The Effects of Temperature on Coral Reefs

"The Rainforests of the Ocean"

The Basics of Coral Reefs

Coral Reefs are commonly referred to as the “rainforests of the ocean" because they are biodiversity hotspots that are home to 25 percent of the ocean’s marine life. They are found in mostly clear, shallow, warm waters. Coral reefs flourish in areas where sunlight can reach the coral and provide nutrients to the algae that preserves the coral. Coral reefs are animals that fall under the phylum Cnidaria and the class Anthozoa and are relatives of jellyfish and anemones. They are unique animals in that they are capable of reproducing both sexually and asexually.

Coral reefs are made out of thin layers of calcium carbonate. Massive reef structures are formed by millions of coral polyps (small colonial animals that look like overturned jellyfish that use excess carbon dioxide in the water from the atmosphere and turn it into limestone). Corals contain
symbiotic algae called zooxanthellae. The coral supplies the algae with a sheltered environment
and the compounds needed to perform photosynthesis. Zooxanthellae are essential in ensuring the
health of reef-building corals.

A Close up coral polyp

Coral eating zooplankton

This video from National Geographic shows the beauty and
immensity of the "Great Barrier Reef," while highlighting how corals
are formed:

Provide Shelter to 25% of Marine Life
The Many Values of Coral Reefs

Coral reefs provide shelter for a wide variety of marine life including protection to
coastal communities from hurricanes. They also provide humans with recreation such
as the scuba diving in Australia which is extremely popular. Coral reefs are a valuable
source of organisms for potential medicines. The chemical compounds extracted
from coral are used in medicine for cancer, AIDS, and other diseases. Coral reefs
also help create sand for beaches and serve as a buffer for shorelines.

Types of Coral

Hard Corals, or scleractinia, generate a hard skeleton by producing calcium carbonate skeletons. They form most of the frame work of coral reefs, especially Colonials corals found in clear, shallow, tropical waters.
Hard Coral
Soft Corals have a spiky, grainy texture for their flesh, that helps deter predators. These spiny
Soft Coral
elements are called sclerites. Most soft corals will readily eat any free floating food such as brine shrimp, making them carnivorous animals.

Sea Fan
Sea Fans are a type of soft coral found throughout the oceans of the world, especially the tropics and subtropics. A colony can be several feet high and across, but is usually only a few
inches thick. Sea fans can be brightly colored, and are often red, purple, or yellow.
Tropical Coral

Tropical Coral Reefs are formed in tropical waters by live organisms such as calcareous algae
(including red algae) and corals.

Threats from High Temperatures

Coral reefs rely on very specific environmental conditions. Most corals require a range from 23 to 29° for optimal growth. Some can withstand higher temperatures, but only for short periods of time. Coral “bleaching” events occur during unexpected temperature drops during seasonal cold-air outbreaks. However, bleaching is recorded more often from elevated water temperatures. A rise of 1 or 2 degrees Celsius for 5-10 weeks throughout the summer will most likely provoke bleaching.

Carbon dioxide, menthane, as well as other greenhouse gases trap heat which leads to global warming. This global warming has caused an increase of ocean temperature, of about 1° C over the last several decades. Although this might seem like an extremely subtle rise in temperature, this miniscule change has caused mass-coral mortality events in oceans throughout the world especially during some of the extremely warm summers of the past ten or so years

In 1998 alone coral bleaching was widespread due to a powerful El Niño (a climate pattern characterized by unusually warm ocean temperatures in the tropical Pacific Ocean). This greatly warmed much of the western Pacific and Indian Oceans, which led to mass coral death across many countries. For instance, in Palau, over 90% of corals on reefs were bleached and more than 50% decomposed. Wiping out coral has effects on entire ecosystems, which is one of the reasons why they are so important and need to be restored.

Healthy vs. Bleached Coral

Healthy, Flourishing Coral
Bleached Coral

Coral Bleaching

Coral bleaching causes corals to frequently lose 60%-
90% of their zooxanthellae, while each zooxanthellae
can lose between 50%-80% of its photosynthetic
pigments. The pale, or “bleached” look of corals is due
to the fact that these corals are nearly devoid of their
pigmented zooxanthallae, so you can see their
calcareous skeleton that shows through the now
translucent tissues.

This video describes how climate change is impacting coral reefs, with a direct impact on coral "bleaching:"
Coral inflicted with the Black Plague

Threats continued: How Global Warming Is Impacting Coral Reefs:

Longer-lasting and more extensive bleaching events are already
on the rise with further temp. increases predicted in the future.
Warmer waters expected to increase the occurrence of other
coral diseases: black band disease, white band disease, white plague,
and white pox melting sea ice and thermal expansion of the oceans
could make reefs to deep to receive enough sun light.

Conservation Efforts:

The United States Coral Reef Task Force was established by President Clinton in June 1998 to lead U.S. efforts, both domestically and internationally with a goal to protect, restore and sustainably use coral reef ecosystems. The themes of this plan focus on understanding coral reef ecosystems and reducing the adverse impacts on human activities on their website some steps they were taking were: to create comprehensive maps of all U.S. coral reef habitats, conduct long-term monitoring and assessments of reef health and trends. There is also human dimensions to this plan: to restore damaged reefs, reduce global threats to coral reefs, establish an informed public for coral reef conservation.

In the last meeting, Feb. 24th plans were made to charter “Review Charter” In 2012, and Assess Progress In 2013: “compile an analysis of USCRTF accomplishments and major” which basically means that over the next few years they will be trying to compile more data such and analyze the trends to see if their efforts are working and if there’s hope for the coral reefs.

Green = areas effected by Bleaching in last 15 years, Yellow = MAJOR bleaching spots

Future for Reefs

Coral Recovering from Damage from High Temps

Some scientists argue that coral reefs may be able to adapt to the change in high temps
and adapt to this major stressor. As noted by one website I came across, reefs devastated by
bleaching in 1998 in countries in the Indian, Pacific and Caribbean oceans are rapidly recovering.

However, many coral biologists are skeptical that adaptation alone will be enough for long-term
survival for the reefs if related threats are not reduced. Reducing human-induced stressors and
restricting climate change, could help maintain the current balance state of reefs or even improved. However, this idea assumes that the impacts of climate change will not increase, which seems
unlikely due to the best available climate forecasts.

This video from World Focus warns the public how serious of a threat
climate change is to coral reefs from a scientific perspective:


1. (MAP of GLOBE found here)
3. (picture of CLOSE up POLYP found here)
4. (picture of RECOVERING coral reef found here)
5. (picture of coral EATING zooplankton found here)
6. (picture of HEALTHY coral found here)
7. ("RAINFORESTS" of the ocean pic. found here)
8. (Hard, Soft, Sea Fan, and Tropical Coral pics found here)
9. (25% of marine life pic found here)
11. diploria_bbd_600.jpg (BLACK BAND disease pic found here)