Southern Polar Front macroecological and biogeographical insights gained from benthic Ostracoda

Abstract

The Southern Ocean is one of the least known marine ecosystems on Earth, but the importance of understanding its biological and geochemical characteristics are urgent, because of the fast changing climate. Primary productivity is a key factor in ecosystem functioning, since this is the only process (except for the rare chemosynthesis) transforming solar energy into organic material, which can later be processed by all other living beings. Herein we investigate how primary productivity in the euphotic zone influences the biodiversity on the sea bed at abyssal depths, using Ostracoda (Crustacea) as a model. We also discuss the biogeographical pattern of the ostracod fauna. Samples collected from the Atlantic sector of the Southern Ocean close to the Southern Polar Front (i.e. ~51°S) during the SYSTCO II expedition are the basis for our analyses. For the statistical tests, we used samples collected with an epibenthic sledge, which has the advantages of sampling a far larger area than traditional gears (i.e. grabs and corers), and also collect Myodocopida and Halocyprida rarely recorded in ostracod studies. However, because of its large mesh size (i.e. 300 and 500μm) the epibenthic sledge fails to recover small sized ostracods. Most benthic and benthopelagic ostracod species inhabiting the Southern Polar Front region are either endemic to the Southern Ocean or occur close to it. We conclude that ostracod assemblages living below areas of high primary productivity seem to be different to those below low productivity zones, but that assemblages living west of the Mid-Atlantic Ridge are not significantly distinct from the ones living to the east of this putative barrier.