Impacts of bleaching on host sea anemones and associated anemonefish in Southeast Asian coral reefs

Abstract

Thermally-induced bleaching events pose significant impacts on coral reefs but current understanding of the bleaching effects on host sea anemones and mutualistic anemonefishes is limited compared to those of scleractinian corals and their associates. Such information is especially lacking in Southeast Asia, despite the region harbouring the highest diversity of host anemones and anemonefishes. In this study, we documented bleaching prevalence and recovery of host anemones and quantified changes in anemonefish abundance at two coral reefs in Singapore during and after the 2016 mass bleaching event. Of the 260 host anemones surveyed, 16% were bleached in July 2016. All Entacmaea quadricolor bleached, in contrast to Heteractis magnifica (1%) and Stichodactyla mertensii (0%). Five months after the warming event, the bleached E. quadricolor had significant size reductions at both sites despite 10% of them regaining pigmentation. In March 2017, recovery rates of E. quadricolor significantly differed between the study sites. Recovered host anemones increased in size while the bleached ones remained the same or continued shrinking. The between-site differences in recovery of bleached E. quadricolor influenced the abundance of associated Amphiprion frenatus, highlighting the importance of bleaching status and associated host anemone size in supporting viable anemonefish populations. Our study represents the first quantitative assessment of anemone bleaching and post-bleaching recovery in Southeast Asia. Considering the increasing frequency and severity of extreme warming events, our findings stress an urgent need to understand climate change impacts on non-scleractinian host organisms and their associates to implement effective management and enhance reef biodiversity conservation.