When coral bleaching points out to serious environmental problems

Corals belong to the most famous cnidarian marine invertebrates around the world. They form compact colonies, which consist of many individual polyps sometimes secreting calcium carbonate skeleton (stony or hard corals) to protect fragile bodies. As sessile organisms with no medusa stage within their life cycle the hard coral colonies are anchored to a substrate and cannot move freely to escape in danger. However for many years they have been forming large coral reefs covering more than 280,000 km2 (under 0.1% of the oceans' surface area). The Great Barrier Reef, composed of almost 3,000 individual reefs in the Coral Sea, off the coast of Queensland, Australia belongs to best known. According to the International Union for Conservation of Nature (IUCN): “Coral reefs, along with seagrass beds, mangrove habitats and other tropical marine environments, support the highest marine biodiversity in the world. More than 500 million people worldwide depend on them for food, storm protection, jobs, and recreation. Their resources and services are worth an estimated 375 billion dollars each year, yet they cover less than 1% of the Earth’s surface“. Recently this unique ecosystem has been markedly affected by numerous environmental and ecological impacts, including water pollution (e.g. oil, fertilizers, herbicides), biological invasions (e.g. crown-of-thorns starfish), diseases or tropical cyclones. But climate change with global warming has undisputedly become the most dangerous problem affecting coral reefs and their valuable extraordinarily productive ecosystems with rich biodiversity including many endemic species. The main symptom of the coral extinction has been known as coral bleaching. Coral bleaching appears in aquatic environment significantly warmed up within the climate change consequences when coral polyps expel symbiotic algae called Zooxanthellae (single-celled dinoflagellates), that provide much of its vibrant color. These microscopic algae transform solar radiation onto chemical energy to obtain essential nutrients to their polyps but under stress and disturbance (e.g. high temperature) they simply die or leave polyps and their symbiotic relationship. As Zooxanthellae provide the corals with almost 100 % of energy, their expelling leads to starving or even death. Corals are generally not able to cope with current increased temperatures. Scientist have documented several current coral extinction events recently. The first disaster appeared in 1998 after a massive heat wave with approximately 16 % of corals killed around the world. The second huge coral bleaching event in 2010 was soon followed by the third global bleaching disaster with enormous ecological consequences on coral reefs. The US National Oceanic & Atmospheric Administration (NOAA) considered the third global bleaching event in October 2015 as the longest event recorded, impacting some reefs in consecutive years. As United Nations Environment documents state almost 93% of the Great Barrier Reef have been hit by coral bleaching according to a comprehensive survey that reveals the terrifying scale of the devastation. What is the plan to save coral reefs? According to the IUCN Reef Manager's Guide to Coral Bleaching the "need for management has become clear, identifying practicable and effective management responses has proven challenging. Traditional management approaches that focus on minimising or eliminating sources of stress are not applicable to coral bleaching. Coral reef managers are unable to directly mitigate or influence the main cause of mass bleaching: above average water temperatures. This makes mass bleaching a uniquely challenging environmental management problem."

Location

globally

Environmental impact

• Water pollution
• Land degradation (e.g. drought, soil contamination, erosion and desertification)
• Biodiversity loss – Ecosystem destruction
• Depletion of natural resources (fossil and mineral, forest, water, etc)
• Hazards related to extreme weather events – natural disaster
• Alteration of landscape aesthetics and built heritage

Ethical/ legal issues

• Health and well-being
• A clean and prosperous environment and a safe and pleasant habitat
• Opportunities to work and leisure
• Access to public goods/ resources and products

Information sources & materials

Contributor(s)

Peter Fedor, Professor of Environmental Ecology

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