Benthos
B.A. Bluhm1, J.M. Grebmeier2, P. Archambault3, M. Blicher4,
G. Guðmundsson5, K. Iken1, L. Lindal Jørgensen6, V. Mokievsky7
1School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, USA
2Chesapeake Biological Laboratory, University of Maryland, Solomons, USA
3Institut des sciences de la mer de Rimouski, Université du Québec á Rimouski, Canada
4Greenland Institute of Natural Resources, Nuuk, Greenland
5Icelandic Institute of Natural History, Gardabaer, Iceland
6Institute of Marine Research, Tromsø, Norway
7Laboratory of Coastal Ecology, PP Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
December 10, 2012
Highlights
- Recent findings on temporal trends in the benthic system include: species range changes in sub-Arctic seas and on inflow shelves; changes in feeding guild composition in the deep Fram Strait; reduction of benthic biomass in the Barents and northern Bering seas; no apparent change in infaunal biomass in the Kara Sea.
- Results from Greenland, and the northern Bering and Chukchi seas show spatial and temporal differences and variability in invertebrate growth, energy budgets and resulting biomass that are related to variation in seasonal sea ice dynamics, temperature and food supply.
- Greatly improved benthic species inventories for Iceland, Greenland and the Russian Arctic show upwards of 1000 species per region.
- Contrary to long-standing belief, terrestrial carbon significantly contributes to benthic food webs on the river-influenced Beaufort Sea shelf.
Introduction
Macrobenthic infauna (animals living within the sediments) act as long-term integrators of overlying sediment processes. They remain relatively stationary in the sediment and their community patterns are thus directly affected by export production from the overlying water column. The distribution, abundance and biomass of infauna vary by region and are related to water mass characteristics and current patterns. Larger epifaunal organisms (animals living on top of the sediment) contribute considerably to carbon remineralization, and through their mobility, to carbon distribution.
This report on the status of Arctic marine benthic communities is pan-Arctic in scope and organized by region. International members of the benthic expert group of the Arctic Council's Circumpolar Biodiversity Monitoring Program under CAFF (Conservation of Arctic Flora and Fauna) summarized new key findings in their regions. The scope of research and nature of those findings vary among regions.
Northern Bering Sea and Chukchi Sea
Bivalves, amphipods, and polychaetes dominate the infaunal biomass south of St. Lawrence Island in the northern Bering Sea, where time series data indicate a decline in overall station biomass and of specific components in recent decades (Fig. 3.10). Amphipods and bivalves dominate in the central region from St. Lawrence Island to Bering Strait, and bivalves and polychaetes dominate in the southern Chukchi Sea to the slope region of the Canada Basin (Bluhm and Grebmeier, 2011).
The nutrient- and phytoplankton-rich water that is transported northwestward through Bering Strait (see the Ocean essay for a description of Pacific Water flow through the Bering Strait) is a major driver of the high benthic faunal productivity of the south-central Chukchi Sea. Macrobenthic infaunal biomass in the south-central Chukchi Sea ranges from 24 to 59 g C m-2 and exceeds 120 g C m-2 at the 'hot-spot'' just northwest of Bering Strait (citations in Grebmeier, 2012). This southeastern Chukchi infaunal assemblage is dominated by tellinid and nuculid bivalves, ampeliscid and lysianassid amphipods (Grebmeier, 2012). In contrast to the very productive western side of the system, benthic communities to the east, which are strongly influenced by Alaska Coastal Water, are more patchy, variable in composition and typically of very low biomass (<10 g C m-2, but occasionally ranging up to 12-23 g C m-2), but are characterized by higher diversity. As this Pacific water mass flows north into the central Chukchi Sea, it becomes progressively depleted of nutrients and phytoplankton. Perhaps not surprisingly, then, infaunal biomass declines from the southern Chukchi Sea ''hot-spot'' to <10 g C m-2 in the central Chukchi Sea (Bluhm and Grebmeier, 2011: Figure 1).
Winter-transformed Bering Sea water flows through Herald Valley and Herald Trough (located in the western and central Chukchi Sea, respectively), where infaunal communities are dominated by maldanid, lumbrinerid, and nephtyid polychaetes. Bivalves and polychaetes dominate the infaunal community of the northern Chukchi Sea, where average infaunal benthic biomass is a moderate 5-15 g C m-2, although recent studies indicate high benthic biomass in upper Barrow Canyon (see the essay on Ecosystem Observations in Barrow Canyon for information about sea ice, hydrography and biology in the Barrow Canyon region). On the upper slope (200-1000 m depth) and extending down into the Canada Basin, the benthic community becomes foraminifera-dominated, with biomasses of <5 g C m-2 (citations in Grebmeier, 2012).
