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Coral Reefs
What are coral reefs?
Coral reefs are unique and complex ecosystems made up of reef-building corals.
Most coral reefs are built from stony corals, which are "colonial organisms" composed of hundreds (sometimes thousands) of individual animals called polyps that embed within calcium carbonate shells. Each polyp has a mouth surrounded by a ring of tentacles and a stomach. The polyp uses the tentacles to collect food and clear debris. The coral's diet includes microscopic animals called zooplankton and occasionally small fish.
Coral polyps do not photosynthesize. Instead, they have a symbiotic relationship with microscopic algae called zooxanthellae. Zooxanthellae live within the coral polyps' tissues and produce oxygen and organic nutrients (glucose, glycerol, amino acids) that the coral polyps will use as building blocks in manufacturing proteins, fats, and carbohydrates, as well as in the synthesis of calcium carbonate. Coral continues to grow when polyps deposit calcium carbonate as a skeletal structure beneath and around themselves, thus pushing the head of the coral upwards and outwards.
Coral polyps reproduce both sexually and asexually. Internally fertilized eggs develop inside the polyp and subsequently produce a larva known as a planula. Externally fertilized eggs develop during synchronized, en masse spawning (usually at night and in phase with the lunar cycle). Once planulae are released, only a few successfully attach to substrates and become polyps.
The varying pigments in different species of the symbiotic zooxanthellae give coral their brown and gold colors. Other pigments such as reds and blues come from colored proteins made by the polyps. If coral loses a large fraction of its zooxanthellae, the polys colony will take on a white appearance and is said to be "bleached," which can ultimately kill the coral.
In the past 40 years, a large percentage of coral reefs have died and disappeared. Thus making coral reefs greatly endangered with the possibility of 90% of coral reefs disappearing by 2050. The major threats to coral reefs are listed below.
A Threatened Ecosystem
The main threat to coral reefs ecosystems, and the key cause to their destruction, are human activities.
The top three activities directly contributing to coral reef destruction are: pollution, overfishing, and coastal development.
In addition, climate change that has been brought on by human activity adversely affects coral reefs by raising ocean temperatures to levels that coral cannot survive in.
For more information on the threats imposed on coral reef ecosystems, see the detailed list below.
