Recent changes in the timing of sea ice formation and retreat, along with increasing seawater temperatures, are driving shifts in marine species composition that may signal marine ecosystem ...reorganization in the Pacific Arctic sector. Interannual variability in seasonal sea ice retreat in the northern Bering Sea has been observed over the past decade; north of the Bering Strait, the Chukchi Sea ecosystem has had consistent earlier spring sea ice retreat and later fall sea ice formation. The latitudinal gradient in sea ice persistence, water column chlorophyll, and carbon export to the sediments has a direct impact on ecosystem structure in this Arctic/sub-Arctic complex. Large-scale decadal patterns in the benthic biological system are driven by sea ice extent, hydrographic forcing, and export production that influences benthic processes. Shifts in species composition and northward faunal range expansions indicate a changing system. The shifting patterns of life and change in key biological processes have the potential for a system-wide reorganization of the marine ecosystem.
In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean ...acidification, with potentially wide-ranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.
Climate-driven changes in seasonal sea ice are expected to affect the timing, magnitude, and fate of phytoplankton production. Production may be increased by longer ice-free periods, or decreased by ...reduced stratification of the water column without freshwater input from melting ice. Benthic deposit-feeders may experience changes in organic matter (OM) supply owing to altered phytoplankton production, increased zooplankton grazing, or redistribution of settling phytodetritus. Where most benthic taxa subsist on a longer-term pool of sediment OM and bacteria, communities may be partially buffered against varied inputs of phytodetritus. We used network models of benthic food webs in 3 sectors of the northern Bering Sea to simulate effects of changes in OM supply. In the models, sediment OM content, which integrates longer-term inputs of microalgae, was gradually reduced or increased over 10 yr to the lowest or highest levels observed among sampling stations. In both samples and model predictions, decreased sediment OM was linked to quite variable declines among trophic groups, with effective loss of some taxa. Increased sediment OM was coupled with moderate to dramatic increases of different taxa, sometimes with lagged peaks and declines of prey and predators. In the models, meiofauna, protists, and bacteria responded quickly, while macrofauna exhibited 2 yr delays, suggesting short-term but limited buffering by the sediment OM pool. Our results indicate that climate-related changes in phytodetrital inputs can lead to important shifts in benthic biomass, community structure, and functional diversity, with loss of various common taxa.
Pelagic larval stages (meroplankton) of benthic invertebrates seasonally make up a significant proportion of planktonic communities, as well as determine the distribution of their benthic adult ...stages, yet are frequently overlooked by both plankton and benthic studies. Within the Arctic, the role of meroplanktonic larvae may be particularly important in regions of inflow from sub-Arctic regions, where they can serve as vectors of advection of temperate species into the Arctic. In this study, we describe the links between the distribution of larvae and adult benthic communities of bivalves, echinoderms, select decapods and cnidarians on the Pacific-influenced Chukchi Sea shelf during August-September in the time period 2004-2015 using traditional morphological and molecular tools to resolve taxonomic diversity. For most taxa, we observed little regional overlap between the distribution of larvae and adults of the same taxon; however, larvae of some organisms (e.g., the burrowing anemone Cerianthus sp., the sand dollar Echinarachnius parma) were only observed near populations of adult organisms. Larval stages of species not commonly observed in the Chukchi Sea benthos were also observed in the plankton; overall, shelf meroplanktonic communities were numerically dominated by larvae of coastal hard-bottom taxa, rather than local soft-bottom shelf species. Our results suggest that most larvae that we observe on the shelf are advected from other areas rather than produced locally, and most likely will not successfully settle to the benthos. Seasonality and distribution of water masses were the most important parameters shaping meroplankton communities. We discuss the implications of changing oceanographic and climatic conditions on the potential of range extensions by temperate species into the Arctic Ocean.
