POLLUTION

TOXIC POLLUTANTS 

Toxic pollutants are an insidious threat to marine life. Some pollutants are so toxic, or are present in such large quantities that they may cause immediate death. Others are more subtle in their effects, but nonetheless may be responsible for weeks, months or even years of prolonged suffering. In most cases, details are still unknown, but they are believed to weaken the animals, gradually causing hormonal imbalances, a lowering of disease resistance, brain damage, cancer, liver troubles and a host of other problems. They may even cause a total loss of fertility.

Minute quantities of toxins are picked up by marine plankton, which are eaten by fish and squid, and these in turn are eaten by the top predators. These toxins can then gradually build up to a level where they become lethal. Toxins enter the sea mainly from rivers and the atmosphere. It is difficult to measure the quantity of toxins globally but it is estimated that 44% of all pollutants entering our seas is from runoff and discharges, 33% is from atmospheric deposition, 12%  is from maritime transportation, 10% deliberate dumping and 1% is from offshore development of mineral resources (UN study).

TRASH VORTEX

Recently a "plastic soup" of waste floating in the Pacific Ocean has been discovered and now covers an area twice the size of the continental United States, scientists have said. The vast expanse of debris – in effect the world's largest rubbish dump – is held in place by swirling underwater currents. This drifting "soup" stretches from about 500 nautical miles off the Californian coast, across the northern Pacific, past Hawaii and almost as far as Japan. Charles Moore, an American oceanographer who discovered the "Great Pacific Garbage Patch" or "trash vortex", believes that about 100 million tons of flotsam are circulating in the region.

DEAD ZONES 

Dead zones are hypoxic (low-oxygen) areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970's. In March 2004, when the recently-established UN Environment Programme published its first Global Environment Outlook Year Book (GEO Year Book 2003) it reported 146 dead zones in the world oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometer, but the largest dead zone covered 70,000 square kilometers.

PLASTICS

Marine animals are known to ingest everything from large pieces of plastic sheeting to tiny resin pellets. Juvenile sea turtles, which live and feed in areas where food and plastic waste concentrate are particularly prone. It is well known that Leatherback turtles mistake plastic bags for their main prey, jellyfish, and can die from intestinal blockage. At least 69 seabird species eat plastic waste, and some feed plastics to their young. For instance on Midway Island, some 1,600 km from the nearest populated land mass, all 300 Laysan albatross chicks had plastic waste in their stomachs, including toys, bottle caps, balloons, condoms and cigarette lighters (Shomura & Yoshida).