Deep-Sea Nematodes Actively Colonise Sediments, Irrespective of the Presence of a Pulse of Organic Matter: Results from an In-Situ Experiment

A colonisation experiment was performed in situ at 2500 m water depth at the Arctic deep-sea long-term observatory HAUSGARTEN to determine the response of deep-sea nematodes to disturbed, newly available patches, enriched with organic matter. Cylindrical tubes,laterally covered with a 500 µm mesh, were filled with azoic deep-sea sediment and 13C-labelled food sources (diatoms and bacteria). After 10 days of incubation the tubes were analysed for nematode response in terms of colonisation and uptake. Nematodes actively colonised the tubes,however with densities that only accounted for a maximum of 2.13% (51 ind.10 cm−2) of the ambient nematode assemblages. Densities did not differ according to the presence or absence of organic matter, nor according to the type of organic matter added. The fact that the organic matter did not function as an attractant to nematodes was confirmed by the absence of notable 13C assimilation by the colonising nematodes. Overall, colonisationappears to be a process that yields reproducible abundance and diversity patterns, with certain taxa showing more efficiency. Together with the high variability between the colonising nematode assemblages, this lends experimental support to the existence of a spatio-temporal mosaic that emerges from highly localised, partially stochastic community dynamics

Effect of submerged structures on the diversity of macrozoobenthos in the Northern Adriatic Sea.

Offshore expoitation of oil and other hydrocarbons requires the installation of platforms or similar structures fixed to the sea bottom. Generally, such structures remain in situ for long time after the end of drilling and pruduction activities. The macrozoobenthic communities of a sea area located in the Northern Adriatic Sea sorrounding one of these platforms were studied on two occasions: the first prior to the installation of the platform (1985), the second 8 years later (1993), after production and other activities had terminated. On both occasions, sampling were performed according to similar sampling grids extended about 3.5. km from the platform site. Comparing the community composition of the two periods, a remarkable decrease of surface deposit-feeders was observed in the second period. Ordering techniques, applied to the entire data set of communities samples of both periods, pointed out not only the expected separation of the sampling points of the two periods but also a different patter of dispersion