Corals Recover After Bleaching Thanks To Soft Tissue


Coral reefs recover after bleaching thanks to a soft tissue that protects the coral's rocky skeleton, a new study in Hawaii revealed.

Researchers from the Hawaii Institute of Marine Biology sought to examine how corals recover from bleaching events and how local factors such as nutrients in seawater or light can influence recovery.

In Hawaii, coral reefs are important for economy, tourism, diving, and recreational fishing. Coral reefs also protect shorelines from coastal erosion and storms.

The findings of the study provide scientists with information that can help save coral reefs from massive bleaching events caused by extreme global warming.

What Happens During Bleaching Events?

When under stress, coral reefs lose the colorful algae that live in their tissues, which results to bleaching and sometimes death of the corals.

Although bleaching is rare in Hawaii, heat stress is becoming more and more common because of climate change. In 2014 and 2015, bleaching events proved that Hawaii is not immune to the extreme effects of global warming.

Led by Chris Wall of UH Mānoa School of Ocean and Earth Science and Technology (SOEST), the team of researchers studied colonies of two species of corals, rice coral, and finger coral, in Kāne'ohe Bay, O'ahu, Hawaii, under extreme conditions.

Seawater in the bay reached unusually high temperatures of 86 degrees Fahrenheit, which is near the maximum temperature that corals can tolerate.

Wall and his colleagues were interested in how colonies of coral reefs that were sensitive to thermal stress recovered from bleaching adjacent to colonies that remained pigmented and did not bleach.

The study took into account factors such as water temperatures, light levels, seawater nutrients, and sedimentation rates to understand how the environment influenced the severity of coral bleaching and recovery.

The Resilience Of Coral Reefs In Kāne'ohe Bay, Hawaii

The diet of a coral is based on food from their symbionts and the consumption of plankton. These two supply the building blocks for coral tissues.

Under bleaching, however, corals are starved from these nutrients, and so Wall and his colleagues wanted to know how corals overcome this starvation.

After three months, researchers found out that the bleached colonies of coral reefs did not die after bleaching and showed remarkable resilience.

The bleached colonies' recovery from starvation was hastened by environmental factors such as cooler water temperatures and water with low nutrient concentrations.

Wall and his colleagues concluded that soft tissues that protect the coral's skeleton are important in the recovery process because corals with abundant and thick tissues are able to survive better from bleaching.

In fact, these soft tissues represent a source of energy for corals. The stored energy in these coral tissues serve as food for corals during stress and help them recover.

"Corals in Kāne'ohe Bay may hold valuable lessons for science as we work to understand the basis for coral tolerance to the environmental challenges experienced today and those to come in the future as humans continue to change our global climate," explained Wall.

In the future, scientists will work to understand what mechanisms underpin the tolerance and vulnerability of coral animals to global warming.

Meanwhile, details of the new study have been published in the journal Limnology and Oceanography.

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