Cascading effects of top predator changes in a seagrass bed under selective fishing

Abstract

Abstract Background With the widespread promotion of selective fishing which may target top predatory fishes, the abundance and species composition of top predators could change, which may further impact species at lower trophic levels through a chain of cascading trophic interactions. However, the top-down effects of changes in predator communities driven by selective fishing remain poorly investigated. Methods Focusing on a seagrass ecosystem, we investigated how changes in two coexisting top predators (Lateolabrax japonicus and Acanthogobius ommaturus) under different selective fishing scenarios would affect species at lower trophic levels in a field manipulative experiment. Results We found that the trophic niches of A. ommaturus and L. japonicus overlapped greatly, although not completely. If loss of L. japonicus led to increases in A. ommaturus, the abundances of herbivorous benthos Barleeia bureri increased likely owing to A. ommaturus’s suppression of low-level predators, while epiphyte and seagrass biomass decreased significantly likely owing to A. ommaturus’s disturbance of seagrasses and sediments. If both predators were depleted, the biomasses of herbivorous benthos Cyclina sinensis and B. bureri increased significantly likely owing to the absence of top predators’ disturbance of sediments, while epiphyte and seagrass biomass did not change. Conclusions Our study showed that loss of one top predator could lead to rapid changes in species at lower trophic levels in seagrass beds, depending on changes in, and the trophic or non-trophic effects (including biological disturbances) of, its competitors. Therefore, in fisheries resource management, the ecological impacts of selectively fishing a target predator must be managed considering changes in, and the trophic or non-trophic effects of, its competitors where present.

Keywords

• Top-down effect
• Top predator
• Trophic niche overlap
• Seagrass bed
• Selective fishing