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Epibenthic sledge (EBS) sorting

imagePhoto: Recovering the Epibenthic sledge. J. Strugnell, BAS

By Jan Strugnell, British Antarctic Survey

Although the majority of the trawling is now completed for the biologists on board, the work has not stopped! There is still plenty of activity in the laboratories and computer rooms to process all of the samples.

Steffi, Dave and Adrian have been spending a lot of time looking down their microscopes sorting the animals that were caught in the Epibenthic sledge (EBS). The animals caught in the EBS typically range in size from 7 mm to 70 cm, although it must be said that some of the largest animals we caught were also captured in the EBS, including a sea cucumber at least 50 cm long!

We are lucky that we have a number of taxonomic experts on board to sort the animals. We have experts on polychaetes (Adrian), bryozoans (Dave) and isopods (Steffi) and so much of the identification and fine level sorting can be done whilst we are on board. Katrin, the group leader (British Antarctic Survey) is also an expert mollusc taxonomist. The rest of the animals that cannot be identified are sorted into taxonomic groups and sent to experts at a later date to be identified.

Photo: A Gastropod (microscopic) caught in the EBS. BAS

The sampling design of the EBS was set up to try and determine the scales upon which biodiversity is organised in the Amundsen Sea region, as very little is understood of the patterns of abundance, dominance and richness of animals in the Southern Ocean. The EBS sampling design was organised to sample at 3 sites (including inside and outside of Pine Island Bay) with 6 replicates at 500 m at each site and 2 replicates at 1000 m and 1500 m. Both a lower and an upper net on the EBS collected at each of these sites. This comprises a total of 60 samples to be sorted through!! Box cores were also taken from each site and these will provide a measure of grain size and organic content of the sediment at each location.

Photo: Cumaceans specimens caught in the EBS. BAS

Commonly there are in order of 1200 animals in a single sample and so this is quite a labour intensive task! So far the initial work on these samples reveals them to be incredibly diverse * with 13 Phyla identified in a single sample. This is an impressive and remarkable level of diversity and represents 1/3 of the major animal body plans that exist on the planet! When completed, this work will provide some strong insight into the geographic and bathymetric scale at which biodiversity is organised in this region, and is likely to turn the Amundsen sea area from perhaps the world

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