Island conservation should focus on links between land, sea life

Research has shown that terrestrial and marine ecosystems reap benefits when invasive species are eliminated from islands.

One way to restore land-sea connections on islands is to eradicate invasive species, such as rats, which can harm native island species like seabirds and crabs. Image: Erwin Kodiat, CC BY-SA 3.0, via Flickr.

Stuart Sandin’s first impression of Palmyra Atoll, a remote island in the central Pacific Ocean, during a visit in 2004, was troubled. There were seabirds, but their presence was fragmented, likely because of the rats that had hitched a ride on board military ships and invaded the atoll during World War II. On walks through the forest, Sandin found broken eggshells and bird skeletons: evidence of rat predation.

But when conservation experts worked to eradicate the rats from Palmyra Atoll in 2011, the island and surrounding sea started to change, Sandin said.

“Within a few years, the sound of the seabirds got a lot louder, and the coconut crabs, once seemingly uncommon, had made the [island’s] field camp into a stomping ground,” Sandin, a community ecologist at the Scripps Institution of Oceanography, said in a press conference.

According to Sandin, seabirds are “connector” species, feeding in the open ocean and depositing nutrients both on the island’s terrain and in the coastal waters. In other words, seabirds create a vital link between land and sea, strengthening the overall island ecosystem.

In a new perspective piece in the Proceedings of the National Academy of Sciences (PNAS), Sandin and colleagues explore this reciprocity between land and sea on islands. Drawing on a vast body of existing research, they argue that island wildlife, ecosystems and even people can thrive when conservation efforts focus on restoring both land and sea together — an approach sometimes referred to as a “ridge to reef” model.

The removal of invasive species is one tool that can be used to reactivate land-sea connections; others include the restoration of native vegetation and the implementation of marine protected areas, the authors say. However, many current conservation efforts tend to focus on either land or sea, but not both. That needs to change, Sandin said.

“If we are only focused on the protections on land, we may end up with more seabirds on a particular island, which would be good for some of the terrestrial conservation goals,” Sandin, the co-lead author of the paper, told Mongabay. “If we only focused on the sea, we may put a marine protected area … but each of them is thinking about each ecosystem independently. If we think about them together, there may be some multiplied benefits.”

​​Islands are one of our last bastions of hope for preserving the biodiversity of the planet because there are so many of these unique species, and probably the most prominent ecological problems or management problems for islands is the preservation of the species.

Stuart Sandin, community ecologist, Scripps Institution of Oceanography

Research has shown how the removal of invasive species not only improves the terrestrial ecosystem, but strengthens the surrounding sea. For instance, a recent study found that eradicating rats from New Zealand’s Mercury Islands not only bolstered seabird populations, but that the seabirds helped fertilise the coastal waters, which enriched nearshore algal communities. Another study suggested that rat elimination enhanced coral reef productivity in the Chagos Archipelago in the Indian Ocean.

While there would be a relationship between land and sea in any coastal region in the world, the connection is most prominent on islands, Sandin said.

“On islands, especially small islands, the ocean’s all around,” he said. Land-sea connections also tend to be more noticeable on islands since changes, both negative and positive, occur over a smaller area of land, he added.

The PNAS piece draws on a suite of studies, many of them published in the last 10-20 years, but also acknowledges that traditional ecological knowledge holders have long known about the interconnections between land and sea on islands and have used this knowledge to manage their environments.

“We really should be listening more carefully to the local island communities and their traditional knowledge that they’re bringing to the table,” co-lead author Penny Becker, vice president of conservation for the nonprofit Island Conservation, said during the press call. “And in this case, Indigenous island people have long recognised the interconnections between islands and oceans. They embrace holistic solutions that span land and sea and community, and it’s woven into the fabric of their culture. And they’ve known for centuries that what happens to land happens at sea, and Western conservation is really just catching up to this idea.”

The authors identify six characteristics that can help strengthen land-sea connectivity, and which can be used to guide conservation efforts: precipitation, elevation, vegetation cover, soil hydrology, oceanographic productivity, and wave energy.

Scott Fitzpatrick, an expert in the archaeology of islands and coastal regions at the University of Oregon, who was not involved in the new paper, said the PNAS piece highlights “the importance of looking at islands and conservation from a ‘ridge to reef’ perspective,” particularly when it comes to the negative impacts of invasive species. However, he said the paper itself is “decoupled” from crucial anthropological, archaeological or paleoenvironmental perspectives, despite the authors acknowledging the importance of harnessing traditional ecological knowledge.

“While they recognise that ‘our understanding of land-sea connections across the globe spans multiple knowledge systems, including long-standing human knowledge from island communities through diverse perspectives,’ there really is no tacit acknowledgment of what these perspectives are, how they are known, and how any future analysis would need to incorporate coordination and cooperation within these communities,” Fitzpatrick said.

Despite this criticism, Fitzpatrick said the paper’s identification of six geographic properties of land-sea connections could be “interesting and useful” to island conservation efforts.

With invasive species being a primary issue for many islands, many conservation efforts have naturally focused on their eradication. For instance, experts recently eliminated rats from the Tetiaroa Atoll in French Polynesia, and have also attempted to rid the island of yellow crazy ants (Anoplolepis gracilipes), both of which wreaked havoc with the atoll’s native wildlife.

In April 2022, conservationists also launched the Island-Ocean Connection Challenge, a program focused on restoring and rewilding about 40 island ecosystems to benefit islands, their surrounding marine environments and local communities by 2030. Experts have identified Floreana Island in Ecuador’s Galápagos Archipelago and Palau’s Sonsorol Island as two places that could benefit from restored land-sea connections. Rats and other introduced species have invaded both islands.

“​​Islands are one of our last bastions of hope for preserving the biodiversity of the planet because there are so many of these unique species, and probably the most prominent ecological problems or management problems for islands is the preservation of the species, especially things like seabirds, or crabs or even iguanas,” Sandin said.

“In some cases, we’ve lost hope that we can protect things,” he added, “but we recognise that we do have agency and that we can increase or improve the livelihood of both our people and our ecosystems.”

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