Day–night ecophysiology of the photosymbiotic bioeroding sponge Cliona orientalis Thiele, 1900
2016
Marine bioerosion is projected to increase under future environmental conditions, and interest in investigating the ecological roles of bioeroding sponges has grown substantially over recent years. Cliona orientalis Thiele, 1900 is an important bioeroding sponge on Indo-Pacific coral reefs that belongs to the Cliona viridis species complex, which is a group of Clionaidae that are symbiotic with dinoflagellates of the genus Symbiodinium. The present study aimed to investigate the intracellular Symbiodinium and the holosymbiont of C. orientalis under a day–night cycle. Measurements of chlorophyll fluorescence confirmed significant day–night relocation of Symbiodinium by C. orientalis, in which Symbiodinium mostly resided at the surface during the day to enhance light availability. Under the light regime within C. orientalis, Symbiodinium displayed efficient photosynthesis as indicated by its oxygen production rate. At night, Symbiodinium was drawn deeper into the sponge. As a holosymbiont, C. orientalis did not significantly change net uptake of heterotrophic carbon between day and night. During the day, the host presumably received autotrophic carbon translocated from Symbiodinium and displayed faster bioerosion measured as dissolution of calcium carbonate. The present findings advance our understanding of how diurnal rhythms may influence energy acquisition strategies and ecological performance of a sponge–photosymbiont association.
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