Effects of summer 2003 hypoxia on macrobenthos and Atlantic croaker foraging selectivity in the northern Gulf of Mexico

Abstract

Bottom-water hypoxia (≤ 2 mg O 2 L − 1 ) occurs on an annual basis on the northern Gulf of Mexico continental shelf from mid-May through mid-September over a large area (up to 22,000 km 2 in mid-summer). We predicted that when Atlantic croaker migrated away from hypoxia to inshore and offshore areas their available benthic infaunal prey would differ within and outside of the hypoxic zone, i.e., with lower density and diversity in the region exposed to hypoxia. Benthic infaunal densities during August 2003 hypoxia were not significantly different among the inshore, hypoxic and offshore areas. However, species richness within the hypoxic zone was lower than offshore but not inshore of the hypoxic zone. Hypoxia effects on benthic communities were likely diminished by two tropical storms that mixed the water column during the month prior to our sampling. Benthic communities were dominated by polychaetes and mollusks, two important prey items for demersal fishes. Atlantic croaker stomach contents were dominated by small polychaetes and small crustaceans in proportions similar to benthic communities, which are consistent with opportunistic feeding. The effects of hypoxia on benthic density and composition that may alter the availability of food resources to benthic foragers were difficult to detect in this summer of moderate hypoxia.