Group V

Three stations north of Cape Espenberg and at the entrance to the Sound, had an abundance of 9,065 ind. km−2 and biomass of 1,226 kg km−2. Asterias dominated abundance and biomass. Actiniidae was also abundant.

Group VI

Six stations within the inner Sound, with an abundance of 28,676 ind. km−2 and biomass of 1,357 kg km−2. Chionoecetes dominated abundance, but P. trigonocheirus, N. heros, O. sarsi, and A. lar were also abundant. Neptunea heros and Asterias dominated the biomass.

Group VII

Four inshore stations, two along the coast adjacent to Cape Espenberg within the Sound and two stations along the coast extending from Cape Krusenstern to just south of Kivalina. The abundance was 29,756 ind. km−2 and biomass of 2274 kg km−2. Pagurus trigonocheirus, Asterias, P. capillatus, Actiniidae and N. heros dominated the abundance . Asterias dominated the biomass.

Group VIII

Two stations in the southwestern region of the Bight northeast of Cape Prince of Wales with an abundance of 43,428 ind. km−2 and biomass of 2,217 kg km−2. Chionoecetes and P. capillatus dominated the abundance, but Asterias and N. heros were also abundant . Asterias dominated the biomass.

Group IX

Nineteen stations extending west from the mouth of the Sound into the central Bight. It had an abundance of 51,184 ind. km−2 and biomass of 2,865 kg km−2. Chionoecetes dominated in abundance, but Asterias, Ophiura, Actiniidae, and P. trigonocheirus were also abundant. Asterias dominated the biomass. Three sea-star taxa (Asterias, Lethasterias nanimensis and Evasterias) accounted for 66% of the total group biomass.

Group X

Six stations in the western region of the Bight oriented in a north-south direction, with an abundance of 29,314 ind. km−2 and biomass of 999 kg km−2. Asterias and Hyas dominated abundance with O. sarsi, L. polaris and P. trigonocheirus also being abundant . Leptasterias dominated the biomass.

Epifaunal comparison between 1976 and 1998

A comparison of the trawl surveys of 1976 and 1998 is summarized in Table 4. The planned sampling density of the 1998 survey was identical to the 1976 survey. However, the 1998 survey used a trawl with a narrower opening (12.2 m vs. 17 m), was towed at a slower speed (3.9 km h−1 vs. 6.5 km h−1), covered a shorter total distance (118.3 km vs. 222.3 km), and successfully occupied fewer stations (65 vs. 70). However, most of the dominant taxa, as measured by percent frequency of occurrence, abundance, or biomass, increased in the most recent survey and community composition was similar between surveys.
Table 4

Comparisons of demersal trawl surveys between 1976 (this paper) and 1998 (Fair and Nelson 1999)

Trawl type

1976

1998

Modified Eastern Otter Trawl

400 Eastern Otter Trawl

 

(17 m horizontal opening)

(12.2 m horizontal opening)

Planned sampling density

SE Chukchi Sea—1 station/750 km−2

SE Chukchi Sea—1 station/750 km−2

Kotzebue Sound—1 station/375 km−2

Kotzebue Sound—1 station/375 km−2

Trawl duration

30 min

30 min

Mean trawl speed

6.5 km h

3.9 km h

Mean distance trawled

3.176 km

1.820 km

Total distance trawled

222.340 km

118.300 km

Stations successfully trawled

70

65

Dominant taxa

% Frequency of occurrence

% Frequency of occurrence

Relative change 1976–1998

Asteroidea

100

100

=

Paguridae

97

100

=

Argis lar

84

98

+

Urochordata

83

95

+

Chionoecetes opilio

89

91

=

Hyas coarctatus alutaceus

90

75

Pandalus goniurus

23

60

+

Gorgonocephalus caryi

50

51

=

Eunephthya rubiformis

33

49

+

Neptunea heros

60

40

Telmessus cheiragonus

30

37

+

Ophiura sarsi

57

34

Neptunea ventricosa

53

34

Crangon dalli

10

31

+

Strongylocentrotus droebachiensis

67

29

Sclerocrangon boreas

27

28

=

Dominant taxa

Mean abundance (ind. km−1)

Mean abundance (ind. km−1)a

 

 

17 m net

Converted to 12.2 m net

12.2 m net

Chionoecetes opilio

87

62

628

+

Asteroidea

135

97

313

+

Ophiura sarsi

90

65

286

+

Strongylocentrotus droebachiensis

39

28

78

+

Argis lar

36

26

73

+

Paguridae

93

67

43

Urochordata

188

135

37

Pandalus goniurus

5

4

33

+

Sclerocrangon boreas

33

24

16

Hyas coarctatus alutaceus

27

19

16

=

Holothuroidea

1

1

13

+

Gorgonocephalus caryi

6

4

11

+

Telmessus cheiragonus

3

2

4

=

Crangon dalli

<1

<1

4

+

Neptunea ventricosa

8

6

3

=

Neptunea heros

43

31

3

Dominant taxa

Mean biomass (kg km−1)

