Quantitative characterization of the polychaete communities and the impacts of dredged material disposal offshore from Tampa Bay, Florida

An investigation of the near-bottom water column and benthic habitats at one historical dredged material disposal site* one existing site* and at two proposed alternative sites located 7 to 20 nautical miles offshore from Tampa Bay* Florida was conducted during May 1982. One hundred macroinfaunal and sediment samples were collected at twenty stations in order to; (I) quantitatively characterize the polychaete communities and their relationships to environmental variables* and (2) assess the impacts of dredged material disposal.

The near-bottom salinities were euhaline and increased with increasing depth. The heterogeneous sediments were characterized by coarse to fine sands interrupted by patches of gravel* with the silt fraction increasing with increasing depth. The species diversity and density of the polychaetes decreased with increasing depth* increasing percent fines* and increasing sediment homogeneity* with the gravelly habitats generally supporting the most diverse communities. A synthesis of the environmental and community analyses results yielded six polychaete communities characteristic of the following habitats: (1) very gravelly sands* (2) coarse sands with seme gravel* (3) medium and fine sands in deep water* (4) fine sands in shallow water* (5) fine sands and silts in deep water* and (6) widespread across all habitats.

The polychaete communities at the historical site have completely recovered from dredged material disposal impacts since the cessation of disposal in 1973. Near the center of the existing disposal site* the accumulation of dredged material has buried the resident infauna. The polychaete community near the center of the existing site was characterized by opportunistic species in low numbers* indicating that the sediments were in the initial stages of recolonization.