David M. Knott

Invertebrate communities associated with hard bottom habitats in the South Atlantic Bight

Abstract Epibenthic invertebrates associated with nine hard bottom areas in the South Atlantic Bight between South Carolina and northern Florida were collected with dredge, trawl, suction and grab samplers to evaluate species composition, biomass, abundance, diversity, spatial distributions, and seasonality (winter and summer). Species composition changed noticeably with depth and season. Inner and outer shelf stations were least similar in species composition. Middle shelf areas were transitional and contained taxa characteristic of both inner and outer sites. Bryozoa (88 taxa), Cnidaria (85 taxa), Porifera (67 taxa), Annelida (261 taxa) and Mollusca (203 taxa) represented the richest taxonomic groups of the 1175 taxa collected. Both diversity (1175 total taxa) and biomass (1995 kg total) of invertebrates from hard bottom areas exceeded those reported in the literature for sand bottom communities. Sponges accounted for >60% of the total invertebrate biomass collected by dredge and trawl during both seasons. High diversity values were attributed primarily to habitat complexity and did not exhibit any discernible pattern with depth or latitude.

Effects of pipeline construction on the vegetation and macrofauna of two South Carolina, USA salt marshes

We examined the recovery of vegetation and salt marsh macrofauna in a pipeline construction corridor at two locations where it intersected intertidal salt marshes near Charleston, SC. The impacts of construction were evaluated prior to construction and for subsequent periods of 34 and 46 months at the two sites using aerial photography and three field sampling methods. Quadrats were used to estimate densities of selected salt marsh invertebrates, as well as stem densities and aboveground wet-weight biomass ofSpartina alterniflora; pit traps were employed to simulate natural tidal pools for sampling small, motile epibenthic macrofauna that remained on the marsh surface at low tide; and flume nets were used to sample the natant macrofauna that used the marsh edge at high tide. The analyses of vegetation by quadrat and aerial imagery clearly showed that the recovery ofSpartina was more rapid and complete at the Ashley River site (88%) than at Wappoo Creek (48%). In contrast to this apparent, if partial, vegetative recovery, several salt marsh invertebrates, including,Littorina irrorata andGeukensia demissa, were eliminated from the corridor during construction and showed scant recovery by the end of our study. Differences in species composition and abundance of natant organisms in the flume net collections also supported the conclusion that faunal recovery was incomplete after 3–4 years at these sites. The recovery of functional equivalency of the excavations, compared with natural marshes, was not evaluated during our study, but we speculate that their functioning may equilibrate over time, since preexisting hydrologic conditions are more or less intact, seedstock forSpartina revegetation is nearby, and macrofauna will probably eventually reestablish themselves from adjacent areas.