Mean biomass (kg km−1)

 

 

17 m net

Converted to 12.2 m net

12.2 m net

Asteroidea

20.73

14.88

28.94

+

Chionoecetes opilio

2.37

1.70

17.19

+

Urochordata

4.19

3.01

6.68

+

Strongylocentrotus droebachiensis

2.77

1.99

3.19

+

Ophiura sarsi

0.36

0.26

1.44

+

Gorgonocephalus caryi

1.49

1.07

1.07

=

Paguridae

2.37

1.70

1.05

Eunephthya rubiformis

0.06

0.04

0.99

+

Hyas coarctatus alutaceus

0.69

0.50

0.73

+

Telmessus cheiragonus

0.40

0.29

0.73

+

Argis lar

0.22

0.16

0.47

+

Neptunea heros

4.42

3.17

0.42

Neptunea ventricosa

0.60

0.43

0.36

=

Sclerocrangon boreas

0.21

0.15

0.24

+

Paralithodes platypus

0.02

0.01

0.21

+

Holothuroidea

0.23

0.17

0.18

=

Chlamys spp.

0.03

0.02

0.15

+

aMean abundance calculated by dividing total number of individuals per taxon by total distance trawled

Two groups that dominated the three measures in both surveys were Asteroidea and the snow crab Chionoecetes opilio. Sea stars occurred at 100% of the stations in both years. Sea-star abundance in 1998 (313 ind. km−1) was three times higher than in 1976 (97 ind. km−1). Similarly, sea-star biomass in 1998 (28.9 kg km−1) was two times greater than in 1976 (14.9 kg km−1). Snow crab occurred at about 90% of the stations in both years. The abundance of this crab in 1998 (628 ind. km−1) was an order of magnitude higher than in 1976 (62 ind. km−1). In both years, crab composition was sublegal males and immature females with mean weight per individual nearly identical in both surveys, i.e., 0.027 kg. Other taxa with higher percent frequency of occurrence, and/or abundance, and/or biomass in 1998 included the sea raspberry Eunephthya rubiformis, the scallops Chlamys spp., the shrimps Argis lar, Sclerocrangon boreas, Crangon dalli, and Pandalus goniurus, the crabs Telmessus cheiragonus, Hyas coarctatus alutaceus, and Paralithodes platypus, the brittle star Ophiura sarsi, the sea urchin Strongylocentrotus droebachiensis, sea cucumbers Holothuroidea, and Urochordata. Neptunea heros decreased in all three measures in 1998. Hermit crabs also decreased in abundance and biomass; little change was noted in percent of station occurrence. Little or no change was noted between years for the basket star Gorgonocephalus caryi.

Discussion

General

Most dominant epifaunal taxa in our study were reported in earlier qualitative benthic investigations in the northeastern Bering and southeastern Chukchi Seas (Ellson et al. 1950; Neiman 1963; Sparks and Pereyra 1966). In all studies, most species were of boreal Pacific rather than Arctic origin. Near absence of Arctic species is not unexpected in view of the strong northerly currents that prevail during ice-free summer months on the eastern side of the Bering and Chukchi Seas (Weingartner et al. 1998).

Epifaunal data from the northeastern Gulf of Alaska and southeastern Bering Sea show arthropod crustaceans dominating the invertebrate biomass, with 71% and 59% present in the respective regions (S. C. Jewett and H. M. Feder, unpublished data; Jewett and Feder 1981). Total echinoderm biomass from each area was 19% and 18%, respectively. In contrast, echinoderms dominated invertebrate biomass in the northeastern Bering and southeastern Chukchi Seas (Feder and Mueller 1974; Sparks and Pereyra 1966; Feder et al. 1991a; this paper). The echinoderm biomass (primarily asteroids) in the northeastern Bering and southeastern Chukchi was 81% and 60%, respectively, with crustacean biomass in the two areas only 8% and 14%, respectively (Jewett and Feder 1981). Change in biomass dominance from crustaceans to echinoderms in northern waters appears attributable to increased presence of benthic food for echinoderms. This food availability may reflect, in part, the absence of large crabs and frequent absence of demersal fishes in the northern regions, many of which use similar food items (Neiman 1963; Feder and Jewett 1981; Jewett and Feder 1981). Demersal fishes only move into the northeastern Bering and Chukchi Seas during warm years (Jewett and Feder 1980; Feder and Jewett 1981). Differences in distribution of large crabs and demersal fishes are reflected by commercial catch statistics, which demonstrate that the southeastern shelf, unlike the colder northeastern portion of the shelf, is a major fishing area for these organisms (Feder and Jewett 1981). Sea stars make up 69% and 50% of total epifaunal biomass in the northeastern Bering and southeastern Chukchi Seas, respectively, while only 7% and 15% of epifaunal biomass in the Gulf of Alaska and southeastern Bering Sea, respectively (H. M. Feder and S. C. Jewett, unpublished data; Jewett and Feder 1981).

