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Zooxanthellae (/ ˌ z oʊ ə z æ n ˈ θ ɛ l iː /; sg. zooxanthella) is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs.
Coral can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the coral's chances of survival diminish. In order to recover from bleaching, the zooxanthellae have to re-enter the tissues of the coral polyps and restart photosynthesis to sustain the coral as a whole and the ecosystem ...
Coral bleaching is the result of the loss of vital zooxanthellae; any of the stressors can cause bleaching. [14] The corals expel their symbionts because they are trying to get rid of any foreign bodies that might be causing them stress. Corals can survive up to a week without the zooxanthellae, but it is difficult. [15]
There is a symbiotic relationship between coral polyps and the photosynthesising algae called zooxanthellae, without which, neither would survive. When sea surface temperatures exceed approximately 29 °C or more, even for a couple of days, the relationship between the coral and its zooxanthellae becomes unbalanced. [ 5 ]
Symbiotic Symbiodiniaceae are sometimes colloquially referred to as Zooxanthellae, though the latter term can be interpreted to include other families of symbiotic algae as well. [7] While many Symbiodiniaceae species are endosymbionts, others are free living in the water column or sediment.
One of the major consequences that can occur with stress is the coral expelling its zooxanthellae, which are mutualistic algae that live inside coral. Corals without their symbionts become bleached , which effectively kills them since they are unable to gain the correct nutrients without their symbionts.
An increase of about 1 or 2 °C can cause the collapse of the relationship between coral and zooxanthellae, possibly leading to bleaching. [15] The average sea surface temperature in the Great Barrier Reef is predicted to increase between 1 and 3 °C by 2100. [ 6 ]
Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. [23] Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure. [24]