Investigating the cumulative effects of multiple stressors on fish assemblages in a semi-enclosed bay

Abstract

The growing intensity of anthropogenic activities has led to an increase in the number of studies assessing the effects of stressors on marine ecosystems. Yet, the cumulative effects of multiple stressors are rarely studied although they seldom operate in isolation of each other. Our study aimed to investigate the effects of multiple stressors on fish assemblages in a series of semi-enclosed bays. We quantified fish assemblages using baited remote underwater video across five sites with varying environmental and anthropogenic stressors. We also sampled across two seasons and in protected and unprotected areas. We found that fish assemblages were most influenced by effluent input and aquaculture, but not fishing pressure. Relief, season, salinity, and pH were also included in the best model highlighting the importance of environmental variables in structuring fish assemblages. Total abundance was not affected by anthropogenic stressors but individual species showed variable responses from reduced abundance (e.g. Neoodax balteatus and Cyanea rosella) to increased abundances (e.g. Arripis spp.). We found no evidence that increased number or intensity of stressors affected overall fish abundance or diversity. Our findings highlight the diverse effects anthropogenic stressors can have on fishes with both environmental and anthropogenic influences playing a role in structuring fish assemblages over both short temporal and spatial scales.