Did you know that it’s possible to rebuild coral reefs?
Here in Curacao, there is one such coral conservation mission called Reef Renewal Curacao. Through carefully planned coral fragmentation in nurseries around the island, Reef Renewal Curacao has successfully outplanted thousands of critically endangered staghorn and elkhorn corals to revitalize degraded local reefs.
I recently joined the mission by completing my PADI Reef Renewal Diver Distinctive Specialty and joining the volunteer program at Ocean Encounters Curacao. In the Reef Renewal course, students learn all about coral and the techniques involved in the reef restoration process.
So get ready to discover the fascinating world of coral reefs and what you can do to help save them!
What Exactly is Coral?
Believe it or not, corals are animals! They belong to the group Cnidaria, along with some other simple stinging animals such jellyfish and anemones. However, unlike their other cnidaria cousins, corals live in enormous groups of genetically identical individuals.
That’s right, what might appear to be a single coral, is actually an enormous family of clones. Each individual animal in this group is called a polyp. These polyps grow copies of themselves in a process called budding to form these colonies.
While there are hundreds of known species of corals, almost all can be classified into two categories, hard and soft corals. Soft corals are appropriately named as they’re soft in texture; think sea fans. On the other hand, hard corals are hard due to the calcium carbonate skeleton they build using abundant calcium and carbonate in the ocean.
What Are Coral Reefs?
Coral reef structures are formed by large communities of hard corals. These reef-building corals follow the life cycle of any other animals - they live, reproduce, and die. But when coral dies on a healthy reef, they create layers of calcium carbonate skeleton for new polyps to move in and grow atop.
Over hundreds of thousands of years, this rebirth cycle has built the coral reefs as we know them today. That’s right; it takes between 100,000 to 30,000,000 years to fully form a coral reef. With growth rates as low as 0.3 centimeters per year for massive corals and up to 10 centimeters per year for branching corals, building a coral reef is slow work!
What is Coral Bleaching?
To understand coral bleaching, you need to know about zooxanthellae. Besides being a super fun word, zooxanthellae are photosynthetic algae that live inside the coral. Being the strange animals they are, corals have a symbiotic relationship with these plants and depend on them for their survival.
Zooxanthellae rely on their coral hosts for a protected environment to live in. Meanwhile, the coral needs the zooxanthellae for most of its nutrients. In the clear, warm, tropical waters most coral reefs are, there are far fewer free nutrients than in cold, murky water.
Therefore, the coral and zooxanthellae thrive using a tight nutrient recycling loop. As part of this loop, the coral’s primary food source is the organic material produced by the zooxanthellae through its photosynthesis.
Not only does the zooxanthellae provide the coral with the nutrients it needs to live and grow, but they’re also responsible for giving the corals their beautiful colors. The corals themselves are actually see-through to allow as much light as possible to reach their algae buddies.
But unfortunately, the zooxanthellae are easily affected by rising temperatures. Despite some misconceptions, the zooxanthellae actually can photosynthesize better in warmer water. The problem is that they will start to photosynthesize so quickly that they cannot repair themselves. This leads to them releasing compounds that are toxic to corals.
The coral, in turn, is like, “you got to go, or we’re both going to die,” and will literally move the algae into their guts and spit them out to expel them from their bodies. Now without their colorful sun protection, the coral’s white skeleton becomes visible or “bleached.”
Fortunately, newly bleached corals aren’t dead - yet. If conditions improve, the coral can recover their zooxanthellae and survive. Still, they’re damaged and won’t be able to reproduce as quickly. However, if conditions do not improve, the coral will starve to death without their biggest food source.
What is Ocean Acidification?
Besides coral bleaching, the leading global threat to coral reefs is ocean acidification. Remember how coral grows their skeletons from calcium carbonate? Well, this makes them incredibly sensitive to the ocean’s chemistry.
Simply put, ocean acidification is the lowering of the water’s pH level due to the absorption of carbon dioxide. A quick review from grade school science of the carbon cycle reminds us that plants take up CO2, which they use to photosynthesize. Despite being in the ocean, aquatic plants such as phytoplankton perform the exact same function, essentially sucking carbon dioxide into the waterThe ocean carbon cycle. Image credit: IAEA
As the concentration of carbon dioxide in the Earth’s atmosphere increases, so does the amount absorbed into the ocean. During this absorption process of CO2 in the ocean, the carbon dioxide molecules react with the water to form carbonic acid. Then, this carbonic acid is converted to bicarbonate and carbonate ions.
