With the recent news that irreversible damage will be done to our planet if we do not have climate change under control by 2030, it seems as though we will be seeing many changes in biodiversity of all kinds in years to come. Some of the most threatened habitats, however, are those in aquatic environments, in particular coral reefs. A 2°C increase in global temperatures would mean a decline in 99% of all coral reefs, causing immeasurable damage to these beautiful underwater oases.
Coral reefs are dominant primary producers and provide structural habitat to many organisms- they are home to more than one quarter of all marine fish species. Warmer temperatures, increasing CO2 levels, and rising sea levels are changing these underwater ecosystems and forcing species living there to adapt, relocate, or die.
How is climate change affecting these ecosystems?
Corals have a symbiotic relationship with an algae (zooxanthellae) living inside their tissues; the coral provides a habitat for the algae, while the algae give coral its bright colours and carry out photosynthesis, providing energy for it to survive and grow. Increasing temperatures and pollution levels cause stress on the corals and they expel the algae in order to ensure their short-term survival. This is known as coral bleaching. Corals can survive for a short while without the zooxanthellae, but with extensive bleaching, the corals die. This has been observed all over the world, most notably in the world’s largest reef system, the Great Barrier Reef. Global warming is the main cause of coral death. Since 2016, half of the Great Barrier Reef has been bleached to death.
Carbon dioxide in the atmosphere is absorbed by the ocean, causing ocean acidification. A higher level of CO2 causes there to be a lower amount of calcium carbonate in the water, which corals use to build their skeletons. There has been a 26% increase in ocean acidity since the pre-industrial period. High CO2 emissions alongside temperatures increasing are resulting in the inability of corals to repair themselves at a normal rate, leading to further decline.
Rising sea levels caused by global warming also mean light has to penetrate further into the ocean to reach corals, so they do not receive enough light to photosynthesise and grow. Any hope of their recovery is fading as sea levels continue to rise.
The damage being caused to coral reefs has a flow-on effect on the species that rely on them for habitat and food. Reefs have a complex 3-D structure that provide protection from predation, shelter, and ideal mating grounds, as well as producing much of the carbon in the surrounding area and housing algae that are a food source for many marine species. Coral is a key indicator species due to it being so fundamental to its ecosystem- as coral reef cover declines further we will see a loss of biodiversity in these areas.
Further problems faced by our oceans
The decline in coral reefs is just one of the issues caused in the oceans by climate change and other human induced problems. For example, over-fishing is rapidly reducing the biodiversity of aquatic species, both deliberately and through by-catch, as well as the fishing methods themselves causing damage. Plastic pollution seems to be in the news constantly- microplastics are harming aquatic species and entering our food chain. Oil and gas drilling, shipping, and tourism are also disturbing these delicate ecosystems. On top of it all, many areas of the ocean have inadequate protection (most of the ocean lies outside the legal jurisdiction of any country).
So what is being done to manage these problems?
Coral reefs are massively important socially and economically. For example, the Great Barrier Reef attracts US$5.7 billion each year in terms of direct and indirect economic activity, and employs approximately 69,000 people. Measures are in place to protect the Great Barrier Reef- the seven zoning categories only allow certain activities in certain areas. While this protects coral reefs to some extent from other forms of human impact and gives them the greatest chance of recovery, it does not help stop the damage being caused by climate change.
The Paris Agreement talks in 2015 resulted in almost 200 countries coming together and setting a target to keep the global temperature “well below 2°C”. The Intergovernmental Panel on Climate Change (IPCC) has recently estimated that a global temperature increase of 1.5°C would mean an 80% loss in coral reefs, and virtually all coral reefs would be gone with an increase of 2°C. Current estimates using the proposed plans say that there is an overwhelming probability that we will exceed these levels within the next century. The 1.5°C increase is likely to be seen between 2030 and 2052 if we continue the way we are now. In order to keep levels around 1.5°C, CO2 emissions would have to fall 45% below the 2010 levels and be “net zero” by 2050. After that point, our focus would be on techniques to remove CO2 from the atmosphere.
Huge numbers of people rely on the resources provided by the ocean for their livelihoods, so it is difficult to apply conservation methods to the extent needed to see real improvement. However, promising results have been gained by governments shifting to community-based co-management arrangements and economic incentives for conservation.
But what can we do as individuals? Be as environmentally friendly as you can! I don’t need to repeat to you all the ways we have been told we can reduce our carbon footprints, you’ve heard them a million times. All ways to help reduce global warming are helping our coral reefs. Aside from global warming, practices such as buying from sustainable fisheries (or cutting down on seafood) really help in conserving coral and coral-associated biodiversity. This issue is just the tip of the iceberg; climate change will affect us in so many ways in the near future. The time to act is now!