Combined effects of hyperthermic stress on photosynthetic rate in symbiotic sea anemones

Background/Question/Methods

Coral reefs have low tolerance for high temperatures in tropical oceans and are in great danger due to global warming. Corals are animals usually found in tropical oceans, living symbiotically with the algae Zooxanthellae which provide corals with up to 90% of their energy. In this experiment we examined how anemone starvation, by both zooplankton limitation and bleaching, affect photosynthesis among the Zooxanthellae.  How does hyperthermic stress and starvation effect on photosynthetic rates in symbiotic sea anemones? Sea anemones Aiptasia pallida (Marathon and Torch Keys, Florida, USA.) were acclimated for 2 weeks and fed Artemia nauplli. They were placed in two 25 gallon salt water (pH 8.1) aquaria (Oceanic ™), at 32^oC to induce bleaching. A12-hours light-dark cycle was maintained. Samples were homogenized, centrifuged, and pallet re-suspended. Cell counts of Zooxanthellae were made and host biomass was quantified (Bio Rad DC II protein assay) to determine the density (cells/ mg host protein). Photographic images were collected for each sample using a digital camera. Data were subjected to natural log transformation. Regression analyses were performed and slope intercepts were compared using one tail t-test assuming unequal variance.
Results/Conclusions
Bleaching and starvation had an effect on Aiptasia pallida sea anemones. The algae compensated the photosynthetic rate due to starvation. Bleaching reduced densities of the algae. However, bleaching did not impair their photosynthetic yields. After bleaching, host coral relies most on the algae for energy. Increased photosynthesis compensated for lack of the algae and/or starvation. The algae density remained significantly different, over the 12-hour period. Under prolonged starvation the algae did not increase photosynthetic yields. Starvation also had an effect on host coral. Host coral did not receive protein and the anemones were unable to repair and rebuild their tissues. Eventually, anemones shrunk in size and shape and died.  We concluded that compensatory response was limited, as starved/bleached anemones were failing by the third week.