Invasive rats are harming coral reefs by eating both the eggs and chicks of native bird species, according to a new study published in the journal Nature. Islands are their own ecosystems, and few things fuel them more than bird droppings. That is because the guano contains essential nitrogen that helps plants grow and fuels the cycle of life.
As a result, if bird populations decline it affects many other plants and animals. The new study — which comes from researchers at Lancaster University — found that it affects coral reefs as well.
The team made the discovery by comparing six rat-free islands in the Indian Ocean’s Chagos Archipelago to six infested ones from the same region. That allowed them to quantify the rodent’s ecological damage and track specific types of nitrogen across the islands.
Soil samples collected from islands without rats showed those landmasses had 250 times more nitrogen input from bird droppings than rat-infested regions. In addition, the fish and algae of coral reefs in rat-free areas had higher levels of nitrogen.
Researchers next compared the data against nature surveys taken of wildlife on the different islands, a process that revealed fish biomass in the reefs around rat-free islands was 50 percent greater than ones near the rodents. Seabird populations also tended to be 750 times greater on rat-free islands.
That is important to note because when seabirds die there are less droppings on the island, which then negatively affects coral populations by offsetting the balanced input of nitrogen and phosphorous into the ecosystem. Another way the lack of droppings harms reefs is because it makes it harder for coral to reproduce and bounce back from disasters.
This study shows that getting rid of rats could then bolster coral reefs and help them recover. Though that may seem like a large task, conservationists have already attempted some rat eradication programs with success rates of 85 percent. That solution can cause harm to local species, but scientists believe it is worth that risk.