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The summer of 2023 will go down as the hottest in recorded history (thus far). Sadly, hot ocean water means coral bleaching, and Florida’s corals suffered tremendously this year. Fortunately the Coral City Camera was in position to create the world’s most comprehensive in-situ coral bleaching timelapses ever documented by human technology. Many attempts have been made to record a coral bleaching event, but to our knowledge, this is the most complete and longest running coral time lapse made underwater in a coral reef environment. The time lapse begins on May 1st, 2023 and you can see that the staghorn corals start growing and branching quickly. However, by mid-July water temperatures have reached the critical bleaching threshold of 87 degrees Fahrenheit (30.5C) and quickly turn white. The transplanted staghorns and elkhorn corals not only bleached, but they subsequently died. You can see how after turning white, they turn gray-brown as they are colonized by turf algae in August and September, and then they erode almost as quickly as they grew, expedited by the abundant parrotfish that graze this algae from the corals’ limestone skeletons.
Bleaching occurs when the metabolism of the golden-brown symbiotic algae that live in the coral tissue known as zooxanthellae goes into thermal overdrive. The algae’s production of photosynthetically-produced oxygen exceeds the limit the coral can safely handle inside its tissues, resulting in expulsion of the zooxanthellae (and its brown color) from its host. Because zooxanthellae normally provide a coral with photosynthetically-produced sugars, it begins to starve without these symbionts. Fast-growing corals like the endangered staghorn (Acropora cervicornis) and elkhorn (Acropora palmata) lack the energy stores that fleshier corals like brain corals have, and die from bleaching stress much more easily.
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