Marine life in reefs and coastal waters critically endangered

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Many marine ecosystems are facing mass extinction as a result of human activity, such as habitat destruction, acidification of sea-water and overfishing. New research into the regions and species most at risk suggests that up to 90 per cent of large predatory fish stocks have disappeared, transforming complex food webs into simplified ecosystems dominated by microbes and algae.

The research reviews data from several sources and compares the ecological condition of the oceans to that of tropical rainforests: dire and potentially irreversible losses will take place if action is not taken promptly. Problems associated with long-term over-fishing are now being exacerbated by habitat loss, global climate change and pollution from chemicals and nutrients. The study concludes that there has been drastic and rapid degradation of marine ecosystems over the last few decades.

The research focuses on the biodiversity of four different marine zones which are critically endangered, endangered or threatened:

Coral reefs - Critically Endangered. The amount of global live coral has diminished by between 50 per cent and 93 per cent, most notably in the Caribbean and the Indo Pacific. Fish stocks are down by 90 per cent, with large predators almost completely absent, and a sharp decline in sponges and turtles. Corals, especially species such as elkhorn and staghorn, are affected by disease, coral bleaching, acidification and rising temperatures.

Coastal Seas and Estuaries - Critically Endangered. Marshlands, mangroves and oyster reefs have reduced in size by between 67 per cent and 91 per cent. Fish and shellfish are affected by eutrophication, hypoxia (a shortage of oxygen), toxic blooms and disease, caused by runoff of nutrients, sea-warming and overfishing.

Continental shelves - Endangered. Stocks of large fish are down by 50-90 per cent. As many predator species, found at the top of the food chain, are now absent there has been an increase in numbers of non-commercial species such as small rays and sea urchins. This has further knock-on effects: the increase in numbers of these smaller species has led to a reduction in the number of other, often commercial, species that they consume, such as scallops and kelp. Problems associated with overfishing are exacerbated by destruction of marine habitats through trawling and nutrient discharge. Nutrient discharge can lead to 'dead zones', home to only jellyfish and microbes, such as the region that extends 500 km west of the Mississippi delta in the USA.

Open Ocean - Threatened. There has been a decline of between 50-90 per cent in population size and mass of open ocean species such as tuna, shark and billfish. Global warming and acidification of the deep ocean is slowing the natural process whereby cooler, nutrient rich water rises. It also inhibits the growth of calcareous plankton, organisms which are vital to the cycling of carbon and the CO2 storage capacity of the ocean.

Measures to halt these extinctions include sustainable fisheries and aquaculture, increased taxation of fertilisers and alternative, non-fossil forms of energy. Local protection measures against overexploitation and pollution also help protect coral reefs and other marine ecosystems.

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