As you snorkel over a coral reef you see thousands of living organisms. Sponges, sea squirts, anemones, soft corals, hard corals, crinoids, algae. The list is endless. Each wacky life form begs the question, what are you? Animal or plant? Individual or a group? What do you eat? How do you reproduce? When it comes to coral, the answers are truly mind boggling.
So What is Coral?
At first glance corals look like plants but they are, in fact, animals. Most of the corals we see on a reef consist of hundreds, often thousands, of coral polyps that together form a coral colony. The individual polyp is often microscopic, but if we zoom in close we can see that polyps resemble tiny upside-down jellyfish. A coral polyp has a central cavity (its mouth) surrounded by tentacles, which it uses to capture plankton drifting through the water. So how can such small animals, feeding on even smaller prey, build habitats visible from space? Millions of years ago, corals formed an extraordinary alliance, a friendship as I like to think of it, with a microscopic, plant-like organism called a zooxanthellae.
Zooxanthellae are photosynthetic cells that live in coral tissue. They have a symbiotic relationship. Corals provide the zooxanthellae with a safe place to live, and in turn the zooxanthellae photosynthesizes, producing energy that fuels the corals growth and reproduction. Hard corals use this energy to make calcium carbonate, which is the stony outer structure that coral polyps live in and which forms the foundation of coral reefs. This vital step in coral evolution is how minute coral polyps have built reefs the size of countries.
The green speckles are the symbiotic zooxanthellae in the coral polyp tissue
Coral Color and What It Tells Us
As well as providing corals with their primary food source, zooxanthellae are responsible for giving coral its signature spectrum of dazzling colors. The symbiotic algae in the coral tissue expresses certain pigments that vary from neutral tones of browns and greens, to bright blues and purples. The color of a coral can be a useful indicator of its health, if interpreted correctly.
Like all animals, corals require specific environmental conditions to thrive. Water temperature, clarity, salinity and acidity can all impact coral health. When conditions stay outside the healthy range for too long corals become stressed and react by expelling their symbiotic algae. This process, known as coral bleaching, leaves the coral deprived of its main food source and colour. The coral appears bright white. In a bleached state, the coral is still alive, but very weak. If harsh conditions persist the polyps eventually die, leaving behind only the bare stony structure.
The good news? If conditions return within their healthy range corals can recover from a bleaching event. They can welcome back algae into their tissues, restoring both their color and their health. The Images below show the same patch of reef bleaching and recovering as temperature fluctuates.
The Future of Coral Reefs
The biggest threat to shallow-water corals is rising ocean temperature. On top of that, local stresses like wastewater runoff, severe storms, and overfishing make survival even harder. Yet research shows that corals can adapt to changing conditions if we give them the time and support they need. That means combining local conservation with global efforts to reduce carbon emissions.
As snorkelers, we know there are still vast stretches of thriving reef worth protecting. Fortunately, the global coral community is constantly developing innovative strategies to restore and preserve these ecosystems.
Coral Planting
Although corals are animals, you can grow them much like plants! Coral planting is a widely used conservation method, and the process is wonderfully simple:
- Step 1: Harvest a fragment.
This can be a loose, living fragment that has come loose from the reef or a small piece intentionally taken from a healthy colony. - Step 2: Nurture the fragment.
Fragments are attached to nursery structures either in the ocean or in aquariums where they can grow in stable, protected conditions. - Coral nursery
- Step 3: Outplant the fragment.
Once healthy and strong, the fragment is attached to damaged areas of the reef, where it can grow into a new colony and help restore the ecosystem.
Coral planting can be highly effective and has helped reefs recover after major disturbances like cyclones and mass bleaching. But planting alone isn’t enough, we must consider the bigger picture.
A Global Effort
Coral conservation requires collective action. Organizations globally are collaborating with coastal communities to advance sustainable practices, including promoting sustainable fishing, minimizing pollution, and controlling sedimentation. Simultaneously, others are leading the way in developing renewable energy solutions, reinforcing the growing momentum toward cleaner energy worldwide.
Corals powerfully demonstrate that even small, individual actions collectively lead to massive outcomes. The monumental scale of a coral reef, built by countless tiny polyps, mirrors the collective effort needed for its conservation. It takes millions of polyps to build a reef, just as it takes millions of people to preserve it!
