Coral reefs are built by colonies of coral polyps that form a symbiotic relationship with algae. Rising ocean temperatures cause coral bleaching where the algae leaves the coral, making it vulnerable. Climate change has increased the frequency and severity of mass bleaching events that affect entire reef systems. The Great Barrier Reef experienced moderate to severe bleaching in 2020 during which 40% of surveyed reefs showed no bleaching but 25% had severe bleaching. Saving coral reefs requires reducing global warming through lowering carbon emissions to prevent further bleaching caused by temperature increases.

1. Coral
reef
Climate change and its effects- CORAL BLEACHING
A coral reef is an underwater ecosystem characterized by reef-
building corals.
Reefs are formed of colonies of coral polyps held together
by calcium carbonate.
Most coral reefs are built from stony corals, whose polyps
cluster in groups.
They are most commonly found at shallow depths in tropical
waters, but deep water and cold water coral reefs exist on
smaller scales in other areas.
The great majority of corals live in a symbiotic relationship with zooxanthellae, a type of single-celled dinoflagellate
algae. These microscopic algae live within the coral's tissues. Zooxanthellae produce energy-rich compounds through
photosynthesis, providing a food source that is absorbed and used by the coral.
In general, corals are highly dependent on this symbiotic relationship, receiving up to 90 per cent of their energy
requirements in this way.
Bleaching is a stress response that results when the coral algae relationship breaks down.
The term 'bleaching' describes the loss of colour that results when zooxanthellae are expelled from the coral hosts
or when pigments within the algae are degraded.
Because the photosynthetic pigments found in zooxanthellae give corals most of their colouration, the loss of
zooxanthellae renders the tissue largely transparent.
The white of the calcium carbonate skeleton is then clearly visible through the un-pigmented tissue, making the coral
appear bright white or 'bleached'.
In some instances, coral bleaching will result in corals taking on a pastel shade of blue, yellow or pink rather than
turning bright white.
This is due to proteins produced by some corals, which tint the coral tissue and become the dominant pigment during
bleaching, when zooxanthellae are absent.
The primary cause of mass coral bleaching is increased sea temperatures.
At a local scale, many stressors including disease, sedimentation, cyanide fishing, pollutants and changes in
salinity may cause corals to bleach.
Mass bleaching, however, affects reefs at regional to global scales and cannot be explained solely by localized
stressors operating at small scales.
Rather, a continuously expanding body of scientific evidence indicates that such mass bleaching events are closely
associated with large-scale, anomalously high sea surface temperatures.
Temperature increases of only 1-2ºC can trigger mass bleaching events because corals already live close to their
maximum thermal limits.
AR.POOJA KULKARNI ROLL NO- COLLEGE- SKNCOA 2021-2023
SEM II F.Y.M.ARCH
The Great Barrier Reef
Coral
Bleaching
Causes
SUBJECT- ECOLOGY SIGN- STAMP-
Climate
Change
Climate change is a shift in the average climate over a long period of
time. Climate affects nearly every aspect of our lives, from our food
sources to our transport infrastructure, from what clothes we wear, to
where we go on holiday. It has a huge effect on our livelihoods, our
health, and our future.
Contemporary climate change includes both global warming and its
impacts on Earth's weather patterns. The average temperature of the
planet has risen by around 1.5°C since the industrial revolution and
the last ten years was the warmest decade ever recorded.
The dramatic rise in global temperatures is caused by human emissions
of greenhouse gases into the atmosphere. Greenhouse gases are
gases that absorb heat energy. They act like a blanket wrapped around
the earth, trapping some of the sun’s heat within our atmosphere. The
more greenhouse gases in our atmosphere, the more heat is trapped.
Almost 90% of the extra heat trapped in our atmosphere by greenhouse
gases is being absorbed by the oceans, and warmer atmosphere and
oceans are causing steep declines in Arctic sea ice and increasing sea
levels.
One such impact of rising sea and ocean levels is observed on coral
reefs which are very sensitive to temperature change. These corals
undergo bleaching as temperature rises.
CLIMATE
CHANGE
INTENSE
DROUGHTS
HEAT
WAVES
MELTING
GLACIERS
WARMING
OCEANS
RISING SEA
LEVELS
STORMS
EFFECTS OF CLIMATE
CHANGE.
