Low trophic redundancy among temperate wrasse species implies ecosystem risks associated with a multi-species inshore fishery

Abstract

Understanding levels of resource-use overlap or trophic redundancy both within and between species can help predict ecosystem-level impacts of fishery removals and ultimately help define management priorities to preserve ecosystem function. Here, we use stable isotope analysis to investigate inter- and intra-specific variation and overlap in resource use among co-occurring temperate wrasse (Labridae) species. We use the results as a first step to predicting the potential for ecosystem-level impacts of the recently developed multi-species inshore fisheries for live wrasse in England and Scotland. We highlight the likely importance of the primary target species (ballan wrasse), particularly individuals of a landable size, to maintaining the overall function of inshore reef ecosystems, evidenced by the unreciprocated resource use overlap that this species provides for other wrasse species. We also highlight that trophic redundancy is typically low both between and within wrasse species, suggesting that the maintenance of both species diversity and demographic structure of wrasse populations should be a priority when developing fishery management measures. Live wrasse fisheries operate within various marine protected areas (MPAs) across the south coast of England and in Scotland. An overarching aim of ecosystem-based fisheries management, particularly within MPAs, is to support diversity and redundancy within an ecosystem to help maintain resilience to future perturbations. Our study provides some of the first quantitative evidence to support the classification of wrasses (particularly ballan and corkwing) as influential species—defined as having a key role affecting the structure and function of the habitat—within MPAs designated for reef habitats.