Consider bumphead parrotfish, so named because of a cartoonish bump on their heads. Iridescent green with a pink nose, they are as big as scrawny teenagers, and they are on the International Union for the Conservation of Nature’s Red List of threatened species.
But they’re not rare at Palmyra Atoll, a U.S.-administered island in the Pacific Ocean, where the waters are teeming with these coral-eating hulks. A decades-long conservation program there has led to a boom in parrotfish numbers, so much so that they are now harming local populations of corals and other species.
This is not an isolated case: Ecologists are facing similar dilemmas with elephants in a South Africa reserve that are killing trees in the savanna and with protected sea turtles in the Bahamas that are harming meadows of invaluable sea grass.
These instances show how even the best-thought-out conservation efforts can have unintended effects on the environment, benefiting some large-bodied species over less charismatic ones. That’s because reintroducing a species into an environment that lacks predators or other mechanisms to keep populations in check, or protecting a population that would otherwise disappear, can make the entire ecosystem unstable, said Douglas McCauley, an ecologist at the University of California at Santa Barbara. He recommends fixing all the damaged parts of an ecosystem at the same time.
“Ecosystems run a little bit like car engines,” he said. “If you wreck an engine, then try to run [it] after repairing only a few of the broken parts, you are likely to see a whole new set of parts start to break.”
From a dock on Palmyra one day seven years ago, McCauley watched a plume of foam approach on the ocean’s surface, heard the crunch of teeth on coral and soon saw a school of parrotfish move through the reef like a herd of buffalo feasting on grassland. To McCauley, then a graduate student studying reef ecology, it was a eureka moment. The parrotfish had to be a major player in the reef ecosystem and ought to be studied, he thought.
“The reef was basically being sucked up by them and pooped out,” McCauley said.
To appreciate the drama of what McCauley saw, one must understand Palmyra Atoll, an island of palm trees and white beaches that time assembled painstakingly atop an underwater volcano. Eons ago, the volcano had no living thing on it. Then, some coral larvae arrived on ocean currents. Fish larvae made the journey next, followed by plant life possibly carried over by sea birds from Hawaii a thousand miles away. Nature composed a symphony of life.
The atoll is made entirely of coral and is uninhabited except for occasional scientists such as McCauley, who arrive by a charter plane that lands on a runway made of crushed coral; there is little soil. The island, owned by the Nature Conservancy, an environmental organization, is far from civilization.
Still, human influence — in the form of overfishing of all species, including the parrotfish, which is somewhat of a delicacy — crept in. To protect the dwindling population, the U.S. government set up a marine protected area at Palmyra in 2001 and made fishing illegal. The parrotfish flourished in the shallow reefs where their natural predators — gray reef sharks — were too big to reach. Large numbers of them happily chomped away at their primary food source — coral.
When McCauley saw the parrotfish destroying the reef, he dived in to inspect, following one fish around, noting what it ate and what type of coral it preferred. At one point, the parrotfish joined a group of five others, and they spotted McCauley. One male, weighing perhaps 100 pounds, charged full force at McCauley, who was both worried and struck by the wonder of the moment.
“It is the aesthetic pleasure of being knocked out of the way on a reef by a hungry school of buffalo-like bumphead parrotfish,” he explained.
Using data collected over four years at Palmyra, McCauley and his colleagues created a simple computer model of the reef. They found that each parrotfish ate about two tons of coral every year. At that pace, the fish would damage the shallow reefs within decades, causing them to shrink and become much less diverse. The findings were published last year in the journal Conservation Biology.
So, how should a species like the bumphead parrotfish — threatened and yet, in large numbers, destructive — be managed? In the past, conservationists have tried to give specific species an advantage, McCauley said. For example, to save sea turtles, people have protected the beaches where the turtles lay eggs and have given fishermen devices to reduce unintended harvesting of the animals. But rather than protect particular species, a better approach may be to protect entire assemblages of species in an ecosystem, some conservationists believe.
In the parrotfish case, that might mean protecting its predators. (Some parrotfish appear to avoid reefs that attract especially large numbers of sharks.) While this approach would not apply to Palymra, where sharks are already protected but too large to reach shallow reefs, it can be applied at a nearby atoll, Tabuaeran, whose reefs also have been damaged by parrotfish.
“We expect sharks are confining the bumphead to particular parts of the reef, controlling the impacts they have on the reefs,” McCauley said. “You need this rare bumphead, but in order to keep things more or less in balance, you also need the predators of this fish.’’
Creating such a balance of protection is complicated. Ecologists know little about the intricate interactions between species in many ecosystems. Case in point is the parrotfish, which was once thought to primarily benefit reefs by eating algae and dead corals and creating space for new growth. Now, it appears the species can both benefit and harm the ecosystem.
