Coral Bleaching – September 11, 2019
After the Science in the Wild Kilimanjaro expedition, it was off to explore Zanzibar, a semi-autonomous archipelago off the coast of eastern Africa. This region is known for its gorgeous water and coral reefs. Mnemba Atoll, in particular, on the eastern side of the main island, is a big tourist location for snorkeling. While we saw a lot of colorful fish, the coral….unfortunately was bleached. You can imagine, in the future, how much this will potentially impact Zanzibar, which relies heavily on tourism for revenue.
Coral reefs are comprised of two partner organisms: an animal (coral) and a unicellular photosynthetic algae (dinoflagellate). The interaction where two different organisms live together for mutual benefit is called symbiosis. In this case, coral (the animal) provides protection and raw materials for photosynthesis while the photosynthetic algae produces food. This enables both partners to grow and reproduce. The beautiful color we see in coral comes from the photosynthetic algae, which have pigment.
Coral bleaching is the disappearance of the coral’s color, revealing the underlying white coral skeleton. It occurs due to either the breakdown of symbiosis between coral and photosynthetic algal cells or the degradation of photosynthetic pigments of the algae cells. This occurs as a result of stressful conditions caused by, in most cases, high temperatures. Given global climate change, ocean temperatures are continuing to increase.
This particular region in Zanzibar has seen 90% coral mortality in the last two decades! Will the coral reefs eventually recover? Unfortunately, not completely, as there is no way we can stop current trends of global climate change at the local level. What IS being done in Tanzania and Zanzibar is the restoration of highly degraded coral reefs, involving growing nursery reared coral transplants in areas with highly degraded reefs.