55344130
Community structure of epibenthic megafauna in the Chukchi Sea
Climate change and increased focus on resource development in Arctic Seas have fueled interest in the Chukchi Sea, yet few quantitative studies have been conducted on the larger, epifaunal component of seafloor communities, which serves important roles in sediment biogeo- chemical processes and provides a food source for fishes and marine mammals. Here we provide quantitative data on the present condition of benthic epifaunal abundance and biomass from the Chukchi shelf and examine the influence of environmental variables on epifaunal communities. We collected 45 beam trawl samples in the Russian and United States sectors of the Chukchi Sea in 2004, 2007 and 2008. Gross abundance estimates ranged from 229 to 70 879 ind. 1000 m -2 , and gross bio- mass estimates ranged from 1628 to 217 023 g wet wt 1000 m -2 . Overall, abundance and biomass were dominated by echinoderms (66 and 45%, respectively) and crustaceans (17 and 31%, respec- tively). The ophiuroid Ophiura sarsi and the snow crab Chionoecetes opilio overwhelmingly domi- nated abundance and biomass. The holothurian Myriotrochus rinkii also occurred in large numbers, and the urchin Strongylocentrotus pallidus was another major contributor to biomass. A total of 165 taxa (mostly species) were identified; the highest numbers were Mollusca (45) and Crustacea (33). Cluster analysis identified 6 distinct groups plus 6 unique stations with 54 to 88% between-cluster dissimilarity, with separation based largely on substrate type and latitude. Water mass characteristics and indices of food availability appeared less influential in generating the observed composition, abundance and biomass patterns. Comparisons with previous studies suggested an increase in over- all epibenthic biomass since 1976, including an increase in the biomass of C. opilio.
126474385
Bering Strait the Regional Physical Oceanography
Find loads of the bering strait the regional physical oceanography book catalogues in this site as the choice of you visiting this page. You can also join to the website book library that will show you numerous books from any types. Literature, science, politics, and many more catalogues are presented to offer you the best book to find. The book that really makes you feels satisfied. Or that's the book that will save you from your job deadline.
129471327
Ecosystem dynamics of the Pacific-influenced Northern Bering and Chukchi Seas in the Amerasian Arctic
Abstract The shallow continental shelves and slope of the Amerasian Arctic are strongly influenced by nutrient-rich Pacific waters advected over the shelves from the northern Bering Sea into the Arctic Ocean. These high-latitude shelf systems are highly productive both as the ice melts and during the open-water period. The duration and extent of seasonal sea ice, seawater temperature and water mass structure are critical controls on water column production, organic carbon cycling and pelagic–benthic coupling. Short food chains and shallow depths are characteristic of high productivity areas in this region, so changes in lower trophic levels can impact higher trophic organisms rapidly, including pelagic- and benthic-feeding marine mammals and seabirds. Subsistence harvesting of many of these animals is locally important for human consumption. The vulnerability of the ecosystem to environmental change is thought to be high, particularly as sea ice extent declines and seawater warms. In this review, we focus on ecosystem dynamics in the northern Bering and Chukchi Seas, with a more limited discussion of the adjoining Pacific-influenced eastern section of the East Siberian Sea and the western section of the Beaufort Sea. Both primary and secondary production are enhanced in specific regions that we discuss here, with the northern Bering and Chukchi Seas sustaining some of the highest water column production and benthic faunal soft-bottom biomass in the world ocean. In addition, these organic carbon-rich Pacific waters are periodically advected into low productivity regions of the nearshore northern Bering, Chukchi and Beaufort Seas off Alaska and sometimes into the East Siberian Sea, all of which have lower productivity on an annual basis. Thus, these near shore areas are intimately tied to nutrients and advected particulate organic carbon from the Pacific influenced Bering Shelf-Anadyr water. Given the short food chains and dependence of many apex predators on sea ice, recent reductions in sea ice in the Pacific-influenced sector of the Arctic have the potential to cause an ecosystem reorganization that may alter this benthic-oriented system to one more dominated by pelagic processes.
128891413
Tracking the Arctic's shrinking ice cover: Another extreme September minimum in 2004
[1] Satellite passive microwave observations document an overall downward trend in Arctic sea ice extent and area since 1978. While the record minimum observed in September 2002 strongly reinforced this downward trend, extreme ice minima were again observed in 2003 and 2004. Although having three extreme minimum years in a row is unprecedented in the satellite record, attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind, temperature and oceanic forcings.
84465795
Role of echinoderms in benthic remineralization in the Chukchi Sea
Abstract. The role of large, epibenthic organisms in carbon cycling at high latitudes is difficult to assess using standard ship-board collection techniques. We used a remotely operated vehicle equipped with video imaging to examine the distribution and abundance of epibenthic organisms in the northeast Chukchi Sea during June 1998. At each of 11 sites, we collected between 25 and 50 images from a minimum of 20 min of video. We observed 15 different epibenthic taxa, with the echinoderms (Ophiura sarsia, O. maculata, Ophiopholis aculeata, Stegophiura nodosa, and Echinarachinus parma) overwhelmingly dominating the epibenthos. Echinoderm density was highly variable, ranging from 0.2 to 256.6 individuals m–2 (median=16.3), and echinoderm biomass varied between <0.5 and 4,988 mg C m–2 (median=737). The highest biomass of ophiuroids recorded (3,388 mg C m–2) is 30% higher than the highest previously reported from an Arctic shelf. Using a relationship between biomass and respiration developed for deep-sea organisms living at cold temperatures, we estimated respiration rates from <0.1 to 15.0 mg C m–2 day–1 (median=1.9). Respiration rates measured on board were several orders of magnitude higher than those obtained from the predictive equation. Further work is needed to assess echinoderm respiration rates accurately under in situ conditions. Even with calculated minimal values for respiration rates, a comparison of epifaunal and infaunal respiration at four stations revealed that echinoderm respiration accounted for as much as 25% of total respiration. High epifaunal respiration rates and biomass values are likely supported by high concentrations of particulate organic carbon carried by Bering Sea water flowing through the eastern Chukchi Sea. Our observations support observations from the Eurasian Arctic that echinoderms dominate the epibenthos of Arctic shelves and that the role of these organisms in carbon remineralization must be considered if we are to generate accurate models of carbon cycling in the Arctic.
59404365
Partitioning of benthic community respiration in the Arctic (northwestern Barents Sea)
For marine benthos communities, the assessment of a respiration budget encompassing the entire size range from microbes to mobile megafauna has seldom been attempted. An interdisciplinary field study in high Arctic waters (northwestern Barents Sea) in June/July 1991 provided the opportunity to concurrently est~rnate the oxygen uptake of the different benthic community fractions by a variety of approaches at water depths of 80 to 1010 m. The bulk respiration of micro-, meioand small macrobenthos was assessed by sediment community oxygen consumption (SCOC) rates measured by shipboard sediment-water incubations of virtually undisturbed cores. The oxygen uptake of community portions not sampled adequately by corers (megabenthic inand epifauna, including fish) was estimated by applying individual metabolic rates to density or biomass figures derived from seabed images, box corer samples or trawl catches. The respiration estimates of the various community fractions were subsequently compiled in synoptic models of the total benthic community oxygen consumption (BCOC) and its partitioning. In the study area, 2 benthic habitat types were distinguished, differing substantially in depth, sediment texture and, thus, benthic respiration pattern: (1) shallow shelf banks (<200 m) where the seabed is composed of coarse sediments and stones, and (2) deeper trenches or slopes (>200 m) characterized by fine sediments. On the banks, the patchiness of epibenthic brittle stars, which locally occurred in very high densities (up to 700 ind. m-'), controlled the benthic community respiration. On average, the megafauna was estimated to contribute about 25% to the median BCOC of about 90 pm01 0, m-' h-' (equivalent to an organic carbon mineralizat~on rate of 21 mg C m-? d-'). In the shelf trenches and on the slope, however, smaller endobenthic organisms predominated. SCOC, according to our estimates of meioand macrofaunal respiration, was dominated by the oxygen uptake of microorganisms and accounted for about 85% of the median BCOC of about 140 ~lmol 0, m-' h-' (35 mg C n r 2 d-l). Our results suggest that current models of benthic community respiration should be amended, particularly for Arctic shelf b~otopes where abundant megafauna may represent an important pathway of the benth~c energy flow.
