Downslope migration of free-living corals (Scleractinia: Fungiidae) in typhoon-exposed reef habitats at Okinawa, Japan

Mushroom to manoeuvre? Using photogrammetry to track the movement and survival of free-living corals

“…3). Despite the lagoon's protection from storm disturbance, the overturning of the larger Halomitra pileus is suggestive of passive movement from wave surge, and so movement is likely to be a combination of passive and active movement over the year (Hoeksema 1988;Ohara et al 2021).…”

“…Differential bleaching between species is consistent with similar observations by Hoeksema and Matthews (2011), whereby individuals of the same species may vary in susceptibility according to size and depth. While intraspecific heat-stress tolerance also varies by depth, this greater susceptibility to bleaching in shallower (typically warmer) waters may induce active downslope migration to help reach a cooler environment (Hoeksema 1991;Ohara et al 2021). Halomitra pileus showed the highest level of mortality and, once overturned, appeared unable to right themselves (making them more susceptible to substrate scour and inhibited feeding).…”

“…Traditionally, the collection of this kind of data for slowmoving mushroom corals is both logistically difficult and laborious, and therefore is typically conducted over a small scale, e.g. 0.25 m 2 quadrats (Ohara et al 2021), with a restricted range of metrics collected. However, the development of underwater imaging tools such as 'structure from motion' (SfM) photogrammetry now enables researchers to track millimetre-scale changes in reef environments over large areas (> ~ 500 m 2 ) within a single dive (Bayley and Mogg 2020;Ferrari et al 2021).…”

“…However, reefs are highly dynamic environments, which are affected by human and natural disturbances, such as storms, heatwaves, pollution events, and exploitation at a range of scales. Reef habitats dominated by these free-living corals are therefore generally relatively unstable and transient, and are particularly affected by episodic hydrodynamic disturbances such as storms (Ohara et al 2021).…”

“…While we typically do not think about stony corals moving, the free-living mushroom corals are known to be able to move over small distances to escape competition or harmful environments (Yamashiro and Nishira 1995;Hoeksema and de Voogd 2012) or to be passively swept by storm surge, waves, and strong currents (Ohara et al 2021). Many species are also able to right themselves following involuntary overturning during such storms (Jokiel and Cowdin 1976;Hoeksema and Bongaerts 2016).…”