Arctic Ocean Diversity (ArcOD)
An international collaborative effort that inventoried biodiversity in the Arctic sea ice, water column and sea floor from the shallow shelves to the deep basins using a three-step approach: compilation of existing data, taxonomic identification of existing samples, and new collections focusing on taxonomic and regional gaps.
Bodil Bluhm, Ph.D., Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Alaska, USA
Rolf Gradinger, Ph.D., Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Alaska, USA
Russ Hopcroft, Ph.D., Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Alaska, USA
The Arctic Ocean is the most extreme ocean on the planet in regards to the seasonality of light and its year-round existing ice cover. The Arctic seas hold a multitude of unique life forms, highly adapted in their life history, ecology and physiology to the extreme and seasonal conditions of their environment. Our knowledge of what currently lives in the Arctic Ocean is still rudimentary compared to other oceans, due to the logistical challenges imposed by its multi-year ice and inhospitable climate.
Sea ice with ridges and melt ponds in the Chukchi Sea: habitat for a
unique community of protists and multi-cellular fauna. Photo by
R. Gradinger, Univ. of Alaska Fairbanks.
The Arctic Ocean is also the area where the effect of climate change appears to be expressed the strongest. The already ongoing changes make the effort to identify the diversity of life in the major three realms (sea ice, water column and sea floor) an urgent issue. Changes in the environmental conditions will have direct effects on the marine biota on multiple levels, from populations to individuals. Species level information is, therefore, essential to discussions about climate change or anthropogenic impact, their expressions and effects. These effects can only be detected through long-term monitoring of key species, communities and processes. For monitoring and assessment of changes, the availability of baseline data is crucial.
The Arctic Ocean Diversity (ArcOD) Census of Marine Life project was aimed at documenting the present Arctic Ocean biodiversity on a Pan-Arctic scale. While most recent research efforts in the Arctic Ocean focused on processes, the emphasis of this program was on biodiversity because processes are critically impacted by the composition of biota involved in them. The operational approach was to help coordinate, encourage and support research efforts designed to examine the biodiversity in the three major realms: sea ice, water column and seafloor. This was accomplished by improving the taxonomic resolution of existing samples, increasing the number of new samples, extending the sampling area, providing the material to taxonomic experts worldwide, and compiling the results in a data base accessible to scientists and the public through the Ocean Biogeographic Information System (www.iobis.org), the Global Biodiversity Information Facility (www.gbif.org) and the Alaska Ocean Observing System (www.aoos.org). ArcOD played an active role in the International Polar Year 2007/2008 (www.ipy.org) as the lead project of the Arctic Marine Biodiversity cluster (http://classic.ipy.org/development/eoi/proposal-details.php?id=333).
Major scientific objectives included (but were not limited to):
- Compile a species inventory of the Arctic sea ice, water column and sea floor and to identify species community and richness trends relative to latitude, depth, spatial scale, etc.;
- Identify bio-geographic affinities and barriers and their relevance in the past and present of the Arctic; and
- Identify the relation between species distribution patterns, species richness with environmental data and attempt to draw conclusions and predictions about Arctic climate change.
Arctic Sea Ice
The Arctic sea ice covers approximately 7x106 km2 in summer and twice that in winter. The unique multi-year sea ice of the deep basins reaches a thickness of 2-3m and allowed the evolution of endemic ice-associated (=sympagic) species, meaning species that are not found anywhere else. Ice organisms live either in the tiny (mostly <1mm in diameter), liquid-filled pores and brine channels within the ice or at the ice-water interface. The biota within the sea ice is consequently small (<1mm) and dominated by bacteria, unicellular plants and animals and small multi-cellular animals (metazoa). Protozoans and metazoans (in particular turbellarians, nematodes, crustaceans and rotifers) can be abundant in all ice types year-round. A partially endemic fauna, comprised mainly of gammaridean amphipods, thrive at the underside of ice floes with up to several 100 individuals m-2. The amphipods are important as the major prey for the Arctic cod (Boreogadus saida), which in turn acts as the major link to seals, birds and whales.
While previous studies provided a glimpse of the seasonal and regional abundances of ice-associated biota, biodiversity in these communities is virtually unknown for most groups, from bacteria to metazoans. Many taxa are likely still undiscovered due to the methodological problems in analyzing ice samples. The study of diversity of ice-related environments is urgently required before they ultimately change with altering ice regimes and the predicted loss of the multi-year ice cover. ArcOD-related efforts have increased our knowledge of sea ice biodiversity. Its broad approach included the exploration of life at thick pressure ridges in the Canada Basin by SCUBA divers, a search for the diversity of life in coastal fast ice using ice cores, and a first pan/arctic mapping and modeling effort for sea ice fauna based on published literature.