129678223
Mollusks in the Northeastern Chukchi Sea
Infaunal and epifaunal mollusks of the northeastern Chukchi Sea were sampled and 139 molluscan taxa were identified. The pattern of spatial distribution of molluscan species was determined by cluster analysis, which resulted in six infaunal and five epifaunal station groups. Species characterizing various faunal groups are defined. Stepwise multiple discriminant analysis was applied to correlate benthic biological associations with environmental variables. Delineation of infaunal groups was mainly due to percentage of sand and bottom salinity, while epifaunal groups were separated by percent gravel and bottom temperature. An increase in abundance and biomass of infaunal mollusks occurred adjacent to and north and northwest of an identified bottom front between the Bering Shelf and Resident Chukchi Water and Alaska Coastal Water. Epifaunal molluscan abundance and biomass were highest near the coast. Mollusks, especially smaller species and the juvenile stages of larger species, represent a food resource for bottom-feeding predators in the study area. Key words: Chukchi Sea, mollusk, benthic, infauna, epifauna, bottom front, bottom-feeding predators, cluster analysis, discriminant analysis
129373065
The paradox of pelagic food webs in the northern Bering Sea—III. Patterns of primary production
Abstract The advective supply of nutrients to the Bering-Chukchi continental shelf via a north-flowing “river” of oceanic water originating along the continental slope in the Bering Sea maintains a large portion of these shelf waters in eutrophic bloom summer-long. Known as the Anadyr Stream, this nutrient injection sustains conditions of high phytoplankton productivity and biomass in a region of the western Arctic that would otherwise be unproductive, as are adjacent shelf areas unaffected by the current. A production plume dominated by large chain-forming diatoms extends from the Gulf of Anadyr in the south to the southern Chukchi Sea in the north, has daily carbon uptake rates as high as 16 g C m −2 day −1 , and has an estimated annual production of about 470 g C m −2 year −1 . Maximum production occurs in three pools of especially prolific growth (Gulf of Anadyr, Chirikov Basin and southern Chukchi Sea) where rates could be as great as 720–840 g C m −2 year −1 . Outside of the plume, nutrients remain low following the spring bloom and a typical successional flora is dominated by flagellates and small diatoms throughout summer. Post-bloom productivity in this region is generally about 0.5 g C m −2 day −1 , and annual production is approximately 80 g C m −2 year −1 . The contrasting primary production regimes lead to major differences in food webs and in the energy transferred to higher trophic levels within the western Arctic.
54174530
Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic bio-mass
The shelf waters of the northern Bering and Chukchi Seas are ice-covered for 7 mo of the year, but despite thls harsh environment, they are characterized by high benthic biomass. Coupling between water column primary production and the benthos was investigated in summers 1984 to 1986 by measurements of sediment characteristics in relation to those of the water column. Low surface sediment C/N ratios (5.8 to 7.6) suggested a higher quality, nitrogen-rich marine carbon supply to the benthos in the highly productive (ca 250 to 300 g C m-' yr-') Bering Shelf-Anadyr Water (BSAW) compared to lower quality, higher C/N ratios (7 7 to 14 0) in sediment under the less productive (ca 50 g C m-' yr-l) Alaska Coastal Water (ACW). Stable carbon isotope ratios suggested a manne origin for organic matter in BSAW compared to a mixture of manne and terrestrial input in ACW. Mean benthic biomass was significantly different between water locations, with mean benthic biomass decreasing from 20.2 g C m-* under BSAW to 6.3 g C m-2 under ACW Summer benthic biomass remained seasonally constant for the 3 yr. Benthic communities underlying BSAW received a high quality marine food supply on a regular basis interannually, while those in ACW received an interannually variable amount of temgenous organic matter in addition to marine organic matter. We conclude that the quality and quantity of organic carbon deposited to the benthos directly influence benthic biomass.
4354919
High productivity of northern Bering Sea benthic amphipods
POLAR regions, particularly Arctic seas covered by ice for a significant portion of the year, have been considered to be relatively unproductive14. In the western Arctic, including the northern Bering Sea, high water column productivity5,6, and well developed benthic communities79 have recently been reported. Ampeliscid amphipod crustaceans are the benthic community dominants in vast areas of the northern Bering Sea and are the major prey of the migratory California grey whale, Eschrichtius robustus 10,11. Our study indicates that productivity of the benthic amphipods is remarkably high, given the latitude. The dominant species, Ampelisca macrocephala, is the most productive benthic marine amphipod ever reported and the amphipod community is more productive then entire benthic communities investigated elsewhere. biomassPolar marine ecosystems clearly have the potential to be highly productive
67758614
Productivity of arctic amphipods relative to gray whale energy requirements
Amphipod crustaceans domlnate the ben th~c community in vast areas of the northern Benng Sea, they are the major prey of the California gray whale Eschncht~us robustus The protected whale population is growing steadily and may be approaching the carrying capacity of the arnphipod community, one of the most productive benthic communities in the world The abundance and biomass of the amphipod community decreased dunng the 3 yr penod 1986 to 1988, resulting in a 30 % decline in production High-latitude amphipod populations are characterized by low fecundity and long generation t ~ m e s Large long-lived individuals are responsible for the malonty of amphipod secondary production A substantial reduction in the density of large individuals in the population wlll result in a significant, long-term decrease in production
25532188
Unusual abundance of macrobenthos and biological invasions in the Chukchi Sea
The data from the expedition of the program RUSALCA conducted in 2004 showed unexpectedly high quantitative indices of macrobenthos in the southeastern Chukchi Sea. Extensive areas of the bottom northwest of the Bering Strait were dominated by the bivalve Macoma calcarea. The greatest biomass of benthos in Macoma-dominated areas was 4232 g/m2 with an average of 1382 g/m2 for the investigated region. Such a high biomass of soft-bottom communities, which is extremely uncommon even in the temperature regions of the oceans, is reported for the Arctic for the first time. The long-term existence (more than 70 years) of highly productive benthic communities dominated by Macoma calcarea in one and the same area of the Chukchi Sea can most likely be attributed to gyres, which constantly arise in the region northwest of the Bering Strait. These cyclonic gyres carry nutrient-rich bottom water to the surface and hinder larval transport away from mother populations. They also keep and concentrate major food sources of benthos (live and dead phyto-and zooplankton and fecal pellets) over the benthic community locations. Most likely, a significant proportion of the primary production in the southeastern Chukchi Sea is used by benthos within the investigated Macoma community. Findings of three relatively large warm-water Pacific species near Point Hope in the Chukchi Sea are probably indicative of the progressive climate warming during the last century.
129714921
Studies of pelagic-benthic coupling extended onto the Soviet continental shelf in the northern Bering and Chukchi seas
Abstract Studies of pelagic-benthic coupling and benthic carbon cycling in the northern Bering and Chukchi seas were extended onto the Soviet continental shelf as part of the third U.S.A.-U.S.S.R. Oceanographic Expedition to the Bering and Chukchi seas in 1988. High sediment oxygen uptake rates (an indicator of food supply to the benthos) and benthic biomass were observed in the western shelf regions of the Gulf of Anadyr, Chirikov Basin and southern Chukchi Sea. Low sediment respiration and faunal biomass were observed in the central and slope areas of the Gulf of Anadyr and near the Alaska coastline. Both high sediment respiration and benthic biomass were related to regions of high carbon deposition to the benthos and sediment organic carbon content. Preliminary studies of sediment accumulation, measured using organic carbon content and atmospherically-derived 210 Pb values in surface sediments, were low in the sandy regions of the northern Bering Sea, with higher sediment accumulation zones occurring in the silt and clay regions in the central Gulf of Anadyr and southern Chukchi Sea. Hydrodynamics have a major influence on organic carbon loading and sediment composition, which in turn influences benthic community structure, biomass and sediment respiration in this Arctic region.
129112024
The Bering Sea Green Belt: shelf-edge processes and ecosystem production
The concept of a highly productive habitat, or Green Belt, along the edge of the continental shelf in the Bering Sea is based upon compelling but fragmentary and often anecdotal observations of a variety of physical and biological features acquired from many sources over many years. Enhanced production at continental margins is not a novel concept, but in the case of the Bering Sea its importance has been overlooked during studies of the unusually broad continental shelf. The limited data reported from the vicinity of the shelf edge in the Bering Sea indicate that annual primary production can be as high as 175 to 275 g C m˜ year-, or approximately 60% greater than production in the adjacent outer shelf domain and 270% greater than in the oceanic domain. Estimates of annual secondary production at the eastern shelf edge also average approximately 60% higher than estimates for the outer domain and 260% higher than those for the oceanic domain. Physical processes at the shelf edge, such as intensive tidal mixing and transverse circulation and eddies in the Bering Slope Current, bring nutrients into the euphoric zone and contribute to enhanced primary and secondary production and elevated biomass of phytoplankton and zooplankton. Fishes and squids concentrate in this narrow corridor because of favourable feeding conditions and because of a thermal refuge from cold shelf-bottom temperatures that can be found at the shelf edge from fall to spring. The abundance of zooplankton, fishes and squids, in turn, attracts large numbers of marine birds and mammals. In aggregate, the observations suggest that sustained primary productivity, intense food web exchange and high transfer efficiency at the shelf edge are important to biomass yield at numerous trophic levels and to ecosystem production of the Bering Sea.
