Shallow rocky nursery habitat for fish: Spatial variability of juvenile fishes among this poorly protected essential habitat

Coastal nursery habitats are essential for the renewal of adult fish populations. We quantified the availability of a coastal nursery habitat (shallow heterogeneous rocky bottoms) and the spatial variability of its juvenile fish populations along 250km of the Catalan coastline (France and Spain). Nurseries were present in 27% of the coastline, but only 2% of them benefited from strict protection status. For nine taxa characteristic of this habitat, total juvenile densities varied significantly between nursery sites along the coastline, with the highest densities being found on the northern sites. Recruitment level (i.e. a proxy of nursery value) was not explained by protection level, but it was moderately and positively correlated with an anthropization index. Patterns of spatial variations were taxa-specific. Exceptional observations of four juveniles of the protected grouper Epinephelus marginatus were recorded. Our data on habitat availability and recruitment levels provides important informations which help to focus MPA management efforts. •A very small portion of essential nursery habitats for coastal fish are under protection.•Juvenile densities among nurseries varied in space but not as a function of protection level.•Juvenile densities were moderately and positively correlated with an anthropization index.•Juvenile densities displayed contrasting spatial patterns according to the taxa.•Juvenile E. marginatus, unseen in the last 20years, were seen in four sites in 2015.