Arctic Pelagic Realm
Planktonic research in Arctic waters can be traced back more than a century, with the earliest records restricted primarily to the coastal waters. Waters of the continental shelves have been studied in variable taxonomic detail in the Barents, Kara, Laptev and Chukchi/Beaufort Seas, while the East Siberian Sea, and Canadian Archipelago through northern Greenland have been particularly understudied. The deep basins remained even more mysterious due to the logistic challenges of penetrating their year-round ice cover, and the much greater effort required to properly sample to several kilometers of depth. ArcOD made significant progress on filling this sampling gap in the deep Canada Basin.
Due to their high abundance and ease of capture, the taxonomic composition and life history of the larger more common copepods in the Arctic Ocean was relatively well understood. The same cannot be said for the smallest copepod species that are invariably missed by collection techniques, all deep-water species, and the more fragile gelatinous forms. Although copepods typically predominate, there is a broad assemblage of other planktonic groups in the Arctic that are only occasionally reported in detail. ArcOD demonstrated that these non-copepod groups, in particular, hold the greatest promise for discovery of new species and trophic importance because they have been largely ignored or biased against by collection techniques. The basic biodiversity of all these gelatinous animals has been grossly underestimated in polar waters, not only due to undiscovered species, but also through undocumented occurrences of deep-water species found elsewhere in the oceans. In addition to new observations, ArcOD made significant progress in getting sampling records from pelagic sampling programs available through OBIS.
It is the food supply and not the low water temperatures per se that restrains growth and survival of the seafloor (benthic) animals in the Arctic. On some Arctic continental shelves such as the Chukchi and Bering Seas, the benthos receives large food input from the water column and, therefore, plays a greater role than at lower latitudes. This explains the locally high abundance of bottom-feeding mammals like gray whales and walruses. In contrast, food availability and benthic biomass in the deep Arctic basins are substantially lower than on the shelves.
The large Arctic seafloor fauna has received most attention while the meiofauna (<1 mm) and microbial communities are less well studied. On the continental shelves, crustaceans (in particular amphipods, sand fleas), polychaetes (bristle worms) and bivalve mollusks dominate the fauna living inside the sediments. The larger animals living on top of the Arctic seafloor are often dominated by brittle stars with up to several hundred individuals per square meter. The Arctic deep-sea had received much less attention because of the permanent ice cover and, hence, difficult access, but ArcOD was able to sample part of the Arctic deep-sea. The main groups (but not the species) of animals in the Arctic deep-sea sediments appear to be similar to those of shallow regions, but they occur in much lower densities.
Over 90% of the known approximately 5000 species of Arctic marine invertebrates live at the seafloor. About 350-400 of those occur in the Arctic deep-sea. While more research is needed for an adequate overview of the biodiversity of the Arctic seafloor, ArcOD-related research has added new benthic species and range extensions, plus knowledge of previously unsampled regions and faunal assemblages to the Arctic map.
Fish can be found in association with all three Arctic realms described above. Just over 400 fish species are known from Arctic seas and adjacent waters including marine, diadromous (mostly anadromous), and freshwater fish species which enter brackish water. Most of these species are living on or near the bottom. The dominant Arctic fish families are cods, eelpouts, snailfishes, sculpins, and salmonids. One of the key species in the Arctic is the Arctic cod Boreogadus saida, because it is a critical link between lower trophic levels (copepods and under-ice amphipods) and birds, seals, and whales. The Arctic cod is the most northerly distributed gadid, occurring roughly between 60°N and the North Pole, nearshore as well as offshore.
Unlike most other oceans, commercial fisheries do not exist in the high Arctic, while they are extensive in the sub-Arctic southern Barents and southeastern Bering Seas. The lack of high-Arctic fisheries catch and by-catch data yields a void of even basic knowledge. The traditional methods of collecting fish by trawls do not work well in ice-covered waters, making it difficult even today to advance our understanding of fish biodiversity and biology. Efforts contributing to ArcOD made significant progress in cataloging and verifying museum (and some new) collections of arctic fishes.
Cyclocaris guilelmi, a pelagic sand flea from the high
Arctic Canada Basin. Photo by R. Hopcroft, Univ. of
Alaska Fairbanks, (funded through NOAA Office of
Ocean Exploration). See full version of image.
Visit the Arctic Ocean Diversity website.