Point Source - Oil Spills
Oil spills are one example of point source pollution and a major concern for marine animals. Oil spills can come from a variety of different sources. For example, a careless human mistake can cause an oil tanker ship to leak fuel into the ocean. Or, the winds from a natural disaster like a hurricane can cause such a ship to flip over and spill its oil.
Once oil has been spilled into the ocean, it remains at the surface for a long time, anywhere from several weeks to a month or more. In this time, the oil directly and indirectly affects living organisms and their ecosystems.
Organisms that live at the sea surface are most directly affected by oil spills. For example, seabirds spend much of their time floating on the surface of the water, where the oil floats because it is much less dense than water. The oil coats the birds feathers. Due to the weight of the oil on their feathers they cannot fly, and some even drown. The birds naturally begin to clean themselves, and in doing so, ingest (eat) the oil, which poisons them.
When their feathers or fur become coated with oil, many animals including seabirds, seals, sea lions, and sea otters are unable to regulate their body temperature. Normally, fur and feathers are excellent at trapping body heat. The oil interferes with the heat-trapping, and body heat escapes. For animals that live in water, releasing heat is not a good thing. Many of these animals die when their body temperatures get too low, a condition called hypothermia.
Oil can also result in the death of organisms by preventing them from getting oxygen. Many marine animals get their oxygen from the air, and must come to the surface to breathe. In cetaceans like whales, dolphins, and porpoises, the oil gets into their blowhole, creating a plug that clogs their blowhole and prevents them from exchanging gases. When the oil gets into the lungs of other animals such as seals, sea lions, and sea turtles, it clogs their airways. In either case the result is suffocation, or the cutting off of the fresh supply of oxygen to the organism needed for life.
Fish and other organisms that live below the surface are more not directly affected by oil spills. Indirectly, however, the oil may damage their food chain. Floating oil on the oceans surface blocks the Suns rays from entering the water. As a result, marine producers like phytoplankton and seaweed are not able to produce food for themselves and die. This sets off a chain reaction in the food web from the base up. If the phytoplankton population dies out, there is less food available to the zooplankton, the animals that eat the zooplankton, and so forth. The result is that organisms die because of the lack of food available. Keep in mind that other animals food source depend on organisms that eat plankton. For example, a sea turtles diet consists of organisms such as jellyfish, shrimp, clams, sponges, and mussels that eat plankton directly.
Oxygen in the ocean comes from two major sources: photosynthesis by marine producers and gas exchange with the atmosphere. Oil floating at the sea surface negatively affects both of these sources of oxygen. The oil decreases the sunlight available to producers for photosynthesis and prevents contact between the water and the air, making gas exchange difficult. nTherefore, there is less oxygen available in the water. Organisms such as fish and invertebrates like crabs, squid, lobsters, and clams all may suffer from lack of oxygen.
Oil spills also affect organisms reproduction. Some fish, like tuna, lay their eggs at the surface of the ocean. When the eggs come in contact with the oil they will no longer continue to develop into a fish. Thousands upon thousands of eggs can be lost in a short period of time, dramatically reducing the number of fish in the next generation.
Seabirds have been known to abandon their nests, leaving their eggs or in some other cases not producing as many eggs as they normally would. Sea turtles will often not come out of the water to lay their eggs. Since sea turtles lay hundreds of eggs at a time, this change in behavior will have an extremely negative impact on the population.