Lonely giant on the sand: unexpected massive Taiwanese coral, Polycyathus chaishanensis in the Datan algal reef demands a conservation focus

Polycyathus chaishanensis Lin, Kitahara, Tachikawa, Keshavmurthy & Chen, 2012 is an extant caryophyllid first observed in 1990 in a single tidal pool (<3 m in depth) containing less than 50 small individual colonies at Chaishan, Kaohsiung, Taiwan (Lin et al. 2012). Due to its rarity and vulnerability to anthropogenic disturbances, namely coastal development and pollution at the holotype locality, it is listed as a highly-endangered species by the Taiwan Wildlife Act (COA 2017). Remarkably, a second population of P. chaishanensis (Fig. 1A), located at 150-170 cm below average sea level and exposed to air during the monthly low tide, was discovered during a recent biodiversity survey of the unique crustose coralline algal (CCA) reef in Taoyuan, Taiwan (Liou et al. 2017). The colony size averaged 13.49 cm in diameter (n=29), and the range was between 3.3 to 27 cm, similar to the holotype described from Chaishan (Lin et al. 2012). A third location with a massive colony of P. chaishanensis (Fig. 1B), 110 cm long and 80 cm wide, was discovered at the southern Datan CCA reef (N25.03898°, E121.04770°). This colony and other smaller colonies nearby lie on a CCA platform surrounded by sand at 200 cm below average sea level, and are exposed to cold air (12°C) around sunrise during the annual spring low tide in winter. Exposure to high wave stress and occasional exposure to low air temperature, combined with competition for space from CCA (Fig. 1C) suggests that P. chaishanensis might be adapted to highlydisturbed natural environments. However, large-scale anthropogenic disturbance, such as recent approval of an environmental impact assessment for the planned construction of a liquefied natural gas receiving terminal (Chen et al. 2019) not only threatens the unique ecosystem of the CCA reefs (Liou et al. 2017), but also raises great concerns over the future survival of those endangered and giant P. chaishanensis colonies.