(CN) — Climate change is disrupting the effectiveness of traditional methods for protecting coral reefs, a finding that demands rethinking a decades-old strategy for preserving the building blocks of marine biodiversity, scientists concluded in a study released Friday.
Coral reefs support a sizable portion of Earth’s marine life. The multicolored corals cover less than 0.1% of ocean surfaces but house a third of the planet’s distinctive subaquatic beings. More than 500 million people depend on coral reefs for food, coastal protection and tourism income, according to a 2004 study by the Global Coral Reef Monitoring Network.
For decades, conservationists have relied heavily on one tactic: establishing marine reserves, where fishing is banned or restricted, to safeguard these biodiversity hot spots.
But climate change and warming seas are upending the effectiveness of that strategy, according to a new study published in the journal Nature Communications.
“The role of those marine reserves has completely changed,” said Nick Graham of Lancaster University and lead author of the study. “Now they are not really helping or having much of an impact on the amount of coral.”
Several factors threaten the survival of coral reefs, including overfishing and pollution from agricultural runoff. One of the most urgent threats today comes in the form of a changing climate as warming seas can cause coral bleaching.
Bleaching occurs when temperatures get too hot, producing a reaction in which corals start ejecting algae, causing them to lose their color and energy. The coral becomes translucent and exposes its white limestone skeleton. In this state, the coral can die within two weeks, Graham explained.
“We’re seeing increasingly frequent and widespread severe bleaching events,” Graham said.
A severe bleaching event can cause up to 90% of coral to die in a sizable area within two months. Once gone, the reef starts to erode and gets overtaken by other organisms such as seaweed. It can take up to 10,000 years for coral reefs to grow back, according to the National Oceanic and Atmospheric Administration.
Researchers from England, Australia and East Africa examined about 23 years of data from 1994 to 2017 on the diversity, abundance and physical changes of coral reef and marine life in the Seychelles, an archipelago of 115 islands in the Indian Ocean off East Arica.
Graham and his fellow researchers discovered that after a coral bleaching event in 1998, the amount of coral reef in the Seychelles marine reserve was about the same as coral reef in in areas where fishing is allowed.
The apparent ineffectiveness of a no-fishing zone in helping the coral thrive is believed to result from warming seas caused by human-driven climate change.
“It’s influencing the structure of the reefs and the composition,” Graham said.
The marine ecologist warned this revelation should not be construed as a sign that marine reserves are useless or unimportant. They still serve vital roles, such as allowing certain fish species to thrive and grow in population, which can benefit the fishing industry.
“Some of those fish start swimming outside the reserves and start benefiting adjacent fisheries or producing offspring that settle other reefs and are available to fisheries,” Graham explained.
Prior to the 1998 coral bleaching, researchers found that predator fish such as groupers and snappers were more abundant in no-fishing zones. After a massive die-off of coral reef, that trend reversed and herbivores, which feed on seaweed, algae and small invertebrates, grew larger in number in those marine reserves.
“The types of species benefiting from management are changing,” Graham said.
The results of this study suggest that both conservationists and fishermen will need to start reevaluating strategies for fishing and coral reef protection, taking into account the effectiveness of marine reserves as ocean temperatures continue to rise.
“Fishermen may need to adapt or change the species of fish they are prioritizing because some will be doing better than they were, and they might not be the ones these fishermen or the local market were used to fishing,” Graham said.
To follow up on this study, researchers will continue exploring the impact of climate change on coral reef in the Seychelles over a longer period of time, Graham said.
“We’re also working with fishermen in the Seychelles to understand how it’s affecting them,” Graham added.