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How does climate change threaten coral reef ecosystems?

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How does climate change threaten coral reef ecosystems?

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Climate change is the greatest global threat to coral reef ecosystems. Scientific evidence now clearly indicates that the Earth's atmosphere and ocean are warming, and that these changes are primarily due to greenhouse gases derived from human activities.

As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Additionally, carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in reef-building and reef-associated organisms by altering seawater chemistry through decreases in pH. This process is called ocean acidification.

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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 which are made up of tiny, soft colonial organisms called polyps. Polyps look a lot like a sea anemone, as they are related to these animals. They are invertebrates in the Cnidaria phylum.
Source: Wikipedia + https://www.thoughtco.com/how-do-coral-reefs-form-2291791

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As the polyps live, reproduce, and die, they leave their skeletons behind. A coral reef is built up by layers of these skeletons covered by living polyps. The polyps reproduce either through fragmentation or sexual reproduction through spawning.
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Reefs are centers of biodiversity, where you'll find many types of fish, invertebrates and other marine life. But did you know that coral reefs are also alive?

What Are Coral Reefs?

Before learning how reefs form, it's helpful to define a reef. Acoral reef is made up of animals called stony corals. The stony corals are made up of tiny, soft colonial organisms called polyps. Polyps look a lot like a sea anemone, as they are related to these animals. They are invertebrates in the Cnidaria phylum.

In stony corals, the polyp sits within a calyx, or cup that it excretes. This calyx is made of limestone, also known as calcium carbonate. The polyps are interconnected to form a mass of living tissue over the limestone skeleton. This limestone is why these corals are called stony corals.

How Do Reefs Form?

As the polyps live, reproduce, and die, they leave their skeletons behind. A coral reef is built up by layers of these skeletons covered by living polyps. The polyps reproduce either through fragmentation (when a piece breaks off and new polyps form) or sexual reproduction through spawning.

A reef ecosystem may be made up of many species of corals. Healthy reefs are typically colorful, highly biodiverse areas made up of a mishmash of corals and the species that inhabit them, such as fish, sea turtles, and invertebrates such as sponges, shrimp, lobsters, crabs, and seahorses. Soft corals, like sea fans, may be found within a coral reef ecosystem, but do not build reefs themselves.

The corals on a reef are further cemented together by organisms like coralline algae, and physical processes like waves washing sand into spaces in the reef.

Zooxanthellae

In addition to the animals living on and in reefs, the corals themselves host zooxanthellae. Zooxanthellae are single-celled dinoflagellates that conduct photosynthesis. The zooxanthellae use the waste products of the coral during photosynthesis, and the coral can use the nutrients provided by the zooxanthellae during photosynthesis. Most reef-building corals are located in shallow water where they have plenty of access to the sunlight needed for photosynthesis. The presence of the zooxanthellae helps the reef to thrive and become larger.

Some coral reefs are very large. The Great Barrier Reef, which stretches more than 1,400 miles off the coast of Australia, is the world's largest reef.

3 Types of Coral Reefs

Fringing reefs: These reefs grow close to the coast in shallow waters.

Barrier reefs: Barrier reefs, like the Great Barrier Reef, are large, continuous reefs. They are separated from land by a lagoon.

Atolls: Atolls are ring-shaped and located near the sea surface. They get their shape from growing on top of underwater islands or inactive volcanoes.

Threats to Reefs

An important part of coral reefs is their calcium carbonate skeleton. If you follow ocean issues, you know that animals with calcium carbonate skeletons are under stress from ocean acidification Ocean acidification causes a lowering of the ocean's pH, and this makes it difficult for corals and other animals that have calcium carbonate skeletons.

Other threats to reefs include pollution from coastal areas, which can affect reef health, coral bleaching due to warming waters, and damage to corals due to construction and tourism.

References and Further Information:

Coulombe, D.A. 1984. The Seaside Naturalist. Simon & Schuster. 246pp.

Coral Reef Alliance. Coral Reefs 101. Accessed February 22, 2016.

Glynn, P.W. "Corals." In Denny, M.W. and Gaines, S.G. Encyclopedia of Tidepools and Rocky Shores. University of California Press. 705pp.

NOAA Coral Reef Conservation Program. Coral Anatomy and Structure. Accessed February 22, 2016.

