Ocean Pollution
Introduction
For eons the earth has swept its waste down into the seas. Over the ages, the debris of life and land was easily incorporated into the natural cycles of the ocean. More recently, people have also given their discards to the sea. But this practice has disrupted, rather than enhanced, the ocean ecosystem. Pollution is now a serious threat to the survival of many marine creatures and habitats.
The most obvious type of pollution is physical. Physical pollution includes all of the solid, liquid, and dissolved materials that harm marine organisms or alter marine ecosystems. All of the substances that people use on land, release into the air, or take out onto the water can eventually be washed, precipitated, or spilled into the oceans. The most widespread and dangerous of these are trash, toxins, and oil.
Trash is deliberately dumped into the sea as well as blown or washed in from land. Some of this material quickly sinks to the bottom or breaks down rapidly. But much of it, particularly plastics, can drift through the ocean for miles and for years. Trash kills in many ways—animals that get tangled in trash, or lost fishing gear, are maimed, drowned, or strangled. Those that swallow debris choke or starve. Material that settles to the seafloor crushes and smothers bottom dwellers.
Toxic materials – chemicals and heavy metals – attack organisms from the inside, causing disease, genetic mutations, birth defects, reproductive difficulties, behavioral changes, and death. Toxins flow into the ocean mainly from the runoff and discharge of industrial, agricultural, and human wastes into rivers that then empty into the sea. Many of the most dangerous toxins settle to the seafloor and then are taken in by organisms that live or feed on bottom sediments. Because these compounds aren’t digested, they accumulate within animals that ingest them, and become more and more concentrated as they pass along the food chain. This process, called biomagnification, means that higher-level predators—fish, birds, and marine mammals—are most severely affected.
Many toxins, like mercury, dioxins, PCBs, and radioactive isotopes, are clearly hazardous. But even otherwise beneficial compounds can act as dangerous pollutants at high enough levels. Nutrients such as phosphorus, nitrogen, and ammonia disrupt the balance of ecosystems when they are flushed from lawns and gardens and farms into the sea. The resultant bloom and then decay of algae and other plants can use up all the oxygen in shallow or slowly circulating waters and lead to the formation of “dead zones.”
Oil spills combine the worst effects of trash and toxins. Some plants and animals smother quickly when coated with oil. Birds and marine mammals die of exposure when sodden feathers and fur lose their insulating abilities. Fish, reptiles and mammals erupt in skin and eye lesions and can develop serious infections and blindness. Animals that swallow or inhale oil can suffer organ damage, develop crippling and fatal diseases, and experience reproductive failure.
Nearly 1 billion gallons of oil are released into the oceans each year. Large spills from oil tankers are spectacular and garner much attention, but are responsible for only 5% of all oil pollution. By far the largest source is motor oil. More than half of the oil that contaminates the sea each year is dumped a few quarts at a time into drains or dripped slowly onto roads and parking lots and then washed into sewers, rivers and finally the sea.
Physical pollution is a clear and obvious danger to marine ecosystems. Floating garbage, oil slicks glinting in the sunlight, or the sight of diseased animals are all disturbing and easily understood evidence of the severity and effects of ocean pollution. Other types of pollution are less obvious and harder to assess. For example, noise pollution has only recently been recognized as a threat in the oceans.
The depths of the ocean appear quiet and calm, but they are filled with ever louder and more relentless human-made noise. Because of ship traffic, oil and gas exploration, research activities, and the use of military sonar and communications equipment, ambient marine noise has increased by two orders of magnitude in the last 60 years. The rising noise is especially hard on marine mammals.
In the oceans, where distances are long and visibility is short, many species rely on sound to communicate, navigate, and monitor their surroundings. These essential activities are becoming more and more difficult as background noise overwhelms the animals’ hearing. Noise pollution can inhibit the ability of seals, sea lions, and cetaceans to find food or escape predators, drive them from feeding and breeding areas, and cause mothers and offspring to become separated. Recent studies attribute an increase in whale strandings and deaths to hearing loss and confusion caused by intense noise.
People have long found it convenient to throw trash into the sea, where it would quickly sink or drift out of sight and out of mind. Now, however, the impacts of ocean pollution are becoming too striking to ignore. The seas are an increasingly important source of human food and medicine. More than twenty percent of the global population gets the majority of its protein from seafood. Drugs and medical therapies derived from marine plants and animals are being developed at a rapid rate. The ocean fishing and pharmaceutical industries are economic powerhouses that, together, support millions of workers. But ocean pollution threatens to cripple these valuable resources.
Trash, toxins, and oil spills are all taking a toll on the health of many marine species. Sick and contaminated plants and animals are unusable for food or medical studies. When reproduction and growth are hampered by pollution, population size falls, and the fish catch drops accordingly. Even worse, ocean-going toxins become concentrated up the food chain through biomagnification. Many species of seafood are now so tainted with pollutants, such as mercury, lead, and dioxin, that they are no longer safe to eat in large amounts.
Harder to measure, but no less painful, is the spiritual cost of ocean pollution. Many people are deeply touched by the beauty and wonder of the sea and its creatures. The sight and smell of polluted shorelines and seas, and the knowledge that many species may be driven to extinction by human carelessness, are profoundly troubling.
Arising out of these practical and emotional concerns are a number of local to international efforts to stop and even reverse the rising tide of marine pollution. However, ocean waters and sediments are already heavily polluted, and both the human population and the waste it generates are growing exponentially. Marine scientists now rank pollution as the greatest threat facing ocean life and ecosystems, now and for the foreseeable future.