Beaufort Sea
Both the International Polar Year and ongoing and planned fossil fuel development recently sparked several new benthic research projects in the Beaufort Sea. Studies continue, but first results confirm trends found in the 1970s when the benthos was last surveyed. Epibenthic invertebrate biomass dominates significantly over demersal fish biomass (>90% in trawl hauls versus <10%, respectively) (Rand and Logerwell, 2011), with dominant epibenthic taxa (brittle stars, other echinoderms, and crustaceans) similar to those on other Arctic shelves. Biomass generally decreased from west to east in US waters, but high variability was observed farther east as well as hot spots in the Cape Bathurst polynya. Benthic remineralization in the region increases after ice break-up, although interactions of food availability, benthic biomass and remineralization are complex and often more spatially variable than seasonally (Link et al., 2011). A new ice algal biomarker detected in a variety of benthic taxa supports previous research that suggested that ice algae contribute significantly to the nutrition of Arctic shelf benthos (Brown and Belt, 2012) (see the Primary Productivity and Nutrient Variability essay for further information about sea ice algal production). In the shallow coastal lagoons of the Beaufort Sea, terrestrial carbon can add substantially to the productivity of marine nearshore Arctic habitats, as reflected in terrestrial stable isotopic signatures and high prevalence of benthic omnivorous and detritivorous fauna (Dunton et al., 2012). Comparatively short-lived and fast colonizing fauna dominate the benthic community in those lagoons, where they are preyed upon by water fowl, fish and seals.
Canadian Arctic
The establishment of ecologically or biologically significant marine areas (EBSA) through application of scientific criteria as promoted by the Convention on Biological Diversity (decision IX/20) will be a baseline for sustainable use and development of the marine ecosystem in the future. Kenchington et al. (2011) used the Canadian identification criteria (uniqueness/rarity; aggregation; fitness consequences; with naturalness and resilience used to prioritize amongst sites identify possible EBSAs) based on benthic attributes for the Canadian Arctic (Fig. 3.11). Specifically, benthic diversity and biomass, the density of coral and sponge beds, and benthic remineralization and sediment pigment concentration were used to identify benthic EBSAs for the Hudson Bay Complex, Eastern Arctic and Western Arctic regions. High concentrations of soft corals and sponges are observed in the Hudson Strait compared to Hudson Bay. In the Eastern Arctic, the Baffin Bay-Davis Strait areas are characterized by important aggregations of sea pens, large gorgonian corals and sponges (Kenchington et al., 2010). Franklin Bay and the Prince of Wales Strait in the Canadian Arctic Archipelago were also suggested as benthic EBSAs. Benthic assemblages differ among seven regions on the Canadian Arctic shelf, with taxonomic diversity higher in eastern regions than in the central and western Canadian Archipelago. Currently known macrobenthic (infaunal) species richness in the Canadian Arctic is 992 taxa, similar to the more highly sampled Atlantic Canada (1044 taxa) and Pacific Canada (814 taxa) regions (Archambault et al., 2010). Lancaster Sound and the North Water Polynya support particularly high benthic diversity, benthic biomass and high benthic boundary fluxes. Lancaster Sound also supports important populations of Pennatulacean sea pens with the continental slope off Baffin Bay.
Greenland
The poorly studied benthic invertebrate fauna off Greenland (i.e., the Greenlandic sector of Baffin Bay and Davis Strait, Denmark Strait and Greenland Sea) lacks historical data on basic ecosystem components necessary to document the state of the environment and potential future changes. However, recent research initiatives have been undertaken as a consequence of climate change, ongoing oil and mineral exploration, and an increasing market demand for environmental certification of industrial fisheries. On a species level, geographic and inter-annual differences in the growth of dominant coastal primary and secondary producers are related to variation in seasonal sea ice dynamics (Krause-Jensen et al., 2012). Similarly, the energy budget of commercially exploited scallops is negatively affected by increasing temperature (Blicher et al., 2010). Exploring such relationships (Fig. 3.12) is critical when considering direct economic implications of climate change. On a community level, data are too scarce to document such relationships, although a recent macrozoobenthic survey on a shallow bank in Davis Strait did not show any difference in species richness between 1976 and 2009. The recent studies in West Greenland documented the presence of highly diverse macrozoobenthic communities and also suggest that the benthos plays a key role in carbon flux in the regional shelf and coastal systems. Several organisms recovered during these surveys are potentially new to science.
