Wave height reduction by coral growth within the context of increased wave heights owing to sea-level rise and tropical cyclones in Ryukyu Islands and the main island of Japan by 2100

Abstract

Coral reefs act as green infrastructure by forming coral- and reef-based natural breakwaters. Numerous studies on existing and future reefs have investigated the effectiveness of reef crests associated with upward coral growth in dissipating waves. However, estimates of wave height reduction by completely emergent reef crests at tectonically active sites and non-reef structures are poorly constrained. In this study, we present a quantitative analysis of the changes in wave height reduction owing to emergent reef crests and non-reef structures in Ryukyu Islands and the main island of Japan, while also considering the effects of sea-level rise and intensified tropical cyclones by 2100. Our findings indicate that the more emergent the reef crest, the greater is the effectiveness of wave height reduction. Moreover, our data showed that the rate of wave height reduction was diminished by reefs with fewer emergent crests and non-reef structures. However, at these sites, reefs expected to grow in response to sea-level rise until 2100 exhibit significantly greater wave height reduction than degraded reefs without reef growth. One reason for this is that in non-reef structures or reefs where the reef crest is not exposed, the accommodation space for coral growth in both the vertical and horizontal directions is created owing to sea-level rise.