Oceans
losing oxygen at unprecedented rate, experts warn
Sharks,
tuna, marlin and other large fish at risk from spread of ‘dead zones’, say
scientists
Fiona
Harvey in Madrid
Sat 7 Dec 2019 09.00 GMT
All fish
need dissolved oxygen, but biggest fish such as tuna (above) are particularly
vulnerable because they need much more to survive. Photograph: Mark
Conlin/Getty Images
Oxygen in
the oceans is being lost at an unprecedented rate, with “dead zones”
proliferating and hundreds more areas showing oxygen dangerously depleted, as a
result of the climate emergency and intensive farming, experts have warned.
Sharks,
tuna, marlin and other large fish species were at particular risk, scientists
said, with many vital ecosystems in danger of collapse. Dead zones – where
oxygen is effectively absent – have quadrupled in extent in the last
half-century, and there are also at least 700 areas where oxygen is at
dangerously low levels, up from 45 when research was undertaken in the 1960s.
The
International Union for the Conservation of Nature presented the findings on
Saturday at the UN climate conference in Madrid, where governments are halfway
through tense negotiations aimed at tackling the climate crisis.
Grethel
Aguilar, the acting director general of the IUCN, said the health of the oceans
should be a key consideration for the talks. “As the warming ocean loses
oxygen, the delicate balance of marine life is thrown into disarray,” she said.
“The potentially dire effects on fisheries and vulnerable coastal communities
mean that the decisions made at the conference are even more crucial.”
All fish
need dissolved oxygen, but the biggest species are particularly vulnerable to
depleted oxygen levels because they need much more to survive. Evidence shows
that depleted levels are forcing them to move towards the surface and to
shallow areas of sea, where they are more vulnerable to fishing.
Some ocean
areas are naturally lower in oxygen than others, but these are even more
susceptible to damage when their oxygen levels are depleted further, the
report’s authors said. Species that can more easily tolerate low oxygen levels,
such as jellyfish, some squid and marine microbes, can flourish at the expense
of fish, upsetting the balance of ecosystems. The natural oceanic cycles of
phosphorus and nitrogen are also at risk.
The world’s
oceans are already being overfished, and assailed by a rising tide of plastic
waste, as well as other pollutants. Seas are about 26% more acidic than in
pre-industrial times because of absorbing the excess carbon dioxide in the
atmosphere, according to the Intergovernmental Panel on Climate Change, with
damaging impacts on shellfish in particular.
Low oxygen
levels are also associated with global heating, because the warmer water holds
less oxygen and the heating causes stratification, so there is less of the
vital mixing of oxygen-rich and oxygen-poor layers. Oceans are expected to lose
about 3-4% of their oxygen by the end of this century, but the impact will be
much greater in the levels closest to the surface, where many species are
concentrated, and in the mid to high latitudes.
Intensive
farming also plays a major role. When excess artificial fertiliser from crops,
or manure from the meat industry, runs off the land and into rivers and seas,
it feeds algae which bloom and then cause oxygen depletion as they decompose.
The problem
of dead zones has been known about for decades, but little has been done to
tackle it. Farmers rarely bear the brunt of the damage, which mainly affects
fishing fleets and coastal areas. Two years ago, the meat industry in the US
was found to be responsible for a massive dead zone measuring more than 8,000
sq miles in the Gulf of Mexico.
This year’s
UN climate conference, known as COP25, was originally billed as the “Blue COP”,
with a spotlight on the oceans for the first time in the history of the
negotiations. The focus was chosen because of the original location in Chile, a
country with more than 4,000km of coastline and a strong reliance on the marine
economy.
But the
move to Madrid, forced by political unrest in Santiago, has meant many of the
planned events have been curtailed. Scientists and activists gathered in
landlocked Madrid are trying to highlight the issues by demonstrating how vital
the seas are in protecting us from climate chaos – as they absorb so much of
the excess carbon dioxide, and excess heat, in the atmosphere – and how much
they are at risk from its impacts.
Protecting
marine life could help the oceans to function better, soaking up more carbon
and providing barriers against sea level rises and storm surges, in the form of
coral reefs and mangrove swamps.
“A healthy
ocean with abundant wildlife is capable of slowing the rate of climate
breakdown substantially,” said Dr Monica Verbeek, the executive director of the
group Seas at Risk. “To date, the most profound impact on the marine
environment has come from fishing. Ending overfishing is a quick, deliverable
action which will restore fish populations, create more resilient ocean
ecosystems, decrease CO2 pollution and increase carbon capture, and deliver
more profitable fisheries and thriving coastal communities.”
Campaigners
says ending overfishing would restore fish populations, create more resilient
ocean ecosystems and reduce CO2 pollution. Photograph: Rebecca Griffiths/Sea
Shepherd
“Ending
overfishing would strengthen the ocean, making it more capable of withstanding
climate change and restoring marine ecosystems – and it can be done now,”
explained Rashid Sumaila, professor and director of the fisheries economics
research unit at the University of British Columbia. “The crisis in our
fisheries and in our oceans and climate are not mutually exclusive problems to
be addressed separately – it is imperative that we move forward with
comprehensive solutions to address them.”
A study
published at COP25 by Greenpeace International showed that restoring marine
ecosystems could play a major role in tackling climate chaos.
Sem comentários:
Enviar um comentário