Vulnerability of newly settled red drum (Sciaenops ocellatus) to predatory fish: is early-life survival enhanced by seagrass meadows?

Abstract

We conducted predation experiments to evaluate the vulnerability of red drum Sciaenops ocellatus (Linnaeus) larvae and early juveniles to pinfish Lagodon rhomboides (Linnaeus) predators. Experiments were designed to analyze the effects of habitat complexity, prey size, and rearing condition on prey vulnerability. Three structurally different habitats [unvegetated (substrate only), shoal grass Halodule wrightii (Aschers) and turtle grass Thalassia testudinum (Bank ex König)] were simulated in experimental mesocosms. Instantaneous hourly mortality rates (Z h⁻¹ predator⁻¹) for hatchery-reared red drum were significantly higher in the unvegetated habitat (0.189) than in either shoal grass (0.069) or turtle grass (0.046). A similar trend in predation mortality was observed for wild-caught red drum; instantaneous hourly mortality rates were 0.166, 0.047, and 0.021 in unvegetated, shoal grass, and turtle grass habitats, respectively. Mortality rates (adjusted means) for hatchery red drum were higher than for wild individuals in all three habitats; however, the differences were not significant. Predation mortality decreased with increasing prey size (3 to 9% decrease in Z per mm increase in length), suggesting that small red drum (i.e. new settlers) were most vulnerable to predators. We conclude that habitat complexity is critical to the survival of newly settled red drum, and changes in the complexity or areal coverage of natural seagrass meadows may affect early-life survival and possibly recruitment levels.