Habitat Influences on Feeding Ecology of Red Snapper

Artificial reefs in the Gulf of Mexico are well known aggregators of reef-fish, including red snapper (Lutjanus campechanus), which supports a valuable commercial and recreational fishery.  However, there is little known about how these reef structures function in the overall life history of red snapper and other reef-associated species.  Previous research has indicated that little nutrition is derived directly from small low-relief artificial reefs; rather the majority of the prey comes from surrounding soft bottom habitat.  However, the Gulf of Mexico also has approximately 3500 oil and gas platforms that act as large high relief artificial reefs that provide substrate for the entire water column.  In previous years, many of these structures had been modified and converted into artificial reefs upon decommissioning.  From a management perspective, it is important to determine how these structures function in the ecology of red snapper, and whether or not the conversion of decommissioned platforms is beneficial to the associated reef fish assemblage.  The goal of this study is to determine if there are differences in the feeding ecology of red snapper between standing oil and gas platforms, and toppled platforms designated as artificial reefs.  Fish from these habitats were also contrasted with those collected over natural reefs on the continental shelf edge.  A combination of gut content analysis and stable isotope analysis was conducted to determine trophic ecology of red snapper at the three habitats.  Preliminary results indicate that fish dominated the diets at all three sites, but that pronounced differences exist in the contribution of major prey items by percentage dry weight between the all three habitats.  Red snapper collected from standing platforms consumed primarily antennae codlet (Bregmaceros atlanticus), as well as squid, shrimp, and other crustaceans.  At the toppled sites red snapper consumed a large percentage of Bathyal swimming crab (Bathynectes longispina), squid, shrimp, and other crustaceans.  On the natural reef habitat antennae codlet and lizardfish (Synodontidae) dominated diets, with only minor contribution from other prey items.  Results of the stable isotope analysis suggest that fish collected over the standing platforms are more enriched in d¹⁵N, implying red snapper may be feeding at a higher trophic level than the other sites, while fish collected over the toppled platforms were more depleted in d¹³C, possibly indicating more contribution from benthic algae as a basal resource.