Benthic Communities in the Filchner region: a description of composition and abundance


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Dieter.Gerdes [ at ] awi.de

Abstract

Although benthic communities in the Weddell Sea have been studied intensively during the last three to four decades, there still are some regions within the Weddell Sea that are virtual white spots due to only little information gathered. One of these subregions is the Filchner Trench, which is considered as an key spot for the formation of the Antarctic bottom water as an important driver of the global water circulation. Located in front of the Filchner-Rønne Ice-Shelf, this system is highly understudied due to the heavy sea ice conditions during the whole year. However, during the Antarctic summer of 2013/14 the Polarstern expedition PS82 was carried out to study this area and prove the hypothesis whether it is a biological hotspot or not. The present study was carried out during this expedition and describes different benthic communities of the Filchner Outflow System. The benthos was mapped from underwater pictures obtained via an underwater camera attached to a multibox-corer. All organisms present were counted and taxonomically identified to the lowest unit possible, diversity and evenness were calculated as well as the percentage of organism coverage; additionally the organisms were differentiated in 4 types of feeding guilds. Environmental parameters used were bottom temperature, salinity, dissolved oxygen and fluorescence recorded via a CTD; current data were obtained from a current meter deployed bottom-near in a mooring. Additionally, three sediment types were distinguished and their percentage of coverage was estimated from the underwater pictures. Biological and environmental data were arranged in a set of data matrices for multivariate statistical analyses in order to define different benthic communities in the Filchner Outflow System and possible relationships to environmental parameters. From the pictures 61 different taxonomic units were identified comprising different levels from species to phylum. The richest fauna (25 taxonomic groups) occurred at St. 305 on the east shelf of the trench. The diversity values ranged from 0.10 to 2.88, evenness from 0.04 to 0.81. Ophiuroids were the most dominant group, counting for 37.6% of the total organism abundance, followed by bryozoans (19.9%) and holothurians (13.7%). Benthic mean abundance was 72±56 ind/m2 with variations among stations from 8 to 196 ind/m2. The most abundant feeding guild was suspension feeders (63.4%), followed by deposit feeders (26.6%), predators (8.2%) and scavengers (1.8%). There was no strong or statistically significant correlation between benthic distribution and oceanographic variables (best Rho value = 0.186; p > 0.05). Due to the enormous size of the area with very different environmental characteristics at a first step the benthic fauna of 5 FOS subregions was compared. The similarity within these different regions was low (<60%), thus reflecting a highly variable and patchy distribution of benthic organisms. Further multivariate statistical analysis, however, revealed three distinct communities: a), a Eastern Shelf Community living on the east and west shelves of the trench, dominated by suspension feeders b) a Southern Trench Community living on fine sediment bottoms in the deep parts of the trench dominated by deposit feeders and, c) a Northern Filchner Community living on gravel bottoms in the outer slope of the Filchner Region dominated by deposit feeders. The results show a clear differentiation between the Southern Trench Community with the other two communities of the Filchner Outflow System. However, due to the weak correlation found via statistical analysis, it can only be speculated that the main reason for this differentiation is the distinct characteristics of the water masses of each region. The results of this study validate two communities previously described for the region (Eastern Shelf and Southern Trench communities) and the description of a new community for the Filchner Outflow System, the Northern Filchner Community. Furthermore, a comparison with studies from other regions of the Weddell Sea shows that the Filchner region presents higher abundance than the Antarctic Peninsula and Eastern Weddell Sea Shelf.



Item Type
Thesis (Master)
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Primary Division
Programs
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Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
43406
Cite as
Pineda Metz, S. (2014): Benthic Communities in the Filchner region: a description of composition and abundance , Master thesis, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany and University of Bremen, Germany.


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