Faunal composition and distribution

The southeastern Chukchi Sea is dominated by epifaunal predator-scavengers, with suspension-feeders occasionally abundant and dominant. Crustaceans were the most abundant organisms at all stations, although they did not dominate biomass. Foraging crustaceans represent disturbance factors that affect meiofauna and small infauna (Hall 1994), and are important in carbon mineralization. Although the crangonid shrimp Argis lar and hermit crabs (Paguridae) occurred at most stations, highest numbers were at the mouth of Kotzebue Sound, along the coast to Point Hope and west of the hydrographic front. The brachyuran crabs Chionoecetes and Hyas were widely distributed, usually at the same stations. However, there appeared to be an inverse relationship in their distributions. Chionoecetes was also common in the northeastern Chukchi Sea (Feder et al. 1991b; Paul et al. 1997). These crabs mainly feed on infauna, and the presence of high numbers throughout the area reflects availability of a widespread and abundant infaunal prey (Feder and Jewett 1981). The helmet crab Telmessus was present near shore (particularly off Kivalina) where Chionoecetes was uncommon or absent, suggesting competitive interaction between the crabs. The red king crab Paralithodes camtschaticus is close to the northern limit of its range, and occurred in low numbers. The farthest-north commercial fishery for this crab is Norton Sound in the northeastern Bering Sea (Natcher et al. 1996) where an abundant population occurs within a localized region far from its center of abundance in the southeastern Bering Sea. The shrimp Pandalus goniurus was only abundant along the Lisburne Peninsula. Since the shrimp utilizes benthic and pelagic food, it is often present where POC and zooplankton are transported to an area by water currents and maintained in the water column by turbulence (Rice et al. 1980; Carpenter 1983), physical conditions found along the coasts within the Chukchi Bight.

The broad distribution of sea stars, as major invertebrate predators in the area, is of importance because of their overall influence on community structure (Himmelman and Dutil 1991; Ross et al. 2002). Leptasterias was most abundant under BSAW in the northwestern region of the area where high carbon mineralization supports elevated benthic production, leading to abundant food resources for the sea star (Grebmeier and McRoy 1989; Feder et al. 1991a). Distribution of the other common sea stars (Asterias, Lethasterias, Evasterias) overlapped, but they mostly occurred in shallower water within and immediately outside the Sound, extending along the coast to Point Hope. Leptasterias was also common at a few stations (B22, B26) of the inner Sound where Asterias was uncommon. Asterias also occurred within the central Bight and was present in high abundance at some western stations where Leptasterias was absent or uncommon. In the northeastern Bering Sea Asterias and Leptasterias are segregated by depth with Asterias mainly in Norton Sound while Leptasterias is primarily in deeper water north and northeast of St. Lawrence Island (Jewett and Feder 1981). A negative correlation of Asterias abundance with depth occurs in Sendai Bay, Japan with maximum densities at 20 m (Hatanaka and Kosaka 1959). Asterias vulgaris and Leptasterias polaris in the Gulf of Saint Lawrence, Canada, also demonstrate spatial segregation by depth (Gaymer et al. 2001a). They suggest that segregation reflects avoidance interactions that enable the sea stars to coexist (Gaymer et al. 2002). Separation of the species in the Chukchi might be related, in part, to aggressive interactions with the smaller Asterias (mean diameter 25 cm) avoiding the larger Leptasterias (mean diameter 42 cm).

The brittle star Ophiura sarsi was common within the Sound and most abundant in the deepest portion of the Bight, extending to the western region of the study area where polychaetes, small gastropods and bivalves utilized as food were abundant (Feder and Pearson 1988; Feder et al. 1991a, 1994a). In the northeastern Chukchi Sea O. sarsi was the most abundant echinoderm in 1986 (Feder et al. 1991b) and 1998 (Ambrose et al. 2001). The infaunal ophiuroid Diamphiodia craterodmeta occurred throughout the study area with greatest abundance in the inner Sound (Feder et al. 1991a). Another ophiuroid Stegophiura nodosa was present at eight stations with the greatest abundance at A54 and B15 (H. M. Feder and S. C. Jewett, unpublished data). Numerous ophiuroids in northern waters may be related to the infrequent presence of bottom-feeding fishes that utilize ophiuroids as food (Jewett and Feder 1980; Feder and Jewett 1981).

Although the urchin Strongylocentrotus droebachiensis occurred throughout the area, it was only abundant in the presence of strong currents north of Bering Strait (A54) and off Point Hope. Urchins in this region adapt to strong currents by placing shells or small rocks on their aboral surface. Removal of these weights results in transport of the urchins in the direction of the current (Jewett et al. 1999).

Occurrence of the basket star Gorgonocephalus caryi is also related to the presence of strong bottom currents on hard or gravely bottoms (Patent 1970). Piepenburg and Juterzenka (1994) suggest that the feeding mode of basket stars, sponges and soft corals in Arctic waters of east Greenland depend on sufficiently strong bottom currents that laterally advect POC and small zooplankters in the nepheloid layer. Basket stars, as well as soft corals, occurred in highest abundance along the coast of the Lisburne Peninsula and west of the hydrographic front, regions characterized by strong bottom currents.

