RATS AND PLASTICS: THESE ARE, MAY BE, THE TWO BIGGEST THREATS TO CORALS

Reproduced from  BBC News - Environment

RATS
But scientists studying reefs on tropical islands say the animals directly threaten the survival of these ecosystems.
A team working on the Chagos Islands in the Indian Ocean found that invasive rats on the islands are a "big problem" for coral reefs.
Rats decimate seabird populations, in turn decimating the volume of bird droppings - a natural reef fertiliser.
How do rats harm coral reefs?
The Chagos Archipelago provided a large-scale natural laboratory to answer this question; although the islands are uninhabited by humans, some of them are now home to invasive rats, brought by ships and shipwrecks. Other islands have remained rat-free.
"The islands with and without rats are like chalk and cheese," said lead researcher Prof Nick Graham from Lancaster University.
"The islands with no rats are full of birds, they're noisy, the sky is full and they smell - because the guano the birds are depositing back on the island is very pungent.
"If you step onto an island with rats, there are next to no seabirds."
By killing seabirds, this study revealed, rats disrupt a healthy ecosystem that depends on the seabird droppings, which fertilise the reefs surrounding the island.
On rat-free islands, seabirds including boobies, frigatebirds, noddies, shearwaters and terns travel hundreds of kilometres to feed out in the ocean. When they return to the island, they deposit rich nutrients from the fish they feed on.
"These nutrients are leaching out onto the reef," explained Prof Graham.



PLASTICS
One third of corals entangled with plastics
More than 11 billion items of plastic were found on a third of coral reefs surveyed in the Asia-Pacific region.
This figure is predicted to increase to more than 15 billion by 2025.
Plastic raises by 20-fold the risk of disease outbreaks on coral reefs, according to research. Plastic bags, bottles and rice sacks were among the items found.
"Plastic is one of the biggest threats in the ocean at the moment, I would say, apart from climate change," said Dr Joleah Lamb of Cornell University in Ithaca, US.
"It's sad how many pieces of plastic there are in the coral reefs ...if we can start targeting those big polluters of plastic, hopefully we can start reducing the amount that is going on to these reefs”.
It's thought that plastic allows diseases that prey on the marine invertebrates that make-up coral reefs to flourish. Branching or finger-like forms of corals are most likely to get entangled in plastic debris.
These are important habitats for fish and fisheries, the scientists say.
"A lot of times we come across big rice sacks or draping plastic bags," said Dr Lamb, who led the study.
"What we do find is these corals with a lot of complexity like branches and finger-like corals will become eight times more likely to be entangled in these types of plastics."
In the study, published in the journal Science, international researchers surveyed more than 150 reefs from four countries in the Asia-Pacific region between 2011 and 2014. Z