Marine pollution has long been a topic of concern, but what do you really know about the pollutants affecting the world’s waters? We asked Judith Weis, author of Marine Pollution: What Everyone Needs to Know, to delve into the various forms of pollutants, and the many ways they can harm our environment and bodies.
(1) Marine debris is much more than an aesthetic issue. In the United States, over 100 species of marine mammals, sea turtles, birds, fish, and invertebrates are injured or die after getting entangled in marine debris. Lost fishing nets are the biggest culprit. Seals are often affected by marine debris. For endangered species such as Hawaiian monk seals, entanglement in marine debris can cause declines in the already low population. In addition to entanglement, marine debris can cause problems when animals consume it. The ingested debris consists largely of plastics from industrial and recreational products, or personal care products. Clear plastic bags are often eaten by sea turtles, who mistake them for jellyfish.
(2) Some chemical pollutants are gender benders, altering the sexual development of marine animals. Hormones in birth control pills are not broken down by sewage treatment and find their way into water bodies where they exert their effects on fishes. Some fish living near sewage treatment plants are intersex with male testes producing eggs as well as sperm. The chemical TBT, which was a popular anti-foulant used in boat paint to keep barnacles off boat bottoms, caused female snails to grow male reproductive structures. When the contamination was high, the male ducts blocked the ability of eggs to go down the female duct, preventing reproduction. The snail populations plummeted but recovered once this chemical was banned for use in boat paints.
(3) Ocean acidification, a side effect of climate change, is affecting marine life by impairing the ability of young shellfish to make their shells (which could have major economic consequences for fisheries and aquaculture), and affects the homing and prey detection behavior of fishes. Much of the CO2 we release into the atmosphere dissolves in the ocean, which reduces the effects of global warming. However, once in the ocean, it reacts to form carbonic acid, which makes the ocean more acidic.
(4) Nutrients are essential for all life, but in excess they become one of the most serious and widespread pollutants. Nutrients come from human and animal wastes, and as fertilizers applied to agricultural crops and suburban lawns. Nutrients stimulate blooms of algae which can’t sustain themselves and die. When the dead algae sink to the bottom of oceans they are decomposed by bacteria. The decomposition uses up the oxygen in the water creating a zone of low oxygen that stresses or kills the animals living at or near the bottom. Such “dead zones” are becoming more prevalent around the world.
(5) Harmful algal blooms, frequently associated with excess nutrients, have become more prevalent in recent years, and have been found along the shores of many continents, as well as in freshwater. These harmful algal blooms (HABs) are the result of blooms of algal species that produce toxins. One example is paralytic shellfish positioning, caused when toxins are accumulated in shellfish that eat the algae, and then get passed up to animals that eat the shellfish – including humans. It can result in paralysis and even death.
(6) Water pollution gets worse after a severe rain storm. In rural areas the water that doesn’t soak into the ground runs off into streams, rivers, and estuaries, carrying whatever it encounters along the way, including litter, silt, animal wastes, pesticides, fertilizers, oil, etc. In many cities, storm sewers that collect rain water lead directly to local water bodies, carrying the pollution collected from the streets. In other cities, where the storm sewers combine with the sewer pipes coming from houses and industry, the combined sewers overflow after large rainfalls, which overload the capacity of the treatment plant so that raw sewage gets discharged. This often results in beaches being closed for several days after a major storm.
(7) Invasive species, a type of biological pollution, can have a major impact on biological diversity, fisheries, human health, and economics. Brought into the ballast tanks along with the millions of gallons of water that is needed to stabilize ships that transport goods all over the world, these species are then released in a new location when the ship arrives in port. At this new place, they may be able to reproduce rapidly and thrive because they have no natural enemies here. As their populations grow they often cause problems for the native species. But ballast water is not the only source of marine invasive species. The lionfish (native to the Indo-Pacific), one of the most devastating invasive species, has been eating up enormous numbers of coral reef fishes in the Caribbean, Gulf of Mexico, and South Atlantic ever since it was released from aquariums in Florida in the early 1990s.
Featured image credit: “Maldives – Kurumba Island” by PalawanOz. Licensed under Public domain via Wikimedia Commons.