Catastrophic impact of typhoon waves on coral communities in the Ryukyu Islands under global warming

Abstract

[1] Typhoon-generated storm waves generally cause mechanical damage to coral communities on present-day reefs, and the magnitude and extent of damage is predicted to increase in the near future as a result of global warming. Therefore, a comprehensive understanding of potential future scenarios of reef ecosystems is of prime interest. This study assesses the current status of coral communities on Ibaruma reef, Ryukyu Islands, on the basis of field observations, engineering and fluid dynamic models, and calculations of wave motion, and predicts the potential effects of a super-extreme typhoon (incident wave height, H = 20 m; wave period, T = 20 s) on the reef. On the present-day reef, massive corals occur in shallow lagoons and tabular corals occur from the reef crest to the reef slope. The observed distribution of corals, which is frequently attacked by moderate (H = 10 m, T = 10 s) and extreme (H = 10 m, T = 15 s) typhoons, is consistent with the predictions of engineering models. Moreover, this study indicates that if a super-extreme typhoon attacks the reef in the near future, massive corals will survive in the shallow lagoons but tabular corals on the reef crest and reef slope will be severely impacted. The findings imply that super-extreme typhoons will cause a loss of species diversity, as the tabular corals are important reef builders and are critical to the maintenance of reef ecosystems. Consequently, reef restoration is a key approach to maintaining reef ecosystems in the wake of super-extreme typhoons.

Localized tsunamigenic earthquakes inferred from preferential distribution of coastal boulders on the Ryukyu Islands, Japan

“…Moreover, some Porites boulders in group 2 are clearly microatolls in the moat. Hongo et al (2012) reported that even the maximum possible storm waves that affect the reefs at Ishigaki Island have no wave force suffi cient to move microatolls of >40 cm in diameter in the moat, which are far smaller than the boulders observed in this study (>1 m diameter). Our preliminary survey revealed ~5-6-m-long living Porites coral colonies in the present moat of Ishigaki Island.…”

Typhoon damage on a shallow mesophotic reef in Okinawa, Japan

“…Typhoon damage from direct physical disturbances, turbidity, sedimentation, and salinity changes can be destructive to shallow coral reefs and has been well studied (Van Woesik, Ayling & Mapstone, 1991; Harmelin-Vivien, 1994; Ninio et al, 2000; Cheal et al, 2002; Hongo, Kawamata & Goto, 2012). Declines in coral cover on shallow reefs (<25 m in depth) have been documented, specifically in genera such as Acropora , Montastraea , Porites , Agaracia , Diploria , Millepora , Siderastrea , Pocillopora , Pachyseris , Montipora , and Merulina (Harmelin-Vivien, 1994; Van Woesik, De Vantier & Glazebrook, 1995; Fabricius et al, 2008).…”

Short-term population dynamics of high-latitude <i>Alveopora japonica</i> in Tateyama Bay, Japan

“…Since mortality of both small and large colonies was found in this study, the effect of sedimentation could be a relevant factor affecting the population dynamics of A. japonica. As the small colony mortality was dominant, mortality could also be related to strong wave action during typhoons (Hongo et al 2012). Observations of coral skeletons on the seabed during the daytime surveys in November also suggest that some live colonies were removed by strong water flow occurring during typhoons.…”