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Eradicate rats to bolster coral reefs
Eradicate rats to bolster coral reefs
July 11, 2018, Lancaster University
Researcher surveying a coral reef in the Chagos Archipelago. Credit: Guy Stevens | Manta
Rat control should be considered an urgent conservation priority on many
remote tropical islands to protect vulnerable coral reefs, according to an
international team of scientists.
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% 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, published today in the journal Nature, examined tropical
ecosystems in the northern atolls of the Chagos Archipelago to uncover how
rats have impacted surrounding reefs.
Lead author Professor Nick Graham of Lancaster University, UK, said:
"Seabirds are crucial to these kinds of islands because they are able to fly to
highly productive areas of open ocean to feed. They then return to their island
homes where they roost and breed, depositing guano—or bird droppings—on
the soil. This guano is rich in the nutrients, nitrogen and phosphorus. Until
now, we didn't know to what extent this made a difference to adjacent coral
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 ratfree,
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, largescale
comparing the reef ecosystems around these two types of islands.
By examining soil samples, algae, and counting fish numbers close to the six
and six ratinfested
islands, scientists uncovered evidence of severe
ecological harm caused by the rats, which extended way beyond the islands
and into the sea.
2018 Eradicate rats to bolster coral reefs
Journal reference: Nature
Provided by: Lancaster University feedback to editors
Parrotfish feeding on a coral reef in the Chagos Archipelago. Credit: Nick Graham
islands had significantly more seabird life and nitrogen in their soils,
and this increased nitrogen made its way into the sea, benefiting macroalgae,
sponges, turf algae, and fish on adjacent coral reefs.
Fish life adjacent to ratfree
islands was far more abundant with the mass of
fish estimated to be 50% 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.
"These results not only show the dramatic effect that rats can have on the
composition of biological communities, but also on the way these vulnerable
ecosystems function (or operate)," said coauthor
Dr. Andrew Hoey from the
ARC Centre of Excellence for Coral Reef Studies ,Australia.
"Critically, reductions in two key ecosystem functions (grazing and bioerosion)
will likely compromise the ability of these reefs to recover from future
Professor Graham said: "The results of this study are clear. Rat eradication
should be a high conservation priority on oceanic islands. Getting rid of the
rats would be likely to benefit terrestrial ecosystems and enhance coral reef
productivity and functioning by restoring seabird derived nutrient subsidies
from large areas of ocean. It could tip the balance for the future survival of
these reefs and their ecosystems."
Associate Professor Aaron MacNeil from Dalhousie University, Canada, said:
"These results show how conservation can sometimes be a bloody business,
where doing right by the ecosystem means there is a time to kill. For these
invasive rats, that time is now."
The paper "Seabirds enhance coral reef productivity and functioning in the
absence of invasive rats," is published in the journal Nature.
Explore further: Remote corals pay the price of climate change
More information: Nicholas A. J. Graham et al, Seabirds enhance coral reef
productivity and functioning in the absence of invasive rats, Nature†(2018).