36434130
Southeastern Chukchi Sea (Alaska) macrobenthos
Macrobenthos in the southeastern Chukchi Sea, inclusive of the Chukchi Bight and Kotzebue Sound, were collected in 1985–1987 to determine factors influencing faunal distribution, abundance and biomass. Polychaetes, crustaceans, bivalve mollusks, and ophiuroid echinoderms dominated abundance. Polychaetes, bivalve mollusks, and ophiuroid echinoderms dominated carbon biomass with barnacles, amphipods, bryozoans, and tunicates occasionally dominant. Cluster analysis and ordination revealed relatively high faunal abundance and biomass under Bering Shelf Anadyr Water (BSAW) as well as under Alaska Coastal Water (ACW) in the Bight and Sound. Advected particulate carbon from the highly productive BSAW supported the abundant macrobenthos that served as food for numerous epifauna, which in turn furnished food for resident and transient populations of demersal fishes and marine mammals.
25789978
Southeastern Chukchi Sea (Alaska) epibenthos
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.
51749196
WALRUS, ODOBENUS ROSMARUS, FEEDING IN THE BERING SEA: A BENTHIC PERSPECTIVE
Walrus, Odobenusrosmarus, feed primarily on benthic bivalves and create a distinct record of their feeding activities on the sea floor. The record consists offurrows, pits, and discarded bivalve shells which were ob­ served and sampled with scuba Documentation of this benthic feeding record suggested that walrus com­ monly search for visually conspicuous prey by sight; that, in addition to "rooting" with the snout and vibrissae, walrus excavate bivalve prey by hydraulic jetting; that tusks are notused to excavate prey; and that all prey are excavated before consumption, which generally occurs close to the site of excavation. The mechanism of consumption appears to involve suction from between the shells. Continuous pit·furrow sys­ tems indicate the number of prey consumed in single dives, and suggest that a walrus can locate, excavate, and consume more then six clams per minute. The abundance of small infauna that are not walrus prey (e.g., polychaete worms, small bivalves, and crustaceans) was lower inside all excavations, indicating that the structure of bottom communities is highly modified by the extraction of a few large prey.
25863203
Diet and body condition of spectacled eiders wintering in pack ice of the Bering Sea
Spectacled eiders (Somateria fischeri) winter among leads in the Bering Sea pack ice, where they dive 40–70 m for benthic prey. During the first icebreaker cruises into that area, esophagi of collected eiders contained only clams, mostly Nuculana radiata, with no trace of the once-dominant Macoma calcarea. Alternative prey used elsewhere (snails, amphipods, other bivalves) were available but not eaten. Eiders ate mainly N. radiata 18–24 mm long, although M. calcarea of this length contained 62% more energy. Percent body lipid of eiders averaged 12±3% (SD) for 26 adult males and 14±3% for 12 adult females. Mean body mass (±SE) of these males in late March (1,688±21 g) was higher than reported for 53 males after arriving at breeding areas in late May (1,494±14 g). Body mass of these females (1,550±35 g) was lower (but not significantly) than reported for 11 females upon arrival at breeding sites (1,623±46 g). In 1999, the last spectacled eiders left the wintering area on 21 April, 4–8 weeks before their typical arrival at breeding sites. Their location is unknown in the interim, when habitats used appear critical to acquiring reserves for reproduction.
83689740
Distribution, abundance, biomass, and mineralization potential of the epibenthic megafauna of the Northeast Greenland shelf
The epibenthic megafauna of the high-Arctic Northeast Greenland shelf was investigated by means of seafloor photography and Agassiz trawl catches. At 54 stations in water depths between 40 and 770 m, sequences of color slides, each depicting about 1 m2 of the seafloor, were obtained along photographic transects of about 100 to 600 m length. The photographs were quantitatively analyzed for abundance of epibenthic organisms identified by comparison with specimens collected from trawl catches. Megabenthic biomass was estimated by multiplying density values with averge body mass figures. For five dominant brittle star species, the population oxygen uptake and, thus, organic carbon mineralization potential were approximated by applying individual respiration rates of average-sized specimens to density figures. Multivariate analyses of the megabenthic species distribution revealed a distinct depth zonation. Shallow shelf banks (<150 m), characterized by coarse sediments, many stones and boulders as well as negative bottom water temperatures, housed a rich epifauna (30 to 340 ind m−2, 1.8 to 10.5 g AFDW m−2), strongly dominated (80 to 98% by numbers) by the brittle stars Ophiocten sericeum and Ophiura robusta. The oxygen uptake by brittle stars ranged from 0.4 to 95 μmol O2 m−2 h−1 (i.e., assuming a respiratory quotient of 0.8, an organic carbon mineralization of 0.1 to 21.9 mg C m−2 d−1). At the bank flanks sloping to the shelf troughs (100 to 580 m), finer sediments prevailed, stones were rare, and bottom water temperatures were positive due to the inflow of Atlantic water. Compared to bank sites, total epibenthic abundances as well as carbon mineralization by brittle stars were roughly ten times and total biomass about four times smaller. In deep shelf depressions as well as at the continental slope (200 to 770 m), stones were completely lacking, and sediments very fine. Epibenthic standing stock and carbon mineralization were one to two orders of magnitude lower than on the banks. The estimation of brittle star oxygen uptake indicates that a considerable portion of the organic carbon produced in the polynya and partitioned to the benthos may be remineralized by epibenthic bank assemblages.
84936577
Mega-epibenthic communities in Arctic and Antarctic shelf areas
Abstract Mega-epibenthic shelf assemblages were investigated off Northeast Greenland and in the Weddell, Bellingshausen and Amundsen Seas in the Antarctic using underwater video. In the Arctic a total of 94 taxa represented by more than 100 000 individuals were identified. Echinoderms, particularly brittle stars, were the most important elements of the mega-epibenthic fauna on the shelf off Northeast Greenland. Multivariate analyses of the species distribution revealed a conspicuous depth zonation in which an assemblage on the shallow banks can be clearly distinguished from that in the troughs. Between these a transitional zone with a heterogeneous benthic fauna was found. Physical disturbances are supposed to be responsible for the pronounced dominance patterns observed on the shallow banks. The fauna in the troughs, which consists of more than 50% suspension feeders, is diverse but low in numbers of individuals. In the Antarctic more than 115 000 individuals belonging to 169 taxa were analyzed. Obvious faunal differences exist between the stations in the Weddell Sea and the Bellingshausen/Amundsen Seas. Assemblages of suspension feeders dominated by sponges and bryozoans are prevalent on the shelf of the eastern Weddell Sea, but almost absent in the Bellingshausen and Amundsen Seas. These assemblages seem to be restricted to areas where bottom currents provide favourable feeding conditions. However, motile deposit feeders are more abundant in both regions where there is a soft bottom substrate with presumably slow bottom currents and reduced horizontal transport of organic particles.