The sea stars Asterias, Lethasterias and Evasterias were abundant in all regions where bivalves (Thyasira, Clinocardium, Macoma, Hiatella, Serripes) were common (Feder et al. 1991a; H. M. Feder and S. C. Jewett, unpublished data). Bivalves are important food resources for sea stars, and areas where these mollusks are common attract sea stars (Feder and Christensen 1966; Fukuyama and Oliver 1985). The gastropods Neptunea and Buccinum were common in the eastern Sound and southwestern region of the area, and were broadly distributed in the adjacent northeastern Chukchi Sea (MacGinitie 1955; Feder et al. 1994b; N. Foster, personal communication). Leptasterias and Asterias feed on Buccinum (Himmelman and Dutil 1991; Gaymer et al. 2001a, 2001b) but no observations of predation on Neptunea are reported. Buccinum exhibits escape responses to sea stars (Feder 1967), and females, prior to egg laying, have greater escape abilities than males (Brokordt et al. 2003). Buccinum, in the northern Gulf of St. Lawrence, Canada, gains a high proportion of its food by kleptoparasitizing clams from its major predator L. polaris (Rochette et al. 1995). Rochette et al. (2001) suggest heightened escape response of females prior to egg laying enables them to obtain food (via kleptoparasitism) that contributes to reproductive success. The presence of large numbers of Buccinum in areas of high concentration of L. polaris in the southeastern Chukchi Sea might be explained by a similar interaction between the gastropod and sea star. Neptunea does not appear to demonstrate escape responses to sea stars (H.M.F., unpublished data; J. Himmelman, personal communication), but reduced numbers in the presence of large numbers of L. polaris in the northwestern portion of the study area nevertheless suggest possible avoidance interaction with the asteroid. Neptunea contains a highly toxic salivary gland secretion, which may be used to capture prey as well as for defensive purposes to deter sea-star predation (Fänge 1960). Drilling snails (Natica, Polinices) were also present wherever bivalves were common (Feder et al. 1991a, b). The ubiquitous presence of predatory gastropods in areas where they compete with other epifauna and marine mammals for bivalves again indicates the presence of highly productive prey populations.

Factors related to distribution of fauna

Factors that influence distribution of taxa within benthic systems are numerous, interactive and complex, and the importance of any factor will vary within an area. In the North Sea, Dyer et al. (1983) consider that water masses, circulation patterns, carbon sources, and substrate types are interacting factors that affect epifaunal distribution patterns. In the southeastern Chukchi it appears that much of the spatial distribution of benthic fauna is determined by water mass and circulation patterns linked to the POC present. Grebmeier and McRoy (1989) demonstrated enhanced benthic production and higher infaunal biomass under BSAW in the northeastern Bering and southeastern Chukchi Seas. They found that benthos under BSAW received a higher quality of food on a regular interannual basis as a result of high water-column primary production, and low microheterotrophic and relatively low zooplankton grazing rates in the water column (Cooney and Coyle 1982; Andersen and Fenchel 1986). Inshore, under ACW, they noted that benthos received food of lower quality comprising a variable mixture of terrigenous and marine organic matter, which resulted in reduced benthic populations. Their sampling area did not extend very far to the east of the hydrographic front separating BSAW and ACW. Consequently, substantial benthic populations within the Chukchi Bight and Kotzebue Sound under ACW were not expected. The diversity of feeding habits of organisms in the Bight and Sound indicated the availability of broadly dispersed food resources in the water column, benthic boundary layer and on the bottom.

Dissimilarity between benthic systems of the northeastern and southeastern Chukchi Sea (extending into Kotzebue Sound) is indicated by differences of infaunal distribution within the two areas (Feder et al. 1991a, b; 1994a, b). The differences are attributable to the more complex flow patterns in the southern system and subsequent distribution of POC. In particular, and of greatest importance, is the entrainment of high-quality carbon by mixed BSAW and ACW within the anticyclonic eddies east of Cape Prince of Wales Shoal. Movement of some of this mixed water northward to the coast between Kivalina and Point Hope sustains, in part, taxa in group III with its numerous suspension-feeding and predator-scavenger taxa. Some of this water, as it flows across the Chukchi Bight, must also sustain the numerous taxa within groups IX and X. Annual water-column production is probably increased within a seasonal polynya along the coast between Kivalina and Point Hope to further support fauna within group III (Stringer and Groves 1991). The abundant sea urchin, Strongylocentrotus droebachiensis, within group III and station A54 north of Bering Strait, occurs in regions with strong currents. Although urchins feed mainly on algal debris, they can utilize animal material (Briscoe and Sebens 1998). Presumably plant and animal debris are carried along the bottom through the Bering Strait, and become available to urchins there. A high biomass of suspension-feeding sponges adjacent to the Bering Strait (A54) reflects the availability of concentrated, high-quality allochthonous POC channeled by strong currents through the Strait.

