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Ecological Impact Of CO2 Emissions On Coral Reefs

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Corals are marine invertebrates that secrete calcium carbonate (CaCO3) to form a hard skeleton. They belong to the class Anthoxoa within the phylum Cnidaria. Corals live in large colonies made up of genetically identical polyps that secrete CaCO3 to make up coral reefs.

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Corals receive most of their energy from photosynthetic single celled algae, known scientifically as Zooxanthellae, which live in a symbiotic relationship with the coral. The Zooxanthellae live within the CaCO3 skeleton of the coral. The coral benefits from the Zooxanthellae by being supplied with nutrients such as amino acids and glucose, Yellowlees (2008). These nutrients are converted into CaCO3. The Zooxanthellae benefit with protection of the corals hard skeleton.

This essay will look at the problems caused by carbon dioxide (CO2) on coral reefs and the wider effects on society and the marine ecosystem. It will also look at the steps that can be taken to help reduce damage/threats caused to coral reefs and how coral reefs can be conserved.

Impact of Increased Levels of CO2 on Coral Reefs

The greatest threat to coral reefs is a result of rising greenhouse gas emissions that blanket the atmosphere keeping the heat within, in turn causing climate change. As a result of climate change, acidification is taking place, this is due to the increased levels of carbon dioxide in the atmosphere; an increased amount of CO2 dissolves into the ocean causing acidification, which forms carbonic acid. This carbonic acid breaks down and dissolves the CaCO3 skeleton of the coral.

Coral Bleaching

Coral reefs cover only around 0. 1% of the ocean floor due to the niche habitat requirements corals need to survive. Corals are highly sensitive to environmental changes and require stable conditions. As temperatures rise the number of Zooxanthellae that live within the corals drastically decrease, the coral skeleton becomes transparent exposing a white skeleton this process is known as coral bleaching.

Coral bleaching is not just a rare occurrence it happens in mass events. Mass coral bleaching has become much more regular since worldwide temperature rises starting around the 1970s.

Coral bleaching does not always kill the coral, if the conditions were to stabilize, the Zooxanthellae come back to the corals giving them nutrients and colour again.

These large scale coral bleaching events have a much wider effect on the thousands of species that are highly specialized to live on coral reefs. Species that don’t live on the reefs will also be affected because many species of fish use the reefs as spawning sites to give protection to their young.

Coral reefs help link other ecosystems, some species migrate from coral reefs but come back to them to breed, but the small pelagic juvenile stages of offspring drift out from the safety of the reef into open waters providing nutrients for some of the largest creatures within the ocean or they may settle until sexually mature amongst the reef and be harvested by fishermen, .

Social Impacts of Coral Loss

Humans benefit from coral in many ways; their wonderful shapes and vibrant colours bring millions of people from all around the globe. Local economies rely on the tourist trade for income. The Caribbean tourist industry made over $8 billion US dollars and employed over a quarter of a million people. In other cases, Tribes located on islands connect to some reefs are fully dependent on the life and resources the coral provides. Some cultures hold the waters around the reefs so dearly they manage what they take from the reef to regulate the resources gathered from the reefs.

Coral reefs provide some defense from hurricanes and tsunamis. Coral reefs also provide protection from coastline erosion for fast topical currents, storms and high seas without the coral erosion would be much more rapid on tropical coastlines.

With the very real possibility of whole coral reefs being wiped out by acidification and mass coral bleaching events, worldwide economies could collapse entirely. With over $6 billion a year coming out of the fisheries industry and close to $10 billion a year coming from recreational activities globally.

Worldwide Ecological Significance

Coral reefs have a delicate food web made up of three main parts, Producers, Consumers and Decomposers.

Producers are things such as seagrass, kelp and plankton that take in energy from the sun by means of photosynthesis.

Consumers consist of primary and secondary. Primary consumers such as mollusks, winkles and sea urchins graze on the algae covered rocks. Corals themselves are classified as primary consumers. The consumers feed on plankton and other organic particles that drift around in the water columns. Many species of fish are classed as primary consumers. There are also fish that are classed as secondary consumers, such as cod and sharks. Marine turtles and some types of marine crustacean are also classed as secondary consumers.

Decomposers take the role of breaking up organic matter, they feed on practically anything they can, usually the leftovers from the consumers. Decomposers return the nutrients gathered from breaking down organic matter. These nutrients are then transferred into the sediment for the cycle to begin again.

Conservation Tactics

Physically Moving Coral

It is possible to artificially repopulate areas of coral reefs but it is extremely time consuming and extremely costly. Stocks of sponges and corals can be bred inside sheltered marine environments. Currently this technology is in its infancy. To date there has been a low success rate with this method of growing corals in enclosed marine environments. Even though success rates are low it proves it is possible to revive sections of damaged corals and sponges once transfer to sheltered and closely monitored environment. This allows them to grow the corals for restoration projects and experiments, In a few cases corals have been moved entirely out of the way from impending danger, too artificial habitats inland.

Coral Breeding and Release

A valuable study to the scientific community was undertaken by researchers at the University of Guam. Gravid corals were collected from their local reef. These corals were then taken care of until they spawned, the corals larvey are nurtured and monitored until they are ready to anchor themselves down. These larvae were transported to a coral reef that had recently been damaged by a hurricane. Richmond and his team’s study concluded that many larvae did manage to anchor down and grow on the reef. Structures can be made to fit over the desired location for a higher chance of the coral larvae settling.

Coral Flypaper

One study made a material that attracts coral larvae to settle and metamorphose. The synthesized material is called ‘coral flypaper’ has been successful in the field at attracting coral larvae. The chemical signals given off by the coral flypaper is designed to attract Agaricia agaricites hummlis larvae, with more refining and research it would be possible to tailor make coral flypaper for any species of coral


Corals are under threat from physical, chemical and environmental challenges. The physical damage such as ships running aground and coral mining can be remedied with relative ease compared to the chemical contamination of CO2 dissolving into the ocean. A global agreement to lower our carbon footprint would be needed, unfortunately this isn’t very realistic due to the stubbornness of some of the world’s most powerful nations. Within recent years some governments have taken large steps in the right direction to reduce their country’s carbon foot by introducing electric car scheme.

However this isn’t enough to slow down the rates of ocean acidification, a predicted reduction in ocean surface pH of 0. 4 is expected by the year 2100.

With development of coral conservation tactics such as the semi artificial coral breeding combined with the Coral flypaper could work very well together, but there are issues with costs with these conservation methods. The loss of Coral reefs will send rippling effects through the food web ultimately leading to us.


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09 March 2021

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