Tropical coral reefs are among our most spectacular ecosystems, yet a rapidly warming planet threatens the future survival of many reefs. However, there may be hope for some tropical reefs in the form of feathered friends. A new study led by researchers at Lancaster University has found that the presence of seabirds on islands adjacent to tropical coral reefs can boost coral growth rates on those reefs by more than double. And as a result of this faster growth, coral reefs near seabird colonies can bounce-back much quicker from bleaching events -- which often cause mass die off of corals when seas become too hot -- the international team of researchers also discovered.

The study, published today in Science Advances, focused on Acropora, an important type of coral that provides complex structures supporting fish populations and reef growth, and which is also important for protecting coastal areas from waves and storms. The researchers found that Acropora around islands with seabirds recovered from bleaching events by around 10 months faster (approx. three years eight months) compared to reefs located away from seabird colonies (four years six months).

Researchers say these shorter recovery times could prove the difference between continuing to bounce back for some reefs in the face of a warming planet where damaging bleaching events now occur much more frequently than in earlier decades. The key to how seabirds can help tropical coral reefs to grow and recover more quickly is through their droppings. Seabirds feed on fish in the open ocean far from islands, and then return to islands to roost -- depositing nitrogen- and phosphorus-rich nutrients on the island in the form of guano. Some of the guano is washed off the islands by rain and into the surrounding seas where the nutrients fertilise corals, and other marine species. Seabird-derived nutrients are directly driving faster coral growth rates and faster recovery rates in Acropora coral.