Placement of zooxanthellae in coral polyps
Change in
ocean
temperature
Runoff and
Pollution
Overexposure
to sunlight
Extreme low
tides

2. Climate change and its effects- CORAL BLEACHING
AR.POOJA KULKARNI ROLL NO- COLLEGE- SKNCOA 2021-2023
SEM II F.Y.M.ARCH
Coral bleaching is a common response of a coral under
stress, and isolated colonies or small patches of bleached
coral are not necessarily cause for concern. However, mass
bleaching events that span tens or even hundreds (and
sometimes thousands) of kilometers can affect entire
ecosystems and are a significant cause for concern for coral
reef managers and stakeholders.
Mass bleaching events are primarily triggered by sea
temperatures exceeding the normal summer maximum for
prolonged periods (weeks). The frequency and severity of
mass-bleaching events have been increasing over the last
few decades, causing reef degradation at a global scale.
These events are expected to occur even more often as
sea-surface temperatures continue to rise under global
climate change.
SUBJECT- ECOLOGY SIGN- STAMP-
Stages
from
Healthy
Coral
to
Dead
Coral
1. HEALTHY CORAL
Coral and algae depend on each
other for survival.
Corals have a symboitic relationship
with microscopic algae called
zooxanthellae that live in their tissue.
These algae are the corals primary
food source and give them their
colour.
2. STRESSED CORAL
If stressed the algae leaves the coral.
When the symboitic relationship
becomes stressed due to increased
ocean temperature or pollution, the
algae is expelled from coral tissue.
When temperatures exceed certain
thresholds, incoming light overwhelms
the photosynthetic apparatus,
resulting in the production of reactive
oxygen species that damage cellular
structures. Corals cannot tolerate high
levels of these toxic molecules, and
they must expel the zooxanthellae to
avoid tissue damage.
3. BLEACHED CORAL
Coral is left bleached and
vulnerable.
Without the algae, the coral
loses its major source of food,
turns white or very pale, and is
more susceptible to disease.
4. DEAD CORAL
Coral is left bleached and
vulnerable.
Without enough plant cells to
provide the coral with the food it
needs, the coral soon starves or
becomes diseased. Soon
afterwards, the tissues of the
coral disappear and the
exposed skeleton gets covered
with algae.
5. RECOVERING CORAL
At bleaching stage the coral can be
recovered and restored to its healthy
stage .
This can take place only when time
between two bleaching incidents is
more and algae growth is not dominant.
The coral can regain its zooxanthallae
naturally and redevelop its ecosystem
as before.
This process takes time and it also
builds immunity in corals to sustain
higher temperature.
But if the temperature increases during
this process and coral undergoes
another bleaching
then the risk of that coral dying
increases.
Recovering
of
coral
Mass
Bleaching
Incidents
Time line of Great barrier
reef bleaching incident
The
Great
Barrier
Reef
The Great Barrier Reef is the world's largest coral
reef system composed of over 2,900 individual reefs and 900
islands stretching for over 2,300 kilometres (1,400 mi) over an
area of approximately 344,400 square kilometres
(133,000 sq mi). The reef is located in the Coral Sea, off the coast
of Queensland, Australia, separated from the coast by a channel
100 miles wide in places and over 200 feet deep.
Out of 1036 reefs surveyed by scientists in a plane, 40% had no or
negligible bleaching, 35% had moderate bleaching and 25% had
severe bleaching. Based on these numbers, the 2020 event is not
as bad as the 2016 event, but is worse than the events in 2017,
2002 and 1998.
Longer and more frequent bleaching events are only
expected to become increasingly common as human-caused
climate change warms the planet. The more severe a marine
heatwave, the less likely corals are to recover from bleaching.
• https://reefresilience.org/stressors/bleaching/mass-bleaching/
• https://en.wikipedia.org/wiki/Coral_bleaching
• https://www.aims.gov.au/docs/research/climate-change/coral-bleaching/bleaching-
events.html#:~:text=Mass%20bleaching%20events%20in%201998,by%20an%20influx%20of
%20freshwater.
