What is Marine Debris?
Marine debris is trash that gets into the marine environment as a result of careless handling or disposal. Two characteristics of trash, its buoyancy and ability to be blown around, affect how easily trash becomes marine debris, while the ease with which trash degrades dictates how long it remains in the marine environment. Marine debris includes all the objects found in the marine environment that do not naturally occur there. Although items such as tree branches and the bones of land animals can be considedred marine debris, the term generally is reserved for trash. The most common categories of marine debris are plastic, glass, rubber, metal, paper, wood, and cloth.
Where does Marine Debris Come From?
Marine debris comes from many different sources. Any trash that is improperly disposed of, as well as any materials that are improperly transported or stored, can be become marine debris. The main sources of marine debris are: beach-goers, improper disposal of trash on land, stormwater sewers and combined sewer overflow, ships and other vessels, industrial facilities, waste disposal activities, and offshore oil and gas platforms.
Every year, thousands of people visit our bay area beaches. Many of them leave behind materials that become marine debris, such as food wrappers, cans, cigarette butts, and toys like shovels, pails, and beach balls. This trash can be blown into the ocean, picked up by waves, or washed into the water when it rains.
Landlubbers also can generate marine debris. Trash can be blown or washed directly into the ocean. Even trash that is generated hundreds of miles inland can become marine debris if it is blown or washed into rivers or streams and carried to sea.
Stormwater runoff (the water that flows along streets or along the ground as a result of a storm) can carry street litter into sewer pipes, which flow to the ocean. Where there are older sewer systems, sewage (the wastes flushed down toilets and drains) also is carried in the same pipe system as stormwater runoff. Pipes that carry a combination of sewage and stormwater are known as combined sewers. Unlike independent storm sewers, combined pipes turn to a sewage treatment plant rather than directly into a nearby body of water. At the sewage treatment plant, sewage is separated into sludge (solid waste materials) and water. The sludge is dried and either disposed of in a landfill or treated and sold as a fertilizer. The treated water is discharged into a river or other nearby waterway, free of solid waste.
Combined sewer pipes cause problems when heavy rainstorms cause too much water to enter the sewer system. When this happens, the amount of water in the sewer pipes exceeds the sewage treatment plant's handling capacity. To prevent major operating problems in the plant, a safety overflow valve diverts the excess water from the plant into a nearby waterway. The problem with this system, however, is that untreated sewage and debris also are diverted into the waterway.
Boats are also sources of marine debris. Sometimes, trash is purposefully thrown overboard. One major reason for the overboard disposal of trash is that there is limited storage space aboard these vessels. Most of the time, however, trash is disposed of in the ocean by people who are unaware of the problems we can cause. Trash can also accidentally fall, blow, or wash off vessels into the water. In addition, fishing nets and lines, and other types of equipment, can be lost at sea and become marine debris.
Industrial facilities contribute to the marine debris problems when waste items generated by industrial processes are improperly disposed of on land. Finished products also can become marine debris if they are lost during loading and unloading at port facilities, or they are lost when they are transported through waterways or over land.
Waste disposal activities can cause a problem when trash is lost during collection or transportation, or when trash blows or is washed away from disposal facilities.
Once debris has found its way into the ocean, it is very difficult to
trace the source of the debris. A plastic cup, for instance, could
have been left by a beach-goer, littered in a city street and washed into
a storm sewer and out to sea, blown off of a recreational boat, used on
a shipping vessel and disposed of overboard, and so on. Clearly,
marine debris is a complex problem whose answer will require that many
sources of marine debris be controlled.
What's One Way to Reduce Marine Debris?
Recycling is one way to reduce trash. Recycling is the collection and reprocessing of materials so they can be used again. Before materials can be processed for reuse, they must be separated into different types (such as plastic, glass, and metal). Although recycling has become widespread, not every type of material can be recycled.
Paper is the most frequently recycled type of trash. Three types of paper are recycled: high-grade paper, such as computer paper, newspaper, and corrugated cardboard. Metals also are commonly recycled, particularly aluminum cans. All types of glass, except light bulbs, ceramic glass, dishes, and plate glass, currently can be recycled. Overall, very little plastic waste is recycled, with the exception of plastic milk jugs and soft drink bottles.
Even better than recycling is adopting pollution prevention strategies that produce less waste in the first place. Ways to produce less waste include reusing materials, using reusable items rather than disposable ones, and reducing the amount of packaging we use.
We can also take steps to keep waste from getting into the ocean. Most importantly, littering should be prevented. Boaters and beach-goers should ensure that trash and other items are not blown or washed away. Before trash is left out for collection, it should be tightly secured in bags or trash cans to ensure that trash stays in its proper place.
