This awkward fish works harder than you

The ocean is full of strange creatures. The parrotfish is no exception.

Its teeth are embedded in its sharp beak, giving it the appearance of a bird. It is hermaphroditic and changes sex mid-life. And to sleep, some parrotfish immerse themselves in a mucous cocoon.

While it may seem strange and awkward, this creature is a true hero of the ocean.

Rising global temperatures, various diseases and coastal development are killing the world’s coral reefs, iconic ecosystems that support as much as a quarter of all marine life. According to some estimates, the world’s living coral area has halved since the 1950s.

But the situation would almost certainly be worse if it weren’t for the parrotfish.

Parrotfish are basically caretakers who are very good at their job. As they circle the reef, these animals, which live in oceans around the world, use their beaks to scrape colonies of bacteria and algae from the rocks. If left unchecked, the algae can grow out of control, choking out the reefs and preventing new corals from growing. And that makes it harder for reefs to recover after, say, extreme ocean warming, which kills lots of corals. So where you find a hungry parrotfish, the coral has more room to grow.

The problem is that on many reefs, parrotfish numbers – especially the large ones in the Caribbean – have plummeted. Meanwhile, other algae-eating animals, such as sea urchins, also disappeared. Some scientists say this is why Caribbean reefs have failed to recover from climate impacts such as bleaching and superstorms; there is simply too much algae for the coral to grow back.

On the other hand, this dynamic offers a glimmer of hope for an ecosystem that seems almost doomed: by protecting parrotfish, as well as efforts to stop climate-warming emissions, countries may have a better chance of saving the reefs.

If there’s one thing people know about coral reefs, it’s that they are colorful – an intricate mosaic of blues, reds, pinks and oranges.

However, more and more often, only one color begins to dominate: green.

As the number of corals decreases, the number of algae, or seaweed, increases. When corals die, this green, plant-like organism quickly grows on their skeletons. And as the seaweed spreads, it can prevent corals from growing again.

Baby corals that begin their lives swimming in the ocean need a bit of bare rock to grow and harden until they become adults. When the seabed is covered with algae, coral larvae have nowhere to grow. Seaweed can also release chemicals that harm corals, and when they grow in abundance, they shade out reefs.

“The biggest enemy of corals is actually seaweed,” said Nancy Knowlton, a marine scientist and author who formerly worked at the Smithsonian National Museum of Natural History. “It goes without saying that reefs will recover better if they don’t have to deal with a lot of seaweed.”

Studies show that over the past 50 years, algae have proliferated in coral reefs around the world, especially in the Caribbean.

Algae grows on human waste, such as sewage and runoff from farmlands. Water pollution is full of nutrients like nitrogen and phosphorus that algae need to grow. When water flows into the ocean, algae grows rapidly.

Moreover, one of the most voracious algae eaters, the long-spined black sea urchin, began dying in the Caribbean in the 1980s, possibly due to a waterborne pathogen. On average, Caribbean reefs lose more than 90 percent of their sea urchins within a matter of weeks, and the population has yet to recover.

Now the important task of reducing algae – giving corals a better chance to grow and recover after dying out – has fallen to some vegetarian fish, including parrotfish. In some parts of the Caribbean, a parrotfish may be the only thing standing between a relatively healthy reef and one shrouded in green, noxious goo.

The parrotfish’s life consists mainly of chewing up rocks and dead corals, grinding them into sand and releasing them through their hind ends. Some beaches around the world are largely made up of parrotfish excrement.

It’s not entirely clear what parrotfish actually eat. Research suggests that their main food source is colonies of bacteria, including cyanobacteria and other microbes, that live on rock surfaces, often alongside the more visible clumps of seaweed. The parrotfish are probably not looking for the seaweed itself – substances known to be harmful to coral growth and regeneration. But according to Andrew Shantz, who studies parrots at the University of Hawai’i at Mānoa, as they feed on the microbes, they eventually remove them from rock surfaces.

“No matter what they target, they end up removing the algae from the reef,” Shantz told Vox. “This gives the corals a place to come in and settle or grow and occupy that space.”

