ECOSYSTEMS AT RISK – CASE STUDY 2
PART 1: CORAL REEFS – OVERVIEW
Coral reefs are often referred to as “the rainforests of the sea” because of they form some of the most diverse ecosystems on Earth. Its massive structure is formed from coral polyps (tiny animals that live in colonies) that support approximately 25% of all known marine species by providing essential habitats. Factors affecting reef development and survival include temperature, light, sedimentation and salinity of the water. Without the right balance of these factors, the reef ecosystem will not survive; meaning thousands of species would become endangered. The wellbeing, abundance and diversity of the organisms that inhabit the reef ecosystem are directly linked to the surrounding terrestrial and marine environments. Predominately, mangrove forests and seagrass beds are the most important features of the greater coral reef ecosystem. Mangrove’s root systems stabilise the shore line, filter pollutants and produce nutrients as well as provide habitats and nurseries for breeding and the feeding of marine life. Many animals then migrate to coral reefs for food and habitat. Seagrasses form meadows between mangroves and coral reefs and are the foundation of many food webs, providing vital nutrients as well as protection and shelter for species like lobsters and stone crabs. They also filter the water column, prevent seabed erosion and release oxygen. These two facets are vital to the long-term health of coral reefs and the functionality of the vast range of biodiversity within the ecosystem at risk. CORAL REEF: An erosion-resistant marine ridge or mound consisting chiefly of compacted coral together with algal material and biochemically deposited magnesium and calcium carbonate skeletons of coral Cross-section of a coral polyp animals known as polyps. The skeletal material is broken down and piled up by wave action, producing a massive formation that supports living corals and a wide variety of other plant and animal life. They are found in both temperate and tropical marine environments.
GLOBAL DISTRIBUTION LINKING TO BIOPHYSICAL REQUIREMENTS
As with all biomes, coral reef distribution is mainly determined by a particular set of environmental conditions that allow dominant species that build the ecosystem to thrive; these include temperature, salinity levels, specific light for photosynthesis and sedimentation. The hard corals that build coral reefs require warm water. Although many species may survive brief exposures to more extreme temperatures, the typical limits tolerated for long periods are from about 17-34o C, however optimal temperature for coral growth is 23-25o C all year round. So mostly, coral reefs are found in tropical and subtropical waters around the Equator between 30 degrees North and 30 degrees South. Hard corals do not tolerate sea water salinity values that exceed those normally found in the open ocean; most will not survive prolonged exposure to water outside a range of about 30-38 parts per thousand. Light levels are critical in maintaining a coral-algal symbiotic association as the intensity of light affects photosynthesis rates. In clear tropical waters, corals may live as deep as 48m, with very limited species beyond this depth. Excessive sedimentation restricts the reefs access to available light for growth. Therefore, coral reefs can only develop in areas away from rivers that bring silt and freshwater into marine environments. Silt also settles on coral surfaces and blocks feeding and respiration as well as preventing photosynthesis from occurring.
Source 1 - Location of coral reefs
Source 2 – Global distribution of coral reefs
EXAMPLES OF LOCATIONS OF MAJOR REEF SYSTEMS
Fig 1: Indo-Pacific Reefs
Fig 2: Red Sea...
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