• https://www.smithsonianmag.com/smart-news/mass-coral-bleaching-hits-australias-great-
barrier-reef-180979823/
• https://www.gbrmpa.gov.au/the-reef/reef-health/coral-bleaching-101
• https://www.britannica.com/story/coral-bleaching-a-threat-to-our-reefs
• https://cdn.britannica.com/90/190990-050-4AD3EC3F/sector-portion-Australia-bleaching-
Great-Barrier-Reef-2016.jpg
References

3. Climate change and its effects- CORAL BLEACHING
AR.POOJA KULKARNI ROLL NO- COLLEGE- SKNCOA 2021-2023
SEM II F.Y.M.ARCH
SUBJECT- ECOLOGY SIGN- STAMP-
Why
to
save
Coral
Reefs?
• As the result of global warming, coral bleaching has been the general problem
for all coral reefs on earth. If no effective measures done quickly, the bleaching
process will become irreversible in decades.
• There are methods to mitigate the heat stress effect on coral.
• Coral nurseries can also help in restoring coral reefs with new bioengineered
heat resistant corals.
• Human-directed acclimatization and genetic modification increase coral heat
tolerance.
• Ecosystem migration to higher latitude can also avoid coral bleaching.
• However, all the aforementioned methods are no more than temporary
measures.
• The fundamental way to eradicate coral bleaching is to stop global warming and
atmospheric carbon dioxide concentration.
INFERENCES
• https://iopscience.iop.org/article/10.1088/1755-1315/474/2/022006/pdf
• https://www.fisheries.noaa.gov/national/habitat-conservation/restoring-coral-reefs#how-we-
restore-coral-reefs
• https://www.boatinternational.com/destinations/clever-ways-scientists-are-trying-to-protect-
coral--27697
• Many organizations have been working on saving corals from bleaching or
reversing the bleaching process.
• Some of those organizations are:
• NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
FISHERIES (NOAA FISHERIES)
• THE NEW HEAVEN REEF CONSERVATION PROGRAM
(NHRCP)
• CORAL RESTORATION FOUNDATION (U.S.)
• CORAL REEF ALLIANCE
• THE NATURE CONSERVANCY
• In some instances corals can recover from bleaching. If conditions return to
normal, and stay that way, corals can regain their algae, return to their
bright colours and survive.
• However prolonged warmer temperatures and other stressors, like poor water
quality, can leave the living coral in a weakened state.
• It can struggle to regrow, reproduce and resist disease – so is very vulnerable
to coral diseases and mortality.
• It can take decades for coral reefs to fully recover from a bleaching event,
so it is vital that these events do not occur frequently.
Organizations along with scientists haveidentified some methods bywhich dead
corals can be restored.
Some of the methods are as follows:
• Planting nursery-grown corals back onto reefs.
• Making sure habitat is suitable for natural coral growth.
• Building coral resilience to threats like climate change.
• Manipulating clouds to protect corals from bleaching
• Using breeze blocks to create new reefs
• By studying coral “bright spots” to learn from them
• Monitoring coral health from satellites in orbit
• Using 3D printing to create new coral reefs
• Rearing endangered coral species in laboratories to replant in reefs
• Using assisted evolution to create “super coral”
• Cross breeding to pass on heat-tolerant genes
• Using vinegar to kill coral predators
• Using electrical currents to stimulate growth
METHODS
USED
BY
SCIENTISTS
AND
DIVERS
TO
RESTORE
CORALS
PRECAUTIONARY
MEASURES
Using vinegar to kill coral
predators
Using 3D printing to create
new coral reefs
Using breeze blocks to create
new reefs
Cross breeding in nurseries to
pass on heat-tolerant genes
Ways a common man can help in saving coral reefs
As coral reefs are affected majorly by rising temperatures of
oceans we should take some measures to help reduce global
warming. This process is very slow but little changes in our day-to
day life will help restore coral reefs.
Choose sustainable seafood
Conserve water
Volunteer for coral cleanups
Dive carefully don’t touch Corals
Practice safe boating
Check sunscreen for active ingredients
Don’t use synthetic fertilizers and pesticides
Separate garbage before dumping
Recycle materials
Use sustainable mode of transport