Rat control should be considered an urgent conservation priority on many remote tropical islands to protect vulnerable coral reefs, according to an international research collaboration including The University of Western Australia.
New research has confirmed that invasive rats decimate seabird populations, with previously unrecognised consequences for the extensive coral reefs that encircle and protect these islands.
Invasive predators such as rats – which feed on bird eggs, chicks, and even adults birds – are estimated to have decimated seabird populations within 90 per cent of the world’s temperate and tropical island groups, but until now the extent of their impact on surrounding coral reefs wasn’t known.
The new study, led by researchers at The University of Western Australia, Lancaster University, ARC Centre of Excellence for Coral Reef Studies and Dalhousie University, examined tropical ecosystems in the northern atolls of the Chagos Archipelago to uncover how rats have impacted surrounding reefs.
An extraordinary set of remote tropical islands in the central Indian Ocean, the Chagos islands provided a perfect laboratory setting as some of the islands are rat-free, while others are infested with black rats - thought to have been introduced in the late 1700s and early 1800s.
This unusual context enabled the researchers to undertake a unique, large-scale study directly comparing the reef ecosystems around these two types of islands.
By examining soil samples, algae, and counting fish numbers close to the six rat-free and six rat-infested islands, scientists uncovered evidence of severe ecological harm caused by the rats, which extended way beyond the islands and into the sea.
Rat-free islands had significantly more seabird life and nitrogen in their soils, and this increased nitrogen made its way into the sea, benefiting macroalgae, filter-feeding sponges, turf algae, and fish on adjacent coral reefs.
Fish life adjacent to rat-free islands was far more abundant with the mass of fish estimated to be 50 per cent greater.
The team also found that grazing of algae – an important function where fish consume algae and dead coral, providing a stable base for new coral growth – was 3.2 times higher adjacent to rat free islands.
David Stacey (UWA Media and Public Relations Manager) (+61 8) 6488 3229/ (+61 4) 32 637 716