Processes affecting macrofaunal community structure in sandy sediments on the New Jersey inner continental shelf with a focus on the dominant polychaete, Polygordius jouinae.

摘要

Continental shelves contain a rich array of habitats that appear significant for macrofauna and play an essential role in managing living resources. Yet, many habitats have not been adequately defined or quantified, temporally or spatially. Macrofaunal communities were examined at spatial and temporal scales within the context of known distributions of topographic habitats and associated sediment properties on the shelf off New Jersey, USA (39° 28' N, 74° 15' W). Focusing on a dominant polychaete, species identification and natural history information, together with manipulative experiments on behavior and habitat selection, provided a multi-pronged approach to research. Nested sampling designs were employed. Samples taken at large-spatial scales (m-km) showed that community differences were most pronounced among sampling dates, however, on any single date differences were related to crests and troughs in the rippled sandbeds. At small-scales (cm-m) community patterns and sediment properties corresponded with crests, flanks, and troughs. Concentrations of organic matter associated with finer sediments in troughs were ∼1.2 times higher than in crests and flanks. Density of P. jouinae Ramey, Fiege and Leander, 2006, was higher in troughs than in crests. This species appears to thrive in sandy sediments from Massachusetts to southern New Jersey. The reproductive period occurred from May-August. Individuals that spawn, live for one year. Recruitment begins no later than July. The smallest individual was 2.01 mm long providing an estimate of size at initial recruitment. It was hypothesized that heterogeneity in organic matter generated by rippled beds may influence small-scale distribution patterns of P. jouinae . In a racetrack flume under realistic flow, almost all P. jouinae moved through the sediment to patches containing higher amounts of organic matter in 48-h. Subsequent experiments showed that locating organic patches was not the consequence of a directed search. Rate of movement indicated that P. jouniae could potentially travel the wavelength of a typical ripple (14-30 cm) in 35-75 min. Thus subsurface movement is a plausible mechanism accounting for the similar small-scale spatial distributions of P. jouinae and food resources. This research reveals the fundamental influence of topographic differences in habitats on a member of the benthic macrofaunal community.