In efforts to maintain or restore populations of snow crabs Chionoecetes opilio, identifying important habitats requires knowing prey preferences and availability for different sexes and life stages. ...We analyzed the diets of juvenile, adolescent, and adult snow crabs of both sexes relative to available prey throughout a large area of the northern Bering Sea. Snow crabs of all sizes consumed a wide variety of prey including bivalves, gastropods, polychaetes, ophiuroids, and crustaceans. The proportions of different taxa in snow crab diets corresponded closely to the relative abundance of those taxa in different areas; thus, in this region, diets of respective sexes and ages can be predicted fairly accurately from the local abundance of different prey. The only apparent differences in diet between sexes were related to the larger and stronger claws of adult males. Larger crabs consumed larger prey that required greater handling ability and claw strength, such as harder-shelled bivalves and gastropods, larger polychaetes, and other snow crabs. Juvenile crabs consumed softer, more easily manipulated prey, such as amphipods and small bivalves with thin or incompletely calcified shells. Areas of high abundance of juvenile snow crabs, previously not recognized in designating essential habitat in this region, were characterized by high abundance of amphipods and small bivalves. Quality and importance of habitat for snow crabs appeared to depend jointly on several factors: hydrographic patterns that determine locations of larval settlement and subsequent ontogenetic migration, the combined abundance of all prey taxa, and ontogenetic capabilities for handling different sizes of prey.
A temperature and salinity hydrographic profile climatology is assembled, evaluated for data quality, and analyzed to assess changes of the Bering and Chukchi Sea continental shelves over seasonal to ...century-long time scales. The climatology informs description of the spatial distribution and temporal evolution of water masses over the two shelves, and quantification of changes in the magnitude and throughput of heat and fresh water. For the Chukchi Shelf, linear trend analysis of the integrated shelf heat content over its 1922–2018 period of record finds a significant summer and fall warming of 1.4 °C (0.14 ± 0.07 °C decade−1); over 1990–2018 the warming rate tripled to 0.43 ± 0.35 °C decade−1. In contrast, the Bering Shelf's predominantly decadal-scale variability precludes detection of a water column warming trend over its 1966–2018 period of record, but sea surface temperature data show a significant warming of 0.22 ± 0.10 °C decade−1 over the same time frame. Heat fluxes over 1979–2018 computed by the European Centre for Medium-Range Weather Forecast (ECMWF) ERA5 reanalysis exhibit no record-length trend in the shelf-wide Bering surface heat fluxes, but the Chukchi Shelf cooling season (October–March) has a trend toward greater surface heat losses and its warming season (April–September) has a trend toward greater heat gains. The 2014–2018 half-decade exhibited unprecedented low winter and spring sea-ice cover in the Northern Bering and Chukchi seas, changes that coincided with reduced springtime surface albedo, increased spring absorption of solar radiation, and anomalously elevated water column heat content in summer and fall. Consequently, the warm ocean required additional time to cool to the freezing point in fall. Fall and winter ocean-to-atmosphere heat fluxes were anomalously large and associated with enhanced southerly winds and elevated surface air temperatures, which in turn promoted still lower sea-ice production, extent, and concentration anomalies. Likely reductions in sea-ice melt were associated with positive salinity anomalies on the Southeast Bering Shelf and along the continental slope over 2014–2018. Negative salinity anomalies during 2014–2018 on the central and northern Bering Shelf may be related to a combination of 1) long-term declines in salinity, 2) an increase of ice melt, and 3) a decline of brine production. We hypothesize that freshening on the Bering Shelf and in Bering Strait since 2000 are linked to net glacial ablation in the Gulf of Alaska watershed. We show that the heat engines of both the Bering and Chukchi shelves accelerated over 2014–2018, with increased surface heat flux exchanges and increased oceanic heat advection. During this time, the Chukchi Shelf delivered an additional 5–9 x 1019 J yr−1 (50–90 EJ yr−1) into the Arctic basin and/or sea-ice melt, relative to the climatology. A similar amount of excess heat (60 EJ yr−1) was delivered to the atmosphere, showing that the Chukchi Sea makes an out-sized contribution to Arctic amplification. A conceptual model that summarizes the controlling feedback loop for these Pacific Arctic changes relates heat content, sea ice, freshwater distributions, surface heat fluxes, and advective fluxes.
