Climate Change: Coral Reefs

Coral reefs are one of the most diverse, economically valuable ecosystems on Earth , as well as being source of food and protection for millions. Yet despite this, anthropogenic action is threatening to kill them. With ocean temperatures rising, and acidification occurring due to greater amounts of carbon dioxide in the atmosphere, corals are becoming bleached, which puts them under serious stress.

We are currently undergoing an El Niño  event, meaning that unusually warm waters are occurring in places that they would normally not, causing a mass bleaching event, which is the third largest in history.

Image by NOAA showing the possible impact of ocean temperature rise due to El Nino . Large amounts of coral are seen to be under stress, meaning it is likely that there will be a huge coral loss. In 1997/8, 20% of global coral was lost, and there are fears that this event may cause the same amount of harm.

Mark Eakin, the NOAA’s coral watch co-ordinator has stated “The coral bleaching and disease, brought on by climate change and coupled with events like the current El Niño, are the largest and most pervasive threats to coral reefs around the world”. Meaning that while the natural cyclic event is having an impact on the ocean, this coupled with anthropogenic climate change, as well as ocean acidification, is having a devastating impact on the world’s coral reefs. This is because the events are becoming more intense and closer together, as the last event only occurred in 2010. Bleaching typically occurs due to a change in light levels or temperature, where oxygen is produced rapidly meaning that the coral can not use it fast enough. This toxic oxygen level causes the coral to become stressed, meaning that it may expel its zooxanthellae, which is dinoflagellate found with in the coral that provides it with energy by undergoing photosynthesis. Without this, the coral becomes white in colour, and has become ‘bleached’. While this is reversible, the coral typically becomes weaker and often dies before it has a change to pick up more zooxanthellae, especially when bleaching events are becoming more common as the reefs are having less time to recover.

Example of a bleached coral, with a coloured healthy coral behind it. (Picture: Acropora, 2011)

Ocean acidification is another impact of climate change. This occurs due to the large amount of carbon dioxide in the atmosphere, from human activities such as the burning of fossil fuels. This CO2 dissolves into the sea water, creating carboxylic acid. Under these conditions, the corals are less able to produce calcium carbonate, which is used to create their skeletons. Without this, the reef is unable to grow and protect its self. The increased acidity also erodes existing skeletons, causing great damage to reef systems.

Changes in ocean conditions are not the only threat that face these diverse ecosystems, as destructive fishing techniques, harvesting for building materials, tourism and increased levels of coastal development all play a major role in the decline of the reefs. In order to prevent the disappearance of coral reefs, action needs to be taken. People depending on the reefs for their livelihood, such as local fishermen using dynamite and cyanide fishing, need to be provided with an alternate method of sustaining themselves and their families; the tourism industry needs to become more aware of the dangers that increased use of the coral reefs may bring, as well as stopping cruise liners damaging the reef with sewage and coastal development needs to be undertaken in a sustainable way. Yet this is all easier said than done.

Action needs to be taken against not only these issues, but also the bigger problem of climate change. We can all try and do our bit to help the environment by trying to reduce our carbon footprint by using greener methods of transport, trying to be energy efficient and diminishing our waste, as when it ends up in landfill it often produces methane.

To find out more about the problems facing coral reefs, and to see what is being done to try and conserve them, check out NOAA.




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