When invasive rats prey on island seabirds, coral reefs suffer.
On rat-free islands in the Chagos Archipelago in the Indian Ocean there were on average 1,243 birds per hectare compared with about two birds per hectare on rat-infested islands.
Rodentless islands were found to have healthier coral reef ecosystems because bird droppings, naturally rich in nitrogen, wash into the ocean and help keep reefs productive.
Bird droppings, or guano, are rich in certain heavy nitrogen isotopes — different forms of the element with the same amount of protons but varying numbers of neutrons — which come from the animals’ diet.
Nitrogen can act as a fertilizer for ocean plants and algae. More algae grow, leading to more fish grazing on the reefs and helping clear out dead corals, essential processes for a healthy reef.
Introduced by humans to the Chagos Archipelago in the late 18th century, rats have since devastated native seabird populations, including red-footed boobies and terns. Science News