Geographical and depth-related patterns in nematode communities from some Italian Marine Protected Areas.

A study on the meiobenthic nematode assemblages from three Italian Marine Protected Areas (Miramare, Adriatic Sea; Porto Cesareo, Ionian Sea; and Capo Caccia, Western Mediterranean Sea) was carried out at three different depth ranges from the low intertidal to the shallow subtidal. Nematode community composition was analysed at the genus level, and diversity and taxonomic distinctness were studied to detect possible differences among the MPAs and between intertidal and shallow subtidal zones. There were differences in granulometric variables between sampling depths: medium and coarse fractions were often dominant in the sites at the low intertidal and shallow subtidal, while very shallow subtidal sites were characterised by fine and very fine sand. Nematode densities and diversities were generally high in all sampling areas. Nematode communities changed when different depths were compared. This was due to a decrease in deposit-feeding nematodes coupled with a higher abundance of predators and epigrowth feeders with increasing depths, from the low intertidal to the shallow subtidal. The shallow subtidal is characterised by the presence of a stout nematode community (Length/Width ratio <15) dominated by Epsilonematidae (39%), Desmoscolecidae (16%) and Selachinematidae (9%). The high dominance of the epsilonematids is probably due to the occurrence of coarse sediments. Our study also reveals a possible relationship between body proportions and feeding groups. Changes in depth and sand grain size do not seem to cause drastic variations of diversity. Both Δ+ and Λ+ seem to be more sensitive than other diversity indices in discriminating among different sites, as a consequence of different environmental physical features. The concept of isocommunities might explain the similarities found in the three Italian Marine Protected Areas nematode assemblages; in fact, the same dominant families and genera were recorded in geographically spaced sites at similar depth ranges. [ABSTRACT FROM PUBLISHER]