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Reefs are centers of biodiversity, where you'll find many types of fish, invertebrates and other marine life. But did you know that coral reefs are also alive? Before learning how reefs form, it's helpful to define a reef. Acoral reef is made up of animals called stony corals.

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Coral reefs harbour the highest biodiversity of any ecosystem globally. Despite covering less than 0.1% of the ocean floor, reefs host more than one quarter of all marine fish species, in addition to many other marine animals. Additionally, reefs provide a wide variety of ecosystem services such as subsistence food, protection from flooding and sustaining the fishing and tourism industries. Their disappearance will therefore have economic, social and health consequences.
Source: https://www.iucn.org/resources/issues-briefs/coral-reefs-and-climate-change

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“Corals are important to us for many reasons,” Maurin says. “From a practical point of view, they can help protect coastlines from storm events, for instance, and help maintain fisheries that are essential to a lot of people. And complex compounds found in coral reefs hold promises in modern medicine. These are what we call ecosystem services that would be very difficult and expensive to replace.

Source:

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Coral reefs are important ocean habitats and offer a compelling case of the risks of climate change. Reefs provide a large fraction of Earth's biodiversity-they have been called "the rain forests of the seas." Scientists estimate that 25 percent of all marine species live in and around coral reefs, making them one of the most diverse habitats in the world.

Paulo Maurin, education and fellowship coordinator for NOAA's Coral Reef Conservation Program, says the reefs are invaluable to our planet's biodiversity.

"They act as productive nurseries to many fish species, giving the small fish a home and a chance to grow," he says. "Coral reefs' diversity is so rich that we do not have a firm count on all the species that live within it and every year discover new species."

Reefs provide a variety of economic benefits, including recreational activities, tourism, coastal protection, habitat for commercial fisheries, and preservation of marine ecosystems.

"Corals are important to us for many reasons," Maurin says. "From a practical point of view, they can help protect coastlines from storm events, for instance, and help maintain fisheries that are essential to a lot of people. And complex compounds found in coral reefs hold promises in modern medicine. These are what we call ecosystem services that would be very difficult and expensive to replace.

"They also have a unique ability to inspire us to explore and visit the ocean. Can you think of any other invertebrate that people would come from afar just to see?"

Corals live with algae in a type of relationship called symbiosis. This means the organisms cooperate with each other. The algae, called zooxanthellae, live inside the corals, which provide a tough outer shell made from calcium carbonate. In return for that protection, the algae provide their host with food produced through photosynthesis. Zooxanthellae also provide corals with their striking colors.

This symbiotic relationship is strongly dependent on the temperature of the surrounding water. As the water warms, zooxanthellae are expelled from a coral's tissue, causing it to lose its color and a major source of food. This process is known as "coral bleaching."

Coral bleaching does not always mean the death of a coral reef. Corals can recover their zooxanthellae in time, but the process requires cooler temperatures.

Warmer ocean water also becomes more acidic. Ocean acidification is making it more difficult for corals to build their hard exoskeletons. In Australia's Great Barrier Reef, coral calcification has declined 14.2 percent since 1990-a large, rapid decline that hasn't been seen for 400 years.

Ocean acidification also occurs because of rising carbon dioxide (CO2) levels. The ocean absorbs carbon dioxide released into the atmosphere. Carbon dioxide alters the chemistry of seawater by reducing pH, a measure of acidity. Water that has a lower pH is more acidic.

"When the pH of seawater is lowered as a result of CO2, the availability of carbonate ions-one of the main building blocks in their calcium-carbonate skeletons-is reduced, and corals have a tougher time building up, or even maintaining, their skeleton," Maurin says.

The combination of rising ocean temperatures and increased acidity will likely cause major changes to coral reefs over the next few decades and centuries. New research suggests that corals may begin to dissolve at atmospheric CO2 concentrations as low as 560 parts per million, which could be reached by the middle of this century if emissions are not curbed. In 2010, atmospheric carbon dioxide levels were around 390 parts per million.

Maurin believes there are several ways people can help preserve these valuable resources.

"Over the long term, we need to reduce the amount of CO2 that is up in the atmosphere that is causing both increased bleaching and acidification," he says. "But in the more immediate time, there are other ways to help. By understanding that bleaching and acidification stress corals, we can help by building up what we call 'reef resiliency.' That is, making sure that reefs have this capacity to bounce back.

