ciencia medio ambiente

Out of sight, out of mind? The alarming phenomenon of coral bleaching

As 2020 draws to a close, and 2021 begins, it is exceedingly hard to talk of anything but covid-19. However, the current climate emergency is not something we can ignore. The consequences of this climate emergency will be far reaching, from global pandemics, to flooding and droughts, to the phenomenon known as coral bleaching.

Coral bleaching has been occurring under the sea, in our oceans, at an alarmingly precipitated rate, but largely unheard and unseen. It is time to do something about it.

How does it happen?

Before we dive into how coral bleaching happens, let’s make sure we all know what corals are and how they live. Corals are animals, that we are used to seeing arranged in reefs. Corals are animals, that have special, also known as symbiotic, relationship with algae, plants.

The Great Barrier Reef, Australia, ScienceMag 2016

This relationship between the algae and the coral works as a give and take. The algae lives inside the coral cells and tissues, producing food via photosynthesis, just like any other plant would, that the coral can then take advantage of. It is also due to these algae that coral reefs have the bright, vibrant colours we so often associate with them.

Like all relationships, the one between corals and algae is give and take. While the algae supplies corals with a large proportion of their food source, the coral supplies algae with a comfortable, cosy, safe place to stay.

However, much like all relationships, it is very easy for an external influence to disrupt this partnership. In the case of the corals and algae, the rising water temperatures is enough to break their alliance.

The increase in water temperature causes stress to the corals and their tissues. This stress is enough cause a change in the environment within the corals cells, causing the algae to be expelled into the open water. By expelling the algae the coral has suddenly lost its greatest ally, and most important source of food. The corals are not only going to struggle for food, but they are also more vulnerable and susceptible to disease.

Unless the water temperature drops, these algae will not be able to return to the corals, and the corals are likely to die.

Why does it happen?

The rise of sea and ocean temperatures is a direct consequence of increased global temperatures. Since pre-industrial times there has been a 1°C increase of the earth’s surface temperature. The increase in temperature not directly increases the ocean temperatures, but also wreaks havoc on weather systems such as el Niño. El Niño is a weather phenomenon, usually occurring in the Pacific Ocean, that leads to huge volumes of warm water moving across the ocean. This phenomenon has a huge effect on coral reefs. If this warm water is even just half a degree too warm, it will leave a path of coral bleaching and destruction in its wake. This is exactly what happened in the 1997-1998 mass bleaching event.

Before and after a mass bleaching event in American Samoa. December 2014 vs February 2015.
Photo by XL Catlin Seaview Survey

However, since then we have experienced worse bleaching events. Most recently the 2016 bleaching even in the Great Barrier Reef broke headlines, followed by yet another mass bleaching in 2017. These successive events meant that the reefs were not able to recover, and over half of the shallow reefs in the northern Barrier Reef were lost.

What are the effects?

Apart from the obvious bleaching and subsequent death of these reefs, coral bleaching has far reaching effects. Over 700 million people worldwide, mainly in developing countries, rely on the life that surrounds coral reefs.

Coral reefs only make up 1% of the Earth’s surface, but they are the habitat for 25% of all marine life. The huge biodiversity of these reefs are worth over $30 billion. The domino effect of large scale coral reef destruction would be catastrophic on an environmental, and perhaps more importantly, on a human scale. One in ten humans around the world would be gravely affected.

«with business as usual, 90 percent of coral reefs will be in danger by 2030, and nearly all of them by 2050»

Reefs At Risk, Revisited

How can you help?

The future of coral reefs seems grim at the moment, but there are things you can do to help! Although it is true that the biggest impact will be had by the biggest players in the climate emergency situation, every little does make a difference.

The key to preventing coral bleaching is, as you may have guessed by now, preventing the rise of sea temperatures by stopping global warming. The actions we have all heard of, and probably most of us do to a certain extent do help! From reducing meat consumption, reducing fuel and car use, to going plastic free or even zero waste.

These are all very important, and have to be built over time to have significant effect. But is there more coral reef targeted actions we can do? Yes!

Organizations such as the Coral Restoration Foundation (CRF), based in the Florida Keys, along with other organisations, are focusing their efforts on coral nurseries. These organisations are growing corals in controlled conditions, to be able to repopulate reefs after mass bleaching events.

Reef – safe suncream has recently become widely available, and this is a great way to ensure we do not weaken or harm the already vulnerable reefs.

When consuming fish, or any marine product, it is important to be sure of the fishing method, as many are directly damaging to reefs.

A big impact, that is not often spoken of storm water run-off. When run-off has pollutants, or even fertilizers in it, this will disrupt the balance of the ocean’s chemistry, and harm corals in the process. It is important to be mindful of what we put in our water systems, and where these end up.

Find out more

There are plenty of resources online to learn more about coral bleaching, and what we can all do to help. Chasing Coral is just one of many documentaries about these fascinating animals and their vulnerabilities.

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