83151097
Arctic brittle stars (Echinodermata: Ophiuroidea)
Knowledge of Arctic brittle stars (Echinodermata: Ophiuroidea) has greatly increased over the past 15 yr. Here, I synoptically review novel findings collected by seabed imaging and trawl catches from continental shelves and slopes (14 m to 1100 m) of the Greenland, Barents and Laptev Seas with regard to zoogeography, diversity, standing stock, distribution patterns, community control and carbon demand. In accordance with previous reports, few endemic-Arctic species were found in the study areas. The recurrent finding that most brittle stars are widespread boreal-Arctic species corroborates the paradigm of a comparatively young age and low degree of zoogeographic isolation of Arctic seas. The total number of ophiuroid species known to occur in all Arctic seas is low (15 to 22), especially if compared with Antarctica where more than 100 species have been reported. A comparative case study showed, however, that in the eastern Weddell Sea (Antarctica) both regional and local diversity figures were indeed significantly higher than off northeast Greenland (Arctic), whereas the values assessed for ophiuroid assemblages inhabiting the southern Weddell Sea shelf and shelf trenches were not. These findings indicate that the paradigm of a pronounced Arctic-Antarctic diversity difference is an over-generalisation, at least with regard to the brittle star fauna and to regional or local scales. Numerous faunal inventories in Arctic seas have shown that epibenthic communities are dominated by brittle stars, especially on the shelves. At several locations, dense brittle star beds forming high standing stocks of up to several hundred ind. m -2 and up to several g organic C m - 2 were recorded. These stock figures are among the highest hitherto observed in northern seas, being in the same order of magnitude as those reported for ophiuroid mass occurrences in sublittoral and bathyal habitats of non-polar regions. Within dense brittle star beds, individuals showed a pronounced non-random dispersion on a 1-100 m scale, most likely caused by seabed heterogeneity. A depth zonation in the composition of the brittle star fauna, accompanied by a significant decline of standing stock over two (biomass) to three (abundance) orders of magnitude, was the most conspicuous large-scale spatial pattern. All shelf assemblages ( 10 mg C m -2 d -1 Considering production and assimilation efficiencies of 30% and 80%, respectively, their carbon demand was assessed as up to 20 mg C m - 2 d -1 .
44393952
Macrozoobenthic community structure in a high-arctic East Greenland fjord
Abstract A macrozoobenthic community study was conducted in an East Greenlandic fjord (Young Sound, 74°18′N; 20°15′W) during the ice-free period from July to August in 1996. Grab samples as well as underwater photography were used for quantifying the macrozoobenthos at water depths between 20 and 85 m. Abundance decreased with depth from 2700 ind. · m−2 at 20 m to 900 ind. · m−2 at 85 m. At a time series station at 35 m, abundance increased from 700 ind. · m−2 in mid-July to 1400 ind. · m−2 in mid-August. Polychaetes dominated in grab samples but bivalves constituted an important part of the benthic fauna, especially at the shallow part of the depth gradient. Photographs revealed high abundances of large epifaunal species, especially brittle stars. Diversity was generally high, with around 45 species per 201 individuals, as calculated by Hurlbert's rarefaction term. A gradual change in community structure with depth was observed, which could be related to variation in sediment composition and disturbance intensity.
84967256
Gray whale distribution relative to forage habitat in the northern Bering Sea: current conditions and retrospective summary
Hundreds of gray whales (Eschrichtius robustus) stranded dead along beaches from Mexico to Alaska in 1999 and 2000. The cause of the mortalities remains unknown, but starvation resulting from a reduction in prey, especially in the Chirikov Basin, was suggested as the cause. In the 1980s, the Chirikov Basin was considered a prime gray whale feeding area, but there has been no recent comprehensive assessment of whale or prey distribution and abundance. In 2002, a 5-day survey for gray whales revealed restricted distribution in the basin and a 3- to 17-fold decline in sighting rates. To put these data in context, a retrospective summary of gray whale and benthic fauna distribution and abundance was undertaken. During the 1980s, gray whale sighting rates in the Chirikov Basin were highly variable. Ampeliscid amphipods dominated the benthos where gray whale sighting rates were highest. Available measures of biomass suggest a downturn in amphipod productivity from 1983 to 2000, when estimates of gray whale popu...
128419605
Multi-decadal synthesis of benthic–pelagic coupling in the western arctic: Role of cross-shelf advective processes
Abstract Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll,
140151792
Analyses of Bering Sea bottom-trawl surveys in Norton Sound: absence of regime shift effect on epifauna and demersal fish
Hamazaki, T., Fair, L., Watson, L., and Brennan, E. 2005. Analyses of Bering Sea bottomtrawl surveys in Norton Sound: absence of regime shift effect on epifauna and demersal fish.e ICES Journal of Marine Science, 62: 1597e1602. This study retrospectively examined evidence of ocean climate regime shift effects on epifauna and demersal fish of Norton Sound, Alaska, northeast Bering Sea, based on triennial bottom-trawl surveys from 1976 to 2002. Throughout the period, benthic fauna was dominated by sea stars (48e78%), followed by cods (5e19%), flatfish (5e15%), sculpins (1.5e7%), and crabs (2e6%). From 1976 to 2002, the cpue index of total species increased exponentially (4.5% y 1 ) by threefold with some declines in 1991 and 1999. The increase was also observed in sea stars (5.1% y 1 ), flatfish (6.1% y 1 ), and crabs (2.5% y 1 ). However, trends of cods and sculpins were mixed. Regression analysis showed the cpue index of total species to be positively correlated with survey years and bottom-water temperature. However, bottom-water temperature, when considered by itself, was not significant. Results suggest that regime shifts caused biomass increases of Norton Sound epifauna and demersal fish.
129927006
Retrospective analysis of Bering Sea bottom trawl surveys: regime shift and ecosystem reorganization
Abstract This paper compiles data from bottom trawl surveys using variations on a 400-mesh eastern trawl gear into a 38-year time series (1963–2000), using a robust index of median catch per unit effort (CPUE) as an indicator of regional abundance. Time series are presented for three index sites in the southeastern Bering Sea: the inner shelf in Bristol Bay, the middle shelf north of Unimak Island, and the outer shelf near the Pribilof Islands. All three sites show strong evidence of a shift in benthic biomass and community structure in the early to mid-1980s. During this period, all three sites showed substantial increases in the abundances of walleye pollock, Pacific cod, rock sole, flathead sole, cartilaginous fishes (skates) and non-crab benthic invertebrates. Species composition, especially of flatfish, differs at the three sites, but the trend for groundfish abundance to increase was consistent at all three sites. The similarity in trends both across the region and across both commercial and unexploited groups suggests to us that a complete reorganization of benthic and demersal food webs may have taken place. The timing of change in trawl catch weight is consistent with effects of the strong regime shift observed in climate indices in 1976–1977. There is little evidence of similar biological responses to subsequent, less pronounced changes in climate. Our data are also consistent with recently documented shifts in ecosystem dynamics resulting from changes in ice cover and thermal structure in the eastern Bering Sea. Our analysis indicates that there was a much higher biomass of groundfish at all three sites during 1980–2000 than in 1960–1980. This result provides evidence against the hypothesis that the overall productivity of the eastern Bering Sea has decreased. The precipitous decline of the endangered Steller sea lion in this region from 1975–1985 was concurrent with an overall increase in abundance of groundfish prey.
15010603
Application of a sequential regime shift detection method to the Bering Sea ecosystem
A common problem of existing methods for regime shift detection is their poor performance at the ends of time-series. Consequently, shifts in environmental and biological indices are usually detected long after their actual appearance. A recently introduced method based on sequential t-test analysis of regime shifts (STARS) treats all incoming data in real time, signals the possibility of a regime shift as soon as possible, then monitors how perception of the magnitude of the shift changes over time. Results of a STARS application to the eastern Bering Sea ecosystem show how the 1989 and 1998 regime shifts manifest themselves in biotic and abiotic indices in comparison with the 1977 shift. 2005 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea.
53696101
Pathways of Pacific water across the Chukchi Sea: A numerical model study
[1] Pathways of Pacific Water flowing from the North Pacific Ocean through Bering Strait and across the Chukchi Sea are investigated using a two-dimensional barotropic model. In the no-wind case, the flow is driven only by a prescribed steady northward flow of 0.8 Sv through Bering Strait. The resulting steady state circulation consists of a broad northeasterly flow, basically following the topography, with a few areas of intensified currents. About half of the inflow travels northwest through Hope Valley, while the other half turns somewhat toward the northeast along the Alaskan coast. The flow through Hope Valley is intensified as it passes through Herald Canyon, but much of this flow escapes the canyon to move eastward, joining the flow in the broad valley between Herald and Hanna Shoals, another area of slightly intensified currents. There is a confluence of nearly all of the flow along the Alaskan coast west of Pt. Barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the Beaufort shelf. Thus in this no-wind case, nearly all of the Pacific Water entering the Chukchi Sea eventually ends up flowing eastward along the narrow Beaufort shelf, with no discernable flow across the shelf edge toward the interior Canada Basin. Travel times for water parcels to move from Bering Strait to Pt. Barrow vary tremendously according to the path taken; e.g., less than 6 months along the Alaskan coast, but about 30 months along the westernmost path through Herald Canyon. This flow field is relatively insensitive to idealized wind-forcing when the winds are from the south, west or north, in which cases the shelf transports tend to be intensified. However, strong northeasterly to easterly winds are able to completely reverse the flows along the Beaufort shelf and the Alaskan coast, and force most of the throughflow in a more northerly direction across the Chukchi Sea shelf edge, potentially supplying the surface waters of the interior Canada Basin with Pacific Water. The entire shelf circulation reacts promptly to changing wind conditions, with a response time of ∼2–3 days. The intense coastal jet between Icy Cape and Pt. Barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast. In contrast, there is a relatively quiet nearshore region to the west, between Cape Lisburne and Icy Cape, where dense water may accumulate much longer and continue to become denser before it is carried across the shelf.
