Competitive Exams: Science and Technology Coral Bleaching
Corals are marine animals included in class Anthozoa and phylum Cnidaria. These organisms, producing hard exoskeleton of calcium carbonate, are represented by a colony of genetically similar flower-like structures called polyps. Over many generations the colony secretes a skeleton that is characteristic of the species. Huge deposits of these skeletons over long periods of history may give rise to coral reefs. Each polyp is typically only a few millimetres in diameter and has skeleton cup, tentacles with stinging cells, a mount and a stomach. The tiny tentacles snatch at passing plankton for food.
Rising water temperatures block the photosynthetic reaction that convents carbon dioxide into sugar. This results in a build up of products that poison the zooxanthellae. To save itself, the coral spits out the zooxanthellae and some of its own tissue, leaving the coral a bleached white. This phenomenon is often referred to as coral bleaching.
Many corals form a symbiotic relationship with a class of algae, zooxanthellae, of the genus
Symbiodinium. Typically a polyp harbours one species of algae. Via photosynthesis, these provide energy for the coral, and aid in calcification. The algae benefit from a safe environment, and consume the carbon dioxide and nitrogenous waste produced by the polyp. Due to the strain the algae can put on the polyp, stress on the coral often drives the coral to eject the algae. Mass ejections are known as coral bleaching, because the algae contribute to coral's brown colouration; other colours, however, are due to host coral pigments, such as green fluorescent protein (GFP).
Courtesy: Science Reporter