Predicting effects of environmental variations on species distributions requires knowledge of the trophic niches of potential competitors. We used gut contents, stable isotopes (SIs), and fatty acid ...(FA) biomarkers to investigate the feeding niches of 2 macrobenthic carnivore groups in the Bering Sea: the sea stars Leptasterias groenlandica and L. polaris and the whelks Neptunea heros and N. communis. Sea star guts contained no identifiable items, probably because of external digestion; gut contents were similar between whelk species. SI analyses reflect longer-term diets but require trophic discrimination factors (TDFs) between source and consumer tissues. TDFs are not available for sea stars or whelks, so we present a method for estimating TDFs. Isotopic niche diagrams differed among areas, with either inclusion of the niche of seas stars within the broader niche of whelks—about 40% overlap with similar niche breadth—or complete partitioning with a much broader niche for whelks. Analyzing FAs requires calibration coefficients (CCs) for differential assimilation into consumer tissues, but these coefficients are largely unknown for invertebrates. Moreover, cannibalism or consumption of phylogenetically related prey may confound diet estimates if FAs in carnivores are inherently more similar to those of related prey. Perhaps because of these issues, mixing models for FAs indicated different diets than indicated by SI analyses. Measurements of CCs and TDFs for a broader range of taxa are needed for applying these methods to diverse benthic consumers. Our results indicate that sea stars and whelks have diverse and overlapping diets that change with prey availability.
Major Ecosystem Shift in the Northern Bering Sea Grebmeier, Jacqueline M; Overland, James E; Moore, Sue E ...
Science (American Association for the Advancement of Science),
03/2006, Letnik:
311, Številka:
5766
Journal Article
Recenzirano
Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic ...production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean.
On continental shelves in arctic and subarctic seas, much of the production from spring blooms at the retreating ice edge may sink to the bottom with little grazing by zooplankton, thereby supporting ...abundant benthic communities. The importance of this settled phytoplankton to macrobenthos throughout the year may partly determine effects of long-term changes in ice cover. We studied organic matter (OM) pathways to macrobenthos and macrozooplankton under ice cover in late winter (March–April) and open water in late summer (September) in the north-central Bering Sea. In late winter 2001, only a very small fraction of OM in the water column was particulate. C:N ratios, δ13C, and δ15N in suspended particulate organic matter (SPOM), and sediments indicated very little recent input of fresh ice algae or phytoplankton in ice-covered areas. For the 3 main deposit-feeding bivalves, δ13C and δ15N indicated similar diets among species, with minimal change in food quality between late summer and late winter, and between late winters with very different ice cover (1999 vs. 2001). In winter 2001, there were large increases in δ13C from SPOM to bulk sediments (+3.2‰) and from sediments to near-surface deposit-feeders (+1.6 to +3.0‰), but small differences in δ15N from SPOM to sediments (+1.2‰) and from sediments to deposit-feeders (–0.3 to +1.6‰). These values suggest that the diet of near-surface deposit-feeders during these non-bloom periods included substantial amounts of the cells or products of bacteria that had assimilated well-reworked carbon and isotopically light dissolved inorganic nitrogen (DIN). By late summer and through winter, 4 to 11 mo after the spring bloom, products of bacterial activity appeared to be an important route of OM into the benthic food web. Due to bacterial dependence on annual carbon inputs, and unique nutrient content of fresh phytoplankton for breeding invertebrates, ice-edge blooms might be an important determinant of annual variations in macrobenthic abundance.
The Southern Ocean is very important for the potential sequestration of
carbon dioxide in the oceans and is expected to be vulnerable
to changes in carbon export forced by anthropogenic climate ...warming.
Annual phytoplankton blooms in seasonal ice zones are highly productive and
are thought to contribute significantly to pCO2 drawdown in the
Southern Ocean. Diatoms are assumed to be the most important phytoplankton
class with respect to export production in the Southern Ocean; however, the
colonial prymnesiophyte Phaeocystis antarctica regularly forms huge
blooms in seasonal ice zones and coastal Antarctic waters.
There is little evidence regarding the fate of carbon produced by P. antarctica
in the Southern Ocean, although remineralization in the upper water column
has been proposed to be the main pathway in polar waters.
Here we present evidence for early and rapid carbon export from P. antarctica
blooms to deep water and sediments in the Ross Sea. Carbon sequestration
from P. antarctica blooms may influence the carbon cycle in the Southern
Ocean, especially if projected climatic changes lead to an alteration in the
structure of the phytoplankton community.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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