Response of macro- and meiobenthos from a carbon-poor sand to phytodetrital sedimentation

Abstract

Sandy sediments are widely distributed in marine systems. However, little is known of the impact of large amounts of organic matter deposition on the infauna of these low organic-content sediments. The purpose of this study was to determine whether infauna, adapted to living in low organic-content sediments, are able to cope with the deposition of large amounts of organic material. In laboratory microcosms, the response of macro- and meiobenthos was examined at three levels of phytodetrital addition (0, 100 and 200 g C m −2) to the surface of a carbon-poor (0.4–0.5% C by weight) sand (median grain size, 325 μm). At 3, 12 and 28 days after phytodetrital addition, changes in macrofauna and meiofauna abundance and macrofauna biomass, were noted. Abundance and biomass of macrofaunal taxa were generally either unaffected at even the highest addition level or a positive response was observed at the intermediate level. Capitella spp. exhibited the most striking positive response in the 100 g C m −2 treatment. However, signs of potential population decline were observed at the highest addition level. Unlike the macrofauna, nematodes and total meiofauna decreased significantly in the 200 g C m −2 treatment. Harpacticoid copepods were unaffected by phytodetrital addition with evidence of a recruitment pulse observed in the 100 g C m −2 treatment. The population dynamics of infauna from some organic-poor sandy sediments are likely limited by processes controlling organic matter input or residence time within the sediment, with little adverse effect of increases in organic matter deposition noticeable unless input is extremely high.