Iceland
Within the 200 mile, 750,000 km2 economic zone of Iceland the occurrence of over 1,900 benthic invertebrates species of all major phyla and classes has been recorded over the past few years as a result of the BIOICE (Benthic Invertebrates of Icelandic Waters) program. This area includes a central part of the Greenland-Scotland Ridge, which forms an isolating barrier between the abyssal plains of the North Atlantic and the Arctic oceans (Dauvin et al., 2012). Near-bottom water temperature and the number of benthic species vary greatly north and south of the ridge. Although by far the lowest species diversity occurred in the deeper parts of the Arctic Ocean (>600 m) north of the ridge, a significant portion of endemic species was found here, mostly confined to lower taxonomic levels (Briggs and Bowen, 2012). As a result of climate warming, near-bottom water temperature on the shelf around Iceland has been increasing in recent decades (Sólmundsson et al., 2007). Specifically, a ~2-3°C temperature increase on the shelf areas south and west of Iceland during the last three decades has affected benthic species distributions. An example is the angler fish, Lophius piscatorius, whose distribution has expanded in Icelandic waters.
Barents Sea
As an inflow shelf, the Barents Sea ecosystem is particularly strongly influenced by inter-annual and seasonal climate-driven variations, including factors such as ice cover and the strength of inflowing Atlantic water. Water temperatures have increased by 1.5°C since the 1970s, with the strongest increase in the northern Barents Sea. However, a decrease in Atlantic water temperature between 2006 and 2011 in the Barents Sea Opening is reported in the Ocean essay. Historical benthic data show that dominant boreal-arctic species have their temperature optimum close to the long-term temperature mean, and that any deviations from that mean will have negative impacts on abundance, reproductive success and change distribution range (Anisimova et al., 2011 and references therein). This negative effect is higher in temperatures above than below the long-term mean temperature. The average infaunal biomass in years around the long-term mean temperature is 100-147 g wet weight/m2. As in the Canadian Arctic, the design of Ecologically or Biologically Significant Marine Areas continues in the Barents Sea.
Kara and Laptev Seas
The Kara Sea region has one of the few long-term Arctic benthic time series. Here, infaunal community stability was evaluated for 1927-1945, 1975, 1993 and 2007 (Kozlovsky et al., 2011). The dominant species and infaunal biomass values were quite stable over time, with bivalve mollusks as the predominant taxon. The total number of species amounted to just over 200. Intense study effort has increased the number of known species in the Laptev Sea to almost 1800 (Sirenko and Vassilenko, 2009), relative to 500 in an inventory from 1963. The expected number of species (a diversity measure not biased by the research effort conducted) in the Laptev Sea approaches the same number as in the western Barents Sea. Besides increased investigative effort, a second reason for high species richness is likely the wide range of depths in the area, ranging from the shallows of the Novosibirsky Islands to the lower continental slope.
Arctic Basin
A recent compilation of existing literature documents 1125 taxa in the deep Arctic Basin, with the majority of taxa represented within the arthropods, foraminiferans, annelids and nematodes (Bluhm et al., 2011). Due to low overall sampling effort, this number is expected to increase with further studies of the Arctic deep sea. As known for other deep-sea basins, faunal abundance and biomass decrease with depth, but contrary to the typical mid-depth diversity peak known for other deep-sea regions, no such peak was observed in the analysis of polychaete and nematode diversity. In contrast, studies of ostracod and foraminiferan diversity detected mid-depth peaks, but at a shallower depth than in lower latitude basins (Yasuhara et al., 2012). While several major topographically complex ridge systems bisect the Arctic Ocean basin, they do not seem to present biogeographic barriers, as the fauna in the entire basin (with the exception of rare species) is mostly similar to today's Atlantic fauna owing to Fram Strait being the only deep-water connection to the Arctic Ocean. At HAUSGARTEN (in the eastern Fram Strait and the only Arctic long-term deep-sea observatory for detecting changes in abiotic and biotic parameters in a transition zone between the northern North Atlantic and the central Arctic Ocean; Soltwedel et al., 2005), photographic surveys conducted in 2002, 2004 and 2007 at ~2500 m depth documented significant decreases in megafauna densities, evenness and diversity measures over the study period or for the most recent sampling date (Bergmann et al., 2011). Changes in species abundances and feeding guild distribution coincided with observed increases in bottom water temperatures and changes in food availability related to changes in sea ice cover. The temperature and volume flux of Atlantic Water in Fram Strait are described in the Ocean essay.
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