Human impact on marine life

Human activities affect marine life and marine habitats through overfishing, habitat loss, the introduction of invasive species, ocean pollution, ocean acidification and ocean warming. These changes impact marine ecosystems and food webs and may have consequences for the biodiversity and future of many marine life forms.

The ocean is the world's largest ecosystem and home to many species. Human actions such as global warming, ocean acidification, and pollution harm marine life and their homes. Over the past 50 years, more than 90 percent of global warming from human activity has been absorbed by the ocean. This raises ocean temperatures and causes ocean acidification, which hurts many fish and damages habitats like coral. Coral helps build reefs that provide food and homes for sea creatures and also benefit people.

Ocean acidification from increased carbon dioxide levels leads to coral bleaching, slowing coral growth. Another big problem caused by humans is marine plastic pollution, which dangers marine life. Studies show that many sea species have changed where they live or when they are active because of warmer oceans, less sea ice, and changes in water chemistry. Only about 13% of the ocean remains as true wilderness, mostly in open areas far from shore.

Overfishing

See also: Overfishing and Environmental impact of fishing

Overfishing is a big problem affecting one third of the world's fish stocks, as reported in 2018 by the Food and Agriculture Organization of the United Nations. Many people think that illegal, unreported and unregulated fishing happens in most fisheries and may make up to 30% of all fish caught in some important areas. Because of overfishing, we are catching fish that are higher up on the food chain, which lowers the average mean trophic level of fish in the ocean. This makes it harder for fish populations to stay healthy and grow.

Habitat loss

Coastal ecosystems are suffering damage from human activities, leading to significant habitat loss. Areas like seagrass meadows, mangrove forests, and coral reefs are declining globally. Coral reefs, which are very productive and diverse, have lost one-fifth of their area in recent years due to human disturbances.

Seagrass meadows have lost a large area—30,000 km²—in recent decades. These meadows provide important services, such as nutrient cycling and habitats for animals like dugongs, manatees, and green turtles. Mangrove forests have also lost one-fifth of their area since 1980, and kelp forests face threats from overfishing in coastal areas.

Invasive species

An invasive species is a plant, animal, or other organism that is not native to a place and can cause harm to the environment, people, or the economy. One big way invasive species travel to new places is through ships. Ships can carry tiny sea creatures on their hulls or in the water they take in and release at different ports, called ballast water.

For example, zebra mussels, which are not from the Great Lakes, likely arrived in ship ballast water and caused a lot of trouble there. Another example is a jellyfish called Mnemiopsis leidyi, which ended up in the Black Sea in ship ballast water. It grew very fast and hurt the local fishing industry by eating too much of the small animals that fish need to survive. Invasive species can change whole ecosystems, make it hard for native animals to find food, and cost a lot of money to control.

Marine pollution

Human activities cause pollution in the ocean in many ways. One big problem is nutrient pollution. When too many nutrients like nitrates and phosphates enter the water, they cause algae to grow quickly. When the algae die, bacteria break them down and use up oxygen, creating "dead zones" where most sea creatures cannot survive.

Another serious issue is plastic pollution. Over 300 million tons of plastic are made each year, and much of it ends up in the ocean. Large pieces of plastic can harm sea animals that try to eat them or get caught in them. Even more concerning are microplastics—tiny pieces of plastic smaller than five millimeters. These tiny pieces are eaten by small ocean creatures, and the plastic moves up the food chain, affecting larger animals and even humans who eat seafood.

Climate change

Further information: Effects of climate change on oceans

Human activities are changing the ocean in many ways, which affects the plants and animals that live there. Burning fossil fuels adds carbon dioxide to the air, which then mixes into the ocean. This changes the chemistry of the water and also makes the ocean warmer.

Warmer oceans cause many changes. Some fish and other sea creatures are moving to cooler places. The food web in the ocean is also changing, with some important plants like phytoplankton growing less. In some areas, like the Indian Ocean, this could mean less food for fish and other sea animals. Warmer oceans also affect tiny creatures called krill, which are important food for larger animals like whales and seals.

Rising sea levels are also changing coastal areas. Some places where animals live, like marshes and mudflats, are being covered by water. This can make it harder for these animals to survive. Coral reefs, which are important homes for many sea creatures, also need to grow taller to stay close to the sunlight they need. If they cannot grow fast enough, they may not survive.

Biogeochemical

See also: Marine biogeochemical cycles

Human activities change the chemistry of the ocean in many ways. For example, when extra nitrogen from farms or cities runs into the ocean, it can create areas with very little oxygen, called dead zones, where most sea creatures cannot survive.

The ocean also absorbs a lot of carbon dioxide from the air, which makes the water more acidic. This makes it harder for animals like shellfish and tiny ocean plants to build their shells and skeletons from minerals such as calcium carbonate. As the ocean becomes more acidic, these important creatures may struggle to survive, which can affect the whole ocean food web.

Effect of multiple stressors

When multiple stressors affect the ocean at the same time, their effects can add up. For example, when ocean acidification and rising ocean temperatures happen together, they harm marine life even more than either one alone. These changes are mainly caused by carbon dioxide and other greenhouse gas emissions.

Studies have shown that these combined stressors can greatly impact the ocean and its creatures. Warmer oceans also reduce the amount of oxygen available for marine life, making it harder for them to survive. Experiments have found that these combined effects can seriously disrupt the balance of marine food chains.

Drivers of change

Human activities greatly affect marine life and the ocean's health. Things like fishing, pollution, and changes in temperature and water chemistry all play major roles. These actions can harm the balance of marine ecosystems and the benefits they provide to people.

A 2024 study showed how fishing and other ships impact coastal waters, where most human activity happens. It found that many fish populations are being used faster than they can grow, and many important ocean habitats have been lost. Besides traditional activities like fishing and oil extraction, new activities such as mining, fish farming, and building offshore wind turbines are also affecting the ocean. The study used satellite data to track ships and discovered that many fishing and energy ships are not reported in public systems. It also noted that the number of offshore wind turbines has grown quickly and may soon have as big an impact on the ocean as fishing does.

Shifting baselines

Shifting baselines happen when we measure changes in the ocean using old information as a starting point. This old information might already show damage, so we don’t realize how much worse things have gotten over many years. For example, scientists might use the condition of a fishery when they began their work, instead of how it looked before any fishing happened. This makes it hard to see the true loss of fish and other sea life that has occurred slowly over time. Each new generation might think the damaged ocean is normal, not seeing the big changes that happened long ago.