The distribution of benthic infauna of a Texas salt marsh in relation to the marsh edge

Coastal salt marshes in the northern Gulf of Mexico are often highly fragmented, with a large amount of marsh edge, the interface between the vegetated marsh surface and shallow open water. Nekton predators, including many juvenile fishery species, aggregate near this marsh edge, and benthic infaunal populations are a primary source of prey for many of these predators. We examined the fine-scale (1–10 m) distributions of benthic infauna in relation to the edge of a Texas, USA salt marsh. Every six weeks for nearly a year, we sampled marsh sediments at five locations: on nonvegetated bottom 1 m from the marsh edge and on the vegetated marsh surface at 1, 3, 5, and 10 m from the edge. Surface-dwelling annelid worms and peracarid crustaceans were most abundant in low-elevation sediments near the marsh edge for most sampling periods. Because the marsh slope varied within the study area, we could distinguish between correlative relationships with elevation and distance from the marsh edge. Distributions of common surface-dwelling species were often unrelated to elevation but almost always negatively related to distance from the marsh edge. Abundances of near-surface direct deposit feeders and omnivores were related to both distance from edge and elevation. In contrast to surface dwellers, densities of abundant subsurface deposit feeders (mainly oligochaetes) were frequently greatest in sediments located away from the marsh edge. Surface and near-surface dwelling infauna are an important prey resource for nekton, including many juvenile fishery species that concentrate near the marsh edge. Populations of these infaunal prey fluctuated seasonally, with the greatest densities occurring during winter and early spring when predator abundances are generally low. Infaunal densities decreased dramatically near the marsh edge from the late spring through early fall, and this decrease coincides with historically high seasonal densities of nekton predators. Our data suggest that there is a strong trophic link between infauna and nekton near the marsh edge and that this relationship contributes to the high fishery productivity derived from Gulf Coast marshes.