POLLUTION, GROWTH RATES, AND CONSERVATION OF RED SEA GIANT CLAMS USING ISOTOPE SCLEROCHRONOLOGY

Giant clams are effective sentinels of reef health due to their dependence on high water clarity to maintain their symbiosis-accelerated growth rate. We have compared modern and ancient (2-10 kyr) growth rates among populations of three species of giant clams from the northern Red Sea along the coasts of Israel, Jordan and Sinai. Using Mutvei’s solution combined with validation through oxygen isotope thermometry, we can compare daily shell extension among ancient and modern representatives of these individuals, and have determined that modern individuals are growing more slowly than those of pre-industrial times. We also identified an isotopic offset in carbon isotopic content of the exterior growth layer of these bivalves, with the more symbiotic species displaying a comparative enrichment in δ¹³C relative to the species more reliant on heterotrophy. Work is currently underway devising a method to extract shell organic material for δ¹³N analysis for comparison with growth rate, to identify whether agricultural pollution is responsible for the modern depressed growth rate exhibited by these vulnerable but charismatic bivalves.