Habitat associations of coastal fish: seasonal dynamics of characteristic species and nursery function

Understanding associations between marine organisms and coastal habitats has become pivotal in the light of anthropogenic and environmental stressors threatening coastal systems. Yet, the importance of coastal habitats for fish communities has mostly been examined in few selected habitats and, predominantly, for commercially used fish species. Based on an extensive field data set, we identified characteristic fish species for 5 widely distributed coastal habitat types in a temperate marine system, and examined seasonal occurrence patterns of these species. The nursery function of the habitats was assessed based on juvenile fish densities. Characteristic species were found for 4 habitats, and pronounced seasonal abundance fluctuations were detected for the majority of these species. Rocky reefs were inhabited year-round by species favouring structurally complex environments, goldsinny-wrasse and shorthorn sculpin, while blue mussel beds were characterized by various goby species and cod, presumably attracted to this habitat by the rich food resources. Small sandeel, sand goby and small-sized plaice typically occurred on bare sand, with particularly high densities of small sandeels between spring and early summer. Various pipefish, stickleback and goby species were highly abundant in seagrass meadows during the summer and autumn months. Juveniles of several fish species relied on multiple habitats as nurseries, with the majority utilizing sand, blue mussel or seagrass habitats. Study outcomes indicate potential functional connectivity among coastal habitats, simultaneously underlining strong habitat associations of certain species, and can contribute to identifying essential fish habitats requiring particular attention with regard to management and conservation measures.