Sandy ‘reef stars’ help bring life back to coral reefs

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Coral reefs are extremely diverse underwater ecosystems.They are made of the coral themselves growing on rock, plus the many species of sea life surrounding them. About 25% of all marine life lives in, on, or around coral reefs. The reefs provide a source of money for tourism and fishing, as well as protection from shoreline against erosion and flooding. But some of these ecosystems are in danger of dying out because of a destructive fishing method. Restoring the reefs can be time-consuming, but recent efforts by a candy company have contributed to shortening that time.

Example of a coral reef (Francesco Ungaro, Unsplash.com)

There are several types of coral reefs. Coral itself is an animal, specifically an invertebrate that grows under the sea in temperate or tropical waters usually in compact clusters called colonies. Hard coral (stony coral) forms reefs; soft coral does not.

Coral reef locations around the world (Wikipedia)

Coral colonies are made of soft tubular animals called polyps, all genetically identical. They attach to rock and secrete a type of calcium carbonate to surround their base. As the carbonate increases, the base of the polyp appears to sit inside a cup depression called a corallite, which is less than 3 mm (0.12 inches) in diameter. This carbonate base builds around the soft coral body and increases the size of a reef roughly at 0.3-2 cm (0.1-0.8 inches) per year. In the diagrams of various coral reef types above, the light brown color represents a combination of the living coral colonies on the surface of centuries of carbonate deposits.

Stony coral polyp (modified from Wikipedia)

Coral reefs create an ecosystem for growth of coral colonies, fish, sponges, starfish, mollusks, and crustaceans. Even though they represent only 0.1% of the land area under the seas, they provide environments for about 25% of marine life. 

Fishermen on the coasts of Southeast Asia, the Aegean Sea, South America, Europe, and Africa destroy coral reefs illegally through a process called blast fishing (or dynamite fishing). This stuns fish and ruptures their swim bladders by exploding commercial or handmade bombs underwater, after which they scoop them up from the surface as they float helplessly. More than 275 million people live within 30 km (19 miles) of coral reefs, and the majority of these people come from developing countries where reefs provide food and income. It is estimated that there are 6 million coral reef fishers in the world.

Explosion from blast fishing in Indonesia and a typical bomb (ICLARM Quarterly, 2024)

The map below shows worldwide locations where blast fishing has been reported in the past two decades, and the intensity of the bomb explosions is provided.

1997-2018 reporting of blast fishing (Biological Conservation, 2021)

Blast fishing results from growing populations and the need for greater exports. Fishermen claim it is easier than traditional fishing methods and results in higher yields. Most blast fishers in Indonesia feel this is the most efficient means to survive, despite governmental fines. Some of these fishers have never used other methods of fishing and "showed no inclination to learn more traditional techniques or invest in other gear types" (ICLARM Quarterly, 2024).

Depending on the depth of the reef, the explosive power of the bomb, and the type of fish that are targeted (deep or shallow), blast fishing can create craters in coral reefs 2-3 meters (6-10 feet) in diameter. About 70% of the live coral was killed in the affected area as it becomes uprooted and smothered in the blast rubble (blocking the coral polyps' ability to kill prey and preventing symbiont cells from getting sunlight). The habitat for predator-prey fish and various sea bottom-dwelling creatures is also severely disrupted.

Single blast crater, two years old,  Sulawesi, Indonesia (Fox & Caldwell, 2006)

Coral growth (and, therefore, the local ecosystem) may recover in 5-10 years from a single explosion, but with multiple fishermen constantly performing blast fishing in concentrated areas (sometimes up to 40 sticks of dynamite per day in Indonesia), the damage is often unrecoverable for decades or centuries. 

Extensive damage to coral reef in Sulawesi, Indonesia (Popular Science, 2024)

The Mars, Inc. candy company is working to repair this damage. Famous for its Snickers, Milky Way, and Three Musketeers candy bars and M&Ms, Mars has been involved for the past decade in efforts to recover coral reef habitats in Indonesia. (Here's a link to the Mars company history.)

The MARRS (Mars Assisted Reef Restoration System) began in 2011. It involves installing steel structures called reef stars in the area of damaged coral. The hexagonal steel stars are coated with resin and coral sand to provide a suitable base for coral to grow. Small bits of living coral are strapped on as seeds. Larvae released as the coral grows will settle on the frames, attach, and repopulate on the frames.

Bare, coated, and seeded reef star frames (Mars website)

As an incentive to fishermen, local people are enlisted to help strap coral to the frames.

Attaching coral to reef stars (Mars website)

They may also help in transporting the reef stars to the target sites.

Local storage and transportation of reef stars

Divers then transplant the seeded frames to the damaged section of coral reefs.

Installing reef stars in Australia (BusinessGreen.com)

The rate of growth of new coral can be seen in just a few months, but overall replacement takes a few years (3 years for 60% recovery). Still, this is far better than allowing a damaged area to repair itself, which is not always possible.

Here's a link showing how to avoid classic mistakes when installing reef stars

The world is losing coral reefs to more than just bomb fishing. Climate change raises the temperature of the water, which kills coral. Solutions are needed for that type of harm coral (and ocean life) faces.

MARRS Coral Reef Project (a huge website)

A short video on the MARRS project.