Effects of beach seine fishing on the biodiversity of seagrass fish assemblages

Seagrass systems provide a wide range of services, contributing to the maintenance of biodiversity in other systems through habitat connectivity. However, they are severely exposed to anthropogenic influence, overfishing being one of the most pervasive impacts. The effects of fishing on the functioning of seagrass ecosystems is, however, understudied. We analyzed the effects of beach seining on fish assemblages in seagrass meadows with distinctive fishing pressures, comparing for changes in abundance, diversity and functional roles. Three effects escalated with increased fishing: (1) the reduction in the total abundance of fish; (2) decreased diversity, with selective reduction of rare species; and (3) impoverishment of potential functional roles. Abundance was remarkably decreased by fishing and highly fished sites presented four times less species. A gradual reduction of predatory species was associated with the increment of beach seining, while greater variability of functions performed by fish was observed when fishing was lowest. When fishing pressure is highest, the few remaining species have similar functional traits, reducing the potential ecosystem role of fish communities. Management actions should include limitations to beach seining and the alternative use of more sustainable gears to maintain ecological and economic services provided by fish. •Sites within a gradient of fishing pressure were compared for changes in fish fauna.•Beach seining reduced the total number of individuals in fish assemblages.•Rare species were removed first, leading to losses of distinctive functional traits.•The potential ecosystem role of fish communities was reduced under intensive fishing.•Limitations to beach seining and the use of more sustainable gears is recommended.