31/03/2023
What are coral reefs??? (Borrowed from the EPA website)
Coral reef ecosystems are intricate and diverse collections of species that interact with each other and the physical environment. Coral is a class of colonial animal that is related to hydroids, jellyfish, and sea anemones.
Stony corals, a type of coral characterized by their hard skeleton, are the bedrock of the reef. Stony coral colonies are composed of hundreds of thousands of individual living polyps. Polyps are capable of drawing dissolved calcium from seawater and solidifying it into a hard mineral (calcium carbonate) structure that serves as their skeletal support. When you look at a coral colony, only the thin layer on its surface is live coral; the mass beneath is the calcium carbonate skeleton that may be decades old.
The slow growth of polyps and expansion of the hard skeletal structures build up the permanent coral reef structure over time.
Polyps of reef-building corals contain microscopic algae called zooxanthellae, which exist with the animal in a symbiotic relationship. The coral polyps (animals) provide the algae (plants) a home, and in exchange the algae provide the polyps with food they generate through photosynthesis. Because photosynthesis requires sunlight, most reef-building corals live in clear, shallow waters that are penetrated by sunlight. The algae also give a coral its color; coral polyps are actually transparent, so the color of the algae inside the polyps show through.
Coral reefs provide habitat for a large variety of marine life, including various sponges, oysters, clams, crabs, sea stars, sea urchins, and many species of fish. Coral reefs are also linked ecologically to nearby seagrass, mangrove, and mudflat communities. One of the reasons that coral reefs are so highly valued is because they serve as a center of activity for marine life.
Not all corals on the reef are stony corals.
• Hydrocorals, or fire coral, are reef-building hydroids that have a hard calcareous exoskeleton and stinging cells that can cause a burning sensation when touched.
• Octocorals, or ‘soft’ corals, include sea fans and sea whips, which grow more like fleshy plants and do not form calcium carbonate skeletal structures.
• Antipatharians, or black corals, are another type of branching ‘soft’ coral.
Some soft corals have zooxanthellae to acquire food and energy, but others, such as black corals, exist without this symbiotic relationship.