Learning from the past: investigating the anthropogenic impact on Asia-Pacific reefs since WWII using coral δ15N records

Abstract

Asia-Pacific (AP) coastlines are facing intense coastal development which exerts a strong pressure on coral reefs ecosystems, in particular, by releasing considerable amounts of nutrients (primarily sewage) into coastal waters. Excess nutrients, like nitrogen, increase coral disease, bioerosion, depress fecundity and thus change community structure and function. The decline of coral reefs in the AP region is predicted to have dramatic ecological and socio-economical consequences considering that 76% of all coral species are found in the AP region and that millions of people are reliant on reef resources and services. Although eutrophication is well documented on modern reefs, very little is known about the historical exposure of coral reefs to nitrogen pollution during the last century and how it has shaped modern coral reef ecosystems. World War II and the post-war era provide interesting coastal development scenarios: Japanese military occupation and subsequent withdrawal, triggered punctuated population changes in the AP region which modulated the severity of anthropogenic nutrient release on coral reefs. Given that human sewage is characterized by an anomalously high nitrogen stable isotope ratio (δ15N), and corals use this nitrogen for growth, we can document the increase and decrease of sewage input to the reef over time through the analysis of coral skeletal bands. This talk will present the preliminary results of this retrospective study.