Olfactory discrimination in juvenile coral reef fishes: Response to conspecifics and corals

Coral reef fish use olfaction to respond to a variety of chemical cues that allow them to detect predators, the presence of resident conspecifics and the ‘smell’ of reef water. However, whether olfaction is utilised by juvenile reef fish for discerning among the multiple microhabitat types present on the reef is not known. Additionally the relative importance of chemical cues emitted from habitat types versus those from resident individuals to juveniles has not been assessed. The ability to distinguish and use such cues could be critical in determining spatial distributions of juveniles across coral reef areas. Here we test olfactory preferences for conspecifics, coral health and different branching coral species in newly recruited juveniles of coral reef fishes. Newly settled juveniles of three common coral associated species in Kimbe Bay, Papua New Guinea, Dascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatus, were subjected to a series of pairwise olfactory choice tests using two-channel choice flume. All three species exhibited a significant preference for the scent of conspecifics (60–70%) and live coral (60–70%) over water with no associated reef cues. All species strongly avoided the odour of degraded coral (≥ 80%). Only one species, D. melanurus showed olfactory discrimination among branching coral species, favouring Pocillopora damicornis over Acropora spp. Our results indicate that olfactory preferences for both conspecifics and live coral may combine to determine juvenile and recruitment distribution patterns in these species and local population declines in response to coral degradation but do not necessarily contribute to specific coral habitat associations.

► Juvenile reef fish were subjected to pairwise olfactory choice tests.
► Cues tested included conspecifics, live vs. dead coral and branching coral genera.
► All species exhibited a strong preference for conspecifics and live coral.
► A strong avoidance of the odour of dying coral was apparent.
► Dascyllus melanurus was the only species to discriminate among branching corals.