QUANTIFYING PHOTIC STRESS IN ALGAL SYMBIONTS OF LARGER BENTHIC FORAMINIFERS

Coral reefs are in decline worldwide as a consequence of local- to global-scale impacts. Mass bleaching events are a major cause of mortality in coral populations. Larger benthic foraminifers, which host algal endosymbionts, can provide alternative models to enhance understanding of mass-bleaching events on coral reefs. These protists share several characteristics with zooxanthellate corals, as both precipitate calcium carbonate essential for reef accumulation and both require relatively clear, shallow-water environments where there is sufficient light (solar irradiance) for their algal symbionts to photosynthesize. Moreover, in both cases, too much light can induce photo-oxidative stress, either alone or in combination with elevated temperature. Previous studies have shown that larger foraminifers are more sensitive to light and less sensitive to elevated temperature. Corals tend to extensively bleach primarily when temperatures are elevated, though recorded rates of coral mortalities are highest in the clearest waters, at least along the Florida reef tract. Thus, larger foraminifers may help elucidate how disruption of the photosynthetic pathway within the algal symbionts triggers breakdown of the symbiosis that results in bleaching. Amphistegina gibbosa is used as a model organism in this study. Responses to photic stress are evaluated at various stages of foraminiferal bleaching by generating photosynthesis to irradiance curves using both microrespirometery and pulse-amplitude modulated (PAM) fluorometry. These techniques provide methods to quantify photosynthetic performance of the symbiont while still inside the living host. Similarly, PAM fluorometry provided in-situ chlorophyll fluorescence measurements from selected coral colonies from the same collection sites. Photochemical efficiencies of algal symbionts in two very different taxa living under identical temperatures and similar irradiance are compared in this study.