129045024
The Siberian Coastal Current: A wind‐ and buoyancy‐forced Arctic coastal current
We describe circulation and mixing in the Siberian Coastal Current (SCC) using fall shipboard measurements collected between 1992 and 1995 in the western Chukchi Sea. The SCC, forced by winds, Siberian river outflows, and ice melt, flows eastward from the East Siberian Sea. It is bounded offshore by a broad (∼60 km) front separating cold, dilute Siberian Coastal Water from warmer, saltier Bering Sea Water. The alongshore flow is incoherent, because the current contains energetic eddies and squirts probably generated by frontal (baroclinic) instabilities. These enhance horizontal mixing and weaken the cross-shore density gradient along the SCC path. Eventually, the SCC converges with the northward flow from Bering Strait, whereupon it deflects offshore and mixes with that inflow. Deflection occurs where the alongshore pressure gradient vanishes. That location varies on synoptic and seasonal timescales, because this gradient depends on the winds, buoyancy fluxes, and the sea level difference between the Pacific and Arctic Oceans. Deflection usually occurs on the Chukchi shelf, but the SCC occasionally flows southward through Bering Strait. Such events are short lived (1–10 days) and occur mainly in fall and winter under northerly winds. SCC transport is likely small (∼0.1 Sv), but its dilute waters could substantially freshen the Bering Strait inflow and affect the disposition of Pacific waters in the Arctic Ocean. Arctic river outflows should preferentially form surface-advected fronts rather than bottom-advected fronts because vertical-mixing energy is low on arctic shelves. Surface-advected fronts are more susceptible to upwelling winds (and for the SCC, the pressure gradient between the Pacific and Arctic Oceans) than bottom-advected fronts. The SCC never developed in fall 1995 because of anomalously steady upwelling winds. The western Chukchi shelf could have formed upper halocline source water in the winter of 1995–1996.
54494710
Epibenthic community patterns on the continental slope off East Greenland at 75* N
Megabenthic assemblages on the East Greenland continental slope at 75" N were surveyed at 8 locations between 190 and 2800 m depth using sea floor images taken vertically with a still camera. A total of 91 epibenthic species with 14447 indiv~duals were identified from 422 photographs depicting 297 n12 of the sea floor. Classification and ordination analysis defined 3 fauna1 zones that corresponded to different depth regions of the continental margin: shelf break, upper slope and lower slope. Megafaunal abundance was highest on the shelf (about 200 ind. m-2). In the other zones, the densities were distinctly lower (15 to 30 ind. m-2). Assemblages were frequently dominated by 1 or 2 species, such a s the polychaete Onuphis conchylega at the shelf break and the sponge Polymastia sp. at the lower slope The upper slope was characterized by a diverse octocoral-sponge assemblage. A statistical analysis of the correlation between megafaunal and environmental data at a 10 km scale (between stations) indicated that epibenthic distribution patterns were best explained by sea floor characteristics, whereas no evidence for a direct benthic-pelaglc coupling was found, irrespective of water depth. Additionally, the withln-station distribution of megabenthic organisms (100 m scale) was clearly affected by sea floor properties.
128492851
Distribution patterns of Canadian Beaufort Shelf macrobenthos
Abstract Variation in macrofaunal composition in relation to sediment and water variables was analysed in nine regions of the western Canadian Arctic on the Beaufort Shelf and in Amundsen Gulf. We hypothesized that benthic community composition was distinctive (1) in a recurrent polynya in Amundsen Gulf and (2) in upwelling regions (Cape Bathurst and Mackenzie Canyon) and (3) changed in a linear gradient across the Beaufort Shelf. Analysis was based on 497 taxa > 0.4 mm from 134 samples at 52 stations sampled over 2002–4 in 11–1000 m water depth. Abundance ranged from 490.7 m− 2 in eastern Amundsen Gulf to 17,950 m− 2 off Cape Bathurst. (1) Community composition in Amundsen Gulf was not significantly different from the Beaufort Shelf at similar depth, indicating a lack of benthic effect of the polynya in Amundsen Gulf. (2) The Mackenzie Canyon macrofauna, although abundant and diverse, were similarly indistinct from the shelf community at similar depth. However, there was a 10-fold increase in inshore abundance in the upwelling region of Cape Bathurst due to large numbers of the amphipod Ampelisca macrocephala and the polychaete Barantolla americana, species that were not abundant elsewhere. (3) In the inshore fast ice and flaw lead regions of the Beaufort Shelf, under the influence of ice scour, storm effects, coastal erosion and the Mackenzie River, the macrofauna were dominated by the bivalve Portlandia arctica and the polychaete Micronephthys minuta. Offshore, where these influences were less and upwelling of deep Atlantic water occurred, the polychaete Maldane sarsi dominated. Faunal distribution across the Beaufort Shelf correlated with depth, water and sediment changes but was not significantly linear.
129380563
The Kara Sea ecosystem: phytoplankton, zooplankton and benthos communities influenced by river run-off
Phytoplankton, zooplankton and macrozoobenthos in the estuaries of Ob and Yenisei and the adjacent southern Kara Sea were investigated during three expeditions with RV "Akademik Boris Petrov" in August/September 1997, 1999 and 2000. Plankton and macrobenthic community structures were distinguished by cluster analysis and multidimensional scaling. Differences in species number, abundance and biomass as well as the zonation pattern of biological assemblages reflected the continental outflow from the rivers Ob and Yenisei along a salinity gradient from south to north. Additionally, strong regional variability in species composition between the two river systems Ob and Yenisei was obvious. The spatial biomass distribution of phytoplankton, zooplankton and macrozoobenthos along a transect from the inner Yenisei to the open Kara Sea was related to the influence of different water masses.
127861935
Distributional Patterns of Echinoderms in the Eurasian Sector of the Arctic Ocean
Our knowledge of echinoderms, including echinoids, asteroids, and ophiuroids from the Eurasian Arctic seas (Barents, Kara, Laptev, East Siberian, and Chukchi seas), were established with the studies of Diakonov (1926, 1933, 1950, 1952, 1954), Shorygin (1982), Gorbunov (1932, 1933a,b), Baranova (1964, 1977), Khodkina (1964), and Moskalyov (1980).
128960790
Spatial structure within a dense bed of the brittle starOphiura sarsi (Ophiuroidea: Echinodermata) in the bathyal zone off otsuchi, Northeastern Japan
Photographic observations of the brittle starOphiura sarsi were conducted at a depth of approximately 280 m in the Pacific Ocean off Ōtsuchi, northeastern Japan. Bottom photographs showed that this ophiuroid occurred in high densities, uniformly covering the sea floor and that other megafauna was rare. The mean density and biomass of ophiuroids in the dense bed were estimated to be 373 m−2 and 124 g m−2, respectively. Ophiuroids comprised 99% of all megabenthic organisms in terms of number of individuals, and megafaunal assemblage of the dense bed showed very low species diversity.O. sarsi exhibited a regular spatial pattern avoiding contact with conspecific neighbors. This regular spatial pattern was disrupted by certain other organisms, around which halo-like, bare areas were observed. The size and shape of these halo-like areas varied and were apparently related to the body size and/or motility of the organisms. In the present observation areaO. sarsi covered 96% of the sea bottom, and the remaining 4% was occupied by other organisms and their halo-like bare areas.
