DailyMail reports that researchers from the University of Southampton conducted a series of controlled laboratory experiments at their coral aquarium facility. Using an underwater drone, they captured the corals in an astonishing display emitting hues of blue, pink, red, and green coral reefs in global waters.
The authors of the study determined that the phenomenon is an active sunscreen layer in the form of a colorful display that comes from unique pigments. Furthermore, they say that the pigments offer an alternative to the glaring white light during bleaching that can discourage the algae from returning to the corals.
Professor Jörg Wiedenmann, the head of the University of Southampton's Coral Reef Laboratory, says that their research displays colorful bleaching that has something to do with an automatic mechanism that involves both partners of the union.
He adds that when corals lose their symbionts, the light bounces back and forth inside the coral's tissues, resulting in a white coral skeleton. Excessive internal light possessed by the corals can be stressful for the symbionts, which could cause them to retreat and possibly delay their return.
The researchers say that the production of the sunscreen layer will then promote the return of the symbionts. After they return, the algae start using the light for photosynthesis. Furthermore, the levels of light inside the coral will decrease, and the coral cells will lower the need to produce the colorful pigments.
The scientists are enlivened by recent reports saying that colorful bleaching has occurred in some areas of the Great Barrier Reef during the last mass bleaching episode from March to April this year.
The findings of the research have been published in the journal Current Biology on May 21, 2020.
Coral Bleaching in the Oceans
According to the US National Ocean Service, coral bleaching occurs when corals are stressed due to changes in conditions. Most of these changes could be brought about by light, temperature, or nutrients. The bleaching episodes drive away the symbiotic algae living in their tissues, which causes them to turn ghostly white.
According to Dr. Cecilia D'Angelo, a lecturer of Molecular Coral Biology at the University of Southampton, bleaches don't automatically pose as a death sentence for corals, and many still survive after an episode of bleaching. In mild events, she says that corals can eventually re-establish the symbiosis with algae.
The most recent coral bleaching event occurred in the Great Barrier Reef in Australia in March. Officials have confirmed that very widespread bleaching of about 344,000 square kilometers was detected in the area.
Coral and Algae Mutualism
The National Oceanic and Atmospheric Administration say that corals and algae have a mutualistic relationship in which the coral provides the algae with a protected environment and compounds necessary for their photosynthesis.
Reciprocally, the algae produce oxygen that helps the coral to remove wastes. Most importantly, zooxanthellae, which are single-celled dinoflagellates, supply the coral with glycerol, glucose, and amino acids, which are the photosynthesis products. The coral uses these products to produce fats, and carbohydrates, and calcium carbonate.
According to the researchers of the study, the relationship between coral and the tiny algae entrenched in coral cells is a mutually beneficial 'symbiosis.' However, they add that if ocean temperatures rise 0.8°F above the usual summer temperature, this symbiosis tends to break down.