When we think of animals, they usually have two eyes and paws, and sometimes we even attribute them human behaviours. This is called anthropomorphism.
However, this conception of what is an animal would imply missing an important part of the fauna on Earth, such as shellfish, worms or jellyfish. (Yes, obviously worms are not your favorite animal!)
Ok, no eyes, no paws, but they move! So, we could simply describe an animal as motile creatures?
Once again this isn’t completely true: Corals are fixed to the floor!
Did you really mean that corals are animals?
Yes indeed, corals have long been a trouble for naturalists. After being considered as
plant-animals, or even minerals, people generally thought corals to be plants until the beginning of the nineteeth century, when the scientist William Herschell finally established that corals cells were more similar to those of animals.
Corals are definitly different. So different from us that it’s difficult to imagine them not classified as plants. What makes them so special? It’s what you will discover in this article.
What are corals?
Cnidarians generally have two shapes: polyps (anemones) and medusae (jellyfish). Both Polyps and medusae have soft bodies but while polyps are always fixed somewhere, medusae are free living creatures.
Corals are a colony of polyps with the same genetic material. These polyps have either six or eight tentacles depending on the species. Soft corals do not have hard skeletons, unlike hard-corals. From now on, I will more focus on hard-corals.
Hard corals have a live part on their surface (polyps) and a dead solid part produced by aggregation of calcium carbonate (limestone), absorbed in water and deposited by polyps. Coral-reefs are essentially made of coral skeletons.
Each polyp live in a little pit at the surface of the hard skeleton. This is called a calyx.
Zooxanthellate corals (or reef-building corals) have established a symbiotic relationship with photosynthetic algae. [Symbiotic means that both species need the help of the other and are beneficial to the other.] zooxanthellae algae (the photosynthetic algae) produce energy thanks to sunlight and polyps waste products, and live inside the polyps that offer their protection. Because these algae require sunlight, corals develop in shallow and clear waters.
This video here summerizes what I have just said.
Destruction of coral reefs
As stated on the coral reef alliance website, coral reefs are subject to two scales threats: Global threats and local threats.
Global threats: The impact of global warming
Climate change is responsible for most (if not all) the causes of coral decay at a global scale. Global warming increases the tempretature of the oceans which are melting the ice still present on continents. Thus, it rises the oceans levels and zooxanthellate corals lack sunlight.
Coral bleaching has been found to be increasing for the last few years as a result of stress due to environmental changes such as temperature. The zooxanthellae algae are ejected, the coral dies and becomes white. Moreover, a warming environment is suitable for diseases development, and greenhouse gases absorption in water modified the pH, which further weakens corals.
Climate change modified the pattern of storms which are becoming more frequent, and altered ocean currents. It results in reefs being destroyed or lack of food.
A document provided by the national ocean service provides a good summary here
Locally, corals are threatened by:
- Overfishing: It creates an inbalance among the population of the reef.
- Unsustainable tourism and pollution: Wastes thrown to the sea or any product spilled into the sea can harm corals. Tourists can destroy corals by mistake and corals containing jewelry is sold as souvenirs.
- Costal development: Some buildings directly sit on top of corals, and deforestation prevent trees to act as a filter. As a result, corals are smothering due to increased sedimentation.
Why are corals so important
You could say: “Ok, another kind of species disappearing, what’s the matter?”
Infact, every species on earth live in an intricate relationship with its environment. If you remove or add an element to this ecosystem, you can be sure that there will be consequences.
Let’s see with corals:
Firstly, corals have many different shapes and colors, they contribute to the beauty of the sea but this is only a superficial threat.
Secondly, with their hard structures, corals act as a barrier to protect shorelines against erosion.
Thirdly, corals form complex structures which are ideal places to hide for fishes and a base for plants to develop. Coral reefs are rich ecosystems [Group of all the organisms living in a defined area which are interacting as a system, a balance that must not be disturbed], the Great Barrier Reef is even thought to have the highest biodiversity on earth. If corals were to disappear, hundreds of species could vanish with them.
If corals are condemned to extinction, a complete ecosystem may collapse with consequences both for the wildlife and us. Marine species are incredibly varied and as you might have noticed, most of the examples of animals that didn’t have a common body pattern (Jellyfish, worms, and shellfish) live in the sea. A lot of them have not been studied yet, and more information on their behaviour and particularities might enlighten us on our own condition as it was the case with octopuses brains. Further more, in modern medicine, some conpounds are extracted from nature and cannot be synthetised artificially. Coral reefs ecosystems might be potential sources for a remedy against HIV or cancer who knows?
To conclude, corals do not look like an animal. But is it a reason not to care about it? Obviously not. Nothing should have to be cute to be protected, and although my website is dedicated to animals it must also apply to plants.
Aquarium Anemone Fish Fish Amphiprion Clown Fish, Public Domain
Coral polyps in symbiosis with unicellular dinoflagellates, by Nbharakey. Public Domain
Coral polyp, by NOAA, Public Domain