Human impact on marine life

Marine life and their homes are affected by many things people do. These include overfishing, habitat loss, adding invasive species, ocean pollution, ocean acidification and ocean warming. All these changes can hurt marine ecosystems and food webs. They may also affect the biodiversity and future of many sea creatures.

The ocean is the biggest home for many kinds of animals. Things people do, like making the Earth warmer, can hurt the ocean and the creatures living there. In the last 50 years, a lot of the heat from global warming has been taken in by the ocean. This makes the ocean warmer and causes ocean acidification, which can harm fish and damage places like coral. Coral helps build reefs. These reefs give food and homes to many sea animals and are also important for people.

When there is more carbon dioxide in the air, it can cause ocean acidification. This can lead to coral bleaching, which slows down how fast coral grows. Another big problem is marine plastic pollution, which can danger sea life. Because of warmer oceans, less sea ice, and changes in the water, many sea animals have had to change where they live or when they are active. Only a small part of the ocean, about 13%, remains as true wilderness, and it is mostly in areas far from land.

Overfishing

See also: Overfishing and Environmental impact of fishing

Overfishing is a big problem for many fish in the world's oceans. It happens when people catch fish faster than they can grow back. The Food and Agriculture Organization of the United Nations said this affects a lot of fish groups. Some fishing happens without rules or reports, which makes the problem worse. Because of overfishing, we take fish from higher levels of the food chain. This makes it harder for fish groups to stay strong and healthy.

Habitat loss

Human activities are harming coastal areas, causing habitat loss. Places like seagrass meadows, mangrove forests, and coral reefs are shrinking all over the world.

Coral reefs, which are full of life, have lost a lot of their area because of human actions. Seagrass meadows have lost a big space—30,000 km²—over the past years. These meadows help keep the water clean and give homes to animals like dugongs, manatees, and green turtles. Mangrove forests have also lost a lot of their area since 1980, and kelp forests are in danger because of overfishing.

Invasive species

An invasive species is a plant, animal, or other living thing that is not from a place and can cause harm to nature, people, or money. One big way these 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 let out 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 problems 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. Invasive species can change whole ecosystems and make it hard for native animals to find food.

Marine pollution

Human activities pollute the ocean in many ways. One big problem is nutrient pollution. When too many nutrients like nitrates and phosphates enter the water, algae grow very fast. When the algae die, bacteria break them down and use up oxygen. This creates "dead zones" where most sea creatures cannot live.

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. Big pieces of plastic can hurt 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

People do many things that change the ocean. This hurts the plants and animals that live there. Burning fossil fuels puts carbon dioxide into the air. This gas then mixes into the ocean.

Warmer oceans cause big changes. Some fish and other sea creatures move to cooler places. The food chain in the ocean changes, and some important plants like phytoplankton grow less. In places like the Indian Ocean, this means less food for fish and other sea animals. Warmer oceans also affect tiny creatures called krill. Krill are important food for bigger animals like whales and seals.

Rising sea levels change areas near the coast. Some places where animals live, like marshes and mudflats, get covered by water. This makes it hard for these animals to live. Coral reefs, which are important homes for many sea creatures, 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 ocean's chemistry in many ways. For example, when extra nitrogen from farms or cities flows into the ocean, it can create areas with very little oxygen, called dead zones. Most sea creatures cannot live in these areas.

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

Effect of multiple stressors

When many problems happen in the ocean at the same time, they can make things worse. For example, when the ocean becomes more acidic and the water gets warmer together, it hurts sea creatures more than just one of these changes alone. These changes happen mainly because of carbon dioxide and other greenhouse gas emissions.

Research has shown that when these problems happen together, they can change the ocean and its animals a lot. Warmer water also means less oxygen for sea life, which makes it harder for them to live. Tests have proven that these combined problems can upset the balance of the ocean's food chains.

Drivers of change

Human activities change marine life and the ocean's health. Things like fishing, pollution, and changes in temperature and water chemistry are important. These actions can upset the balance of marine ecosystems and the help they give to people.

A 2024 study showed how fishing and other ships affect coastal waters, where most human activity happens. It found that many fish populations are being caught 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 also affect 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 affect the ocean as much as fishing does.

Shifting baselines

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