Are fish associations with corals and sponges more than an affinity to structure? Evidence across two widely divergent ecosystems

Abstract

The role of deep-sea coral and sponge ecosystems as habitat for marine fishes has been widely studied, with many finding significant associations, especially for rockfishes. However, rockfishes also thrive in areas largely devoid of corals and sponges. We compared the use of deep-sea corals and sponges by fish species in two ecosystems. Rockfishes (Sebastes spp.) and Pacific cod (Gadus macrocephalus) densities were significantly correlated to structured seafloors at the scale of transects across both regions. Regional effects were not significant for most rockfish species and Pacific cod. At smaller scales only Pacific cod and rockfishes had significant associations with structure. The size of the individual fish and the size of the structure both had significant impacts on the distance of fish from structure, with smaller fish closer to structure and closer to smaller structure. Over half of the individual fishes surveyed were associated with sponges. The implication of this research is that the presence of structure increases the density of rockfishes, and removal of deep-sea corals and sponges is likely to reduce the overall density of rockfishes.