Climate change affects the entirety of the earth’s surface, and nowhere more so than our oceans. While our seas cover about two-thirds of the earth’s surface they absorb over ninety percent of the additional heat attributable to global warming. Both land masses and bodies of water absorb and reflect solar radiation that rebounds off of the greenhouse gases trapped in our atmosphere, but the latter is generally more absorptive and holds on to heat longer due to differences in physical properties. This of course has led to increases in global seawater temperatures, which has and continues to endanger several aquatic species. This article will examine one of those species and go over human efforts to preserve it.
What is Coral?
At first glance many corals look like colorful rocks, though this belies their true nature. Corals can be broadly categorized into two groups: hard corals and soft corals. The exterior mass of hard corals are actually their calcium rich limestone skeletons, which protect their insides similar to the shells of clams or oysters. Soft corals on the other hand lack these calcium carbonate skeletons and instead rely on more flexible body structures that end up resembling underwater versions of trees, bushes, and other plants. Both hard and soft corals are made up of individual polyps, creatures that usually group together and form colonies. Sharing a phylum with jellyfish and sea anemones, coral polyps have mouths ringed with tentacles that only come out when it is time to feed. Rather than actively hunting for sustenance, corals are stationary animals that eat what particulates (usually zooplankton) they are able to catch as they drifts by.
When people think of corals, their next thought is often coral reefs. The bulk of any coral reef, of which there are several varieties, is made up of hard corals, specifically their rocky skeletons. Hard corals build their impressive skeletons by taking calcium and carbonate ions from the surrounding seawater and using these to fashion calcium carbonate, or limestone. When polyps are first birthed they lack these structures, floating through the water until they find a solid surface to latch on to. Oftentimes this surface is the skeleton of another coral, frequently one that has already died. This is one cycle that leads to the construction of reefs, and what led to the building of earth’s largest biological structure: the Great Barrier Reef. While hard corals are responsible for the buildup of reefs, soft corals can also be found in and among these limestone forests.
Akin to forests on land, coral reefs provide various ecosystem services to other sea creatures and humans alike. Coral reefs act as habitats that attract and provide shelter for many species of smaller fish, allowing them to safely reproduce. Coral reefs also break up strong ocean currents that might otherwise crash against nearby shorelines and further erode them. Due to these and other reasons, reefs degradation impacts more than just corals. The ongoing disappearance of coral reefs has a cascading effect that harms all of the other species that rely or benefit from their existence.
Among those species losing out as corals are further endangered by climate change is its symbiotic partner, algae. Algae, usually zooxanthellae, live inside hard corals. These corals provide zooxanthellae with specific nutrients, and in exchange the algae give their hosts most of the energy they produce from photosynthesis. This partnership is crucial to the healthy growth and maintenance of coral reefs and is also one of the main casualties of rising sea temperatures.
Increased water temperatures cause the algae living inside coral to leave. Zooxanthellae are responsible for a substantial portion of the nutrients consumed by certain corals as well as their coloration. With the algae gone, corals reefs do not die immediately, and occasionally they are able to recover, but they do become skeletal white forests, hence the term bleaching. Bleaching, overfishing, pollution, and other factors have contributed to severe reductions in coral reefs, with more than half having died in the past three decades. This includes large portions of Australia’s Great Barrier Reef, and projections have shown that up to ninety percent of remaining reefs will face annual bleaching events by 2055 given current emission trends.
Ocean acidification is the other major threat endangering coral reefs that is a direct consequence of climate change. Beyond increases in heat due to the greenhouse effect, abnormal levels of gases like carbon dioxide have other negative impacts. Because of the hydrological cycle, pollution that is initially pumped into the air does not always stay there. Carbon dioxide from emissions enters water sources through rain and other atmospheric phenomena, and when it ends up in the sea it imbalances the ocean’s pH. A lower pH means that seawater is more acidic and this adversely effects the biochemical processes of several sea creatures, including corals. Overly acidic waters interfere with hard corals’ ability to build and repair their calcium carbonate skeletons, which directly imperils the structural foundation of coral reefs the world over.
Coral farms, or nurseries, can be located in the ocean or on land in aquaculture tanks. Corals are farmed by either taking pieces from living coral specimens, called fragments, or by rescuing corals that have been detached and are rolling along the sea floor. Corals require hard, stable structures to take root and prosper, so underwater farms often use some form of metal to anchor their fragments. Sometimes these structures are naturally occurring, such as shipwrecks, while other times objects are placed in the ocean specifically for the purpose. This might be a statue, or as is often the case some form of metal lattice that can offer both stability and resist strong water currents thanks to a low surface area. The goal of coral farming is to reintroduce most of the corals back into nature, with some specimens being retained so they can fragmented again and replenish the farm’s livestock.
Biorocks and Electric Reefs
Electric reefs are a more technologically involved type of underwater coral farm. As the name suggests, they are electrified metal structures that give corals a safe place to grow. The voltage is relatively low, but it stimulates coral growth and healing in the case of damaged fragments. This is because the electric current causes electrolysis to occur, breaking up some of the surrounding water into its base molecules. This more easily frees them up to be converted into limestone, and it also causes calcium carbonate to accrue on the structure itself, producing what are called biorocks. Biorock closely resembles hard corals’ own skeletons and thus they readily take to electric reefs. While this kind of coral farm has better results, it is also more challenging to engineer and maintain, especially since it requires a constant stream of electricity. Just like with natural reefs, electric ones afford shelter to smaller sea creatures and they also help break apart and slow down faster, more destructive currents that can lead to shore erosion and flooding. At present, these preservation methods are helping to slow the disappearance of coral reefs, but alone they are not sufficient to halt the endangerment of most if not all corals in the wild.
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Silver, Katie. “Could electric biorocks save coral reefs?”. bbc.com, BBC Future, May 6 2015, https://www.bbc.com/future/article/20150506-why-we-should-electrify-the-ocean, Accessed Jan 3 2021
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Great article on corals!
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Excellent article! Enjoyed the read the impact of climate change on our coral reefs!
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Corals are amazing
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I love corals! And these new artificial coral reefs look like great ways to help them so far. 🙂
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