Millennial-scale episodic coral growth on the northern margin of the South China Sea

Abstract

Rising sea surface temperatures (SSTs) are exceeding the thermal tolerance of tropical corals, causing widespread bleaching and prompting attention to high-latitude subtropical regions as potential thermal refuge. To evaluate the past response of high-latitude reef growth to climate change, this study reconstructs the growth history around Daya Bay, located on the northern margin of reef-building corals in the South China Sea (SCS), since the mid-Holocene. Results from UTh dates of 99 subfossil coral rubbles show coral ages range from 6808 ± 46 to −67 ± 8 years BP (before present, present = 1950 CE). These data demonstrate that coral growth may be episodic since the mid-Holocene, and three distinct periods of coral colonization have been revealed: the mid-Holocene (6280–5593 years BP), the late Holocene (3970–3657 years BP), and the Modern Era (−67–45 years BP). This episodic coral growth pattern is closely tied to warm climate conditions. Corals thrived mainly during the mid-Holocene, consistent with observations of mid-Holocene coral growth from other subtropical waters in the Western Pacific. Notably, although flourishing coral growth coincided with accelerated temperature increases in the latter half of the 20th century, highlighting the potential for high-latitude subtropical regions to serve as refuge for corals, there was a significant loss of coral cover and a shift in community structure. This emphasizes the urgent need to understand past coral dynamics and environmental interactions to inform conservation strategies and address ongoing coral degradation.