Coral reefs
Coral reefs are intricate stony formations created by colonies of coral polyps that deposit calcium carbonate exoskeletons as they grow. Found primarily in shallow tropical seas, these reefs are among the most diverse ecosystems on Earth, supporting approximately one-fourth of all marine life. They provide essential habitats and nutrients for a wide variety of organisms, including fish, mollusks, and sponges. Coral reefs rely on a symbiotic relationship with zooxanthellae, tiny protozoa that live within the coral tissues and supply energy through photosynthesis. However, coral reefs are highly sensitive to environmental changes and face significant threats from climate change, pollution, and destructive fishing practices. Coral bleaching, a process where corals lose their color and expel their symbiotic partners due to stress, is a major concern linked to rising sea temperatures and ocean acidification. These fragile ecosystems cover less than 1 percent of the ocean's surface yet play a crucial role in marine biodiversity. As human activities continue to impact these vital habitats, there is a growing emphasis on raising awareness of their ecological and economic importance, including their roles in shoreline protection and supporting fisheries.
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Coral reefs
Coral reefs are stony formations created by the depositing of exoskeletons by colonies of coral polyps.They are some of the most diverse ecosystems on the planet, supporting a wide variety of marine life, including fish, mollusks, and sponges. Coral reefs are most famously found in shallow tropical seas, but certain types exist in other parts of the ocean as well. They are very sensitive to environmental conditions, and are globally threatened by climate change, pollution, overfishing, and other human-induced factors.
There are approximately one thousand known species of coral, some of which live in colonies. These colonies of coral polyps deposit their exoskeletons of calcium carbonate as they grow and thus provide the durable formations that the polyps, along with other species of coral and many other animals, live on and around. These stony formations are arguably the best-known type of reef, a term that refers to any large, ridgelike structure beneath the surface of a water body.
Typical coral reefs occur in shallow water ecosystems of the Indo-Pacific and Western Atlantic regions. Lesser known cold-water reefs are found at depths between 40 and 3,000 meters along continental shelves, continental slopes, seamounts, and fjords worldwide.
Reef-building corals generally need to be in shallow water to get energy from the sunlight that filters down through the water column. The corals themselves do not photosynthesize sunlight; rather, they have a symbiotic relationship with protozoa called zooxanthellae. These organisms live within the tissues of the corals and provide them with the by-products of photosynthesis, such as glucose and amino acids, that the corals use for energy. Reef-building corals are thus almost wholly dependent on the zooxanthellae.
Coral reefs cover a total area equivalent to less than 1 percent of the surface area of the oceans, yet they are believed to support about one-fourth of all marine life. For organisms such as and algae, which use corals for shelter and for the raw materials they need to produce energy, and larger animals such as fish and sea snakes, coral reefs offer sources of nutrients in addition to shelter. The diversity and sheer numbers of marine life make up a complex food web, with the corals and their symbionts at the center. It is because of their richness that most coral reefs are so important to so many different species of marine life. Given the variety of animals that live in reef communities, any threat to the corals is a threat to the entire ecosystem. Coral reefs are very fragile owing to their susceptibility to changes in water temperature and acidity.
Some significant threats to coral reefs come directly from human activities, such as the destructive fishing practices of overfishing, bottom trawling, and blast fishing. However, scientists have identified coral bleaching as the biggest threat facing coral reef ecosystems. The term “coral bleaching” refers to the whitening of corals when the protozoa lose their pigmentation or the corals expel their symbionts in reaction to some form of external stress, such as pollution. The main causes of coral bleaching are related to climate change: increases in water temperature and increased acidity of the oceans. Coral reefs tend to continue to undergo bleaching even if the source of the stress is removed, and if the colonies survive the bleaching, the zooxanthellae do not immediately reappear, sometimes taking months to come back.
The prospect of higher sea levels associated with climate change is also a threat to coral reefs, as corals need to be in shallow waters with a lot of sunlight to survive, and corals cannot grow fast enough to keep up with predicted sea-level rises. More than half of the world’s coral reefs are threatened directly or indirectly by human activity, a situation that has led environmentalists increasingly to promote public awareness of the economic value of the reefs and the ecosystem services they offer, such as shoreline protection and well-stocked fisheries.
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