Distribution patterns of meiofauna and free-living nematodes in beaches of a remote tropical South Atlantic Island (Trindade, Brazil)

Abstract

Characterizations of meiofauna, as well as of Nematoda assemblages, are rare in oceanic islands due to logistical difficulties and, until now, no study on the vertical distribution of this fauna has been conducted in these environments. Therefore, this study shows vertical distribution patterns in the meiofauna community and Nematoda assemblage on two beaches with different sediment characteristic (volcanic and carbonate) of Trindade Island, a remote oceanic island in the Atlantic Ocean. Samples were collected in December 2014 at Príncipe and Portugueses beaches in three intertidal zones (high, mid-, and low) at two sedimentary column depths (0–10 and 10–20 cm). Overall, meiofauna was comprised of seven major groups, with Oligochaeta (57%) and Nematoda (12%) as the most abundant. Higher density and richness of meiofauna and Nematoda assemblage were found at Portugueses beach with the carbonate sediment. Nematoda assemblage was mainly comprised of non-selective deposit-feeders, with a total of 27 genera and 12 families; Cyatholaimidae and Xyalidae were the most abundant and had the highest diversity. Composition and density of meiofauna and Nematoda assemblage showed similar vertical distribution where the surface layer (0–10 cm) presented lower densities. Sediment characteristics (grain size, sorting, and composition) were primarily responsible for the regulation of the structure and distribution of meiofauna and Nematoda assemblage in Trindade Island beaches.