From traits to life-history strategies: Deconstructing fish community composition across European seas

Aim: The life history of a species is determined by trade-offs between growth, survival and reproduction to maximize fitness in a given environment. Following a theoretical model, we investigate whether the composition of marine fish communities can be understood in terms of a set of life-history strategies and whether the prevalence of the strategies follows specific spatial patterns that can be related to the environment. Location: European seas. Time period: 1980-2014. Major taxa studied: Fish. Methods: An extensive set of scientific bottom trawl surveys was collected to obtain the species composition of fish communities across European seas. We complemented these data with species-specific information regarding six life-history traits, reflecting reproductive, growth and feeding modes. We then calculated the optimal number of strategies needed to summarize the information contained in the traits by using archetypal analysis. The proportion of each obtained strategy in the communities and their spatial patterns were explained as a function of the environment and their temporal changes were investigated. Results: The species could be decomposed into a continuum of three life-history strategies-opportunistic, periodic and equilibrium-resulting from trade-offs between traits. The marked spatial patterns of these strategies could be explained by depth, temperature and its seasonality, chlorophyll and fishing effort. In recent years, opportunistic and equilibrium strategies significantly increased, probably due to an increase in temperature and decrease in fishing effort. Main conclusions: Our empirical analysis supports a theoretical framework outlining three life-history strategies of fish. The strategies vary predictably in space and time in response to the environment. This highlights the underlying process whereby fitness is optimized through trade-offs between growth, feeding and reproduction under different environmental conditions. Due to their response to the environment, life-history strategies provide a suitable tool for monitoring and understanding community changes in response to natural and anthropogenic stressors, including fishing and climate change.