Habitat partitioning by two coral-dwelling scorpionfishes in Hawai‘i

Coral reefs are among the most biodiverse ecosystems on Earth, largely due to the structural complexity created by corals. Coral habitat is crucial refuge for numerous small animals, and competition for habitat can structure populations if in short supply. Reefs in Hawai‘i are largely dominated by the small branching coral Pocillopora meandrina, which supports diverse communities of fishes and invertebrates. Two species of nocturnal scorpionfishes, Sebastapistes coniorta and S. galactacma, are particularly common in P. meandrina, inhabiting the complex branching morphology of their host corals during the day and feeding in and around these corals at night. Surveys of scorpionfishes in 458 P. meandrina between 3 and 22 m deep along the south and west shores of O‘ahu revealed inverse depth distributions over which these species occurred in P. meandrina. Sebastapistes coniorta almost exclusively occurred in coral colonies between 5 and 10 m deep, while S. galactacma were found across all depths surveyed, though were far more common and abundant in deeper coral colonies (15–20 m) below the range of S. coniorta. Further, measurements of host colony morphometrics revealed that these species appeared to use microhabitat in subtly different ways. The larger-bodied species, S. coniorta, was more commonly found in P. meandrina with wider spaces between branches, while the smaller-bodied species was negatively associated with wider branch spacing. These patterns indicate habitat partitioning between S. coniorta and S. galactacma at both the reef and colony scale, which may explain how these species are able to coexist on reefs in Hawai‘i.