Coral community of Holocene coral reef in the southern South China Sea and its significance for reef growth

Abstract

Ancient coral reefs are rich archives of historical process and vital baselines for future development. Coring gives a window into the growth of ancient coral reefs and the fossil coral community's response to paleoenvironment. Well NK-1 drilled from Meiji Reef is the longest scientific core with the highest recovery in the South China Sea. This study focused on the upper section of the Well NK-1 accumulated during the Holocene. From 8200 yr BP, Holocene reef initiated on the substrates of Pleistocene limestone and stopped accreting vertically at 4800 yr BP. It consisted of an initiation and fast reef growth (5.6 mm yr−1) from 8200 yr BP to 7300 yr BP, a shift to slow reef growth (2.0 mm yr−1) between 7300 yr BP and 5400 yr BP, a return to a rapid reef growth (8.8 mm yr−1) from 5400 yr BP to 4800 yr BP, and finally a cessation of upward accretion and a reinforced lateral progradation since 4800 yr BP. A total of 11 coral genera and 16 Acropora species were identified from the Holocene segment of the core. The diversity of coral communities had an impact on reef growth. Coral communities with less genera and absolute predominance of branching Acropora were corresponded with a rapid vertical accumulation of reef framework with higher accretion rate. Acropora corals with rapid growth and dispersion by fragmentation were principal reef-builders during the Holocene, with A.valida being the most prevalent coral species. The highest Acropora species richness occurred at the geological era of 5400–5300 yr BP when reef accumulated with the fastest upward accretion rate of 23.1 mm yr−1. This intricate and detailed pattern presented a new and novel model for the development of Holocene reef, indicating that the coral community and key reef builders were crucial to reef growth. These findings are extremely helpful for understanding the current ecological state of modern coral reefs as well as their potential response to global climate change.