Species specific uptake of radio-labelled phytodetritus by benthic meiofauna from the Baltic Sea

Abstract

The diatom Sheletonema costatum is one of the dominant phytoplankton species during spring in the northern Baltic Sea. We followed the uptake of radio-labelled S, costatum by all major meiofauna species in a laboratory experiment. The uptake of labelled diatom carbon varied greatly among major meiobenthic tars and among species belonging to the same class or phylum. Both total uptake and uptake per unit biomass were by far highest in the ostracod Candona neglecta accounting for 46% of the total meiofauna uptake. The total uptake of C-14 was significantly different among all 3 common ostracod species, Candona neglecta taking 10 and 100 times more than Paracyprideis fennica and Heterocyprideis sorbyana respectively. Nematodes accounted for over 40% of the total uptake of C-14 in the microcosms, of which 84% was taken up by large nematode species such as Paracanthonchus spp. Nematodes with similar buccal cavities and of similar size showed surprisingly large differences in the uptake of the radio-labelled material. There seems to be quite strong selection both for and against the diatom among epistrate feeders as well as among so-called non-selective deposit feeders. Only a small portion of the total meiofauna population was found below 1 cm in the sediment; this was composed almost solely of nematodes. These nematodes assimilated as much C-14 per unit biomass as the surface ones did, which contradicts the hypothesis claiming that meiobenthic animals read in 2 ways to phytoplankton sedimentation, with surface feeders directly assimilating sedimented phytoplankton, while subsurface feeders experience a more stable food supply and rely only indirectly on sedimented phytoplankton. [KEYWORDS: pelagic-benthic coupling; food-web; meiofauna; C-14 radio label]