Page 59 - BBC Wildlife Volume 36 #02

AGENDA OPINION

Mark Carwardine’s

AT A GLANCE...

25
CORAL BLEACHING

WHAT IS CORAL? together cover an area no more frequent, more
When corals
It may look like a plant but bigger than France. intense and more
expel the algae
it is an animal, related to sea living in their widespread, leading
anemones. A tiny, soft-bodied WHY ARE THEY tissues, they to massive die-offs
creature called a ‘polyp’, it UNDER THREAT? turn white. around the world. As
lives with thousands of other Coral reefs are fragile well as a shocking
polyps to form a colony. ecosystems. Major amount of regional
So-called hard coral polyps threats include bleaching, there
extract calcium carbonate pollution, fishing have been three
from the seawater and use with cyanide and Global Bleaching
it to build exoskeletons to dynamite, overfishing, Events – in 1998,
protect themselves. They coastal development, 2010 and, most
build on the exoskeletons of collection for the recently, June 2014
their ancestors and, as the pet and curio to May 2017. Experts
centuries pass, the coral trades, coral mining predict that if greenhouse
reef slowly grows. for building materials and gas emissions are not
sedimentation. According to drastically reduced, these
WHAT ABOUT THE WWF, roughly one-quarter events will become routine.
FAMOUS ‘SPECIAL of coral reefs worldwide are ` SMALL
RELATIONSHIP’? already considered damaged RISES IN HOW IS THE GREAT
Reef-building corals would beyond repair, and most of the BARRIER REEF DOING?
not survive without single- rest are under serious threat. TEMPERATURE The Great Barrier Reef – the
celled algae living inside their FOR A FEW world’s largest living structure
tissues. In this remarkable WHAT ABOUT CORAL – has experienced its worst
symbiotic relationship, the BLEACHING? WEEKS AT ever mass bleaching events in
coral provides the algae The symbiotic algae are A TIME IS the past two years, and these
with a home and nutrients highly susceptible to changes are believed to have killed at
for photosynthesis (from in their environment – it ENOUGH TO least half the coral.
its own metabolic waste) doesn’t take much for them CAUSE CORAL
and, in return, the algae to stop producing food and BLEACHING.” CAN CORAL REEFS
provides the coral with food die. Then they are ejected RECOVER?
(to supplement the food it from the coral. If they go, Yes and no. The polyps can
scoops out of the seawater). so do their vibrant colours catch their own food and
It is these extra nutrients that and all that’s left is the survive for a short time
enable the coral to build reefs. coral’s white skeleton. This without the algae, but they
is ‘coral bleaching’. Many ultimately die themselves if
WHAT IS SO SPECIAL environmental issues cause it, they can’t find replacements.
ABOUT CORAL REEFS? but the single biggest factor is The problem is that they need
It would be hard to exaggerate rising sea temperatures due time – full recovery can take
their importance. Teeming to global warming. Coral reefs as long as a decade. If the
with life, they support are already operating very temperature is too high
MARK CARWARDINE
more species than any near to their upper limit of is a frustrated and for too long, or it peaks too
frank conservationist.
other marine environment heat tolerance, so small rises often, the chances of survival
Every month he
and even rival rainforests of just 1–2ºC above the norm demystifies some of the are slim. And, if the reefs
in their biodiversity. They for a few weeks at a time is most important issues die, everything else dies
Jurgen Freund/naturepl.com support fishing industries HOW BAD IS THE the organisations + FIND OUT MORE
affecting the world’s
act as natural barriers,
enough to cause bleaching.

with them.
wildlife and assesses
that protect it.
and communities, provide
PROBLEM?
employment through tourism,
O Would you like to
National Ocean Service
comment? Email
Very bad. Over the past 30
and much more. Yet all
website: http://bit.ly/2zLZrDy
wildlifeletters@
the coral reefs in the world
February 2018 years bleaching has become immediate.co.uk BBC Wildlife 59