Assessment to 2100 of the effects of reef formation on increased wave heights due to intensified tropical cyclones and sea level rise at Ishigaki Island, Okinawa, Japan

Abstract

ABSTRACT Tropical cyclones (TCs) cause enormous damage to unprotected coastal areas. Healthy coral reefs can reduce this damage and are low cost and maintenance free. We use a wave simulation model to estimate changes that will occur by 2100 in wave height on a coral reef for a healthy reef and a degraded reef under variable TC wave conditions and sea level rise at Ishigaki Island, Ryukyu Islands, Japan. Moreover, we estimate the potential reef production rate based on analysis of a Holocene reef core, and indicate possible reef restoration and conservation strategies, including a selection of appropriate coral communities for transplantation, if the future reef is degraded. Our findings indicate that the significant wave height at the reef flat will increase from 1.69 m at present to a maximum of 3.00 m for degraded reefs and a maximum of 2.63 m for healthy reefs under intensified TCs by 2100. The value of potential reef production rate required for healthy reefs by 2100 is 3–10 kg CaCO3/m2/y. If the reef is degraded by global and local impacts, planning for reef restoration and conservation such as direct coral transplantation of Acropora digitifera and Acropora hyacinthus may be considered.