Sea Bottom Diversity

Currently our impression of seafloor diversity for the invertebrates is as follows:

Group Total Arctic
Macrophytes 191
Porifera 162
Cnidarians 161
Nemertines 77
Annelids 485
Bryozoa 331
Molluscs 480
Arthropods 1,317
Tunicates 57
Echinoderms 150
Sipunculids 12
Platyhelminthes 116
Nematodes 296
Gnathostomulids  1
Tardigrades 4
Hemichordates 1
Brachipods 9
Cepaholorhynchs 13
Gastrotrichs 12
Echiurans 2
Phoronids 1

An overview of the Benthic realm

Food is critical in the Arctic

Seafloor communities in general depend on food supplied from the water column above. It is the food supply and not the cold water temperatures per se that appear to restrain growth and survival of the seafloor animals in the Arctic. On the Arctic continental shelves, the benthos receives large food input from the water column and, therefore, plays a greater role in system production than at lower latitudes. This explains the high abundance of bottom feeding mammal species like gray whale and walrus. Both food availability and benthic biomass in the deep Arctic are substantially lower than on the shelves.

What lives at the Arctic seafloor?

To date, the large Arctic seafloor fauna, the so-called macro- and megabenthos, has received most attention as it is the most obvious and relatively easy to sample. Smaller fauna (meiofauna smaller than 1 mm) and microbial communities are less well studied in the Arctic.

On the continental shelves, crustaceans (in particular amphipods, sand fleas), polychaetes (bristle worms) and bivalve mollusks dominante the macrofauna. Many of these species live inside the sediment and are called 'infauna'. The community composition of the infauna is mainly determined by grain size of sediments and the productivity of the overlying water masses. The epibenthic megafauna (large animals living on top of the seafloor) is often dominated by brittle stars with up to several hundred individuals per square meter. Other conspicuous epibenthic faunal elements include sea urchins in the Barents Sea and sea cucumbers in the Laptev Sea.

In contrast to the continental shelves, the Arctic deep-sea has received very little attention to date due to the permanent ice cover and, hence, difficult access to the deep basins of the central Arctic. The main groups of animals in the Arctic deep-sea sediments are similar to those of shallow regions: polychaetes (bristle worms), crustaceans, and bivalves dominate. Sponges, cnidarians, tunicates, brittle stars and various worms are also found, but they are less frequent.

The Arctic deep-sea animals occur in low densities and most are deposit-feeders. Fresh food is rare in the deep-sea of all oceans.

How many species at the Arctic seafloor?

At present, more than 4000 species of multicellular marine invertebrates are known to inhabit the Arctic. Over 90% of those live at the seafloor. About 350–400 of those species are deep water species living in the central Arctic Ocean. Within this project, we expect to find more Arctic seafloor species.

The Arctic seafloor species represent four biogeographic affinities: cosmopolitan boreo-arctic species are found all over the Arctic as well as in subarctic seas Atlantic- and Pacific-boreal arctic species are found in the Arctic as well as the temperate Atlantic and Pacific, respectively; Arctic endemic species are only found in the Arctic. The distribution pattern of species of these different origins gives evidence about the geological history of the Arctic.

Our project aims at improving the knowledge of the Arctic marine diversity through increasing the number of samples, extending the sampling area, providing the material to taxonomic experts world-wide and compiling the results in a data base accessible to scientists and the public.

Page Author: Bodil Bluhm
Updated: Sept 25, 2010
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