Skeletal Growth Response of Porites Coral to Long-Term Ocean Warming and Acidification in the South China Sea

Identifying the response of corals to anthropogenic ocean warming and acidification remains challenging, but is critical to understanding coral resilience in a changing world. Here, we report composite records of skeletal growth (1847-2014) of nine Porites spp. colonies from the open ocean of the northern South China Sea (SCS), and paired reconstructions of sea surface temperature (SST) and seawater pH (pH(sw)) by examining skeletal Sr/Ca and delta B-11 from two of the cores. The reconstructions demonstrate that the open ocean of the northern SCS has experienced significant warming since the 1960s with an overall temperature elevation of similar to 0.50 degrees C, and persistent acidification since the 1920s with a decline rate of -0.0102 +/- 0.0017 pH units per decade. Under such environmental changes, coral skeletal density represents a long-term mild decline for the past 168 years, demonstrating significant responses to pH(sw) and SST variation; whereas coral extension and calcification appear to be less affected, exhibiting overall increases over the studied period. However, persistent declines of both parameters are evident from the 1960s to 2014, which coincide with the sustained low pH(sw) and elevated SST. Although the general response of coral calcification (mainly dominated by upward growth) to both warming and acidification falls just short of statistical significance over the decadal timescales, the significantly persistent decline in skeletal density and recent downtrends of calcification still underline a pessimistic situation for corals in the northern SCS.

Automated summary

The study reveals significant warming and persistent acidification in the open ocean of the northern South China Sea since the 1960s, leading to a slight decline in coral skeletal density while coral extension and calcification show an overall increasing trend. However, coral calcification has persistently decreased since the 1960s, indicating a pessimistic situation for corals in the northern South China Sea.