Temperature and Prey Availability Drive Seasonal Variations in Diet, Abundance and Condition of Forsterygion lapillum Across Two Coastal Habitats

ABSTRACT Environmental fluctuations in coastal waters have been increasing due to climate change and are likely to affect marine fish physiology and behaviour. Increases in temperature and turbidity can compromise food intake, body condition and abundance, among other vital traits. Environmental variations may also shape macro‐invertebrate community composition, which can lead to changes in food availability and feeding selectivity, given that they are a common food source for higher trophic levels. Both ocean temperature and turbidity are known to vary considerably from season to season, and different populations of a species can be locally adapted to varying environmental conditions. To address gaps relating to the influence of environmental variability on coastal fish populations, this study examines how temperature, turbidity and prey availability influence the diet, body condition and abundance of Forsterygion lapillum throughout the year in two neighbouring coastal ecosystems. We found seasonal and spatial variation in F. lapillum body condition, abundance, total gut volume and diet. Moreover, we found that F. lapillum body condition, abundance and total gut volume were positively correlated with warmer temperatures, while no clear patterns relating to turbidity were found. The macro‐invertebrate community was found to differ between areas and seasons. Our results suggest that prey quality varies seasonally across both study areas, and the composition of macro‐invertebrate community seems to drive F. lapillum diet and prey selectivity in these natural populations.