plastic bottles floating across the oceans may carry more than a message -- they could be transporters of the seeds of ecological chaos for wherever they end up. In a recent survey, scientists from the Cambridge-based British Antarctic Survey (bas) have found that the rising tide of plastic debris has replaced wood as the major shoreline debris and this rubbish is providing a vehicle for marine organisms to travel much further than they normally would and invade new territories. "Plastic debris more than doubles the rafting opportunities for invading species," says David Barnes, a marine biologist at bas. The findings have raised concern among many biologists because as per the estimates of the World Conservation Union, alien invasions are the second most important cause of diversity loss.
The bas findings are based on a 10-year survey, during which scientists studied human litter (mostly plastic) washed ashore on 30 remote islands around the globe, from the Arctic to the Antarctic. The scientists found that human-made rubbish in the seas, especially plastics, has almost doubled the spread of alien species in the subtropics and more than tripled it in high latitudes.
According to them, since the creation of plastics over 50 years ago, floating litter has provided mobile homes for marine organisms such as bryozoans, barnacles, polychete worms, hydroids and molluscs, increasing opportunity for dispersal to new areas. Many seem to prefer plastics to natural matter such as volcanic rock, pumice and wood.
The scientists in particular investigated the potential impact of the debris on Antarctica's native marine animal life. "We particularly focussed on Antarctica because the highest proportion of human-made rubbish is found here," says Barnes. The proportion of this debris is higher in the Antarctica because there are no forests to provide natural flotsam. According to Barnes, the amount of debris in the Southern Ocean has risen hundred-fold in the last decade.
The researchers analysis indicated that with a 2C temperature increase in the Southern Ocean over the next 100 years, Antarctica's natural barrier, which currently freezes out alien species, would become weak. The first warning signs will be seen at the most northerly Antarctic islands. "Polar warming would decrease the freezing seawater ice that is the main barrier to alien organism invasion of Antarctica. Moreover, some native Antarctic marine species are very sensitive to even a small temperature increase. If alien species enter the region they have the capacity to drastically and irrevocably change these ecosystems," said Barnes.
He opines that plastic debris is more important than the contents of ships and aircraft, previously regarded as humankind's prime means of spreading species round the globe. "Immediate steps should be taken to tackle the menace of plastic debris if the ecological balance of the oceans has to be maintained," says Barnes.