A third of the world's reef-building coral species are facing extinction, according to researchers writing in the Science journal. They are more threatened than any land animals (apart from amphibians).
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Warming
waters can devastate coral, bleaching them in the process |
Climate change: loss of algae. When the ocean gets too warm, the shock makes coral go white and eventually die. Biologists call this bleaching. Just as bubonic plague was called the 'Black Death' because it left blackened corpses - an estimated 75 million of them nearly 700 years ago - so coral bleaching is a kind of 'White Death'.
Actually, coral has a certain amount of resilience. It has survived many warming episodes in the past 420,000 years. However, when combined with all the other pressures on coral (pollution, tourism, overfishing, river run-off full of silt and nutrients, invasive species etc), this could be the last straw
When water temperatures rise, coral polyps - tiny animals that build the reefs - expel the algae that usually live with them. Because the algae are no longer there to provide nutrients, the corals lose their colour, with reefs taking on a bleached appearance and begin to die.
Climate change: acidification. The water absorbs some of the atmosphere's extra carbon dioxide, making it slightly more acid - enough to make it more difficult for corals to build their skeletons.
Overfishing. Heavy trawls and the use of dynamite to fish both reduce reefs to rubble.
Pollution. Coastal development and farming discharge effluent into the sea, which stimulates the growth of the wrong types of algae - ones that smother growing coral.
Excavation. Extracting building materials from reefs also is a problem.
Unregulated tourism. Corals are damaged by a variety of physical impacts that include anchor damage, accidental boat groundings, diver and snorkeler touching, and standing and dragging equipment. Propellers tear up shallow seagrasses. Marine debris, especially plastics, damage marinelife and smother corals. Turtles mistake plastic bags for their favorite food: jellyfish.
Ecotourism. This has been defined as “the practice of low-impact, educational, ecologically and culturally sensitive travel that benefits local communities and host countries” or Responsible travel to natural areas that conserves the environment and improves the well-being of local people." Unfortunately, many commercial tourist concerns claim to offer "ecotourist" holidays that actually do not fully meet with ecological principles.
In this stressed condition, coral then fall prey more easily to disease. About a quarter of marine species are believed to depend on coral at some stage of their development. Many fish live their entire lives on reefs, while others use them as nurseries; presumably if the coral dies out, so do the fish. The economic impact of losing coral is also significant.
Corals can recover from short-term bleaching, but
prolonged bleaching -- over a week -- can cause irreversible damage
and subsequent death.
