When they return, their droppings, called guano, fertilise the soil and run off into the water, nourishing plankton and algae, and the fish that feed on them. They nest in native trees, sheltered by branches and foliage, and fly far out to sea to catch fish. Seabirds act as a kind of nutrient delivery service for these remote places. “When you start thinking about atolls, they’re in very, very remote places where there’s very, very little input of nutrients to the environment,” says Rebecca Vega Thurber, a microbiologist at Oregon State University and expert in marine ecosystems. Tropical atolls like Palmyra also present us with a compelling ecological mystery: they are lush and teeming with life, yet exist in very nutrient-poor environments. They make up only 5% of our planet’s land area, but are home to an estimated 19% of its bird species and 17% of flowering plants. Islands play an outsized role in our planet’s biodiversity. The plankton along the palm forest coastlines was less abundant, and there were fewer manta rays, which feed on plankton, than along native forest coastlines. On islets with palm forests, the soil was poorer in nutrients than on those with native forests, as was the water running off them. As the supply of bird droppings declined, the impact rippled through the ecosystem. Seabirds avoided nesting in the palms, preferring sturdy native trees with branches. The coconut palms also damaged the delicate chain of nutrients that sustained life on and around Palmyra. On other tropical islands, evidence emerged that rodent invasions were affecting species as ostensibly far-removed as coral reefs, by disrupting their supply of nutrient-rich seabird droppings. Some crab species were dwindling, or had even completely disappeared from sight. Eight seabird species roaming the wider area were ominously missing – according to conservationists, possibly because the rats had driven them into local extinction. Invasive coconut palms from abandoned plantations spelled further trouble for the birds, depriving them of their native habitat.īy the end of the century, the rats and palms had transformed the atoll’s entire ecosystem. On warm, wet Palmyra, the rodents thrived, quickly multiplying and feasting on young crabs, tree seedlings, and seabird eggs and chicks. But the ships also brought a host of stowaways to the islands: black rats. During World War Two, the US military stationed thousands of sailors on the Palmyra Atoll, a ring of pristine, coral-fringed islets in the Central Pacific Ocean.
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