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This is what the process of coral bleaching looks like

By Leonard Ho - Posted Aug 11, 2016 09:00 AM
Advanced Aquarist readers surely know what coral bleaching is, but few of us have ever seen the process in action. A new study records how the LPS long-tentacle plate coral, Heliofungia actiniformis, actively (and rapidly) sheds zooxanthellae.

Temporal sequence of pulsed inflation by Heliofungia actiniformis to remove Symbiodinium. a Acclimated coral at 26 °C. b Inflation maximum before contraction. c Contraction and expulsion of zooxanthellae. d Even after expulsion the corals often maintain a level of inflation. Scale bar 5 cm

Recent research shows free-living plate corals such as Heliofungia sp. and Herpolitha sp. can use pulsed inflation (a series of rhythmic inflation and deflation) to unbury themselves from sand or as a limited form of locomotion.  New research now shows that LPS corals also use pulsed inflation to expel zooxanthellae, AKA coral bleaching. These corals can control expulsion in a rapid but controlled manner, resulting in non-lethal bleaching to help cope with acute environmental stresses.

The open-access Coral Reefs journal paper describes the process:

Heliofungia actiniformis specimens were exposed to elevated water temperatures in a 10-L aquarium system for up to 8 d to encourage bleaching. An image was collected every 3 s. Temperatures were raised from 26 to 32 °C in the first 12 h and maintained at 32 °C (±0.5 °C) for the duration of the experiment. Within the first 2 h of exposure, H. actiniformis began expelling Symbiodinium from the tissue. A green plume of symbiont cells was expelled via the mouth during tissue inflation and contraction. The intensity and magnitude of the pulses increased over a 55-h period, with coral tissue expanding up to 340% of its original state (Fig. 1b). Corals survived between 2 and 8 d under elevated temperature conditions. There was some degradation of the epidermal tissue during the later stages of the experiments.

Video link:

Author: Leonard Ho
Location: Southern California

I'm a passionate aquarist of over 30 years, a coral reef lover, and the blog editor for Advanced Aquarist. While aquarium gadgets interest me, it's really livestock (especially fish), artistry of aquariums, and "method behind the madness" processes that captivate my attention.


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