W

hen we think at the sea and the thousands of varied animals living in them, certainly an image pops up in our head: the coral reef. Besides being spectacular and colourful ecosystems, home to very diverse organisms, coral reefs are also source of food, medicine, income and provide coastal defence to more than 500 million people [1]. This outstanding underwater ecosystem, comparable to an underwater rainforest, is today being threaten. This complex system, which can take thousands of years to form, risks to disappear in mass, resulting in an inestimable environmental catastrophe.

Coral reefs are large underwater structures composed of colonies of individual organisms, named polyps. The backbone structure is a robust protective exoskeleton derived by calcium carbonate. The polyps host inside them the zooxanthellae algae, which is responsible for their colours. In this symbiotic relationship, the algae produce oxygen and organic products (main source of nutrients for the coral itself) through photosynthesis from the CO₂ and waste provided by the coral. This beneficial cooperation is highly affected by environmental conditions, such as water purity and water temperature.

Different species of coral reefs are found in more than hundred countries all over the planet. They are mostly found in tropical regions, where the right combination of sunlight, water temperature and nutrients allow them to healthily grow at a speed that can range between 0.5 and 10 cm per year. Some of these enormous coral atolls are considered one of the oldest inhabitants of the oceans. One example, the coral triangle, located in the Pacific Ocean around the waters of Philippines, Malaysia and Indonesia, which is recognized as one of the most diverse marine ecosystems on the Earth.

In the past years, thanks to a collaboration between Google Maps and The Catlin Seaview Survey, it was made possible to admire these marvellous ecosystems and to dive into the ocean comfortably from your couch (which can be a real turning point in “Corona-time”, when real life adventures are rarely possible!). For this peculiar project a special underwater camera, Seaview SVII, was designed to acquire unique, stunning imagines in “street-view” mode; now available on Google Maps (https://www.google.com/maps/about/behind-the-scenes/streetview/treks/oceans/). The broadcasting of these ecosystems has great impact in moving the social awareness to an urgent environmental problem, at global scale.

When coral reefs are under stress, they expel the zooxanthellae algae, turning white and losing their inner source of nutrients; this is event is referred as coral bleaching. Most of the big scale bleaching events are linked to the increased temperature in the water. The Intergovernmental Panel on Climate Change (IPCC) declared that with an increase of water temperature of just 1-to-2-degrees, the coral reefs would suffer from high mortality rates. In some circumstances, some corals might be able to recover after a coral bleaching event, but this regeneration can take up to 10-15 years. However, repetitive bleaching events over a short period of time result lethal, as corals do not have enough time to recover. The longest bleaching event was reported from 2014 to 2017, were 70% of earth coral reef were damaged [2]. A recent study has stated that heat stress has caused the Great Barrier to lose significant coral population and that the possibility for the recovery of these corals is uncertain due to increasing intensity and frequency of the disturbance events [3].  A different study has also recorded a drop of 89% below historical levels in the number of newly born larval landing on the reefs [4]. Climate change impact on coral wealth also includes weakening of coral skeletons due to water acidification and the reduction of sunlight due to sea level rise. The extent of these events seriously increases the concern among the scientific community.

Scientists around the world are currently working to increase our understanding on coral reef adaptability and restoration. For example, genetics studies are being undertaken with the hope that in the future reefs could be restored with heat tolerant coral [5]. Many innovative and interesting projects have been launched on artificial 3D printed reef structures, with the aim of saving this ecosystem from a complete disappearance. The Caribbean Marine Biological Institute (CARMABI) research station conducted a study to understand where corals prefer to anchor. The highest rate of repopulation was observed for pink and white coloured structures with holes and crevices [6]. Moreover, researchers from Cambridge University and University California San Diego have made 3D scans of living coral and managed to bio-print reproductions using polymers and hydrogels that contain cellulose materials which imitates optical properties of corals [7]. Furthermore, SECORE International is trying to produce cost-efficient 3D printing seeding substrates to improve the survival rate of coral larvae [8].

In conclusion, mass coral bleaching, and consequent deterioration of coral reefs, is one of the consequences of climate change on large scale. This hidden underwater ecosystem is undergoing tremendous changes, which are not as easily observable as other devastating events occurring on the Earth’s surface. It is important to bring scientific and technologic innovations towards rescuing these unique marine ecosystems and their incomparable biodiversity. Until we can mitigate climate change, it is necessary to raise social awareness on the preservation of any threated ecosystems, including the ones hidden from our view.

[1]        Hoegh-Guldberg O, Pendleton L and Kaup A 2019 People and the changing nature of coral reefs Reg. Stud. Mar. Sci. 30 100699

[2]        https://www.scientificamerican.com/article/scientists-are-taking-extreme-steps-to-help-corals-survive/

[3]        Dietzel A, Bode M, Connolly S R and Hughes T P 2020 Long-term shifts in the colony size structure of coral populations along the Great Barrier Reef Proc. R. Soc. B Biol. Sci. 287 20201432

[4]        Hughes T P, Kerry J T, Baird A H, Connolly S R, Chase T J, Dietzel A, Hill T, Hoey A S, Hoogenboom M O, Jacobson M, Kerswell A, Madin J S, Mieog A, Paley A S, Pratchett M S, Torda G and Woods R M 2019 Global warming impairs stock–recruitment dynamics of corals Nature 568 387–90

[5]        https://www.nationalgeographic.com/science/article/scientists-work-to-save-coral-reefs-climate-change-marine-parks

[6] https://www.ted.com/talks/kristen_marhaver_how_we_re_growing_baby_corals_to_rebuild_reefs/transcript?language=en

[7]        Wangpraseurt D, You S, Azam F, Jacucci G, Gaidarenko O, Hildebrand M, Kühl M, Smith A G, Davey M P, Smith A, Deheyn D D, Chen S and Vignolini S 2020 Bionic 3D printed corals Nat. Commun. 11 1748

[8]        https://3dprint.com/217003/3d-printing-restore-coral-reefs/