Investigating incidence and possible causes of pink and purple pigmentation response in hard coral genus Porites around Okinawajima Island, Japan

Abstract

Porites is a major reef building coral genus within coral reef ecosystems, and massive Porites are known to be comparatively resistant to changes in water temperature and pH, and to other environmental disturbances. Pink pigmentation response has often been reported in massive Porites. In this study, around Okinawa, Japan, we not observed only pink but also purple pigmentation response on massive Porites. As there have been few ecological studies investigating the prevalence of these pigmentation responses, we examined their frequency on massive Porites around Okinawajima Island, and attempted to clarify what factors potentially affect pigmentation responses More than 30 Porites colonies at each of 17 sites were examined between February to April 2015. On the basis of images, pigmentation response patterns, pigmentation response occurrence levels, and the presence of epibionts, algae, and other species of coral, were also recorded for each colony. The prevalence of pink coloration was 42% higher than purple coloration. At two sites (Odo and Oujima) the prevalence and levels of pigmentation response were approximately half than at all other sites (SIMPROF, p<0.01). In addition, there were significant positive correlations between epibionts and pigmentation response. It may be possible that pink and purple coloration are fundamentally different phenomena, although the physiological mechanisms of purple coloration have not been clarified.