How Can Marine Debris Affect Wildlife?
The two primary problems that marine debris poses to wildlife are entanglement and ingestion. Entanglement results when an animal become encircled or ensnared by debris. Entangelment can occur accidentally, or when the animal is attracted to the debris as part of its normal behavior or out of curiosity. For example, an animal may try to use a piece of marine debris for shelter or as a plaything, or as a source of food (if other plants and animals are already trapped in the debris or if the debris resembles prey that is a normal part of its diet).
Entanglement is harmful to wildlife for several reasons. Not only can entanglement cause wounds that can lead to infections or loss of limbs, but it may also choke or strangle wildlife. In addition, entanglement can impair an animal's ability to swim, which can cause drowning or difficulty in moving, finding food, and escaping predators.
Ingestion occurs when an animal swallows marine debris. Ingestion sometimes happens accidentally, but generally animals feed on debris because it looks like food. Ingestion can lead to starvation or malnutrition if the ingested items block the intestinal tract and prevent digestion, or accumulate in the digestive tract and make the animal feel "full," lessening its desire to feed. Ingestion of sharp objects can damage the digestive tract or stomach lining and cause infection or pain. Ingested items may also block air passages and prevent breathing, which siffocates animals.
Marine mammals, turtles, birds, fish, and crustaceans all have been entangled in or have eaten marine debris. Many of the species most vulnerable to the problems of marine debris are endangered or threatened. Endangered species are plants or animals that are in immediate danger of becoming extinct because their population levels are so low. Threatened species are plants and animals that may become endangered in the near future.
Approximately 100,000 marine mammals die every year from entanglement or ingestion of marine debris. Of the different types of marine mammals, seals and sea lions are the most affected particularly by entanglement because of their natural curiosity and tendency to investigate unusual objects in the environment. Packing straps and net fragments are a major problem for these animals. Some studies have linked the decline of the northern fur seal of Alaska and the endangered Hawaiian monk seal to entanglement in marine debris. Whales, including endangered humpback and gray whales, have been found entangled in fishing nets and line. Manatees, which are also endangered, have become entangled in crab-pot lines, and dolphins and porpoises may get caught in fishing nets. Ingestion of debris by marine mammals appears to occur less frequently, but it has been reported for elephant seals, sea lions, certain types of whales and manatees. Although few cases of ingestion have been reported, these cases are significant because they have usually contributed to or resulted in the death of animals due to suffocation or starvation.
Sea turtles also have become entangled in marine debris. All of the five species of sea turtles found in the U.S. are endangered species, and all have been found entangled in different types of marine debris, such as fishing line, rope and nets. Ingestion of marine debris is an even greater problem for these species. Sea turtles have swallowed plastic bags because they look like jellyfish, one of their favorite foods. This may cause the turtle's digestive tract to become blocked, leading to starvation. Cases of turtles swallowing balloons, tar balls and debris that has become covered with algae have also been reported.
Nearly a million seabirds are thought to die from entanglement or ingestion each year. Since most seabirds feed on fish, they are often attracted to fish that have been caught or entangled in nets and fishing line. Entanglement in fishing line has been a particular problem for the brown pelican, which is an endangered species. Seabirds are some of the most frequent victims of abandoned nets. As many as 100 birds have been found in a single net. Many birds, including ducks, geese, cormorants and gulls have been found entangled in six-pack rings and other encircling debris. The ingestion of plastic resin pellets (small, round pellets that are used to form plastic products) is a major concern. Many types of birds have been found to feed on these pellets, most likely because they mistake them for fish eggs or other types of food.
Fish and crustaceans such as lobsters and crabs are frequently caught in lost or discarded fishing gear, in a phenomenon known as ghost fishing. For example, a ½-mile section of nylon net was found in Lake Superior that had been abandoned for an estimated 15 years, and contained 100 pounds of fish, much of which was rotten. Lost traps also continue to attract fish and crustaceans, which enter them in search of food or shelter. In New England alone, an estimated half million lobster pots are lost every year.
Wildlife also is affected when marine debris disturbs its environment. For example, lost or discarded fishing gear and nets can drag along the ocean floor or through coral reefs, disrupting the animals and plants that live there. In addition, debris can bioaccumulate in the food chain. Bioaccumulation occurs when organisms low on the food chain consume a substance that builds up in their bodies. When animals higher on the food chain eat those organisms, they also ingest that substance, and it accumulates in their bodies. The higher an animal is on the food chain, the greater the quantity of the substance that is consumed and accumulated. For example, eagles and other predators high on the food chain have been found with large concentrations of plastic pellets in their stomachs after preying on smaller birds, which previously ate the material in fish.