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Some 1,000 miles south of the most southern tip of the Indian subcontinent, there lies a chain of islands quite unlike any other. These are the Chagos Islands, a remote archipelago that comprises seven atolls and more than 60 low-lying islands where the land looks like it is all but guaranteed to melt into the sea at any moment. Covered in tropical forest and surrounded by some of the most biodiverse coral reefs in the world, these islands are both beautiful and under threat.
Rising seas and the effects of climate change on the world’s oceans are urgent and present dangers to the Chagos Archipelago, as do invasive species—and in particular, rats. These rodents, brought to the islands by colonists in the 18th century, decimated the seabird population, which in turn led to fewer nutrients making it into the coastal seas, starving the coral reefs. These islands’ story reveals why conservation efforts to safeguard island ecosystems need to encompass both the land and the sea together.
Islands host an estimated 40 percent of all globally endangered and threatened species.
But Chagos is by no means alone in this experience. In the Caribbean, too, human colonial occupation brought with it invasive species that have had an indelible affect on the land and the sea. These invasions spark trophic cascades: Rats kill the seabirds, no seabirds means fewer droppings into the water, and fewer droppings means less nutrients for coral to grow and thrive. But, as coral scientist Casey Benkwitt explains, scientists like her wouldn’t necessarily notice this kind of connection just by looking at a reef without collaborating with conservation scientists working on land.
To explore these collaborations and how they can benefit island and ocean restoration, Benkwitt came together with two other leading figures in conservation, Pete Carr, whose work focuses on eradicating invasive species in the Chagos Islands, and Jenny Daltry, who studies island ecology in the Caribbean and Asia and is the Caribbean Alliance director for Re:wild. They talked about island connections, their “aha” moments, and what they hope for the future of island conservation.
To start, I think it is helpful to establish what we mean by invasive species in the island context.
Pete Carr: Let me first reintroduce islands. Islands make up about 5 percent of the global terrestrial landmass. But islands also host an estimated 40 percent of all globally endangered and threatened species. Unfortunately, islands have also hosted about 60 percent of all known extinctions since the 1500s. And one of the driving reasons for these extinctions and losses of biodiversity are alien, invasive species. I say “alien” because they shouldn’t be there. And “invasive” means that they come in and they take over.
One of the solutions for these invasive species is eradication. I think that if we were talking about this 25 years ago, we might say that eradication on these kinds of oceanic islands is enough to save the islands, help the people, protect their surrounding oceans, and save nature. For me, a key group are seabirds. For lots of the oceanic islands, too, seabirds are what make their ecosystems tick. That’s been the focus of my research in the Chagos Archipelago.
The Chagos Archipelago is in the Indian Ocean. If you draw a straight line down from India and another straight line across from Madagascar, they will intersect at the Chagos. About 32 of the Chagos islands are environmentally degraded. So coming back to the question—is eradication enough? Well, pulling on research from Palmyra (a coral atoll in the Pacific Ocean) and the Chagos Archipelago, we can say the answer is no, eradication is not enough.
And why is that?
Carr: When humans first colonized these islands, not just in the Pacific but also in the Indian Ocean, they brought invasive species with them—rats, cats, pigs, dogs—and they did a lot of the damage, but some of the damage was done by man changing the landscape of the island. They cut down the native forests and changed the native habitats to build settlements. And a lot of the islands in the Pacific and the Indian Ocean were farmed for coconut. And my research in the Chagos Archipelago, and other work done in Palmyra, has revealed that abandoned coconut plantations are no good for biodiversity.
There are three things that thrive in these abandoned coconut plantations: Mosquitoes, rats, and chickens. None are good for biodiversity.
So what I’ve been doing with the Chagos Conservation Trust is to produce a rat eradication plan, which we’ve finished, and now we are doing a vegetation management plan. We know it’s feasible and we know it can have a positive impact. We looked at the 32 islands in the most need of help, and we’ve prioritized two islands that could be rewilded and won’t be reinvaded by rats, as well as a few other islands. Importantly, we can also put a cost on how much to do it. So it’s not just a green dream any more. We know how to do it, and we know how much it should cost.
And what about other areas of the world? Jenny, how has your work in the Caribbean and Asia evolved over the last few years, and how are we doing in terms of conservation there?
Jenny Daltry: I started working in the Caribbean in the ’90s. The Caribbean is one of the great biodiversity hotspots and it’s also the region with the highest rate of species extinctions. Over the years, I’ve worked with local partners to bring back some of those species from the edge of extinction. I’ve also seen a number of catastrophes and experienced the climate breakdown. I’ve seen how nature can help us when no one else can.
To give some examples of the kind of restoration we do, we’ve restored 30 islands by removing rats, removing goats and other invasive species. And in turn, we’ve helped save dozens of species from extinction, including several reptiles, such as the Lesser Antillean iguana, a snake called the Antiguan racer, and the St. Lucia whiptail lizard. We’ve also seen a huge increase in seabirds—some 20-fold increase. So we’re on the right track.
And how is climate change impacting that work?
