Comparison of Palythoa tuberculosa-dominated and hard coral-dominated benthic communities in Okinawa, Japan

Coral reefs worldwide are experiencing rapid declines due to the effects of climate change and other anthropogenic stressors. Losses of scleractinian hard corals in these ecosystems can lead to shifts in community compositions. Tracking these shifts is necessary to understand the current and future states of coral reefs undergoing such rapid change. In Okinawa, Japan, Palythoa tuberculosa is a common zoantharian species that can dominate the benthos in and around coral reefs. This study compared the compositions of hard coral-dominated benthic communities with those of nearby P. tuberculosa-dominated benthic communities at three Okinawa coral reef sites, representing among the first such datasets from the Indo-Pacific. Image data were collected from each site, and percent covers of different benthic categories were estimated based on stratified random point counts. PERMANOVA showed that benthic community composition differed significantly (P < 0.0001) between sites, and between coral reef and P. tuberculosa patch areas within sites. Specifically, hard coral-dominated communities supported more benthic diversity than the P. tuberculosa-dominated communities, with the absence of macroalgae in P. tuberculosa-dominated communities, and lower cover of hard and soft corals. Hard coral-communities hosted more benthic categories than P. tuberculosa communities across all sites. Further research pinpointing the causes of shifts in benthic dominance could help predict future outcomes of these ecosystems, contributing to coral reef conservation.