Some of the world’s most valuable and fragile ecosystems are found on islands, which are home to a large variety of plants, land and marine species and communities rarely found elsewhere. Understanding the interconnectedness of ecosystems could launch a “new era of conservation”, bringing knock-on benefits to neighbouring ecosystems, such as surrounding marine environments.

The study found that carefully planned actions such as removing invasive species and supporting coastal “connector” species could go some way in supporting island ecosystems. Beyond this, they can also address biodiversity loss, declining ocean health and climate change.

Connector species such as seals, seabirds and land crabs play a key role in ensuring healthy land-sea ecosystems and facilitating the exchange of nutrients between oceans and islands. However, important connector species are increasingly threatened and driven toward extinction by invasive mammals such as rats, which eat young hatchlings or bird eggs. This is aided by the fact that endemic island species do not have evolutionary defence mechanisms against non-native species. The decline of such valuable connector species carries direct consequences to both land and marine ecosystems, such as coral reefs, seagrass meadows and mangroves.

Seabirds, for example, feed in open ocean areas and bring high quantities of nutrients to both island and ocean ecosystems through guano deposits – accumulated excrements which contain natural mineral deposits and high levels of nitrogen, phosphate and potassium that support plant and vegetation growth. Islands with high seabird populations have been linked to higher fish populations, increased coral recovery rates and faster-growing coral reefs.

The isolated nature of islands means their ecosystems are particularly vulnerable to ecosystem changes, including overfishing or the introduction of invasive species. On the other hand, island ecosystems can recover rapidly and bounce back when supported by restoration measures.

The study highlighted six environmental factors, which can inform the selection of locations that would benefit most from the removal of invasive species – rainfall, vegetation cover, soil hydrology, elevation, oceanographic productivity and wave energy. The most significant marine co-benefits are expected to be seen on islands with calmer tides, high rainfall and other conditions associated with high land-sea connectivity.

For instance, Floreana Island in Ecuador’s Galapagos Archipelago, and Sonsorol Island in Palau, are islands with high land-sea connectivity potential. Both islands have joined the environmental campaign Island-Ocean Connection Challenge. Launched earlier this year, the campaign aims to rewild and restore at least 40 island ecosystems of global significance by 2030 to benefit oceans, islands and communities. Achieving this goal could mean the protection of an estimated 600 populations of 250 threatened wildlife species.

“Ridge-to-reef” restoration efforts will prevent further biodiversity loss and restore populations of native and endemic wildlife, which has cascading impacts on marine ecosystems surrounding the island. Healthy island and marine ecosystems also have positive impacts on climate resilience. From a social perspective, these benefits will also support local communities, which can play a crucial role in implementing restoration efforts.

It’s worth highlighting the interlinkages between healthy land and ocean ecosystems have been understood and managed by Indigenous island communities for a long time, but Western conservation has largely overlooked this approach, according to study co-author Penny Becker. Indigenous Hawaiians, for example, use ancient ahapua’a (watershed) resource management systems to manage fishponds, ocean areas and farming zones to ensure sustainable natural resources and protection from flooding and storms.

Scripps Institution of Oceanography