Although many people think that corals are rocks or plants (or don't even think about corals at all?), they are actually animals. Corals belong to the phylum cnidaria, along with anemones and jellyfish, are are actually a colony of small animals working together to act as a larger animal. Each coral polyp has its own mouth, and corals typically extend their tentacles during the night to catch small prey items that float through the water. However, corals get the majority of their nutrition from microscope algae living inside of them, a type of dinoflagellate known as zooxanthellae. These zooxanthellae use the sun's energy to photosynthesize and produce food energy that the coral then uses. In return, the zooxanthellae get a safe home and nutrients.
A close up shot of the polyps of a great star coral (Montastrea cavernosa), one of my favorite corals. Although corals usually stay closed up during the day and open at night to feed, sometimes you can catch the great star corals with its tentacles out to catch some food during daytime as well. The hole in the center of the coral its mouth!
However, if corals get stressed - most often due to high temperatures but also low oxygen or other stressful environmental conditions - they will expel their zooxanthellae. Because zooxanthellae are what give corals most of their color, corals without zooxanthellae appear white because all you see is their calcium carbonate skeleton underneath their tissue, and that is why this process is known as coral bleaching. Corals can live without their zooxanthellae for a little while, so if for example the temperatures return to normal within a week, the zooxanthellae can recolonize the corals and everything will be fine. However, if the corals are without zooxanthellae for too long, they will no longer have enough nutrition and will die. Global climate change and the associated bleaching is the greatest threat to corals around the world, but unfortunately there are also a host of other threats that corals face, including ocean acidification, sedimentation, increased nutrient loads (which can lead to both increased algae growth and low oxygen levels), overfishing, and direct damage by humans. If you are interested in learning more about threats to corals, I recommend watching this video.
A bleached Agaracia coral
So why are corals important? They literally create habitat - as hard corals grow their produce a skeleton of calcium carbonate that creates reefs. This in turn provides a habitat for fish and other organisms to live, grow, hide, and find food. They also protect our coastlines from storms and wave action, and are important to tourism and local economies in many areas.
Below is an series of infographs I created for the community of Bocas del Toro to explain a bit about the importance of corals and a few of the main species we have here. You can download my coral identification guide in Spanish, Corales de Bocas del Toro, and see photos of more species of corals under my "Marine Life of Bocas del Toro" page on my site. Two other great resources put out by the Smithsonian Tropical Research Institute are A Field Identification Guide to Hard Corals of Bocas del Toro Archipelago, Panama and Photographic Identification Guide to Some Common Marine Invertebrates of Bocas Del Toro, Panama.
Below are the infographs I created with basic information about corals in Bocas in Spanish - please download and share!
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