Another branch of mixed water flows along the Seward Peninsula into the Sound, presumably contributing high-quality allochthonous POC to the benthos along the coast within groups I and V and the gyre behind Cape Espenberg in the Sound. This POC would then be distributed throughout the Sound supporting sizeable infaunal (Feder et al. 1991a) and epifaunal populations (group VI and stations B23 and B27 of group VII). Carbon flux to the bottom within the Sound is supplemented by carbon derived from ice algae, sea grass and terrigenous carbon. Bottom water flows out of the Sound most of the year entraining POC along the deepest channel northwestward (Feder et al. 1991a). The current moves along the coast between Cape Krusenstern and Point Hope, where it merges with the POC-enriched BSAW water along that coast to sustain the abundant benthic fauna there. Fauna within group IX (in the Chukchi Bight) probably also receives additional POC from water flowing out of the Sound.

A factor that may influence fauna is local hypoxia on the bottom. In July 1987, in the central Sound, dead juvenile (20–25 mm carapace width) Chionoecetes were observed floating among ice floes (Feder et al. 1991a). Additionally, villagers observed dead juvenile Chionoecetes along beaches in the northern Sound after June ice breakup. Samples in the area at 14 m in 1986 and 1987 were qualitatively different from adjacent stations (Feder et al. 1991a, b). The sediment had a sulfide odor with blotches of black mud; infauna was depauperate compared to surrounding stations; and trawls contained decaying organisms and many empty bivalve shells. Kvitek et al. (1998) suggest a possible explanation. They found that ice floes gouged the bottom, leaving depressions in the sediment on the shallow sea floor of Resolute Bay, Northwest Territories. Brine formed during winter ice formation accumulated in the depressions, and remained isolated from the overlying water by ice cover, which prevented mixing of the water column. Benthic respiration in depressions resulted in anoxic conditions. Subsequent mortality of infauna and bacterial decomposition resulted in hydrogen sulfide production that killed motile forms moving into depressions. It is probable that ice gouging within the Sound contributes to hypoxia and faunal mortality. Ice gouges up to one meter deep at depths of 5–30 m are ubiquitous in the adjacent northeastern Bering Sea (Thor and Nelson 1981). Kvitek et al. (1998) indicate that depressions serve as brine drainage catchment basins in subsequent years, and suggest seasonal occurrence of hypoxic brine pools could be widespread in shallow, protected polar areas. In Resolute Bay after summer sea-ice breakup, mixing conditions flush depressions, and fauna reoccupies the depressions. This may, in part, explain the presence of some infaunal and epifaunal organisms in the stressed area within the Sound. Additionally, some species may be tolerant to oxygen stress, and recruit, survive and grow within or adjacent to hypoxic areas, as noted elsewhere (Sagasti et al. 2000).

Trophic interactions related to food availability

The feeding methods used by epibenthos reflect the relationship of water-current patterns to the delivery of POC and other food resources to these organisms. The numerous predator/scavenger and suspension-feeding taxa highlight the availability of abundant food resources for benthic organisms under mixed ACW in the Chukchi Bight and Sound, as opposed to the low food availability on the bottom under ACW outside the Chukchi Bight (Grebmeier et al. 1988, 1989). An abundant infauna, sustained by high-quality carbon derived from BSAW advected into the area, local primary production and ice algae, represent important food resources for epifaunal predator/scavengers (Feder and Jewett 1978, 1981; Jewett and Feder 1981; Feder et al. 1991a, b). Marine mammals and transient populations of demersal fishes consume many of these epifaunal organisms (Feder and Jewett, 1981; Feder et al. 1991a, b). The broad distribution and continued presence of numerous mobile epifaunal predators and marine mammals further highlight the presence of a widely distributed and productive food resource (Feder and Jewett 1981; Jewett and Feder 1981).

The crab Chionoecetes consumed barnacles along the coast between Kivalina and Point Hope where barnacles were dominant, but utilized a broad spectrum of organisms wherever it occurred (Feder and Jewett 1981). Deposit-feeding clams were important in the diet with Nucula being a dominant food (Feder and Jewett 1978). The helmet crab Telmessus preyed on small polychaetes, mollusks, crustaceans, and brittle stars common in inshore waters (SCJ unpub). Presence of numerous hermit crabs suggests widespread availability of small prey and food fragments resulting from predatory activities of other epifauna and marine mammals.

The common to abundant neptunid and buccinid snails in the study area and adjacent northeastern Chukchi Sea (Feder et al. 1991a, 1994b), utilize polychaetes and bivalves, a widely distributed prey, in their diet (Pearce and Thorson 1967; MacIntosh and Somerton 1981). Distribution of the predatory gastropods Natica and Polinices in the southeastern and northeastern Chukchi Sea overlapped the densest populations of bivalves on which they preyed (Feder et al. 1991a, 1994b).