"For instance, ensuring that there is less pollution entering the ocean can help far-away corals. Also, people can help by making sure that the seafood consumed is sustainable and not contributing to a depletion of fish species that keep algae in check, following fishing regulations when fishing, as well as supporting marine protected areas in key conservation sites."

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Coral Reefs | National Geographic Society

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Coral reefs are important ocean habitats and offer a compelling case of the risks of climate change. Reefs provide a large fraction of Earth's biodiversity-they have been called "the rain forests of the seas." Scientists estimate that 25 percent of all marine species live in and around coral reefs, making them one of the most diverse habitats in the world.

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The ocean is being disproportionately impacted by increasing carbon dioxide (CO₂) and other greenhouse gas emissions (GHG) from human activities.

This causes changes in water temperature, ocean acidification and deoxygenation, leading to changes in oceanic circulation and chemistry, rising sea levels, increased storm intensity, as well as changes in the diversity and abundance of marine species.

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Contributing factors that increase greenhouse gases in the atmosphere include burning fossil fuels for heat and energy, producing some industrial products, raising livestock, fertilizing crops, and deforestation. Climate change leads to:

A warming ocean: causes thermal stress that contributes to coral bleaching and infectious disease.

Sea level rise: may lead to an excessive sedimentation for reefs located near land-based sources of sediment. Sedimentation runoff can lead to the smothering of coral.

Changes in storm patterns: leads to stronger and more frequent storms that can cause the destruction of coral reefs.

Changes in precipitation: increased runoff of freshwater, sediment, and land-based pollutants contribute to algal blooms and cause murky water conditions that reduce light.

Altered ocean currents: leads to changes in connectivity and temperature regimes that contribute to lack of food for corals and hampers dispersal of coral larvae.

Ocean acidification (a result of increased CO₂): causes a reduction in pH levels which decreases coral growth and structural integrity.

Source: https://oceanservice.noaa.gov/facts/coralreef-climate.html#

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People first noticed coral bleaching events in the 1980s. The problem intensified in 2016, when an El Niño weather pattern, which causes warmer waters in the Pacific Ocean, mixed with an already unseasonably warm ocean and killed off a third of the corals on the Great Barrier Reef. Since then, roughly half the corals on Australia’s famous reef have died in subsequent bleaching events, jeopardizing an underwater landscape 1,500 miles long.
Source: https://www.nationalgeographic.com/science/2020/06/scientists-work-to-save-coral-reefs-climate-change-marine-parks/

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If corals are bleached for prolonged periods, they eventually die. Coral bleaching events often lead to the death of large amounts of corals.

Reefs around the world have suffered from mass bleaching events for three consecutive years. Iconic reefs such as the Great Barrier Reef in Australia and the Northwestern Hawaiian Islands in the United States have all experienced their worst bleaching on record with devastating effects. The bleaching of the Great Barrier Reef in 2016 and 2017, for instance, killed around 50% of its corals.
Source: https://www.iucn.org/resources/issues-briefs/coral-reefs-and-climate-change

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Percent of coral bleaching and probability of coral bleaching measured at 3351 sites in 81 countries, from 2002 to 2017.

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Percent of coral bleaching and probability of coral bleaching measured at 3351 sites in 81 countries, from 2002 to 2017.

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Source: https://www.nature.com/articles/s41467-019-09238-2

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Shrink your carbon footprint to reduce greenhouse gases.

Drive less. Take public transport.

Reduce, reuse, or recycle.

Purchase energy-efficient appliances and lightbulbs.

Print less. Download more.

Open windowds instead of using air conditioners.

Dry clothes on the line.

Do your part to help improve overall coral reef condition!

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Impacts of Climate Change on Coral Reefs

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First bleaching event

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One of the most intense bleaching events
It led to the bleaching of 42% of the world's corals

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One of the severest bleaching events too
It led to the bleaching of 54% of the world's corals

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The most severe bleaching event that has occured in the Great Barrier Reef which killed around 50% of its corals.

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https://1drv.ms/v/s!AutjwYGFxtJAxjY4vWzvf7fIi-H7?e=BQ1UTp

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Store photos and docs online. Access them from any PC, Mac or phone. Create and work together on Word, Excel or PowerPoint documents.