It’s a bit like weeding your garden before planting seeds to give them room to grow.

A number of studies have shown that if you exclude large fish, including parrotfish, from a reef, they become covered with more algae, which appears to limit the growth of some corals. For example, one study in Belize found that there was less algae and more baby coral around large parrotfish.

Similarly, a 2017 study Nature communication linked parrotfish to reef growth in Panama by examining historical records of fish teeth and coral fragments. The study used reef sediment cores: tubes of material excavated from the seafloor containing layers of coral, shells and animal remains. These cores allowed scientists to see how quickly the reef was growing and, by looking at the number and shape of the teeth, how many parrot fish lived on the reef.

This type of research supports the simple idea that parrotfish help coral reefs, but the relationship between fish and coral is complex and somewhat controversial in marine biology. For example, smaller parrotfish do not seem to limit the amount of seaweed they eat, even when there is plenty of it. Some studies have also failed to find links between the fishing restrictions they typically lead to more parrotfish – and the amount of algae and live coral. Parrots also eat live coral to some extent, although scientists do not suspect this causes much damage to the reefs.

“The impact of parrotfish on reef dynamics is not always clear,” said Joshua Manning, a postdoctoral researcher at the University of Colorado Boulder who studies parrotfish. “It’s still safe to say that parrotfish are good for the reef.”

People have been eating parrotfish in the tropics for centuries, and they are still common in many coastal communities around the world. (According to a quick Google search, they taste like sweet crustaceans). Although global population data is sparse, it is clear that overfishing has caused the decline of parrotfish, especially large parrotfish that are favored by fishermen, in some regions such as Jamaica and Micronesia.

These declines have almost certainly contributed to an increase in algae numbers.

But there are also places that have been protecting parrotfish for decades, where these animals are still abundant and clearly doing their job well. For example, the Dutch island of Bonaire has banned spearfishing, a common method of catching parrotfish, since the early 1970s. The island, which is located east of Curacao in the southern Caribbean, also banned parrotfish fishing entirely in 2010. Although the number of large parrotfish on Bonaire continues to decline, parrotfish numbers are at least twice as high compared to most other Caribbean reefs, according to a report by the Dutch 2018 non-profit Dutch Caribbean Nature Alliance.

According to Robert Steneck, a professor emeritus at the University of Maine who studies the Bonaire Reef, all these parrotfish reduce the growth of algae on the Bonaire Reef. This, in turn, helped the local corals survive, he said. Indeed, although most of the Caribbean’s coral has died off in recent decades due to bleaching and disease, Bonaire’s reef is still intact; part of it still blooms.

Moreover, according to Steneck’s research, the reef in Bonaire was able to recover from past mass extinctions. Parrotfish essentially make this ecosystem more resilient, he said.

The reality is more complicated. There are many reasons, apart from the abundance of parrotfish, why the Bonaire Reef is healthier than other parts of the Caribbean. The island, for example, lies below the path of most Atlantic hurricanes. The coral in Bonaire is also not as healthy as it once was. Bleaching has been harming the reef for years. And in the spring of 2023, a wildlife disease began to spread and kill hundreds of corals, some of which were centuries old.

There is little that parrotfish can do against these growing threats. As corals die inexorably and pollutants continue to flow into the ocean, reefs are overrun by seaweed. Once that happens, there’s not much the parrotfish can do to bring them back to life, Manning said. “At some point, with the intensity and frequency of these disturbances, grazing parrotfish will not be able to keep up,” he said.

Nevertheless, reefs still do better when there are more of them. Saving coral reefs depends primarily on policies and corporate efforts to reduce greenhouse gas emissions, but that doesn’t mean that effective fishing regulations don’t help, too.

Parrotfish reveal that individual parts of the ecosystem matter. Take out one part and the system starts to fail.

“We have to protect them, even if only to give the reefs a chance,” Manning said. “As long as we have parrotfish, we may have a chance to at least extend the potential for the reefs to come back.”