Introduction
Corals, often called “the architects of the oceans,” are fascinating marine organisms that form reefs that are home to exceptional biodiversity. Although they may seem similar at first glance, there is actually a great diversity of coral species, each with unique characteristics. This article takes you on a journey to the heart of coral reefs to discover the different coral species, their particularities and their crucial role in marine ecosystems.
1. Hard corals (Scleractinia): reef builders
Hard corals, or scleractinian corals, are the main building blocks of coral reefs. These corals have an external skeleton made of calcium carbonate (limestone), which allows them to form solid structures on which reefs grow.
Main species:
Acropora : This genus of corals is one of the most prolific in tropical reefs. It forms branched colonies resembling branches or tables. Acropora is often the species most affected by coral bleaching due to its sensitivity to temperature variations.
Porites : Unlike Acropora, Porites coral is slower growing and forms massive spherical or dome-shaped colonies. This genus is more resistant to environmental disturbances and can survive in harsher conditions.
Favia : Favia corals are distinguished by their massive shape and distinct polyps, often visible as small alveoli on their surface. They are also quite robust and participate in the construction of reefs.
These hard corals form the structural basis of reefs, providing shelter and breeding grounds for many marine species. In addition to their architectural role, they actively participate in the carbon cycle in the ocean.
2. Soft corals (Alcyonacea): underwater flexibility
Soft corals, unlike hard corals, do not have a calcareous skeleton. Their structure is more flexible and their appearance more supple. They are often found in the same reefs as hard corals, but they do not participate in the formation of the reef skeleton.
Main species:
Sarcophyton : Known as leather coral, Sarcophyton has a soft, thick texture. It is characterized by a mushroom shape with a flat surface covered with small polyps.
Sinularia : This genus is easily recognized by its long, fleshy branches. Sinularia corals are often dominant in certain areas of reefs, especially in nutrient-rich waters.
Dendronephthya : These corals are distinguished by their bright and flamboyant colors, ranging from pink to red to yellow. Unlike other corals, Dendronephthya do not contain zooxanthellae (symbiotic algae) and therefore rely solely on the capture of plankton for food.
Soft corals play an important role in reef biodiversity. They provide temporary habitats for certain species and contribute to water filtration by capturing food particles.
3. Solitary corals: a solo life
Some species of coral do not live in colonies, but rather individually. These solitary corals, although less known, are just as fascinating.
Main species:
Caryophyllia : This solitary coral has a circular or oval appearance and is found mainly in deeper waters. It attaches itself to rocks and solid substrates, capturing plankton that passes nearby.
Fungia : Called mushroom coral, Fungia is another example of a solitary coral. It is usually flat, circular, and free to move on the seabed. Its vibrant colors and ability to move slightly to escape sediment make it a unique species.
These solitary corals, although they do not contribute directly to the construction of reefs, play a role in the ecological diversity of the seabed.
4. The role of zooxanthellae in the life of corals
Most corals, both hard and soft, live in symbiosis with microscopic algae called zooxanthellae. These algae provide corals with most of their energy through photosynthesis. In return, corals provide them with shelter within their tissues. This relationship is essential for the survival of coral reefs, as it allows corals to thrive in nutrient-poor waters.
However, when environmental conditions become too stressful, such as during marine heat waves, this symbiosis breaks down, leading to coral bleaching. Without zooxanthellae, corals are deprived of their main source of energy and are at risk of dying.
Conclusion
The different species of coral, whether hard, soft or solitary, are wonders of underwater nature. Their diversity contributes to the richness of the reefs and the maintenance of exceptional biodiversity. However, these species are now threatened by environmental changes, including global warming and ocean acidification. Protecting these fragile ecosystems is crucial to ensure the survival of the oceans and the species that depend on them.
Scientific references:
Veron, JEN (2000). Corals of the World . Australian Institute of Marine Science. Available here
Hoegh-Guldberg, O. (1999). “Climate change, coral bleaching and the future of the world’s coral reefs.” Marine and Freshwater Research , 50(8), 839-866. Available here
Lough, J.M. (2008). “Coral calcification from skeletal records revisited.” Marine Ecology Progress Series , 373, 257-264. Available here
