Phoenix, AZ

Fish are critical for maintaining coral and algae on coral reefs, according to scientists

Victoria Nogales

PHOENIX, AZ - Coral reefs are filled with beautiful colors and structures, and that's what draws people to them. Coral reefs offer many benefits in addition to aesthetic pleasure, including food security, coast protection, and cultural preservation. In spite of their small size, reefs support about 25% of marine life and have earned the nickname "the rainforests of the sea.".

Whether corals can survive climate change is the greatest challenge facing reefs today. Climate change can affect corals in a number of ways. For example, it can stimulate the overgrowth of algae, which can pose a serious threat to new coral growth.

The Center for Global Discovery and Conservation Science at Arizona State University looked into the role of herbivorous fish in maintaining a balance between corals and algae, specifically, turf algae, which are the main antagonist to corals in the coral-algae battle for reef space. Coral Reefs, the Journal of the International Coral Reef Society, published their findings on Aug. 9.

Shawna Foo leads the team that conducted 1,476 surveys on fish and benthic communities between 2010 and 2019 in the main Hawaiian Islands.

“We found that control of turf algae cover differs by water depth, and herbivore fish numbers were the best indicator of reductions in turf algae cover," Foo stated. He also stated that smaller fish are more successful at controlling turf algae than larger fish.

Herbivorous fish play an important role in controlling algae, but there has been little study examining how this role differs by reef depth and with different types of fish. Researchers found relationships between three types of herbivore fish - scrapers like parrotfish, browsers like angelfish, and grazers like tangs - and the number of turf algae on shallow, mid, and deep reefs.

At each site, divers from the National Oceanic and Atmospheric Administration recorded fish counts, sizes, and classifications. Additionally, the researchers estimated what was covering the ocean floor, allowing them to distinguish between coral and different types of algae. Through these surveys, the ASU team determined how herbivorous fish composition and fishing intensity varied depending on depth and salinity.

In Hawaii and throughout the world, this study will provide new insights into reef management. Managing herbivorous fish is a key strategy for reducing algae on turf and boosting coral survival rates. A warming climate has caused turf algae to overgrow, and it appears that maintaining the number of mouths on the reef is the key goal of managing corals in the future rather than focusing on the total biomass of herbivorous fish.

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