Daltry: Being on the ground, my eyes have been opened to what climate change means. Not only sea level rise, or worsening drought, but more intense and frightening hurricanes. In my lifetime, the frequency of category 4 and category 5 hurricanes has more than doubled. That means wind speeds of more than 130 miles an hour, sometimes as much as 190 miles an hour. When the hurricanes come, they bring storm surges, which are like tsunamis that smash into the coastline where most of the people live, but also torrential rain, which brings landslides and mudslides.
Being on a small island when a category 5 hurricane is coming is absolutely terrifying. But it’s not just a frightening disaster; we can see nature helping us. For example, in 2017, Hurricane Irma hit Anguilla and brought with it storm surges of 20 feet high. This had a colossal impact, and smashed or destroyed a lot of buildings, and left many buildings submerged in floods. But then other parts of the island were completely untouched. Some great scientists from Environmental Systems Ltd, who are based in Wales, along with Anguilla National Trust, and local scientists started looking at Anguilla and trying to understand why some bits of the island were destroyed while others weren’t. They showed that there was a clear, positive impact of forests, mangroves, wetlands, seagrass beds, and coral reefs, on the infrastructure.
When you set out to go rewilding, don’t just monitor the main thing you’re targeting, monitor everything.
Using that model, they started to trace where could be restored to help prevent damage or disaster the next time a hurricane comes. I started sitting in meetings with the Red Cross, with disaster management committees, and with hotels to talk about the need to restore those natural boundaries. We all recognized that we need to restore the forests, we need to plant. It’s no longer just a batty conservationist like me saying we need to save the parrots and iguanas or we need to make a nicer environment for tourists. This is our defense. It’s a more practical, affordable, living, and beneficial guard against hurricanes than just building sea walls and other hurricane infrastructure instead.
Ultimately, the conversation around conservation on these island communities is starting to change. I am a herpetologist, but I’m starting to understand the values of these ecosystems for people as well.
Casey, when you hear stories about these islands and seabirds and the changing climate, what is your perspective as a marine ecologist who studies life underwater?
Casey Benkwitt: I’ve been studying coral reefs for more than 10 years now, and almost every coral reef ecologist will tell you the biggest threat is climate change. No one will say it’s terrestrial, invasive species that are a threat to reefs. But through our research, we see that what happens on land does make a big difference.
Coral reefs are threatened by climate change and they’re threatened by these marine heat waves that are getting more and more intense. Corals are already living at the edge of their thermal tolerance. So when it gets too hot, they lose all their color and bleach and die. We’re already locked in—even if we do something about climate change right now—to a few more degrees of heating. So we really need these more local solutions to help coral reefs survive in the meantime.
So through our work, we’ve been able to see what benefits seabirds specifically can have for reefs to help them withstand these effects of climate change and become more resilient systems as we continue to deal with the other big issues. Our work has shown that where there are seabirds we see corals grow twice as fast than around islands where there’s no seabirds because of the invasive rats and the coconut plantations. And because of this, the reefs recover faster. So in the Indian Ocean, the reefs were wiped out in 2015 and 2016 by a big bleaching event. And in less than four years, coral cover has completely recovered. And again, this was way faster around the islands with seabirds than those with rats.
This shows that these local, nature-based solutions can make a big difference, to not only promote healthy coral reefs, but then this can also feed back to the islands as well. Where you have healthy coral cover, the islands might be more able to withstand things like storm surges and sea level rise, which are also becoming more intense as climate change continues. These connections are even more important in the face of climate change.
We’re building on traditional and cultural knowledge of these connections that perhaps western science has to relearn. What was your “aha” moment, the moment when you suddenly saw things differently?
Carr: It took me three goes to have that “eureka” moment. The first one was in 1996. I was fortunate enough as a Royal Marine commando to be sent to one of the atolls in the Chagos Archipelago, Diego Garcia to do some work. I sat on the end of a place called the short pier, and I looked out to sea, and I just sat there with my binoculars. I raised my binoculars up and there were just thousands of red-footed boobies and frigate birds streaming past me, going on to these islands. I’ve been a fanatical birder all my life, and sitting on that pier on Diego Garcia, I thought, I’m going to commit myself. I was on the island for three days, and I knew I was going to commit myself to doing something for the Chagos Archipelago.
My second moment came when there was a visiting party of British Members of Parliament coming over to the Chagos Archipelago and I was hosting them. I took them out to this island group called the Three Brothers. We were in a small craft, sailing toward the Three Brothers at dawn. And one of the MPs tapped me on the shoulder and said “I think that island’s on fire!” And it wasn’t fire at all—it was seabirds leaving the island at dawn to go out into the ocean to fish. There were red-footed boobies leaving the side of the island like rapier missiles and there were frigate birds circling up above like a cloud of smoke and noddies flashing all around us. And I said, that’s not smoke, that’s seabirds leaving a pristine island.
Then the third time, when it really sunk home that conservation is what I should be doing with my life, was when I took the same MPs to another island. And I asked one of them, “do you think it has seabirds or not, or do you think it has rats or not?” And I remember saying, “look at the island. There is no noise, no turtles around, no seabirds flying above.” That’s when the hammer fell. I knew I had to get involved in the conservation of the Chagos.
