Oyster predation by black drum varies spatially and seasonally

Oyster reefs (Crassostrea virginica) supply important ecosystem services to estuarine habitats in the northern Gulf of Mexico, but little is known of the role of fish predators in controlling their structure or areal cover on soft sediments. At two sites and during fall and spring, we employed gill nets and trot lines to remove black drum (Pogonias cromis) from experimental reefs, and assessed oyster survival in comparison to control reefs. Numbers and biomass of black drum removed from reefs varied seasonally, among sites, and among removal methods. In the fall, black drum were rare at one site and abundant at the other, but did not significantly lower oyster survival on control reefs at either site. In the spring, black drum were common at both sites, and significantly lowered oyster survival on control reefs. Oysters and epizoic hooked mussels comprised roughly a third of the fishes' diet, and oyster mortality was closely related to the percentage of drum feeding on oysters. There was little evidence of mortality from other predators of seed oysters like stone crabs or Southern oyster drills, and a repeated measures analysis of variance indicated black drum biomass was significantly depressed on experimental reefs during the experiments. Black drum thus appear to be potentially important predators on oyster reefs, but more work needs to be done on what factors explain the temporal and spatial variation in their abundance and oyster consumption.