These pesky fish work harder than you

The sea is full of strange creatures. Parrotfish is no exception.

Its teeth merge into a sharp beak, giving it a bird-like appearance. It is hermaphroditic, changing sexes throughout its life. And to sleep, some parrotfish wrap themselves in a mucus cocoon.

Despite its strange and awkward appearance, this creature is a true hero of the sea.

Rising global temperatures, various diseases and coastal development are destroying the world’s coral reefs, iconic ecosystems that support as much as a quarter of all marine life. by Some guessesThe live area of ​​coral worldwide has halved since the 1950s.

But without parrotfish, the situation would be worse.

Parrotfish are basically gatekeepers who are very good at their job. While traveling around reefs, these animals – which live in oceans around the world – use their beaks to tear apart colonies of bacteria and algae. If left unchecked, that algae can grow out of control, suffocating reefs and preventing new coral from growing. And it destroys a bunch of coral, making it harder for reefs to recover after, say, extreme ocean warming. So where you find hungry parrotfish, there’s more room for coral to grow.

The problem is that, on many reefs, parrotfish numbers – and especially large ones in the Caribbean – have declined. Other algae such as sea urchins, meanwhile, have disappeared. Some scientists say this is why Caribbean reefs have failed to recover from climate-related impacts such as bleaching and superstorms; There is too much algae for coral to regrow.

On the upside, these dynamics offer some hope for an ecosystem that seems doomed: By protecting the parrotfish, alongside efforts to curb climate-warming emissions, countries can have a better shot at saving the reef.

The walls are turning green

If there’s one thing people know about coral reefs, it’s that they’re colorful—a complex mosaic of blues, reds, pinks, and oranges.

But more and more, only one color began to dominate: green.

The rise of algae or seaweed in step with the decline of corals. When corals die, these green, plant-like organisms grow rapidly over their skeletons. And as it spreads, that seaweed can prevent corals from regrowing.

Baby corals, who begin their lives swimming in the ocean, need little bare rock to grow into adults. When the seafloor is covered with algae, larval corals do not develop. Seaweed can also release chemicals that damage corals and, when it grows in abundance, shade reefs.

“The biggest enemy of corals is really seaweed,” he said Nancy KnowltonA marine scientist and the writerFormerly with 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.”

Research shows That in the last 50 years or so, algae have expanded on coral reefs worldwide and particularly in the Caribbean.

Algae flow from human waste, such as sewage, and agricultural land. This water pollution is full of nutrients like nitrogen and phosphorus that algae need to grow. Hence the buoyancy of algae as it drifts into the ocean.

Also, one of the most voracious algae-eaters, the long-spined black sea urchin, began dying off in the Caribbean in the 1980s, possibly from waterborne pathogens. Caribbean reefs have lost, on average, More than 90 percent In a few weeks their urchins, and that population has yet to recover.

Now, the important job of suppressing algae — giving corals a better shot at growing and recovering from die-off — has fallen to certain herbivorous fish, including parrotfish. In some parts of the Caribbean, parrotfish can be the only thing covered in relatively healthy reefs and green noxious gunk.

Parrot fish to the rescue

A parrotfish’s life is spent mostly curling up on rocks and dead coral, grinding them into sand and releasing them with their rear end. There are few beaches in the world Originally made from parrotfish feces.

It’s not entirely clear what parrotfish actually eat. Research suggests that their main food source is the colonies of bacteria, including cyanobacteria and other microbes, that live on rock surfaces, often alongside the more visible clumps of seaweed. Parrotfish probably don’t seek out seaweed – known to be detrimental to coral growth and recovery. But when they graze on the microbes, they still remove them from the rock surface, according to Andrew Schantz, who studies parrotfish at the University of Hawaii at Manoa.

“Whatever they notice, they end up removing the algae from the reef,” Schantz told Vox. “It makes room for corals to settle in or grow and take over that space.”

It’s like how you weed a garden before planting seeds so that your seeds have room to grow.

A the number of Study showed that when you remove large fish, including parrotfish, from a reef, it becomes covered with more algae and this appears to limit the growth of some corals. A study For example, in Belize, less algae and more baby corals have been documented when large parrotfish were around.

Similarly, a 2017 study in Nature communication Examination of historical records of fish teeth and coral fragments has linked parrotfish to the growth of the Panamanian reef. The research relies on reef sediment cores: tubes of material extracted from the seafloor that contain layers of coral, seashells and animal remains. These cores allow researchers to see how fast the reef is growing and—by looking at the number and shape of the teeth—how many parrotfish are in the reef.

Studies like these support the simple idea that parrotfish help coral reefs, yet the relationship between fish and coral is complex and somewhat controversial in marine biology. Small parrotfish, for example, do not seem to limit the amount of seaweed, even though they have large amounts. some study There is also Failed to find link between fishing restrictions – which usually leads more Parrotfish – and amounts of algae and live coral. Parrotfish also snack on live coral to some extent, although scientists do not suspect it does much damage to the reef.

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

What does a reef full of parrotfish look like?

Humans have been eating parrotfish for centuries in the tropics and are Still common today Among many coastal communities around the world. (According to a quick google search they taste like sweet shellfish). Although global population data are sparse, it is clear that overfishing has led to declines in parrotfish – and especially large parrotfish, which are favored by fishermen – in some of these areas, e.g. jamaica And Micronesia.

These declines almost certainly contributed to the algae blooms.

But there are places that have protected parrotfish for decades, where these animals are still abundant and apparently doing their job well. For example, the Dutch island of Bonaire banned spearfishing – a common method of catching parrotfish – in the early 1970s. The island, just east of Curacao in the southern Caribbean, also banned the harvest of parrotfish in 2010. Although some of Bonaire’s larger parrotfish are still in decline, it has at least twice as many parrotfish as most other Caribbean reefs. According to A 2018 report by the Dutch Caribbean Nature Alliance, a non-profit.

All of these parrotfish help limit algae growth on Bonaire’s reefs, according to Robert StanekProfessor Emeritus at the University of Maine, who has been studying Bonaire’s reefs for more than 20 years. This has helped the corals here to survive, he said. Indeed, while much of the Caribbean’s coral has died in recent decades due to bleaching and disease, Bonaire’s reefs are still intact; Parts of it are still thriving.

What’s more, Bonaire’s reef has been able to bounce back from large-scale die-offs in the past, According to Stanek’s research. Parrotfish essentially make this ecosystem more resilient, he said.

The reality is more complex. There are many reasons, beyond the abundance of parrotfish, why Bonaire’s reefs are healthier than those in other parts of the Caribbean. The island lies under the path of most Atlantic hurricanes, for example. Bonaire’s corals are also not as healthy as they used to be. Bleaching has been damaging reefs for years. And in the spring of 2023, a wildlife disease broke out and began killing hundreds of corals, some of which were centuries old.

Against this mounting threat, parrotfish can do little. When coral die-off is relentless and pollution continues to flow into the ocean, reefs are overrun by seaweed. Once that happens, there’s not much parrotfish can do to bring them back to life, Manning said. “At some point, with the intensity and frequency of these disturbances, parrotfish won’t be able to keep up the grazing pace,” he said.

However, the riffs are better with more of them. Coral reef conservation depends, above all, on policies and corporate efforts to reduce carbon emissions, but that doesn’t mean effective fishing regulations don’t help, too.

What the parrotfish expresses is the individual component of an ecosystem. Take out one piece and the system starts to fail.

“We need to protect them, even if only the wall is given a chance,” Manning said. “As long as we have parrotfish, we may at least have a chance to prolong the reef’s return.”

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