Water Quality


Plastic debris constitutes one of the most serious threats to ocean health. It makes up some 90% of the trash floating on the ocean’s surface, and it can take up to 1,000 years to decompose in nature. Unlike other types of trash, plastic does not biodegrade; instead, it is broken down into smaller and smaller pieces that never really disappear. Birds, turtles, fish, and other marine life then ingest the plastic pieces, mistaking them for fish eggs, plankton, or other food items. Every year, hundreds of thousands of sea creatures, both large and small, die from complications relating to plastic debris – they may have a stomach full of plastic that they cannot digest, or they may have become fatally entangled in the debris.

Solid Waste

While human trash is more or less continuously and deliberately dumped in the ocean, natural disasters can cause a greater influx of debris to enter the sea from land. Tsunami debris from Japan is washing up on shores from Alaska to California. Events like this remind us of the interconnectivity of international ocean communities and of the inexorable power of ocean currents.

Fishing gear left in the sea can alter the ocean bottom and inadvertently kill sea life. Nets become snagged on rocks and are lost, but continue to ensnare fish, birds, sea turtles, and marine mammals (whales, dolphins, seals and sea lions). Crab, lobster, and fish traps get lost in storms, lose their marker buoys to propellers, or are abandoned, but continue to capture marine life for months or years after being lost.

Chemical Waste

Many of the chemicals that we use to improve our quality of life find their way into rivers, estuaries, and oceans after they are discarded. Some of these chemical compounds are toxic, long-lasting, and accumulate in living tissue—disrupting the vital functions of ocean wildlife and humans. Pharmaceuticals are now accumulating in aquatic environments, affecting the plants and animals exposed to them in different ways. Some disrupt reproduction, while others alter innate behaviors. Some chemicals designed to kill pests incidentally increase the mortality rates of many other species. Particularly well known, even if only by their initials (DDT, PCB, TBT, BFR), these organic compounds are known collectively as Persistent Organic Pollutants (POPs). Once these compounds escape our control and flow into the sea it is virtually impossible to retrieve them. To avoid the unintended consequences, we must become more vigilant and prevent them from escaping into the ocean in the first place.

Toxic Waste

The immense size of the sea makes it easy to believe that the ocean is capable of absorbing anything put into it without changing. We are discovering, however, that the ocean has limits. Heavy metals, like copper, lead, zinc, and mercury, contaminate the water and the plants and animals living in it. Emissions from coal-fired power stations and worldwide economic development and industrialization contribute to contamination. The concentration of methyl mercury in sea bird feathers, for example, can be compared over the last two centuries and shows an exponential rise from the 19th to the 21st century. This poisonous substance accumulates in ocean food chains, which means that large predators such as swordfish, tuna, and dolphin carry the largest amounts of it.

Harmful Algal Blooms

Sunny days, warm water, and increased nutrients are the perfect recipe to grow algae. When algae grow rapidly, it’s called an algal bloom. Some algae growth is important to a healthy ecosystem. Many animals eat algae, and most species of algae are not dangerous. Some species of algae, however, are toxic to humans, animals, and the environment. When these algae bloom, it’s called a harmful algal bloom (HAB). HABs occur in both fresh and coastal waters and range in colors from green to red to purple. Climate change and increased lawn and agricultural runoff into waters have created ideal conditions for HABs, and HABs are occurring more often in more places than ever before.


As the ocean absorbs unprecedented levels of human trash and toxins, new diseases have begun to develop in the altered marine environment. Pathogenic micro-organisms are appearing in ocean life in epidemic proportions, for the first time in human experience. Two of the most important reef-building corals in the Western Atlantic and Caribbean Sea are now in danger of extinction, in part as a result of diseases contracted from sewage released into the ecosystem. Sea otters in California are dying of infections from domestic cat parasites. Huge ‘dead zones’ devoid of life have been created when runoff containing excess nutrients from farm fields and suburban lawns overwhelms coastal waters.

Oil spills

Since oil began fueling our industries, oil spills have been an unfortunate fact of our lives. Much has been learned about spill prevention and cleanup since 1969, when an oil well failure in the Santa Barbara Channel surrounded an entire island in what is now Channel Islands National Park. But more work remains to be done. In 2010 the BP Deepwater Horizon spill in the Gulf of Mexico reminded us of the limits of our control, knowledge, and technology. Even though the world’s top engineers and scientists worked for 87 days to stem the flow, they could not prevent the release of 4.9 million barrels of oil and 1.84 million gallons of chemical dispersants into the ocean. The environmental impacts of this catastrophe were immense, leaving over 400 Gulf species at serious risk from habitat destruction, loss of oxygen, and toxins that could cause serious mutations, birth defects, and death. Five years later, significant amounts of oil still remain in the area, threatening the recovery of marine ecosystems.


Did you know that whales sing? A major ocean discovery of the past century is that Jacques Cousteau’s ‘Silent World’ was never truly silent, but actually teeming with noise. In an environment as opaque as the ocean, vision is of limited value. Many forms of marine life, such as humpback whales and snapping shrimp, use sound for communication, navigation, and detection of predators. The undersea acoustic landscape is a critical part of ocean health.

The nature of sound in the sea, however, is rapidly changing for the worse. Since the 1950s humans have increased noise in the ocean eight-fold over the past 60 years, with such activities as ship traffic, seismic surveys, drilling, mining, construction, and sonar. Some areas near ports and oil fields are as much as 100 times noisier than they were in the 1950s. This huge increase can seriously affect the ability of marine life to navigate and survive in the ocean environment. We need to study and understand more about the effects of our noise on ocean plants and animals in order to protect and improve marine health and wellbeing.


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    Last updated: May 3, 2016


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