Plastic responses in the coral Pocillopora acuta to extreme low light conditions with and without food provision

Abstract

This study examines plastic responses in Pocillopora acuta collected from a highly urbanized reef environment to extreme low light conditions. While among-species differences in how corals cope with low-light are well-documented, much less is known about within-species responses. It also remains unclear how extreme low light and provision of food may interact and influence coral physiology. Clonal fragments from six colonies (genotypes) of P. acuta were subjected to two light treatments with mean midday irradiances of 4 and 40 μmol photons m-2 s-1 photosynthetically active radiation (PAR), representing just 0.5 and 5% ambient light level, and were either fed with zooplankton or not fed for nine days. Corals maintained in 4 PAR had lower endosymbiont density but higher cellular chlorophyll a concentration than those in 40 PAR. Feeding rates were similar in both light treatments and had no significant effects on endosymbiont density and chlorophyll a concentrations. While genotypes varied in the level of phenotypic plasticity expressed for both photoacclimation and heterotrophy, most displayed similar directions in their responses, indicating photoacclimation in P. acuta is broadly predictable. Our study demonstrates that P. acuta from Singapore is able to acclimate to very low light conditions by adjusting their photophysiology, providing additional evidence that this species is resilient to urbanization-related stress.