User:S8tan.ucsd/Coral bleaching

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Increased sea surface temperature leads to the thinning of the epidermis and apoptosis of gastrodermis cells in the host coral. The reduction in apoptosis and gastrodermis is seen via epithelium, leading to up to a 50% loss in the concentration of symbionts over a short period of time. Under conditions of high temperature or increased light exposure, the coral will exhibit a stress response that includes producing reactive oxygen species, the accumulation of this if not removed by antioxidant systems will lead to the death of the coral. Studies testing the structures of coral under heat stressed environments show that the thickness of the coral itself greatly decreases under heat stress compared to the control. With the death of the zooxanthellae in the heat stressed events, the coral must find new sources to gather fixed carbon to generate energy, species of coral that can increase their carnivorous tendencies have been found to have an increased likelihood of recovering from bleaching events.

After the zooxanthellae leaves the coral, the coral structures are often taken over by algae due to their ability to outcompete the zooxanthella since they need less resources to survive. There is little evidence of competition between zooxanthellae and algae, but in the absence of zooxanthellae the algae thrives on the coral structures. Once algae takes over and the coral can no longer sustain itself, the structures often begin to decay due to ocean acidification. Ocean acidification is the process by which carbon dioxide is absorbed into the ocean, this decreases the amounts of carbonate ions in the ocean, a necessary ion corals use to build their skeletons. Corals go through processes of decalcifying and calcifying during different times of the day and year due to temperature fluctuations. Under current IPCC emission pathway scenarios, corals tend to disintegrate, and the winter months with cooler temperatures will not serve ample time for the corals to reform.