Trophic function in estuaries: response of macrobenthos to natural and contaminant gradients

Trophic ecology of macrobenthic communities in estuaries of the northern Gu lf of Mexico was used to infer community function, determine effects of con taminants on macrobenthos, and provide insight into community responses fol lowing disturbance. The taxa that numerically dominated the region included few large, deep-burrowing suspension feeders that typify estuaries elsewhe re. This pattern is indicative of disturbance, and results in dominance by trophic groups that live near the sediment-water interface (early benthic-c ommunity succession). Trophic structure was significantly related to severa l sediment contaminants (especially metals, polynuclear aromatic hydrocarbo ns, DDT), and three environmental gradients (salinity, depth, and sediment silt-clay content). Generally trophic diversity increased and proportion of subsurface-deposit feeders (SSDF) decreased with salinity, meaning that a more even distribution of trophic structure was found at high-salinity stat ions. The trophic shift toward dominance by shallow, subsurface-deposit feeders i n contaminated habitats may have dire implications for fisheries. Several i mportant commercial and recreational fisheries of the region depend on fish that feed primarily at the sediment surface. Higher proportion of subsurfa ce-deposit feeders, coupled with low macrobenthic density in contaminated s ediments, may imply that limited energy is transferred to higher trophic le vels.