Oxygen isotopic evidence for decrease in calcification rate of Porites coral from the Lakshadweep Island

Reef-building corals are under tremendous physiological stress due to the changing climate and industrial pollution. Several studies have documented rapidly declining coral cover and reduced coral diversity in Indo-Pacific regions. The main threats to coral reefs are caused by increasing sea surface temperature (SST) and ocean acidification. However land-based sources of pollution in coastal regions can also contribute in rapid decline of coral cover. We report here a significant decrease in calcification rate (∼10–15%) in a scleractinian coral (Porites lutea) collected from a Lakshadweep (Kavaratti) island in the southeast Arabian Sea. Our observation is mainly based on high-resolution oxygen isotopic record and X-radiography of coral. To investigate seasonal changes, a monthly-scale SST record was developed by using oxygen isotopes. The observed reduction in the calcification rate of Porites coral from 1989 to 2003 A.D. is attributed to climate change and anthropogenic activity in the vicinity of coral growth. This decrease in calcification rate is consistent with the decline in growth rate of genus Porites from the Great Barrier Reef (GBR). Such a reduction in calcification of Porites lutea appears to have been caused by the temperature stress, ocean acidification and local environmental pollution. However it is difficult to assign any one particular reason for the observed change.