84865770
Energy content of macrobenthic invertebrates: general conversion factors from weight to energy
In ecological studies, especially in those dealing with energy circulation in nature, determinations of the energy content of organisms are inevitable. Energy determinations are, however, laborious and time-consuming. Average conversion factors based on different species form various areas and seasons may often be a shortcut for overcoming this problem. To establish general energy conversion factors for aquatic invertebrate groups, we used 376 values of J · mg−1 DW and 255 values of J · mg−1 AFDW, representing 308 and 229 species, respectively. The dry-weight-to-energy factors were highly variable both within and between taxonomic groups, e.g.: Porifera, 6.1 J · mg−1 DW; insect larvae, 22.4 J · mg−1 DW (median values). The energy-conversion factors related to AFDW showed a much smaller dispersion with a minimum median value of 19.7 J · mg−1 AFDW (Ascidiacea) and a maximum of 23.8 J · mg−1 AFDW (insect larvae). Within taxonomic groups, the 95% confidence intervals (AFDW) were only a few percent of the median values. The use of energy-conversion factors based on AFDW is preferable due to their lower dispersion. For aquatic macrobenthic invertebrates, a general conversion factor of 23 J · mg−1 AFDW can be used.
56212536
A photographic survey of the epibenthic megafauna of the Arctic Laptev Sea shelf: distribution, abundance, and estimates of biomass and organic carbon demand
The epibenthic megafauna of the high-Arctic Laptev Sea shelf was investigated in August/September 1993 and October 1995. At 13 stations in water depths of between 14 and 45 m, series of 5 to 29 photographs, each depicting about 1 m2 of the seabed, were taken to assess epifaunal dis t r~but~on patterns and abundances. Furthermore, population biomass of dominant br~ttle stars was estimated by combining abundance values with size-mass relationships and size frequencies established by measuring specimens on scaled photographs. A total of 13 epibenthic species were identified. Species numbers per station were low, ranging between 1 and 6. Total epibenthic abundances, averaging 173.7 ind. m-2, ranged considerably between 0.1 and 579.5 ind. m-2 Except for some stations on shallow shelf banks 30 m, it reached maximum density and biomass values of 566 ~ n d . m-2 and 1.5 g ash-free dry mass (AFDM) m ', respectively. At some sites, the brittle star Ophlura sarsi occurred in abundances of up to 35 ind. m-' and attained a biomass of 3.8 g AFDM m-2 Of local importance were the sea cucumber Myrjotrochus rinckii (up to 7 0 ind. m-') and the bivalve Arctinula greenlandica (up to 33 ind. m-2). All other species were recorded with distinctly lower densities (S1 ind. mT2). Gross estimates of population respiration and production of dominant brittle stars suggest that their organic carbon demand may amount to a pooled average of about 4 mg C m-' d-' in the Laptev Sea, locally even to a maximum of >l0 mg C m-2 d-' This finding indicates that a substantial portion of the energy flow in this high-Arctic shelf ecosystem may be channelled through dense brittle star assemblages.
129155239
Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic)
A radical change in the abundance of invertebrate megafauna on the Porcupine Abyssal Plain is reported over a period of 10 years (1989–1999). Actiniarians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increased significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977–1999) show that prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a localised event. Several dominant holothurian species show a distinct trend in decreasing body size over the study period. The changes in megafauna abundance may be related to environmental forcing (food supply) rather than to localised stochastic population variations. Inter-annual variability and long-term trends in organic matter supply to the seabed may be responsible for the observed changes in abundance, species dominance and size distributions.
28571656
Food web structure of the benthic community at the Porcupine Abyssal Plain (NE Atlantic): a stable isotope analysis
Abstract The deep-sea benthic community at the Porcupine Abyssal Plain (NE Atlantic) is a highly food limited system. The annual input of sedimenting phytodetritus, which reaches the sea floor around May/June, is the major input of energy. The relative trophic position of the most abundant components of the benthos (90 species or higher taxonomic groups), including meiofaunal, macrofaunal, and megafaunal organisms, was evaluated by stable isotope analysis. The majority of the macro- and megafaunal organisms investigated were deposit feeders (N=35), less numerous were suspension feeders (N=17) and predators/scavengers (N=29). Stable nitrogen values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of competition for food. Suspension feeders, mainly cnidarians, have a broad trophic spectrum through feeding on resuspended material as well as capturing pelagic prey; thus during the greater part of the year they can compensate for any shortage in sedimenting fresh POM. Benthic deposit feeders use a variety of feeding strategies to exploit their common food resource. The holothurians, the dominant megabenthic group at PAP, included some highly mobile species, which seem to be quite efficient in tracing and exploiting localised patches of nutritious phytodetritus. Other holothurian species, however, forage successfully on more refractory material, possibly assisted by enteric bacteria. Predators/scavengers fall into two groups, representing two major trophic pathways. Firstly, several of the invertebrate predators prey on deposit-feeding organisms and so are the end consumers of an exclusively benthic food web. Secondly, there are highly mobile benthopelagic predators/scavengers, which are a major link with the benthopelagic food web through their feeding on pelagic prey. Generally, within the benthic community at PAP competition for food is reduced by two alternative evolutionary adaptations: (1) specialization on slightly different food sources and (2) vertical expansion of the trophic spectrum. This leads to a rather complex food web, covering a total δ15N range of at least 10‰.
21173070
Distribution, standing stock, growth, mortality and production of Strongylocentrotus pallidus (Echinodermata: Echinoidea) in the northern Barents Sea
Abstract The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dynamics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80–360 m. Mean abundances along photographic transects of 150–300 m length ranged between <0.1 and 14.7 ind. m−2 yielding a grand average of 3.6 ind. m−2. The small-scale distribution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m−2, and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90 mm. Median values at single stations varied from 14 to 46 mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photographic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0 g ash-free dry mass m−2, averaging about 1.0 g ash free dry mass m−2. An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48 mm. Assuming these bands to represent annual growth marks, the ages of the specimens analysed ranged between 3 and 42 years. A von Bertalanffy function was fitted to size-at-age data to model individual growth pattern (D∞ = 102.3 mm, k = 0.011 year−1, t0 = 0.633 year). The annual mortality rate Z of the population in the northern Barents Sea was estimated from a size-converted catch curve to be 0.08 year−1. Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year−1 and 0.076 g AFDM m−2 year−1, respectively. In conclusion, S. pallidus is characterized by slow growth, low mortality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.
6443048
Antarctic reptant decapods: more than a myth?
The impoverished Antarctic decapod fauna is one of the most conspicuous biodiversity phenomena in polar science. Although physiological and ecological approaches have tried to explain the reason for the low decapod biodiversity pattern in the Southern Ocean, the complexity of this problem is still not completely understood. The scant records of crabs south of the Polar Front were always considered as exceptional, and have mostly been ignored by marine biologists world-wide, creating one of the most dogmatic paradigms in polar science. We herein review the record of both adults and larvae of reptants from the Southern Ocean. At present, several species of only lithodid crabs maintain considerable adult populations in circum-Antarctic waters, although they remain absent from the high-Antarctic shelves.
17690865
Haemolymph Mg(2+) regulation in decapod crustaceans: physiological correlates and ecological consequences in polar areas.
Reptant decapod crustaceans are almost absent from the Southern Ocean south of the Antarctic Convergence. We tested the hypothesis that this may be due to the reduced ability of this group to regulate Mg(2+) levels in the haemolymph ([Mg(2+)](HL)). Mg(2+) acts as an anaesthetic in marine invertebrates and its level is higher in Reptantia (crabs such as Cancer spp., Chionoecetes spp., Maja spp., 30-50 mmol l(-)(1)) than in Natantia (prawns such as Pandalus spp., Palaemon spp., Crangon spp., 5-12 mmol l(-)(1)). We varied [Mg(2+)](HL) in three species of reptant decapod crustaceans, Carcinus maenas, Hyas araneus and Eurypodius latreillei, and investigated heart rate, the rate of oxygen consumption and levels of spontaneous and forced activity at different temperatures. The rate of oxygen consumption and heart rate increased significantly with reduction in [Mg(2+)](HL) over the entire temperature range investigated in E. latreillei. In H. araneus, an increase in metabolic and heart rates compared with control values was found only at temperatures below 2 degrees C. Forced and spontaneous activity levels increased significantly in the group of [Mg(2+)](HL)-reduced animals below 0 degrees C, at which control animals were mostly inactive. At a reduced [Mg(2+)](HL) of 5-12 mmol l(-)(1), which is the [Mg(2+)](HL) of caridean shrimps in the Southern Ocean, Q(10) and activation energy were reduced for all these variables and extended the temperature range over which physiological functions were maintained. We suggest that the high [Mg(2+)](HL) in Reptantia causes relaxation of the animals and reduces their scope for activity, especially at temperatures below 0 degrees C. The hypothesis that the synergistic effects of high [Mg(2+)](HL) and low temperature probably prevented the Reptantia from recolonizing the permanently cold water of polar areas is discussed.
