COMPETITION AND RESOURCE PARTITIONING BETWEEN CONGENERIC CORAL- DWELLING SCORPIONFISHES (SEBASTAPISTES SPP.) IN HAWAI‘I

Abstract

Exposed coral reefs in Hawai‘i are largely dominated by the small branching cauliflower coral (Pocillopora meandrina), which supports diverse communities of fishes and invertebrates. Two of the most common fishes that reside in these corals are the Speckled Scorpionfish (Sebastapistes coniorta) and the Galactic Scorpionfish (S. galactacma). These small nocturnal reef mesopredators use the complex branching morphology of cauliflower coral as protection during the day and feed in and around their host corals at night. Despite their apparent ecological similarities, these species coexist locally, at times even co-occupying the same host coral. Surveys of cauliflower coral communities around O‘ahu revealed inverse depth distributions, with Galactic Scorpionfish found across all depths surveyed, though more commonly in deeper reef areas (> 11 m), while Speckled Scorpionfish almost exclusively occurred in shallow reef areas (5 – 10 m deep). These species also used microhabitat in subtly different ways, with the larger species (Speckled Scorpionfish) being more associated with coral colonies with wider spacing between branches. Reciprocal removal experiments across depths, among clusters of corals, and within individual colonies suggest that competition between these species is not currently occurring, and recolonization experiments showed that colony characteristics played a large role in determining which species recolonized corals. Diet analyses using both visual examination and DNA metabarcoding of stomach contents revealed that Speckled Scorpionfish and Galactic Scorpionfish have minimally overlapping diets with significantly different compositions, though both species typically consume small crustaceans that co-occur with them in cauliflower corals. Further, the diets of these species did not significantly differ whether they co-occurred or not, suggesting that these species have evolved different diets, possibly due to past competition. Thus, these species partition food and microhabitat resources to a degree that presently allows for their coexistence on reefs in Hawai‘i.