Habitat use and ontogenetic shifts of fish life stages at rocky reefs in South-western Mediterranean Sea

The present study aimed at exploring the habitat use by fish life stages and ontogenetic shifts in a South-western Mediterranean rocky reef. The relation with rocky reef habitat structure (complexity, heterogeneity, total cover and depth) was visually surveyed on a monthly basis, in four locations and during one year, for the abundance of young-of-the-year (YOY) and juvenile reef fish. Fish assemblage responded significantly to spatial and temporal variations of structural microhabitat, this response being species-specific. Abundance of fish life stages was directly related to temperature variation, with higher abundances occurring on warmer months. Also, habitat differences occurred between YOY and juveniles of a series of species from shallow steeper rocky habitats to deeper complex rocky bottoms with high total cover. Spatial differences in YOY and juvenile abundance across locations could be attributed to fine-scale habitat preference, from purely rocky, more complex sites, with greater slopes and depths, to sites harbouring more heterogeneous habitats. By characterising the microhabitat association of fish life stages (both YOY and juveniles), and identifying for what species this influence may interfere with spatial and temporal patterns, the present study can be used as a basis for pluriannual monitoring of fish recruitment success in the area in order to better understand their population dynamics.