In an ideal situation, all these forms of carbon would exist in balanced proportions. However, as more and more carbon dioxide is absorbed into the ocean, the available carbonate decreases while the concentration of bicarbonate increases.
This shift results in an ocean with a lower pH and less carbonate available for coral to build their calcium carbonate skeletons. This obviously slows their growth but can actually cause the coral skeletons to dissolve in severe cases.
What Are the Direct Threats to Coral?
While coral bleaching and ocean acidification are global threats to our ancient coral reefs, there are several local threats corals face:
Over-fishing: Leads to overgrowth of algae that can smother coral
Destructive fishing: Unsustainable practices such as blast fishing and dragging anchors can physically break corals
Land-based pollution: Wastewater such as sewage and agricultural runoff introduce chemicals and bacteria that harm the reef environment
Trash and plastic: Disgraded fishing gear, plastic bottles, and more can snag on corals, either breaking them or blocking vital sunlight
Recreational misuse: Scuba divers, snorkelers, and swimmers can harm corals by touching or removing them from their habitat.
Coral harvesting: Taking corals from their reef habitat for aquariums or decoration can lead to overharvesting of specific coral species.
Coastal development: In water buildings such as piers and dikes kill corals directly.
Why Should We Save Coral Reefs?
Coral reefs are the most diverse marine ecosystems on the planet. With thousands of species to be found living on a single reef, protecting them makes sense from a biodiversity standpoint alone. But the preservation of marine animals is not the only reason we need coral reefs.
Coastline Protection
Reefs play a major role in protecting coastlines from natural disasters and erosion. As a coastal barrier, coral reefs can reduce wave energy by up to 97%, providing much-needed protection during weather events like hurricanes and tsunamis.
The Economy
Coral reefs are also precious to local economies. Many coastal societies rely on reef fish for much of their diet, and the tourism that a healthy reef attracts creates jobs. Not only do these tourists spend money on tours and scuba diving, but the economic impact extends to hotels, restaurants, stores, taxis, and more.
Medical Treatment and Research
Did you know that more than half of all new cancer research starts with the ocean? Organisms on coral reefs have led to treatments for everything from cardiovascular disease to leukemia. Protecting the biodiversity of the reef means more opportunities for these life-saving discoveries.
How Does Reef Renewal Work?
The reef renewal process used in Curacao was developed in response to the collapse of staghorn and elkhorn corals throughout the Caribbean that began in the 1980s. These now critically endangered coral species are both fast-growing branching corals that provide shelter for many species of marine organisms.
Coral Propagation
The first step of the reef renewal process takes place in coral tree nurseries. These “trees” are made from PVC and fiberglass, sit just below the ocean surface, and are tethered to the bottom. This structure is designed to allow the most freedom in the water column while minimizing damage, disease, and predation.
Bits of genetically identical coral are hung from these trees using monofilaments. Then, as they grow larger and their branches grow longer, reef renewal divers use pliers to cut small pieces off the large existing corals. These new coral fragments are added to the same tree, creating more corals of the same genotype.
This ongoing process of fragmenting larger coral to create new generations mimics the coral’s natural cycle. When a branch breaks off a coral due to waves or marine life, the branch will continue to grow into a new coral, so long as the conditions are favorable. Nursery propagation only expedites this by creating optimal conditions.
Outplanting
After six to eight months in the nursery, the corals are mature enough to be outplanted to the restoration reef. To outplant, the reef renewal divers collect genetically identical corals from the nursery into a tray and swim to the restoration site where they’re needed most.
The current method for outplanting includes attaching the coral fragments to bamboo structures anchored in the sand using zip ties. Since only corals from the same genotype are planted together, eventually, they will grow together as one system. This also ensures that the coral will grow over the artificial components, the bamboo and zip ties, to create a new reef structure.
Maintenance and Monitoring
A huge part of why the reef renewal process works so well is constant care and attention. For example, nursery trees are highly susceptible to algae and fire coral overgrowth and must be cleaned regularly. Restoration outplant sites also require frequent check-ins to ensure coral fragments are properly positioned to grow into a healthy mature coral.
What Can I Do to Protect Coral Reefs?
Reef Renewal Curacao, formally Coral Restoration Curacao, is a non-profit organization operated by the dive center Ocean Encounters. Their work focuses on restoring elkhorn and staghorn corals in the shallow reef system around Curacao.
You can get involved by joining the Reef Restoration project here on Curacao, or you can donate by adopting a coral.
Well done/written. Thanks for sharing.
Hi! It seems as if we have a similar Substack, both in topic and design. I am actually writing about OA this week, and I really liked your description of how it affects corals. Will let you know when I publish my newsletter!