Variations in massive Porites growth rates at Hainan Island, northern South China Sea

Annual density banding in massive coral skeletons provides a means to retrospectively monitor coral growth rates. In this study, we present new records of annual skeletal density, linear extension and calcification rates for 16 Porites spp. coral cores from northeastern Hainan Island, northern South China Sea. Based on average growth characteristics from 1948 to 2001, P. lobata had significantly higher linear extension and calcification rates and lower density than P. lutea. We also found evidence of an age-related effect on growth, whereby skeletal density de creased and linear extension rate increased through time. This did not affect calcification rates. The average calcification rate for northeastern Hainan Island Porites matches that expected for Indo-Pacific Porites based on average sea surface temperatures (SST) from 1961 to 1990. After removal of the ontogenetic trends, average 16-core calcification rates from 1923 to 2002 showed an initial increase, matching observed SST warming. After 1982, however, calcification significantly decreased, although SST did not continue to warm. We suggest that the lower calcification rates from 1983 to 2002 may be a response to eutrophication of coastal waters as a result of extensive coastal aquaculture development. In summary, our new growth records from Hainan Island show that, despite species differences, calcification rates were typical of Indo-Pacific Porites but that in the latter half of the 20th Century, calcification rates have likely responded to both globally and locally induced changes in the marine climate experienced by the corals