Corals

Fascinating facts about the Corals

• Coral colonies are built by millions of genetically identical polyps, each only a few millimetres wide, that secrete calcium-carbonate called corallites. Over generations these tiny cups fuse into structures up to several metres tall, forming the hard framework of reefs.
• Most corals rely on internal algae called zooxanthellae, which can make up 30 % of a polyp's tissue. The algae photosynthesise, passing glucose, glycerol and amino acids to the host and even raising the coral's internal pH, which aids calcification. In return the coral provides the algae with carbon dioxide and waste nutrients. This partnership fuels reef building in clear, shallow water, usually less than 60 m deep, making sunlight a critical resource for the entire ecosystem.
• Corals reproduce by releasing eggs and sperm in a synchronized night-time spawning that often follows a full moon. The dark window between sunset and moonrise triggers the release, and within 10-30 minutes. A single colony may emit several thousand larvae each year, but because planulae must find a suitable hard surface and avoid sediment, only a tiny fraction survive to become new colonies, highlighting the fragility of reef renewal.
• When ocean temperatures rise, corals expel their zooxanthellae in a stress response known as bleaching. Without the algae, the coral loses its colour and most of its energy source, making it vulnerable to death. About 33 % of coral species are listed as endangered by the IUCN, and rising acidity forces corals to spend extra energy pumping protons out of their calcifying space, weakening skeletons and increasing susceptibility to storms and disease.
• Hard-coral skeletons are biocomposites of aragonite calcium carbonate and an organic matrix of proteins like CARPs and SAPs, secreted by the calicoblastic ectoderm. Enzyme α-carbonic anhydrase converts CO₂ to bicarbonate, supplying the carbonate ions needed for crystal growth. This tightly regulated process allows corals to lay down roughly 1 cm of skeleton each year, a pace so slow that a reef the size of the Great Barrier took about two million years to form.

Sources

Every fact above was checked against these pages, and kept only where one of them states it.

• Wikipedia

At a glance

About the Corals

In the warm, crystal waters of the tropics, coral reefs come alive as vibrant, living cities, their delicate, branching forms swaying gently in the ocean currents like an ethereal ballet. As the tide rises and falls, these underwater metropolises pulse with a kaleidoscope of colors, their intricate, symbiotic relationships with the creatures that call them home a testament to the remarkable resilience and beauty of these vulnerable, yet vital, ecosystems. With each delicate polyp working in harmony to create a thriving, interconnected whole, corals embody the very essence of life's boundless diversity and intricate complexity.

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