Small-Sized Benthic Organisms of the Alpha Ridge, Central Arctic Ocean

Abstract

Abundance, biomass and activity of the small-sized benthic organisms (bacteria to meiofauna, includingforaminifera) was studied in summer 1998 during the expedition ARK XIV/1a to the Amerasian area of theperennially ice covered central Arctic Ocean. With the help of two icebreakers, the German research vesselPOLARSTERN and the Russian nuclear-powered ARCTICA, it was possible to reach this remote, heavilyice-covered region in order to carry out the first benthic investigations. These focus on effects on the benthiccommunity of the expected low food availability under perennial ice coverage. Bacterial and meiofaunalabundances were determined by direct counting. Biomass determinations on bacteria and nematodes wereundertaken by size-imaging techniques. In addition biochemical analyses were carried out to estimate foodavailability (as sediment-bound chloroplastic pigments indicating phytodetritus) at the sea floor, the total microbialbiomass (TMB; i.e. the total amount of sediment inhabiting bacteria, flagellata, protozoa and small metazoa,estimated by phospholipid quantification) and the potential bacterial activity (turnover rates of ester-cleavingexoenzymes). Concentrations of chloroplastic pigment equivalents (CPE) in the main target area (Alpa-Ridge)ranged between 0.10 ± 0.02 and 0.17 ± 0.04 g/ml. A 2-3 times higher concentration was determined at astation on the Lomonosov Ridge crest (0.40 ± 0.15 g/ml). The standing stock of meiobenthic organisms(including foraminiferans) was extremely low and varied between 72 ± 17 individuals 10 cm-2 in the deepMakarov Basin (3,170 m) and 190 ± 56 individuals 10 cm-2 on the Alpha Ridge (1,470 m). Significantly highernumbers (U-test, p = 0.049) were found on the Lomonosov Ridge (297 ± 82 individuals 10 cm-2). Meiobenthicabundances from the area of investigations, were up to ten times lower than those reported from non-ice covereddeep-sea regions. However a significant water depth depending decrease of meiobenthic abundances was stilldetectable.A comparison of biomass data determined by volumetric measurements and biochemical methods showed thatabout 67% of the TMB are held by organisms of nanofauna size (2-32 m), approx. 32% belongs to bacteria.Only 0.5-1.5% of the TMB were held by metazoan meiofauna.