Sea stars in the study area and adjacent Bering Sea consumed a wide variety of infaunal and epifaunal prey, with the organisms utilized determined by the relative abundance of prey species present (Feder and Jewett 1978, 1981, Fukuyama and Oliver 1985). The common and often abundant Ophiura sarsi in the northeastern and southeastern Chukchi Sea fed intensively on small mollusks in the former area, with 92% utilizing bivalves and 50% feeding on gastropods (Feder et al. 1991b, 1994b); presumably it fed on similar prey in the study area. Polychaetes are important prey for Ophiura in areas where mollusks are uncommon (Feder and Pearson 1988), and polychaetes were abundant in the study area (Feder et al. 1991a). Ophiura is also a potential predator on meiofauna, recently settled larvae and small macrofauna, and will influence composition of the benthos wherever it is common (Thorson 1966). They also function as scavengers, a probable role for them in the study area. In regions of high ophiuroid abundance in the southeastern Chukchi Sea they undoubtedly play an important role in carbon remineralization, as suggested for ophiuroids in the Eurasian Arctic and northeastern Chukchi Sea (Piepenburg 2000; Ambrose et al. 2001).

Since sea stars in the northeastern Bering and Chukchi Seas have a broad-spectrum diet, are long-lived, abundant and represent a sizeable proportion of epifaunal biomass, their biological importance cannot be overlooked. They may function as keystone predators in northern benthic systems where large crabs and bottom-feeding fishes are uncommon. Sea stars also represent important food competitors with marine mammals. They can exist for long periods without food (Feder and Christensen 1966), and survive years of food depletion, whereas marine mammals are negatively affected by such events. Further, sea stars are not carbon sinks as often suggested, but instead, some species (Asterias, Evasterias, Crossaster) contribute pulses of high-energy organic material as gametes during spawning periods. This material can serve as a supplementary carbon source in the Arctic where primary production is limited to a narrow window of time (Feder and Jewett 1981). Reproductive material released during spawning by other common, long-lived benthic organisms in the area (cnidarians, bivalves, ophiuroids, sea urchins and tunicates), together with output of sea stars, could represent an important carbon resource in northern benthic systems (Feder and Jewett 1981). Foraging behavior of sea stars often involves excavation for prey, and, in conjunction with similar ophiuroid, crustacean and marine-mammal feeding activities, must be important in carbon mineralization, thereby contributing to continued abundance and diversity of other benthic fauna.

Food requirements of sea stars and other epifaunal predators are similar to those of demersal fishes. However, as discussed above, large populations of demersal fishes are generally absent in the northern Bering and Chukchi Seas. Thus, increased benthic food resources are available for asteroids and other epifaunal predators, which explains, in part, the presence of numerous shrimps, crabs, ophiuroids and sea stars. Shrimps, crabs and ophiuroids feed on small infaunal organisms rarely used by the larger sea stars, which enables the species to coexist.

Large numbers of sea anemones occurred in some regions, particularly at the entrance to the Sound and within the central Chukchi Bight. Anemones were also common under the productive waters of the northwestern region of the study area and adjacent to Kivalina (groups III, VII, IX). The abundance of anemones at the entrance to the Sound, along the coast and central Bight suggests the presence of numerous prey at the sediment–water interface as well as fragments of partially eaten prey in bottom water flushed out of the Sound.

Although predator/scavenger taxa were dominant, the presence of organisms with other feeding strategies resulted in the exploitation of all food resources. The presence, often abundant, of suspension-feeding organisms (Eunephthya, Bryozoa, barnacles, Gorgonocephalus, tunicates) along the Seward and Lisburne Peninsulas, within the Bight and Sound, reflects the presence of a consistent source of food advected in by water currents. A high level of POC in the water column and benthic boundary layer within and exiting the Sound is indicated by the abundant interface-feeding polychaete Galathowenia within the Sound (particularly under the gyre behind Cape Espenberg) and along the coast to Point Hope (Feder et al. 1991a; Taghon and Greene 1992; S.C.J., unpublished data). Galathowenia is favored by organic enrichment, particularly in the presence of strong bottom currents and turbulence (Pearson and Rosenberg 1978; Thomsen et al. 1995), but can switch between surface deposit and passive suspension feeding, depending on the current velocity. Some common bivalves present (cockles, tellinid clams) utilize POC in the water column and carbon in the bottom material resuspended by current-induced turbulence or bioturbation (Feder et al. 1991a; Davis 1992; Hall 1994; Thomsen et al. 1995). Tellinids also feed on the surface-deposit to utilize carbon sources on the sediment surface (Rasmussen 1973).

In 1976 the saffron cod (Eleginus gracilis) and starry flounder (Platichthys stellatus) were the most abundant demersal fishes in the southeastern Chukchi Sea (Wolotira et al. 1977). These and other demersal fishes, when present, prey on epifauna and compete for food with epifaunal predators (Jewett and Feder 1981). Resident saffron cod mainly feed on epifauna but also utilize infaunal polychaetes (Jewett and Feder 1980; Lowry et al. 1981). Flatfishes and sculpins forage on surface-dwelling epifauna.

