The near-bottom zooplankton at the abyssal BIOTRANS site, northeast Atlantic: Composition, abundance and variability

Abstract

The near-bottom zooplankton of the abyssal BIOTRANS site (water depth 4500 m) was studied at two stations 11 nautical miles (nm) apart. Stratified sampling was conducted by means of a double MOCNESS at three depth layers 20, 50 and 100 m above bottom. The composition of the zooplankton showed a predominance of copepods, making up >50% of the total zooplankton abundance. Ostracods and chaetognaths were the most important non-copepods, displaying a slight increase towards the bottom. The variability of abundance and biomass was analysed statistically at different scales. Logarithmic coefficients of variation ranged from 29 to 187% for various taxa. Sampling at the two stations added significantly to the total variance for some taxa. By contrast, vertical gradients were mostly weak. Possible reasons for the observed variability are discussed.