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

Abstract

Trophic ecology of macrobenthic communities in estuaries of the northern Gulf of Mexico was used to infer community function, determine effects of contaminants on macrobenthos, and provide insight into community responses following disturbance. The taxa that numerically dominated the region included few large, deep-burrowing suspension feeders that typify estuaries elsewhere. This pattern is indicative of disturbance, and results in dominance by trophic groups that live near the sediment–water interface (early benthic-community succession). Trophic structure was significantly related to several sediment contaminants (especially metals, polynuclear aromatic hydrocarbons, 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 stations. The trophic shift toward dominance by shallow, subsurface-deposit feeders in contaminated habitats may have dire implications for fisheries. Several important commercial and recreational fisheries of the region depend on fish that feed primarily at the sediment surface. Higher proportion of subsurface-deposit feeders, coupled with low macrobenthic density in contaminated sediments, may imply that limited energy is transferred to higher trophic levels.

Soft-Bottom macrobenthic communities of the Vitória Bay estuarine system, South-eastern Brazil

“…All stations, except station 8, showed that molluscs were the dominant group, primarily M. falcata and M. guyanensis at the intertidal inner-bay stations and A. brasiliana at the subtidal station 10. This contrasted strongly with studies from the Gulf of Mexico estuaries (Gaston et al, 1998) showing crustaceans and gastropods as dominant in waters of high oxygen content (>2.0 mg.l -1 ) and polychaetes in low DO areas (<2.0 mg.l -1 ). M. guyanensis is able to survive in extremely adverse conditions and is tolerant of fluctuating salinities (Nishida & Leonel, 1995).…”

“…4 or 7) (Tables 3 and 4). In contrast to what might have been expected (Harrel & Hall, 1991;Gaston et al, 1998;González-Oreja & Saiz-Salinas, 1998), the least diverse and most depauperated area (station 9) is located only 1 km from the richest and most diverse (station 10; Fig. 1; Tables 3 and 4).…”

“…These organisms alter the physical and chemical conditions at the sediment-water interface, promote the decomposition of organic matter, recycle nutrients for photosynthesis, and transfer energy to other food-web components (Gaston et al, 1998).…”

Spatial Patterns in Diversity and Distribution of Benthic Molluscs in a Weak Tidal Tropical Lagoon

“…Mollusc diversity followed the salinity gradient, with the highest diversity in the downstream stations which were mostly influenced by marine intrusion, and decreasing towards upstream. Community composition gradually changes according to the salinity gradient of the lagoon, a trend similar to those reported in Gaston et al (1998) and Giberto et al (2004). Species (M. edulis, M. perna and C. gazar) known to be intolerant of wide fluctuations in salinity were restricted to station seven where a higher and relatively stable salinity was recorded, this observation has also been reported in other estuarine systems (Oyenekan, 1988).…”

Review and evaluation of estuarine biotic indices to assess benthic condition

“…Nonetheless, for this particular case three submetrics seem to be the most important: pollution indicative taxa, pollution sensitive taxa, and diversity. The subsurface deposit feeders species are considered the trophic group most likely to develop pollution tolerance (Gaston et al, 1998), since they inhabit tubes or burrow beneath the sediment surface (Pinn and Robertson, 2003). In the euhaline estuarine stations there was a relative increase of these species, followed by a diversity (H 0 ) increase and a decrease of the percentage abundance of pollution sensitive species.…”