Marine
food chains at risk of collapse, extensive study of world's oceans
finds
Important
ecosystems could be massively damaged by 2050 unless greenhouse gas
emissions and localised pollution is drastically reduced, researchers
say
Oliver Milman
Tuesday 13 October
2015 07.07 BST
The food chains of
the world’s oceans are at risk of collapse due to the release of
greenhouse gases, overfishing and localised pollution, a stark new
analysis shows.
A study of 632
published experiments of the world’s oceans, from tropical to
arctic waters, spanning coral reefs and the open seas, found that
climate change is whittling away the diversity and abundance of
marine species.
The paper, published
in the Proceedings of the National Academy of Sciences, found there
was “limited scope” for animals to deal with warming waters and
acidification, with very few species escaping the negative impact of
increasing carbon dioxide dissolution in the oceans.
The world’s oceans
absorb about a third of all the carbon dioxide emitted by the burning
of fossil fuels. The ocean has warmed by about 1C since
pre-industrial times, and the water increased to be 30% more acidic.
The acidification of
the ocean, where the pH of water drops as it absorbs carbon dioxide,
will make it hard for creatures such as coral, oysters and mussels to
form the shells and structures that sustain them. Meanwhile, warming
waters are changing the behaviour and habitat range of fish.
The overarching
analysis of these changes, led by the University of Adelaide, found
that the amount of plankton will increase with warming water but this
abundance of food will not translate to improved results higher up
the food chain.
“There is more
food for small herbivores, such as fish, sea snails and shrimps, but
because the warming has driven up metabolism rates the growth rate of
these animals is decreasing,” said associate professor Ivan
Nagelkerken of Adelaide University. “As there is less prey
available, that means fewer opportunities for carnivores. There’s a
cascading effect up the food chain.
“Overall, we found
there’s a decrease in species diversity and abundance irrespective
of what ecosystem we are looking at. These are broad scale impacts,
made worse when you combine the effect of warming with acidification.
“We are seeing an
increase in hypoxia, which decreases the oxygen content in water, and
also added stressors such as overfishing and direct pollution. These
added pressures are taking away the opportunity for species to adapt
to climate change.”
The research adds to
recent warnings over the state of the oceans, with the world
experiencing the third global bleaching of coral reefs.
Since 2014, a
massive underwater heatwave, driven by climate change, has caused
corals to lose their brilliance and die in every ocean. By the end of
this year 38% of the world’s reefs will have been affected. About
5% will have died.
Coral reefs make up
just 0.1% of the ocean’s floor but nurture 25% of the world’s
marine species. There are concerns that ecosystems such as
Australia’s Great Barrier Reef, which has lost half its coral cover
over the past 30 years, could be massively diminished by 2050 unless
greenhouse gas emissions are slashed and localised pollution is
curbed.
Meanwhile, warming
of the oceans is causing water to thermally expand, fuelling sea
level rises caused by melting land ice. Research released in the US
on Monday found that Antarctic ice is melting so fast that the whole
continent could be at risk by 2100, with severe consequences for
coastal communities.
Problems in the
ocean’s food chains will be a direct concern for hundreds of
millions of people who rely upon seafood for sustenance, medicines
and income. The loss of coral reefs could also worsen coastal erosion
due to their role in protecting shorelines from storms and cyclones.
“These effects are
happening now and will only be exacerbated in the next 50 to 100
years,” Nagelkerken said. “We are already seeing strange things
such as the invasion of tropical species into temperate waters off
south-eastern Australia. But if we reduce additional stressors such
as overfishing and pollution, we can give species a better chance to
adapt to climate change.”
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