Eleven species of marine mammals occur in the area, with three species most predictably present and abundant—spotted seals (Phoca larga), ringed seals (Phoca hispida) and belukha whales (Delphinapterus leucas). Bearded seals (Erignathus barbatus) are common when ice is present. These taxa, and the occasional presence of Pacific walrus (Odobenus rosmarus), feed on benthic organisms (Lowry et al. 1981; Sheffield et al. 2001). Spotted seals mainly feed on fishes with occasional consumption of crangonid shrimps. Ringed seals and belukha whales consume small crustaceans, crangonid shrimps and fishes. Bearded seals mainly consume bivalves, crangonid and pandalid shrimps and brachyuran crabs, but also feed on gastropods (Feder and Jewett 1981; Lowry et al. 1981; Hjelset et al. 1999). All of these marine mammals are traditionally harvested in coastal communities in the study area (Frost and Lowry 1988). Persistent presence of marine mammals, under mixed ACW, in a region that also sustains numerous invertebrate predators and demersal fishes, where all utilize similar prey, emphasizes the productivity of the area.

Stable carbon isotope ratios of epifaunal organisms in the study area give support to the sources of carbon (Feder et al. 1991a). Isotope values of suspension (tunicates) and particle-feeding (the basket star) organisms along the coast between Cape Krusenstern and Point Hope are similar to those of Dunton et al. (1989) within an inshore area in the northeastern Chukchi Sea. The water current along the coast of the Lisburne Peninsula, and its entrained POC, moves around Point Hope and swings northward to the coastal area sampled by Dunton et al. (1989) in the northeastern Chukchi Sea (Fleming and Heggarty 1966). Isotopic values of fauna in the study area, and those of Dunton et al. (1989) for the adjacent region, indicate that benthic organisms are closely coupled to primary production. The tunicate Molgula along the Seward Peninsula coast and suspension feeders within the Sound also reflect the presence of a phytoplankton source with carbon isotope values similar to those of fauna along the coast between Cape Krusenstern and Point Hope (Feder et al. 1991a, b).

Between-year comparisons of epifauna

All benthic surveys in the area concluded that no populations of commercially exploitable resources exist there. This includes surveys of 1959 (Sparks and Pererya 1966), 1976 (this study; Wolotira et al. 1977; Feder and Jewett 1978), 1986–1987 (Feder et al. 1991a, b), 1998 (Fair and Nelson 1999) and 1999 (Nelson et al. 2000). Although smaller gear was deployed in 1986–1987, organisms that dominated trawl catches in most areas were the ones that dominated the same areas earlier in 1976 (Feder et al. 1991a). For example, fauna at stations adjacent to the coast between Kivalina and Point Hope were similar for both data sets, reflecting the strong water currents over a coarse substrate. Tunicates, the shrimp Sclerocrangon boreas and the sea urchin Strongylocentrotus droebachiensis, dominated the regions in 1976 and 1986–1987. The most abundant epibenthic taxa in 1976 and 1986–1987 within Kotzebue Sound were Asterias amurensis, Chionoecetes opilio, Ophiura sarsi and Argis lar. The area of group IX, extending out of the Sound into the Chukchi Bight, had similar dominants (C. opilio, A. amurensis, O. sarsi, Actiniidae and Pagurus spp.) in both periods. A single station adjacent to the Bering Strait within the area of 1976 (A54) had S. droebachiensis and Hyas coarctatus as the dominant species in common for both data sets.

In the 1998 trawl survey by Fair and Nelson (1999), as in 1976, sea stars and hermit crabs occurred at all stations. Other invertebrates with high station occurrence in both years included Argis lar, urochordates, C. opilio and H. coarctatus. Of the dominant taxa in 1976 five were more abundant in 1998, all were more than twice as abundant as in 1976. Although the 1998 survey yielded greater abundance and biomass of C. opilio than in 1976, the composition and size was virtually unchanged (Fair and Nelson 1999). Highest urchin catches in 1976 and 1998 were off Cape Prince of Wales and Cape Thompson between Point Hope and Kivalina. Highest abundance of Neptunea was in deeper water, as in 1976 station group IV. Shrimp (several species) were taken at every trawl station in 1998, but P. goniurus was only at 60% of stations. In 1976, pandalid shrimp were less abundant and present at only 25% of the stations. Highest shrimp catches in 1998 were between Cape Krusenstern and Point Hope, where high numbers were also found in 1976. Additionally, relatively large numbers of shrimp were present off Cape Espenberg and at one station off Cape Prince of Wales. Telmessus in 1976 and 1998 were limited to shallow, inshore waters. In 1998 highest numbers occurred along the coast between Shishmaref and southwestern Kotzebue Sound, which agrees with the distribution and general abundance noted in 1976. Additionally, in 1976 high numbers of Telmessus occurred between Cape Krusenstern and Kivalina. No red king crabs (Paralithodes camptschaticus) were taken in 1998, but in a winter pot survey in 1999, low numbers were collected near Cape Krusenstern and off Kivalina (Nelson et al. 2000). Low numbers of this crab were found at four stations in 1976. The blue king crab (P. platypus) occurred at two stations while P. brevipes was taken at one station in 1976. Most benthic seal prey (the shrimps A. lar, S. boreas, C. dalli, and P. goniurus and crabs C. opilio, H. coarctatus, and T. cheiragonus) were more widely distributed, more abundant, or had greater biomass in 1998 than in 1976.

