Disentangling the effects of resource level and temperature dependence on the performance of fish in different guilds.

The ability to predict how fishes respond to changes in temperature and resource variability is paramount to developing sustainable management plans and for projecting the direct and indirect effects of climate change. We developed a versatile, physiological model capable of providing size-specific estimates of fish growth and fecundity across varying temperatures and resource levels. The model includes a mechanistic representation of individual-level life history processes across diverse biogeographic and functional fish guilds, using direct, species-specific parameter estimates. We demonstrate its application to five marine species (Atlantic cod, Atlantic herring, five-bearded rockling, European sprat and thinlip mullet), which differ in life history strategies and biogeographic distributions, but all rely on intertidal nursery habitats-areas particularly susceptible to anthropogenic change. In all simulations, resource availability had a stronger influence on fish performance than temperature. Nevertheless, the model also revealed how and why higher temperatures often decreased fitness and/or survival of specific types of species. We made no changes to the model structure for different species, and the resulting model predictions were not fitted but were based on eco-physiological first principles. Comparison between modelled and empirical data collected in the shallow Wadden Sea (southern North Sea) confirmed benefits of warming to thermophilic, range-expanding species, while core (established) species at their lower latitudinal limits of their distribution face local extirpation. The model allows insight into more variables than often reported from survey and monitoring efforts, such as reproductive output. The model's broad applicability across a range of species, geographic regions and research objectives makes it valuable for generating knowledge needed to buttress actions aimed at addressing ecological and conservation challenges in a future climate.