Coral reefs biodiversity, importance, and conservation

A hidden city in the underwater environment in need of urgent global action


A brief characterisation

Coral reefs have been growing in the world's oceans for more than 450 million years. They constitute massive and bulky structures that shelter not only fascinating biological communities but are also the largest geological structures on the planet that have been formed by living organisms. With the exception of some cold water species, the reef building or hermatypic corals are extremely sensitive to thermal gradients, and only manage to grow where the water temperature does not fall below 21 °C or rise significantly above this temperature. As a consequence coral reefs are restricted to tropical waters (roughly 30° S to 32° N) and are not found on the westward facing coasts of landmasses since these are areas of upwelling that bring cold deep water to the surface, lowering the water to lethal temperatures. Coral reefs around the world are one of the most spectacular underwater environments, benefiting people and the natural world far beyond their boundaries. These natural wonders are complex ecosystems supporting a remarkable diversity of life, safeguarding human settlements, economies and cultures, fostering tourism jobs and opportunities, acting as safe harbours, protecting against erosion, and providing food to sustain local diets. They contain 10 % of the world’s fishing harvest, playing a key role in nutrient cycling, and holding in secret the prospect of scientific and medical advances we are only beginning to discover.


The threatened tropical ecosystem: a coral reef-mangrove linkage

The world’s coral reefs and associated seagrass and mangrove habitats are in serious jeopardy, threatened by an increasing array of over-exploitation, pollution, habitat destruction, invasive species, disease, bleaching and global climate change. The rapid decline of these ancient, complex and biologically diverse marine ecosystems has significant social, economic and environmental impacts around the world. Coral reefs are among the most diverse and biologically complex ecosystems on earth. These rainforests of the sea provide economic and environmental services to millions of people as areas of natural beauty and recreation, sources of food, jobs, chemicals, pharmaceuticals, and shoreline protection. Now under threat from multiple stresses that are overwhelming their natural resilience, coral reefs are deteriorating worldwide at alarming rates.


Conservation strategies must take into account that coral reefs as a whole do not act in isolation. As scientific studies progress, we are aware that these complex systems are linked to other biologically significant entities as for example mangroves and sea grass communities. Mangrove forests are one of the world’s most threatened tropical ecosystems with global loss exceeding 35 %. Juvenile coral reef fish and other creatures in early stages often inhabit mangroves, which seem to be unexpectedly important, serving as an intermediate nursery habitat for protection that may increase the survivorship of young fish as well as providing enough food resources, guarantying an efficient development. Mangroves i.e., in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangrove.
Current research shows indeed that extensive mangrove habitat scan enhance the biomass of fishes and other creatures on coral reefs because tropical coastal ecosystems seem to be functionally linked. Although precise corridors of connectivity between habitats are not fully understood as yet, the results have an important implication for conservation planning: management schemes should explicitly protect areas of connected habitats rather than simply identify representative areas of each habitat in isolation. A multi-ecosystem approach with open connexions to other would-be important habitats should be at the core of the policies to ensure the protection of not only the coral reefs, but also of the entities directly linked to their existence.



Coral reefs valuable services to the world

- Tourism: the tourism industry is one of the fastest growing sectors of the global economy. Reefs are a major destination for snorkelers, scuba divers, recreational fishers, boaters and sun seekers. Diving tours, fishing trips, hotels, restaurants, and other businesses based near reefs provide millions of jobs.
- Fishing: i.e., in developing countries, coral reefs contribute about one-quarter of the total fish catch, providing food to an estimated one billion people in Asia alone as an example.
- Coastal protection: coral reefs buffer adjacent shorelines from wave action and prevent erosion, property damage and loss of life. Reefs also protect the highly productive mangrove fisheries and wetlands along the coast, as well as ports and harbours and the economies they support.
- Biodiversity: reefs support at least a million described species of animals and plants, including about 4,000 documented species of fish and 800 species of hard corals. Another 8 million coral reef species are estimated to be as yet undiscovered. In many ways, coral reefs rival and surpass tropical rainforests in their natural wonder and biological diversity and complexity.
- Natural heritage: coral reefs are an important part of our natural heritage, rivalling the longevity or complexity of some treasured land-based resources and national parks. For example, a well-developed reef may be the manifestation of thousands of years of incremental accretion by its resident coral colonies, sometimes growing only millimetres each year. Many coral species have no known limit on colony size or age and may continue growing indefinitely in favourable habitats.




Dangers to coral reefs

- Pollution, including eutrophication and sedimentation from poor or overly intensive land use, chemical loading, oil and chemical spills, marine debris and invasive alien species.
- Over-fishing and over-exploitation of coral reef species for recreational and commercial purposes, and the collateral damage and degradation to habitats and ecosystems from fishing activities.
- Destructive fishing practices, such as cyanide and dynamite fishing that can destroy large sections of reef.
- Dredging and shoreline modification in connection with coastal navigation or development.
- Vessel groundings and anchoring that directly destroy corals and reef framework.
- Disease outbreaks that are increasing in frequency and are affecting a greater diversity of coral reef species. In some cases these diseases have jumped from land-based entities to coral reefs.
- Global climate change and associated impacts including increased coral bleaching, mortality, storm frequency, and sea level rise.



Strategies regarding the conservation of coral reefs

- Understanding of coral reef dynamics: monitoring of coral reef habitats should be implemented, supporting strategic research on regional threats to coral reef health and the underlying ecological processes upon which they depend, always incorporating the human dimension into conservation and management strategies.
- Control the volume of threatening human activities: stronger networks of federal, state and territorial coral reef Marine Protected Areas should be proposed, reducing the adverse impacts of extractive uses, declining habitat destruction, and pollution, restoring damaged reefs, strengthening international activities and reducing the impacts of international trade in coral reef specie just to name a few measures.
- Science-based ecosystem approaches: coral reef conservation strategies should be based on a scientific framework, recognizing and building policies upon important linkages among adjacent and remote habitats associated with coral reefs.
- Incorporate the human dimension into conservation: management measures should reflect and be sensitive to the local socio-economic and cultural environments. It should be enhanced by all means the presence of a well-informed and educated public, which recognizes and is engaged in choosing reliable alternative options to harmful activities that may eventually impinge on their own community welfare.
- Global leadership and recognition: worldwide awareness and recognition of the problem at a community and individual level. International cooperation, technical and development assistance with a strong building and collaborative capacity.




Mr. Mario Lebrato
Department of Marine Biology and Oceanography
National Oceanography Centre
University of Southampton
www.noc.soton.ac.uk
ml1104@soton.ac.uk


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