83678498
Energetically defining the thermal limits of the snow crab
The snow crab, Chionoecetes opilio , is a cold-water species found naturally at temperatures below 5°C. Its physiology and energetics were examined to understand the metabolic limitations that restrict the snow crab to these temperatures. The species is not confined to cold water because of a limited respiratory system. Routine oxygen demand can be met even at lethal temperatures of 18°C (56 mg O 2 kg −1 h −1 , with a Q 10 of 2.2). Blood lactate levels remain below 1.5 mmol l −1 and actually decline slightly with temperature. Energy budgets, which were constructed from an examination of oxygen uptake, activity and food consumption in morphometrically mature male animals between 0 and 18°C, indicate that the snow crab is energetically restricted to cold water. Rising metabolic costs overtake caloric intake around 7°C. This is probably due to digestive metabolism which is temperature-sensitive. Food consumption increases up to 6°C but then falls. Crabs stop feeding above 12°C. Although the growth equation is positive between 1 and 7°C, it becomes slightly negative below 1°C. This observation is unexpected since snow crabs are commonly found between 0 and 1°C. Slight temperature changes in the natural environment may, therefore, regulate growth and reproduction in this species.
25770320
Evidence for a permanent establishment of the snow crab (Chionoecetes opilio) in the Barents Sea
In the Atlantic the snow crab (Chionoecetes opilio) is naturally distributed on the northwestern side, i.e. eastern Canada and west Greenland. Until recently, there have been no observations of snow crab in eastern Atlantic. However, in 1990s single and occasional reports were made of crabs captured in the eastern part of the Barents Sea, presumably introduced through ballast water. Special attention during the annual bottom-trawl surveys in the Barents Sea during February 2004–2006 were given to include recordings of snow crab to evaluate if the introduced species has succeeded to establish a self-sustaining population in this region. Recordings of snow crabs were systematically noted and biological measurements carried out. The results confirm previous Russian observations of snow crabs in the northern region of Gåsebanken. In addition, a significant number of crabs were also found in the central region of the Barents Sea, mainly in deeper waters from 180 to 350 m depth. The sizes ranged from 14 to 136 mm carapace width. All females above 70 mm were berried with fertilised eggs. A major fraction (31% in 2005; 76% in 2006) of the crabs consisted of juveniles below 50 mm CW, providing evidence for successful recruitment. The small-sized crabs were exclusively found in Gåsebanken, identifying the main recruiting area at present for snow crab in the Barents Sea. The results obtained show that the snow crab is now adapted to the northeast Atlantic.
86295684
THE DIETARY PREFERENCES OF A SUITE OF CARRION-SCAVENGING GASTROPODS (NASSARIIDAE, BUCCINIDAE) IN PRINCESS ROYAL HARBOUR, ALBANY, WESTERN AUSTRALIA
On the seafloor of Shoal Bay, Princess Royal Harbour, Albany, Western Australia, lives a suite of four scavenging gastropod species: Nassarius pyrrhus, N. pauperatus (Nassariidae), Cominella eburnea and C. tasmanica (Buccinidae). Field and laboratory experiments were designed to test whether any of these scavengers showed a preference for (i) either fresh fish or bivalve tissues, (ii) fresh fish or 24-, 48- or 72-h-old fish. In baited-trap field experiments, no preferences were detected, and N. pyrrhus always arrived first, usually followed by either N. pauperatus or C. eburnea, and last by C. tasmanica. Numbers of scavengers on all baits peaked at about 70 min postdeployment and arrived from an estimated surrounding area of 0.5-2.5 m 2 . In laboratory experiments, bait preference results were similar, although fewer N. pyrrhus and N. pauperatus arrived at the 72-h-old fish, and C. eburnea was not attracted to such decaying bait.
54789122
Pelagic benthic coupling on the shelf of the northern Bering and Chukchi Seas-II. Benthic community structure
Benthic fauna abundance, biomass and diversity were investigated in the northern Bering and Chukchi Seas to determine factors influencing faunal distribution in this polar region. The hypothesis tested whether sebmen t grain size and water mass charactenstics, such as organic carbon supply to the benthos and temperature, are regulating factors in benthic community structure. Benthic communities under the cold, highly productive (-250 to 300 g C m-2 yr-') Bering Shelf-Anadyr Water (BSAW) are dominated by a high biomass of amphipods (F. Ampeliscidae and F. Isaeidae) and bivalves (F. Nuculidae and F. T e l l ~ n ~ d a e ) . A diverse, low biomass fauna exists in benthic communities under the warmer, less productive (-50 g C m-' yr-l) Alaska Coastal Water (ACW), includ~ng amphipods (F. Isaeidae and F. Ampeliscidae), bivalves (F Tellinidae and F. Thyasiridae), polychaetes (F. Maldanidae and Nephtyidae), and sand dollars (F. Echinarachniidae). Faunal diversities are lowest for stations under BSAW, characterized by high food supply and moderately homogeneous (well-sorted), sandy sediments. Highest diversities occur at stations in ACW, which is characterized by low food supply and a more heterogeneous (poorly-sorted) mixture of silt and clay, sand and gravel sediments. Faunal diversity also increased to the north in the Chukchi Sea, where food availability in the bottom water and surface sediments was greater and more heterogeneous, finer-grain sediments occur. The findings indicate that sediment heterogeneity, silt and clay fractions, and temperature are major regulating factors on benthic community structure, with each positively influencing faunal diversity. Lower diversity was correlated to an increase in fine sand fractions. Food supply, both in the bottom water and surface sediments, has a more variable Influence on benthic community structure, although i t has a direct posit~ve influence on benthic biomass.
53480025
VARIATION OF FEMALE SIZE AND STAGE AT MATURITY IN SNOW CRAB (CHIONOECETES OPILIO) (BRACHYURA: MAJIDAE) FROM THE EASTERN BERING SEA
Abstract We investigated geographic variation in size and stage (instar) at maturity of snow crab (Chionoecetes opilio) on the eastern Bering Sea shelf. Size-frequency distribution analysis showed that females can reach maturity at four different instars, presumably Instars VIII to XI. Geographic variation in instar structure generates clinal variation in size at maturity, from small size at high latitudes (colder) to large size at low latitudes (warmer). Different pieces of evidence support the hypothesis that geographic variation in mature female size is a phenotypic response to environmental conditions governed by a single reaction norm. Clinal variation conforms to the “inverse Bergmann's rule”. We argue that a single macroecological rule should not be expected to explain all latitudinal size gradients observed in marine invertebrates. Size at maturity fluctuated cyclically, and was negatively and significantly cross-correlated with strength in the recruitment of females to the mature population. Cycles in the latter were manifested as four commensurate and regularly spaced pulses over the last three decades. Mechanisms that may underlay this intriguing phenomenon, including density-dependent growth rate, require further scrutiny.
129013944
The influence of oceanographic processes on pelagic-benthic coupling in polar regions: A benthic perspective
Abstract Benthic community abundance and biomass in polar marine systems is directly influenced by food supply from the overlying water column. Variability in hydrographic regimes, ice coverage, light, water column temperature and pelagic food web structure limit the amount of organic carbon reaching the benthos. Data from the high Arctic and Antarctic indicate that a large percentage of surface-produced organic matter is consumed by both macro- and micro-zooplankton as well as recycled in the water column via the microbial loop. This results in food-limited regimes for the underlying benthos. The few exceptions are nearshore continental shelf systems, such as in the Bering and Chukchi Seas in the western Arctic and portions of the Canadian Archipelago and Barents Sea in the eastern Arctic, where high benthic abundance and biomass occurs due to a tight coupling between water column primary production and benthic secondary production. A major difference between the Antarctic and Arctic is that the nearshore deep Antarctic is characterized by relatively high benthic abundance and biomass despite low water column production, suggesting that stability, low disturbance levels and cold temperatures enable benthic organisms to grow larger than in the Arctic. Both physical and biological disturbance levels are high in the marginal seas of the Arctic may directly influence benthic productivity. The relationship between primary production and sedimentation of organic material to the benthos is nonlinear due to its dependence on the role of the pelagic food web. Therefore, in this review we will only discuss the pelagic system with respect to how it impacts the net food supply reachig the benthos. A major objective of this review paper is demonstrate the influence of oceanographic processes on pelagic-benthic coupling in polar regions from a “bottom-up” perspective, using benthic studies from various regions in both the Arctic and Antarctic. Similarities and differences in oceanographic processes, benthic abundance and biomass, and benthic carbon cycling within these polar marine systems are discussed and areas for further research identified.
