Sekisei Lagoon, Japan's largest coral reef, is a subtropical paradise with over 400 types of coral. Its future, however, hangs on the balance because of climate change.

Warmer Temperatures Damage Corals

A new report revealed that only one percent of its coral reef is now considered in healthy condition because of global warming.

Rising water temperatures and damage caused by coral-eating starfish have already caused the overall volume of the coral to drop by 80 percent since the late 1980s.

The country's environment ministry, however, now reveals that only 1.4 percent of the lagoon is in healthy condition after it was hit by massive bleaching that occurred in 1988, 2001, 2007, and 2016.

Bleaching Events

Coral bleaching happens when corals are stressed due to changes in conditions such as sea temperatures and light. It causes corals to expel photosynthetic algae called zooxanthellae that live in their tissues. This drains the corals of their colors, turning them completely white.

Analysis of satellite photos and information from some 1,000 monitoring sites for the lagoon and two other reefs in Okinawa revealed that the ratio of healthy corals dropped from 14.6 in 1991 to 0.8 percent in 2008. The two neighboring lagoons also had similar results with the ratio of healthy areas being around 1 percent.

Although corals subjected to bleaching are able to recover if the water temperatures become colder and the algae recolonize them, ministry official Chihiro Kondo said that the latest study revealed that corals have not recovered much since 2008 likely partly because of the 2016 bleaching event.

The 2016 bleach was the worst in the reef's recorded history. A survey conducted in December 2016 showed that 70 percent of the reef's coral died and 90 percent were partly bleached as a result of higher than average ocean temperatures that summer.

Threats Of Climate Change To Coral Reefs

Kondo cited the unwanted consequences that could happen if coral reefs do not recover from bleaching events. For one, corals are home to 25 percent of marine life.

"It means a loss of rich fauna for a variety of creatures and would have grave impact on the ecosystem in the region," Kondo said.

Australia's Great Barrier Reef also faces the dangers of warming temperatures. In a study published in April, researchers revealed that two successive heatwaves killed almost half of the corals in the most pristine part of the reef.

Green turtles here are also turning into a female as a result of warmer temperatures, posing threat to the population of the species.