LAUSR

The corallivorous Crown-of-Thorns starfish (COTS), Acanthaster planci (Linnaeus, 1758), has been reported to undergo outbreaks that can decimate scleractinian coral assemblages (e.g. Waheed and Hoeksema 2014; Waheed et al. 2015). In the South China Sea (SCS), reported outbreaks have been limited to the southern portion of the region, and often have not been observed to be directly linkable to terrigenous influences on water quality (Lane 2012; Waheed and Hoeksema 2014; Waheed et al. 2015). In June 2019, we observed the presence of COTS on the southern outer reef of oceanic Dongsha Atoll (20.5853° N, 116.7948° E) in the northern SCS (Fig. 1a). We counted approximately 20 COTS each during four 20-min dives, with the dominant size class being 31–40 cm in diameter, and estimated density at up to 600 individuals/hectare, well above minimum outbreak numbers (Moran and De’ath 1992). Feeding scars were readily apparent between depths of 17–20 m (Fig. 1b), with numerous individuals visible (Fig. 1c) both feeding on the numerous tabular Acropora colonies and sheltering under soft corals or large caves in the reef (Fig. 1d). As with many previous SCS outbreaks, it is difficult to reconcile this event with any noticeable nutrient enhancement, as the site is an oceanic atoll and far from Dongsha Island, which is only inhabited by a small contingent of Taiwanese Coast Guard and Marine National Parks staff. However, the atoll does experience illegal fishing pressure, and it may be that the removal of larger fish and triton snails increases COTS frequencies (Sweatman 2008). Regardless of the cause, this event is one of the first COTS outbreaks reported from the oceanic northern SCS, and continued monitoring of Dongsha Atoll and neighbouring coral reefs in southern Taiwan and the Paracel (Xisha) Islands are needed.