Experimental evidence suggesting slow or weak response of nematode community structure to a large suspension-feeder

An experiment was carried out in a shallow, subtidal site in Mahurangi Harbour, New Zealand, to examine the effects of the large pinnid bivalve Atrina zelandica on benthic communities. Early on in the experiment, after 47 days, samples were taken specifically to examine the response of the meiofauna communities and particularly nematode assemblage structure to the presence of different densities of Atrina. Dead shell treatments were included in the experiment to discriminate between the, effects of the physical presence of Atrina and the effects of their biological activity. There were no observable effects of either different densities of Atrina or of the dead shell treatments on nematode assemblage structure. There were no consistent treatment-related effects on community structure of meiofaunal major taxa. A previous field study had shown that nematode communities differed inside and outside dense natural patches of Atrina. Data manipulations combined with the use of ANOSIM show that the experimental design was sufficiently powerful to have detected these differences if they had occurred in the experiment. Speculations on the current lack of the experimental effect include: (1) the meiofauna communities in field sites containing high densities of Atrina are structured by other factors (which may be coincidentally attractive to the Atrina) rather than by the presence or activities of the Atrina themselves; and (2) Atrina in natural patches may condition the sediment in some way that can affect the meiofauna, perhaps through alteration in flow regime which could affect sediment chemistry or through changes in biodeposit levels within the sediment, but these habitat alterations or the reaction of meiofauna to them do not occur within the 47-day time scale of our experiment. (C) 2001 Elsevier Science B.V. All rights reserved.