Daltry: When I first started working in the Caribbean, the first task I did was at the invitation of the government of Antigua to try and save the Antiguan racer snake, which was down to about 50 individuals. We realized they were being eaten by rats on the islands. The snakes are really small, sweet, and gentle and didn’t fight back. So the first island we worked on was called Bird Island and I asked the local fisherman why it was called that because there were no birds. And they said there used to be birds, but now there are lots of rats. And the “aha” moment for me was when we had eradicated the rats, things started to change on the island. The racer snakes started doing really well, they doubled in number. And then they started getting some birds. There were flowers popping up that a local botanist said had gone extinct. It was becoming more green. The forest was coming back. I realized then that rats don’t just eat the odd seabird egg or attack the odd snake. They fundamentally changed the whole ecosystem. They’re eating all the seeds, the roots, they gnaw on the plants. And when you take them away, it confirms that nature can bounce back and bounce back really fast.
So really, the “aha” is that when you set out to go rewilding, don’t just monitor the main thing you’re targeting, monitor everything. It took me a while to learn about the impacts of the island restoration on the marinescape and that we should all be working together to monitor the marinescape as well as the landscape—as well as the birds, the reptiles, the insects, everything—to truly understand what impact invasive species have and what impact rewilding can have.
Benkwitt: I love being underwater. I spend as much time as possible with my head in the water, which I think is great for my mental well-being but is not so great for actually understanding the reef. And so my “aha” moment has been how important these collaborations and connections are between me, who has focused on the reef and gone through the academic system, and people like Pete who study seabirds and terrestrial researchers like Jenny who see what is going on on land.
Just one example of that is an experiment where we moved little, tiny pieces of corals between islands with seabirds and nearby islands that don’t have seabirds because of rats. And we monitored their growth over three years. The corals around the islands with seabirds outgrew the ones around those without birds by far. To realize that what’s going on above water, with the seabirds bringing in nutrients through their droppings and basically fertilizing the reef, it’s making such a stark difference. By only focusing on the reef, we’re not seeing the whole picture. We need to see what’s happening on land to understand what’s going on underwater.
What are the biggest challenges you see in your work?
Benkwitt: There are a lot of challenges that face coral reefs. They are under threat. Just the other week I was traveling back from fieldwork and talking to the border patrol agent to get back into the United States and he asked what I had been doing and I told him I was a scientist studying coral reefs. His face just dropped and he said, “Oh are they all going to be dead in a few years?” And I think that’s the perception a lot of people have, but I still have hope. It’s a challenge to convey that message that there is still time but in the face of this big, ticking clock it is a big challenge. Hope is really important.
Carr: In some ways, my work is simple. I work on the Chagos Archipelago and there’s only one island that has human habitation, and it’s a military base. Island restoration is easier on uninhabited islands. But there is another side to this: There are political issues with the Chagos Archipelago involving displaced islanders who want to return to the islands. So for me, having a clear path, politically, to restoring the islands would really help our work. And the other big challenge is funding, whether from governments or private companies.
Daltry: Funding is a big challenge, for sure. I’ve worked on rewilding 30 islands, and there’s thousands of islands out there. And so scaling up really quickly is a challenge. It’s not just a question of funding, but it’s also a question of capacity on the ground. We work with a lot of brilliant conservationists, but trying to get them resources and the know-how so that they can take on these challenges themselves. And then, the other big challenge is that throughout the Caribbean, many people are feeling the effects of climate change. The hurricanes are getting worse. The droughts are getting worse. But after these events happen, memories can be short and we slip into old habits and forget what we learned. Ultimately, we need longer-term plans to restore and develop these islands to the benefit of the people and biodiversity.
Can you explain a little bit more about how we can best monitor success objectively, and not just anecdotally?
Daltry: The trouble for conservation practitioners is that doing the work doesn’t leave a lot of time for writing scientific papers, and that means a lot of the data that are being collected and gathered to monitor these projects’ success isn’t going into the literature or be made readily available to other groups doing similar work in other parts of the world. We need help from the academic community to come and help us investigate more closely and get the work written up. But on the other hand, when we’re talking to the decision makers—whether the landowners or the government—sometimes showing a scientific paper or data isn’t actually what inspires them to act so much as simply showing a before and after photo, or taking them to an island and showing them one with seabirds and one that looks dead. So we also need help to capture it visually in ways to show non-scientists what we are doing and have these more informal ways of communicating.
Are any of you doing that kind of documenting, or storytelling now?
Daltry: Yes. But more needs to be done. For example, if you look at videos or images of Redonda Island, you’ll see a clear transformation from what looks like a moonscape to a lush forest full of birds within five years. That’s phenomenally quick. But there are also lots of stories out there that haven’t been told yet. We need to get better at recording these things ourselves, too, because if we document the islands before they are restored and then after, then you will see the island come back to life. And that’s a great story. 
Lead photo by Ed Marshall
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