Influence of turbidity on trophic plasticity in scleractinian corals in the Dampier Archipelago

Tropical scleractinian coral communities and coral reef biodiversity are in a state of decline due to cumulative global and anthropogenic stressors. However, some coral communities are able to survive, and indeed thrive, in stressful environments. The mechanisms that these corals employ to survive in challenging conditions are poorly understood. This study aimed to assess the influence of turbidity on the degree of trophic plasticity expressed by three genera of scleractinian corals (Acropora spp., Porites spp. and Platygyra spp.) and to investigate the temporal variations in the stable δ13C and δ15N isotopes of these three genera in the Dampier Archipelago, Western Australia. This study utilised stable isotope δ13C and δ15N analysis of whole and fractioned (separate host tissue and endosymbiont) corals in conjunction with modern Bayesian isotopic niche analysis to deliver several lines of evidence and provide a representation of the spatio-temporal variability of coral trophic plasticity. This study found that, (i) coral genera exhibited different levels of reliance on heterotrophy under different levels of turbidity, with both Platygyra spp. and Acropora spp. utilising mixotrophic (i.e. both autotrophic and heterotrophic) feeding strategies, whilst Porites spp. was more reliant on heterotrophic resources. (ii) In turbid environments all coral genera increased their reliance on heterotrophy, with clear evidence of a lack of resource sharing between symbiotic partners. (iii) Temporal environmental variability influenced the δ13C and δ15N signatures of corals, whereby signatures were δ13C enriched and δ15N depleted in the wet season (December – April), and the inverse occurred in the dry season (May – November). These results may reflect supressed photosynthetic rates in response to increased turbidity in the wet season. This study provides evidence that some scleractinian corals can adjust their feeding strategies in response to variable turbidity levels. As nearshore coral reefs are expected to become more turbid due to future climate change and anthropogenic activities, the knowledge from this study will allow for improved environmental impact assessment and predictive modelling for future coral reef conservation