Decline in skeletal growth of the coral Porites lutea from the Andaman Sea, South Thailand between 1984-2005

Abstract:

Of the few studies that have examined in situ coral growth responses to recent climate change, none have done so in equatorial waters subject to relatively high sea  temperatures (annual mean >27 °C). This study compared the growth rate of Porites lutea from eight sites at Phuket, South Thailand between two time periods (December 1984–November 1986, and December 2003–November 2005). There was a significant decrease in coral calcification (13.9 %) and linear extension rates (16–19.4 %) between the two sampling periods, while skeletal bulk density remained unchanged. Over the last 46 years, sea temperatures (SST) in the area have risen at a rate of 0.161 °C per decade (current seasonal temperature range 28–30 °C) and regression analysis of coral growth data is consistent with a link between rising temperature and reduced linear extension of the order of 38–46 % for every 1 °C rise in SST. The apparent sensitivity of linear extension in P. lutea to increased SST suggests that corals in the Andaman Sea may already be subjected to temperatures beyond their thermal optimum for skeletal growth. Currently, more reefs around the Thai-Malay Peninsula (~8oN – ~1oN) are being sampled as part of ongoing research to determine the extent of decline in coral growth in the region. The current research is not only attempting to examine variation in growth rates over a larger spatial scale, but also over a longer time period (30–50 years). Additionally, a larger suite of environmental parameters (e.g. aragonite saturation state, sedimentation rates, PAR, nutrient concentrations etc) is being examined in order to ascertain the extent to which rising SST effects growth, and to account for possible interactions with other environmental parameters.