Meanwhile, ecosystems are constantly changing. The world is in what many scientists are now calling the Anthropocene age — the age of humans, who are altering the chemistry of the oceans and atmosphere and hastening climate change. Humans are now the prime shapers of the planet, more so even than nature — building, growing new foods, creating marine reserves and catalyzing change. And humans are overfishing the oceans and removing top predators such as sharks.
As ecologist Daniel Botkin put it in his 1990 book “Discordant Harmonies,” nature is a symphony of several compositions, and ecologists are playing the role of conductors, “forced to choose among these [compositions], which we have barely begun to hear and understand.”
A similar saga is playing out at Kruger National Park in South Africa. The size of Israel, it is the largest national park on the continent and one of the places where the elephant, which is also threatened, is protected from poachers.
Greg Asner, an ecologist at the Carnegie Institution for Science, drove a white truck down a road at dusk in 2011 in Kruger when he came across hundreds of elephants congregated around a watering hole. It was like a platform at Penn Station during rush hour. The young ones, barely three feet tall, were in a frenzy not to get walked on.
“That hit home that, wow, the elephants have got a really large population,” Asner recalled.
The sight was evidence of the booming elephant population in Kruger. Beginning in the 1950s, the park was fenced to protect wildlife from poachers; this had the effect of erasing elephant migration routes, keeping the animals close together and leading them to multiply quickly, Asner said. Park rangers stopped culling elephants in 1995 in response to complaints from animal rights activists. Since then, elephant numbers in the park have doubled to 16,000.
The elephants are ruining the savanna. They push over trees to eat the leaves at the top. The uprooting of trees is also a sign of dominance, and the animals have uprooted more than a million of them since 2007, Asner said.
Trees are key to the largely bare savanna landscape, serving as habitats for giraffes, birds, bugs, impalas and kudus.
“The parallel to the bumphead parrotfish is amazing, because those parrotfish are large-bodied coral-reef grazers, and elephants are large-bodied savanna browsers,” Asner said. “So they have the same kind of effect. You get a lot of them and it can really crash parts of the ecosystem.”
Kruger rangers do not prioritize the elephant over less iconic species such as the acacia tree, which the elephants uproot. So officials are trying to put the population in check by shooting matriarchs with birth control darts every few months and also fencing off sections of the park to elephants. They are also thinking of creating “landscapes of fear,” where rangers would make loud noises, perhaps by shooting guns into the air. That may teach the elephants to avoid their biggest predators — humans with guns.
Kruger is, at its core, a human-created ecosystem, Asner said. The threats that lie outside the park result in its animals’ being confined in an artificial system where they interact in unexpected ways.
“Since we are in a world now where humans are so responsible for the future and management of ecosystems, how do we manage for the right number of the larger-bodied species?” Asner asked.
The task can be complicated, as ecologists studying endangered green sea turtles are finding. Off Bermuda, for example, turtle populations have rebounded due to conservation measures. They feed on seagrass meadows and remove dead matter, which allows for new growth of sea grass.
But there is a catch. There are now so many sea turtles off Bermuda that they are overgrazing those meadows, which are important ecosystems for aquatic life, said Michael Heithaus, executive director at the School of Environment, Arts and Society at Florida International University. The conservation problem now is that the turtles have rebounded into an ecosystem that has been fundamentally altered by humans.
Before the 1980s, tiger sharks near Bermuda kept the turtles in check. But humans have since overfished these predators.
Heithaus does not think it is time yet for a limited culling of turtle populations, because the species is still highly endangered. But at some point, conservationists will have to figure out how to best protect the sea grass meadows. The only answer may be to stop overfishing sharks — action that might require international treaties — and learn as much as possible about species interactions, he said.
To Michael Soulé, who established the central tenets of conservation biology in a landmark article in 1985 and set up the Society for Conservation Biology, the root of these challenges is an overpopulated, overpolluted world.
“It’s not a question of managing species; it is a question of managing people, because it is people that are overexploiting the system in some cases,” Soulé said. “What it boils down to is: There’s too many people in the world trying to make a living off a finite resource.”
Soulé, a professor emeritus of environmental studies at the University of California at Santa Cruz, says humans must curb their appetite for fossil fuels and stop overfishing the oceans. He believes humans have an ethical duty to protect threatened species such as the bumphead parrotfish, even if it proves costly.
McCauley agrees with that, remembering the years he spent tailing the parrotfish of Palmyra.
“There is something special about hanging out on a reef with an iridescent green pink-nosed fish that makes your place on the planet a little bit richer and more special,” he said.
Vaidyanathan is a science reporter based in Washington.