guano

Atoll islands are made from sediment produced by corals, clams, snails, and varieties of algae that secrete carbonate. Under the right conditions, over time, fragments of coral skeletons, shells, and other sediments made by marine life are piled up by waves. Eventually, islands are formed – some large and some small. Atoll islands are home to a diversity of human cultures and are important refuges for a quarter of the world’s seabirds as well as numerous nesting sea turtles and tropical plants.

Rising sea levels – the rate of which has more than doubled over the past 30 years – are a mounting challenge for atoll islands. And by the end of this century, sea level is projected to rise between 11 and 40 inches, depending on the world’s actions with regard to greenhouse gas emissions.

The ability of atoll islands to persist depends on the health of their ecosystems and the extent to which their natural processes have been disrupted by human activity. To protect the most vulnerable islands, some researchers now propose using nature-based solutions – like restoring and protecting coral reefs and native forests.

Reclaiming seabird habitat can help reefs persist and restore the resilience of atoll islands. Seabird guano washes off islands and into reefs, providing nutrients that boost coral growth and fish populations.

Nature-based solutions cannot help the most urbanized atoll islands. These islands have already irreversibly lost their natural adaptive capacity. For those places, engineered approaches such as concrete seawalls are needed.

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How Natural Solutions Can Help Islands Survive Sea Level Rise

Photo, posted July 3, 2014, courtesy of Roderick Eime / MG Media via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

A new study by researchers at Lancaster University in the UK has found that the presence of seabirds on islands adjacent to tropical coral reefs can more than double the coral growth rates on those reefs.

The study found that when coral reefs grow faster, they can bounce back more quickly from bleaching events that occur when the seas become too warm. The focus of the study was a type of coral called Acropora, which provides complex structures supporting fish populations and reef growth.

The researchers found that Acropora around islands populated by seabirds recovered from bleaching events about 10 months faster than reefs located away from seabird colonies. Speeding up coral recovery times could prove the difference between continuing to bounce back from bleaching events and dying off.

The seabirds are helping the coral reefs with their droppings. The birds feed on fish in the open ocean far from islands and then return to the islands to roost. They deposit nitrogen- and phosphorus-rich nutrients in the form of guano, some of which is washed off of the islands by rain and into the surrounding seas. The nutrients fertilize corals and other marine species.

To determine whether the faster growth rates were really due to the bird-supplied nutrients, the researchers studied rat-infested islands that had no bird populations. The study confirmed that it was the presence of seabirds that provided enhanced nutrients for the coral reefs. In fact, a primary outcome of the study was to add further weight to the growing body of evidence of the ecological damage across ecosystems on land and sea from invasive rats on tropical islands.

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Feathered friends can become unlikely helpers for tropical coral reefs facing climate change threat

Photo, posted September 15, 2019, courtesy of Rickard Zerpe via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Natural solutions for disappearing islands

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Seabirds rescuing coral reefs

A new study by researchers at Lancaster University in the UK has found that the presence of seabirds on islands adjacent to tropical coral reefs can more than double the coral growth rates on those reefs.

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