An Introduction to Coral Reefs
By Monica Bhatia
Location: London, UK
Monica is an amateur wildlife photographer and blogger from the UK. She has been published by various nature related blogs and has written about a variety of topics.
An Introduction to Corals
Visualise the ocean. What is the first image that comes to your mind? Probably the divine blue waters and the huge array of marine mammals, but do you envision corals? Corals are marine invertebrates (soft bodied organisms) within the class Anthozoa (marine invertebrates) of the phylum Cnidaria (a taxonomic/classified category of around 9,000 species found only in aquatic and mostly marine environments) that typically live in compact colonies of many individual polyps (tiny, soft-bodied organisms, related to jellyfish). These corals are of a very simple body; a stalk containing a stomach, with a tentacle ring (mechanism allowing the coral to stab micro-prey) surrounding its mouth.
And what do corals do? They are reef builders! Held together by calcium carbonate (this is what the rock limestone is made of, and is a chemical compound protecting the corals soft body, which eventually allows the corals to grow strong and stony), these polyp colonies make up an ecosystem that enables diverse marine life to thrive. They do this by providing an environment where wave power is reduced, and therefore acting as the perfect home to thousands of species on one reef alone. Along with providing a perfect habitat, these reefs are a source of income for millions, and are one of the main reasons for the diversity of life on Earth.
Yet, for an ecosystem that provides so much to life on earth, it is being horrifically mistreated. A severe problem that has come out of climate change is coral bleaching, which occurs at an extraordinarily rapid rate.
As the climate warms, so does the water, and this causes the zooxanthellae (a type of algae living in a symbiotic relationship with corals and responsible for the vibrant colours) to expel themselves, causing the exoskeleton of the corals (the hard ‘shell’ protecting the soft body) to turn completely white.
This algae provides 90% of the coral’s energy. With its source for both growth and reproduction halted, the coral is exposed to an increased risk of disease and seaweed takeover.
Now, corals do have the mechanisms to attempt to restore themselves against this heat stress. Components in the coral’s algae called algal simbions (pigment producers) can expel coloured pigments to protect algae inside the tissue from light stress - almost like a sunscreen - allowing the bleached coral to take back some of its algal partners. This however, is not nearly efficient or fast enough to restore the world's coral reefs. Corals can recover from mild stress- but when met with prolonged stress, the stress withstanding pigments cannot be sustained. Upon realising that corals cannot fully restore on their own, scientists made the decision to intervene. In this article, we are going to discuss some of the ways in which they are making this happen.
The aquaculture of coral
Scientists are working on this rehabilitation through a method known as coral aquaculture. The aquaculture of coral is also known as coral farming/gardening/(a)sexual propagation, and involves the cultivation of corals for reef restoration. This is carried out by using fragments of corals that will have been obtained from donor colonies or ‘corals of opportunity’, which are wild populations that are generated by disturbances, including fragments broken from storms, anchoring (forceful removal of corals using an anchor), or vessel grounding (the impact of a ship on the seabed). These fragments are then relocated to a nursery (like a greenhouse, but huge and filled with water!) in which they are given anything between 6 to 12 months to grow, and are then propagated (grown from a variety of sources), enabling the nursery to expand and further on be outplanted back to an outside area before distribution. These nurseries enable coral colonies to be generated in their hundreds without damaging or risking the other living corals. This seems like cause for celebration; however, before we rejoice at the nurseries’ success, we should gain a full understanding of what they are, and what goes on in them.
©Paul A. Selvaggio
The types of nurseries
There are 2 types of nurseries; land-based and field-based nurseries. Land based nurseries, also referred to as ex-situ nurseries, are the type that is most commonly used for sexual propagation. There are a vast array of benefits that occur when gardening corals in a land based nursery; you can constantly manipulate optimum conditions and you only require small amounts of donor material and larvae (a coral embryo of egg and sperm that join to form a planula/free-swimming larvae) derived from coral gametes (sex cells). However, as with all scientific methods, this type of nursery also has its downfalls. The main concern is the high costs that are required for maintenance (pumps, piping valves, and tanks) and malfunction/failure, which can lead to massive decreases in the coral stocks.
Field nurseries, on the other hand, can supply vast numbers of corals at a level that the site can be restored. These are also known as in-situ nurseries, and are the most common way of growing corals. Not all sites are suitable for the establishment of a field nursery. The site must be of suitable bottom type (on rubble and hard substrate areas, as sandy landscapes might require a floating structure to reduce sedimentation), is of suitable environmental conditions (light availability, water temperature, water movement, salinity, sedimentation and turbidity) and has a good standard of water quality. Other factors to be considered when establishing a field nursery is human activities, site accessibility and size, and also permission. Once a site has been established, it must be protected from disturbances, competition/predators. Once established, the nursery can follow standard procedure of collecting stock material, growing them to a size suitable for nursery expansion, and/or outplanting back to the natural reef. In contrast to the ex-situ nursery, one benefit is its affordable costs. The drawback, however, is that this type of nursery is more susceptible to environmental extremes and therefore, coral damage.
Field Based Nursery © Elizabeth Goergen, NOVA Southeastern University
Successes
So, after all of the hard efforts of water chemists and aquarium husbandry experts, paired with the 6-12 months it takes to actually grow the coral, we need to look back and ask ourselves; is this actually helpful? And (thankfully) the answer to that question is yes! Since these nurseries came about, numerous programmes have grown their coral stock from an initial stock of a hundred colonies to thousands within a few years. The success also lies in its impact on the corals in the first place, taking only 10% of the wild population to the nurseries. However, like with everything in life, consistency is key. As long as we keep seeing our corals bleached, this process needs to occur, and as the planet heats up faster, this process needs to happen on a larger scale than ever before.
Future
Modern science, technology and engineering provide a future full of opportunity for coral aquaculture. For instance, there are 3D printers that can manufacture and place artificial coral among real colonies, and there is the recent development of coral husbandry, CHARM (coral husbandry automated raceway machine) that aims to automate the repetitive tasks involved in growing corals. Clearly, the process is becoming faster and more efficient. On top of this, the recent architectural development of the coral restoration foundations Coral Trees allow for more space to grow boulder corals!
In this article, we have delved into the importance and preservation of one of our oceans greatest assets. We now understand corals and their importance, but also how and why they are being preserved by scientists across the globe.
Corals are just as abundant as a rainforest, and play such an integral part in ocean life. Without them, the vast and diverse ocean we know and love would fail to function. These corals are sensitive to human action, so it is up to us whether we carry on contributing to global warming, or if we keep researching and encouraging scientists to propagate and distribute these corals. It's our choice to allow our oceans to thrive like never before.