Overall, the 1976 and 1998 comparison revealed several of the most dominant taxa (C. opilio, Asteroidea, Ophiura sarsi, S. droebachiensis, and A. lar) to be more abundant and having higher biomass in the more recent period, although community composition did not change between the two periods. In a similar comparison of trawl data from 1976 to 2002 in Norton Sound of the northeastern Bering Sea, total abundance and biomass increased threefold, although species composition remained the same throughout the period (Fair and Nelson 1999). The latter study was unable to attribute abundance and biomass increases to climatic changes through regime shifts.

Test fishing for king crab and marine snails in 1999, using commercial pots, resulted in low numbers of crab (Nelson et al. 2000). Most crabs were caught off Cape Krusenstern in winter and Kivalina in summer. Few crabs were taken off Cape Espenberg and none within the Sound. The crabs taken in 1976 were off Cape Krusenstern and Cape Espenberg, at the mouth of the Sound and off the Seward Peninsula. King crab abundance was considered insufficient to sustain commercial harvest. Neptunea was abundant in some areas but a commercial market for it seemed unlikely.

Conclusions

Grebmeier et al. (1988) demonstrated high benthic biomass under highly productive Bering Shelf-Anadyr Water (BSAW) on the outer shelf of the northern Bering and southeastern Chukchi Seas, while the food-limited benthic system inshore under ACW resulted in fauna with low biomass. They concluded that benthic biomass was related to differences in quality and quantity of organic carbon reaching the benthos. Thus, a sizeable benthic fauna was not expected under ACW within the Chukchi Bight and Kotzebue Sound. It is known that food reaching the sea floor via vertical flux can strongly affect the benthos of adjacent areas by the lateral advection of POC (Graf 1992; Grebmeier and Barry 1991; Mayer and Piepenburg et al.1996; Thomsen and van Weering 1998). Since vertical flux of carbon in areas where low phytoplankton production does not supply adequate food to the benthos (under ACW in the Bight and Sound), resuspension of bottom material from productive areas (BSAW) together with horizontal advective forces can increase availability of carbon to the benthos (Johnson 1988). Near-bottom currents can suspend, spread and transport previously settled particles laterally over great distances (Gili et al. 2001; Tatián et al. 2002). The abundant fauna within the Bight and Sound is attributed to the complex current patterns where organic carbon of high quality, derived from BSAW, is advected into the area. That substantial amounts of usable carbon are in the bottom water flowing out of the Sound into the Bight is reflected by the abundant fauna along the coast of the Lisburne Peninsula. Carbon isotope signatures of epifauna suggest the presence of phytoplankton-rich carbon advected from BSAW into the Bight and Sound. Similar patterns of water movement occur under ACW in Norton Sound in the northeastern Bering Sea (Feder and Jewett 1981; Jewett et al. 1999). Infauna in the study area represented the trophic pathway for most epifauna, and abundant epifaunal scavenger-predators reflected availability of a plentiful food resource. Occurrence of numerous Asterias amurensis, known to decimate bivalve populations (Hatanaka and Kosaka 1959; Ross et al. 2002), other sea-star species and the common presence of drilling naticid gastropods indicated a highly productive bivalve fauna. Presence of a rich benthic fauna also made it possible for the area to support resident and transient populations of demersal fishes and marine mammals. Few differences in epifaunal distributions were apparent between 1976 and 1998, and dominant taxa of the earlier year were still important in 1998. Some dominant taxa were more abundant and had higher biomass in the recent sampling, possibly unrelated to warming in the Alaskan Arctic as suggested by Fair and Nelson (1999) for the adjacent Norton Sound. Our study demonstrates there can be high benthic faunal stocks in Arctic regions with low annual primary production if local carbon is supplemented by POC advected from highly productive areas.

Acknowledgements

The study was funded by Minerals Management Service, Department of the Interior, through an interagency agreement with the National Oceanic and Atmospheric Administration. Samples were collected on the NOAA Ship Miller Freeman. We thank the following for shipboard sampling and taxonomic assistance: Max Hoberg, Institute of Marine Science, University of Alaska Fairbanks and Rae Baxter (deceased), Alaska Department of Fish and Game. We thank Dr. T. Pearson, Dr. D. Piepenburg, and Dr. J. Weslawski for their helpful comments, and Dr. T. Weingartner for the review of the oceanographic section of the paper.

Supplementary material

Appendix S1

300_2004_683_ESM1.pdf (12 kb)
(PDF 11 KB)

Appendix S2

300_2004_683_ESM2.pdf (19 kb)
(PDF 19 KB)

Copyright information

© Springer-Verlag 2004