85399151
Substrate preferences and redistribution of blue king crab Paralithodes platypus glaucothoe and first crab on natural substrates in the laboratory
Abstract Despite the importance of blue king crab (BKC) to the Bering Sea fishery, there has been no detailed study of juvenile habitat preferences. Such information is critical for understanding life history and for development of stock enhancement programs. The aims of this study were to determine the natural substrata that glaucothoe prefer to settle on, and whether they or subsequent crab 1 stage (C1) redistribute to different habitats over time. A laboratory experiment was performed in 24 round containers divided in four equal quadrants each filled with one of the following natural substrata: beach sand, gravel, shells and cobble. Containers were assigned to 8 groups of 3 replicates each and were kept at ~ 6–8 °C. Twenty five glaucothoe were released in each container on day 0, and one group of three replicates was removed for examination at each of the following intervals: 24 h, 7, 14, 21, 28, 35, 42 and 49 days. Numbers of swimming and settled specimens on each substrate and period were recorded. Glaucothoe began to settle immediately after being released since no swimming larvae were found during any sampling periods. Substrata complexity was important for the habitat selection and distribution of blue king crab glaucothoe and crab 1 stage. During the glaucothoe stage, beach sand was rejected and cobble, shell and gravel were chosen equally. After glaucothoe molted to crab 1 stage and became bigger, animals preferred cobble and shell instead of gravel and beach sand. Understanding habitat selection is useful not only for management of crab populations, but also for assessing the potential of various habitats for stock enhancement of blue king crabs.
83935407
Water flow over subtidal rock walls: relation to distributions and growth rates of sessile suspension feeders in the Gulf of Maine Water flow and growth rates
Abstract Moving water delivers food resources to sessile suspension feeding invertebrates and the interaction between water motion and substrate topography may dramatically influence the ecology of these animals. Growth rates of two species of sessile suspension feeders were compared between positions within individual 1.5-m high rock walls at an offshore site at 30-m depth in the Gulf of Maine, USA. The site is characterized by strong, highly variable water flow. Growth rates for the active suspension feeding mussel Mytilus edulis (Linnaeus), were greater at upper than at lower wall positions, while growth rates for the facultatively-active suspension feeding sponge Halichondria panicea (Pallas) showed the opposite pattern, with higher rates at lower than upper wall positions. Mussel and sponge growth rates were related both to patterns of bulk fluid flux across the walls and to naturally occurring distributions of sessile suspension feeders. Dissolution of alabaster and plaster solids indicated that upper wall positions experienced significantly higher bulk fluid flux than lower wall positions. Distribution data show non-random suspension feeder abundances across a series of small rock walls at two offshore sites. The abundance of passive suspension feeders was greatest near the top edges, while active and facultatively-active suspension feeders occur in greatest densities at lower wall positions. The results show that the interaction of small scale, abrupt, topographic features with variable local flow conditions can lead to physical gradients within rock walls. These gradients significantly affect the growth of suspension feeders, and may influence the structure sessile of invertebrate communities on subtidal rock walls.
55587696
The northeastern Chukchi Sea: benthos-environmental interactions
Benthic faunal abundance, diversity, and biomass were examined in the northeastern Chukchi Sea to determine factors influencing faunal distribution. Four taxon-abundance-based benthic station groups were identified by cluster analysis and ordination techniques. These groups are explained, using stepwise multiple discriminant analysis, by the gravel-sand-mud and water content of bottom sediments, and the organic carbon/nitrogen (OC/N) ratio. In contrast to previous benthic investigations in the northeastern Bering and southeastern Chukchi Seas, faunal diversity between inshore and offshore regions in our study area were not related to differences in sediment sorting. Instead, regional diversity differences in the northeastern Chukchi Sea were related to greater environmental stresses (e.g. ice gouging, wave-current action, marine-mammal feeding activities) inshore than offshore. The presence of a high benthic biomass north of Icy Cape in the vicinity of Point Franklin and seaward of a hydrographic front is presumably related to an enhanced local depositional flux of particulate organic carbon (POC) in the area. We postulate that POC-rich waters derived from the northern Bering and northwestern Chukchi Seas extend to our study area and the flux of the entrained POC provides a persistent source of carbon to sustain the high benthic biomass. Annual POC enrichment of the coastal region north of Icy Cape is reflected by the great abundance of amphipods and other invertebrates present there and the concentration in summer of walrus Odobenus rosmarus djvergens and gray whales Eschrichtius robustus that feed on these invertebrates. This study demonstrates that there can be high standing stocks of benthos in arctic regions with relatively low annual primary production if local carbon is augmented by POC advected from highly productive areas.
129816755
Interannual changes in the Bering Strait fluxes of volume, heat and freshwater between 1991 and 2004
Year-round moorings (1990 to 2004) illustrate interannual variability of Bering Strait volume, freshwater and heat fluxes, which affect Arctic systems including sea-ice. Fluxes are lowest in 2001 and increase to 2004. Whilst 2004 freshwater and volume fluxes match previous maxima (1998), the 2004 heat flux is the highest recorded, partly due to ~ 0.5oC warmer temperatures since 2002. The Alaskan Coastal Current, contributing about 1/3 rd of the heat and ¼ of the freshwater fluxes, also shows strong warming and freshening between 2002 and 2004. The increased Bering Strait heat input between 2001 and 2004 (> 2x10 20 J) could melt 640,000 km 2 of 1 m thick ice; the 3-year freshwater increase (~ 800 km 3 ) is about ¼ of annual Arctic river run-off. Weaker southward winds likely explain the increased volume flux (~ 0.7 to ~ 1 Sv), causing ~ 80% of the freshwater and ~ 50% of the heat flux increases. INDEX TERMS: 4207 General Oceanography: Arctic and Antarctic oceanography (9310, 9315); 4215 General Oceanography: Climate and interannual variability (1616, 1635, 3305, 3309, 4513); 4223 General Oceanography: Descriptive and regional oceanography; 4227 General Oceanography: Diurnal, seasonal, and annual cycles (0438).
18140765
Selecting Indicator Species to Monitor Ecological Integrity: A Review
We review critical issues that must be considered when selectingindicator species for a monitoring program that aims to maintainor restore ecological integrity. First, we examine the pros andcons of different management approaches on which a conservationprogram can be based and conclude that ecosystem management ismost appropriate. We then identify potential indicators ofecological integrity at various levels of the ecosystem, with aparticular emphasis on the species level. We conclude that,although the use of indicator species remains contentious, it canbe useful if (1) many species representing various taxa and lifehistories are included in the monitoring program, (2) theirselection is primarily based on a sound quantitative databasefrom the focal region, and (3) caution is applied wheninterpreting their population trends to distinguish actualsignals from variations that may be unrelated to thedeterioration of ecological integrity. Finally, we present anddiscuss different methods that have been used to select indicatorspecies.
53536174
Indicators for Monitoring Biodiversity: A Hierarchical Approach
Biodiversity is presently a minor consideration in environmental policy. It has been regarded as too broad and vague a concept to be applied to real-world regulatoy and managernentproblems. This problem can be corrected ifbio- diversity is recognized as an end in itsea and if measurable indicators can be selected to assess the status of biodiversity over time. Biodiversity, as presently understood, encom- passes multiple levels of biological organization. In thispa- per, I expand the three primay attributes of biodiversity recognized by Jerry Franklin - composition, structure, and function - into a nested hierarcby that incorporates ele- ments of each attribute at four levels of organization: re- gional landscape, community-ecosystem, population- species, andgenetic. Indicators of each attribute in terrestrial ecosystems, at the four levels of organization, are identified for environmental monitoring purposes. Projects to monitor biodiversity will benefit from a direct linkage to long-term ecological research and a commitment to test hypotheses relevant to biodiversity conservation. A general guideline is to proceed from the top down, beginning with a coarse-scale invent0 y of landscape pattern, vegetation, habitat structure, and species distributions, then overlaying data on stress lev- els to identiD biologically significant areas at high risk of impoverishment. Intensive research and monitoring can be directed to high-risk ecosystems and elements of biodiversity, while less intensive monitoring is directed to the total land- scape (or samples thereon. In any monitoringprogram, par- ticular attention should be paid to specifying the questions that monitoring is intended to answer and validating the relationships between indicators and the components of bio- diversity they represent