The structure and carbon demand of the bathyal benthic boundary layer community: a comparison of two oceanic locations in the NE-Atlantic

Estimates of standing stocks were used together with metabolic rates from literature to compare the structure and the respiratory carbon demand of the benthopelagic fauna and epibenthic megafauna at two oceanic locations in the northeast Atlantic. The total standing stock of the benthopelagic fauna and epibentic megafauna (in the following referred to as benthopelagos sensu latu) in the Iceland Basin (59°N/20°W) was 5 times higher than at the BIOTRANS site (West European Basin, 47°N/20°W). While fish were the predominating group at the northern location, followed by epibenthic megafauna, most of the biomass at the southern station could be attributed to epibenthic megafauna whereas fish were even surpassed by zooplankton.The overall respiratory carbon demand of the benthopelagos s.l. in the Iceland Basin was about 50% higher than at the BIOTRANS site. In both areas, a large fraction of the carbon was respired by the megafauna, accounting for 46 % of the total respiratory carbon demand in the Iceland Basin and 86% at the BIOTRANS site. Important consumers in the Iceland Basin were also zooplankton (27%) and fish (26%), whereas at the BIOTRANS site only zooplankton had a significant share (12%) besides megafauna. Compared to the carbon fluxes into the BBL, the faunal groups (without bacteria) remineralize ca. 10–20% of the sedimenting POC. If near-bottom pelagic bacteria are included, the fraction of the POC import flux remineralized by the benthopelagic community amounts to at least 20–50%. That means, the carbon flux as measured in sediment traps is not sufficient to fuel both the benthopelagic community including the megafauna plus the sediment community.