Geographical distribution of coral reefs and their responses to environmental factors in the South China Sea

Coral reefs represent distinctive yet vulnerable marine ecosystems. Recently, these ecosystems have faced threats and degradation from multiple factors. A comprehensive understanding of coral distribution and niche information forms the theoretical foundation for addressing the ongoing coral crisis. This study employed the MaxEnt model to predict coral distribution in the central and southern regions of the South China Sea (SCS), while also obtaining ecological niche information. Utilizing CMIP6 data, the future exposure risk of corals was evaluated under two forcing scenarios (SSP245 and SSP585). The findings revealed that the highly suitable areas for corals in the SCS were approximately 31,360 km2, mainly distributed in the middle and east of Xisha, Zhongsha Atoll, Huangyan Island, and the north of the Nansha Islands. The probability of coral presence in the north and west of Xisha and the south of Nansha was low. The key environmental factors exerting significant influences on coral occurrence included seawater temperature, photosynthetically active radiation, current velocity, and dissolved oxygen. Among them, seawater velocity and nitrate emerged as the primary factors discerning differences in coral fitness across the study regions, which also verified the results of principal component analysis. Under extreme scenarios predicted by the end of this century (SSP585-2090s), over 43 % of coral distribution areas would face the highest exposure risk, mainly concentrated in southern Nansha. The primary drivers of this increased risk were the substantial changes occurring in temperature, dissolved oxygen, and nitrate. This research serves as a reference for coral conservation under climate change in the future.