January 21, 2025
Ha’apai Islets boost Tonga’s Biodiversity Conservation Efforts with Invasive Species Removal
Our work in Tonumea and Kelefesia shows how Tonga is leading the way in restoration and rewilding in the Pacific!
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Published on
August 27, 2024
Written by
Island Conservation
Photo credit
Island Conservation
The Republic of the Marshall Islands (RMI) is home to some of the most remote atolls in the North Pacific, if not the world. Characterized by their low elevation and unique composition, the three Island-Ocean Connection Challenge (IOCC) projects located in RMI—Jemo, Bikar, and Bokak—offer key opportunities to demonstrate what low-lying coral atolls stand to gain from holistic ecosystem restoration.
All the land of RMI’s atolls is composed of fossilized coral. This feature marks these atolls as unique from most other land on our planet: rather than being built up by geological processes such as volcanic activity and plate tectonics, coral atolls are strictly biological.
Coral atolls form when fringing reefs outlive the volcanic islands they once encircled. Thriving in the shallow waters of lagoons, these reefs act like living superorganisms, growing, shrinking, and changing based on environmental conditions.
While this means that everything under the surface of the water is in constant flux, there are not any geologic processes occurring to build up elevation on land. In fact, the entire country’s average elevation is only 7 feet, or just over 2 meters, which means rising sea levels pose a serious existential threat to the people and ecosystems that depend on the land to survive.
Nonetheless, these islands have survived massive transformations in sea level in the millions of years they have existed. The fact that these reefs extend thousands of meters below sea level suggests that coral, growing on top of itself, has built them up over time to counteract a gradual subsidence of the underlying volcanic basalt—accounting for their endurance even as their original volcanic islands eroded away.
Above the surf, plants and animals also keep erosion at bay. Seabirds, bringing key nutrients from the sea to the land in the form of their guano, enrich soil for plants such as Pisonia and Heliotropium to lock their roots into the land.
Storms and waves, which are often thought of as sources of erosion, can also perform the opposite function. Breaking off pieces of coral from the reef, the ocean can add this sediment to existing land, extending the coastline.
But all of these processes depend on the overall health and wellbeing of the island ecosystems that support them. And the delicate balance between land and sea that sustains these communities is currently under threat by a damaging invasive species: rats. Rats predate on baby crabs, seabird eggs, and turtle hatchlings, interrupting the flow of nutrients through the ecosystem and imperiling these low-lying islands. But there’s hope: IOCC partners are working together to holistically restore these islands by removing invasive species and accelerating the return of native plants and animals, securing their futures for generations to come.
Jemo Island is a 16-hectare, uninhabited coral island in the Pacific Ocean, in the Ratak Chain of the Republic of Marshall Islands. The local community of islanders living on Likiep Atoll, about 40km away, treasure Jemo as a source of food. They travel to the island to fish, hunt crabs, and harvest crops such as pandanus and copra (coconut).
The Likiep community shares that the prevalence of rats on the island makes it difficult to access and harvest these resources. Upon making shore, they need to tie up their supplies to keep them safe from rats, and oftentimes they find their harvest raided and destroyed. With their blessing, IOCC partners are removing invasive rats from this beautiful tropical islet.
Jemo is also listed as one of the three major breeding sites for Green Sea Turtles, an endangered species whose population is currently in rapid decline. Restoring Jemo is key to protecting both Likiep’s food security and the breeding sites of Green Sea Turtles, ensuring more hatchlings survive.
IOCC partners are performing similar work on Bikar Atoll, one of the smallest atolls in the Marshalls, located north of Jemo. Along with Bokak Atoll, Bikar may be one of the only remaining semi-arid atoll ecosystems left in the world undisturbed by human habitation. Its three larger islands, Jabwelo, Almani, and Bikar, are composed partially of dry heliotropium landscapes and partially of humid Pisonia forest. The Pisonia forests may be the most intact of their kind in the world, with old-growth trees providing plentiful shelter to birds and hermit crabs.
Bikar’s sheltered lagoon makes it, like Jemo, an important breeding site for Green Sea Turtles, which are similarly vulnerable to invasive rats. Teeming with seabirds, such as Black Noddies, Masked Boobies, and White Terns, Bikar also offers refuge for migratory birds. The IUCN-listed threatened Bristle-Thighed Curlew, which breeds in Alaska, flies down to the North Pacific during winter, along with the Pacific Golden Plover.
In addition to providing a seasonal home for migratory birds and a year-round home for seabirds, Bikar Atoll also fosters unique, delicate corals with abundant fish populations. The pass where its lagoon empties into the sea allows pelagic fish such as sharks and tuna to hunt and mix with shallow-water reef fish such as the Two-spot Red Snapper, Humpback Red Snapper, Leopard Grouper, and Humphead Parrot fish.
Bokak Atoll is like Bikar: semi-arid and remote. But it is much more remote than Bikar, its closest neighbor at 280 km. Also known as Taongi Atoll, Bokak’s flora and fauna have benefitted from this isolation as they’ve developed relatively free from human intervention. It also differs from Bikar in its rainfall, which is more scarce—marking it as the driest atoll in the Marshall Islands.
As a result of its isolation and dryness, its vegetation is very distinct. Rather than containing Pisonia forests, Bokak’s flora consists mainly of Heliotropium and sparse endemic bunchgrass. These savannas are unique in the region—and perhaps the world.
This atoll and its abundant birds and corals are under the same threat as Bikar and Jemo. IOCC partners have identified it as a site where the intervention of invasive species removal stands to yield massive benefits to the ecosystem. Its sensitive corals and endemic grasses will benefit from the increased nutrients that they’ll receive from seabird guano as the bird populations increase.
The people of the Marshall Islands know that their home is under severe threat from climate change impacts such as extreme weather and rising sea levels. Removing invasive mammals is an important first step in the restoration of these three very important ecosystems. Marshallese organizations (the RMI Ministry for Environment and Commerce, the Marshall Islands Conservation Society, and the Marshall Islands Marine Resources Authority) are partnering with international bodies (Secretariat of the Pacific Regional Environment Programme – Pacific Regional Invasive Species Management Support Service – PRISMSS, New Zealand Ministry of Foreign Affairs, Island Conservation, and OneReef) to realize their vision of thriving, vibrant, resilient atolls.
Want more information on Island-Ocean Connection Challenge projects? Please visit our Projects Page.
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