Unravelling multifactor influences on photosymbiosis within a tropical anthozoan (Isactinia sp.)

The symbiotic relationship that photosymbiotic anthozoans share with Symbiodiniaceae is an important aspect of not only their health, but the success of the broader ecosystems in which they reside. This relationship is fragile however and is susceptible to perturbations to physiochemical factors within the environment. Using conditions ecologically relevant to the Great Barrier Reef, the aim of this study was to unravel the individual and combined impacts of temperature and salinity on the population density of Symbiodiniaceae within a small tropical sea anemone (Isactinia sp.) over time. A significant interaction between the three factors was identified. While salinity was shown to be the leading cause of symbiont loss within the first week, over the duration of the 21-day study, temperature ultimately emerged as the primary driver of bleaching. The impact on Symbiodiniaceae density varied however, with instances of the density more than doubling under mid-range conditions. Ultimately the results of this study contribute to our understanding of the complex and dynamic nature of photosymbiosis within tropical anthozoans. By thoroughly unravelling the intricacies of the anthozoan-Symbiodiniaceae we are better able to predict how such species may respond to changing environmental conditions into the future.