The Number One Threat to Marine Animals

Human activity is threatening marine animals' way of life. Instead of asking ourselves how we can fish more sustainably, we should ask what we need to do to ensure their survival.

marine animals

Explainer Climate Oceans

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After watching Seaspiracy, you might be wondering more about who else lives in the ocean. Using scholarly resources and considering the lived experience of people of the global majority, we set out to find answers to the following questions about marine animals, why humans are the number one threat to their survival, and what we can do to help. 

What Are Marine Animals?

Marine animals are animals that live in the sea. An animal is made up of many tiny building blocks known as cells, each of which has a nucleus. Marine animals eat other plants or animals for food. They can move from one place to another—though some, like coral, may end up stuck in one place. Animals can sense and respond to things happening around them. They can also reproduce and make babies. 

Which Animals Are Called Marine Animals?

Cephalopods, Crustaceans, and Shellfish

Cephalopods are a type of marine animal that lives in the sea. They are mollusks, and they have tentacles. These animals include octopuses, squids, and cuttlefish. Cephalopods have a head, a large brain, eyes, thick skin, and arms that can hold and move things. Cephalopods are also carnivores, meaning they eat other animals for food.

According to the Hutchinson Pocket Dictionary of Biology, they are “the most intelligent, the fastest-moving and the largest of all animals without backbones.” Mollusks are “soft-bodied animals with a muscular ‘foot,’” according to the Dictionary of Zoo Biology and Animal Management. Examples of non-marine mollusks include snails and slugs.

Crabs, lobsters, and shrimp are examples of crustaceans that live in the ocean. Crustaceans are a type of arthropod, meaning that they have a segmented body and a hard shell. Crustaceans usually have a head with eyes, mouth-parts, and sensory feelers known as antennae. Each segment of their body has two limbs or antennae to help them eat, feel, swim, walk or grab things. Crustaceans take in oxygen using gills. Most crustaceans live in the sea, but some live in freshwater or even land.

Shellfish are one type of marine animal that humans typically eat. They live in the sea and they do not have a backbone. English and Welsh law defines shellfish as crustaceans and mollusks. Other examples of marine mollusks include abalone, clams, mussels, scallops, and oysters. Crustaceans also include crayfish and prawns. 

Corals and Invertebrates

A coral is a marine animal that does not have a backbone. It lives in groups made of polyps,  tube-like animals that attach themselves to one place. Polyps are covered in “jelly-like, horny, or stony” skeletons that protect them. Coral can be white, red, or black. They usually live in warm waters near the edges of land. A coral reef is made when new polyps build on their dead ancestors’ skeletons. 

Invertebrates are animals that do not have backbones or spinal columns. As mentioned above, invertebrates include cephalopods, mollusks, crustaceans, and corals. Other examples of marine animals without backbones include sponges, jellyfish, sea anemones, roundworms, lugworms, starfish, sea cucumbers, sea lilies, and sea urchins.


A fish is an animal with a backbone that lives in water. They take in oxygen using gills. Fish have hearts, two fins to help them move through the water, and no legs. There are at least three groups of fish: bony, cartilaginous, and jawless. Examples of bony fish are goldfish, cod, and tuna. Sharks and rays are examples of cartilaginous fish. Hagfishes and lampreys are examples of jawless fish. Legal definitions of fish can also include other types of marine life.


Mammals are animals that have backbones and hair. Female mammals make their own milk with which to feed their babies. Mammals have a brain, heart, teeth, and ear bones. They are warm-blooded, which means they can cool or heat the inside of their bodies without having to change the environment they are in. Examples of marine mammals are walruses, sea otters, seals, sea lions, whales, dugongs, and sea cows. 


Seabirds are birds that eat food from the sea and nest on land. Examples of seabirds include gulls, swallows, penguins, puffins, the bald eagle, osprey, and flamingos.

Sharks and Rays

Sharks and rays have skeletons that are not made of bones but of cartilage, a firm but flexible material also known as gristle. They are also known as elasmobranchs, meaning they have five to seven gill slits—unlike most fishes, which have a single gill on each side of their head; rigid fins, many teeth, and an opening behind their jaws. Their scales are also placoid, which means they are very hard and enamel-like. Male elasmobranchs have fins that they use for having sex. Sharks have very good senses of smell and touch. Rays have flat bodies and are sedentary. 

Turtles and Reptiles

Turtles are animals with backbones who lay their eggs on the beach and run to the water once they are born. They belong to a group of vertebrates called reptiles. Reptiles are cold-blooded, which means that their insides change from hot to cold depending on the temperature outside of their bodies. Reptiles are covered in dry scales. Marine reptiles include turtles, sea snakes, a saltwater crocodile, and the marine iguana.

What Are the Main Threats to Marine Animals?           


An aquarium is a box filled with water where humans keep animals and plants for entertainment or study. The ways that people collected animals for aquariums have even hurt plants and animals that are not being collected—one example is the use of sodium cyanide. Also, people have over-harvested marine animals and have shortened their lives by removing them from their natural habitats.

Marine animals such as clownfish, damselfish, angelfish, surgeonfish, gobies, wrasses,  butterflyfish, coral, mollusks, and anemones are popular aquarium picks. Other popular aquarium invertebrates include cleaner shrimp, hermit crabs, giant clams, starfish. 

According to a 2003 report on the aquarium trade, most of the animals used in saltwater aquariums are caught from the wild—usually from coral reefs and other nearby ecosystems. In contrast, most animals used in freshwater aquariums are farmed. The places where the saltwater aquarium animals originated were often in low-income communities in Asian and island countries such as Indonesia, Australia, Fiji, Solomon Islands, Sri Lanka, Palau, Philippines, Maldives, and Tonga. Countries that imported marine animals were typically in the northern hemisphere: USA, Taiwan, Japan, Hong Kong, France, Germany, Netherlands, Italy, Canada, and the Republic of Korea. 

As Food

Fish and shellfish are major food sources for humans, resulting in numerous environmental concerns—two of which are noted in The Oxford Companion to Ship and the Sea. The number of fish being caught has grown smaller and smaller as commercial fishing grew its ability to catch more and more fish. The farming of fish has harmed mangroves, swamps, and other places on the edge of land where animals live. Also, more fish, including most of the sand eels caught in the North Sea, need to be caught to be fed to farmed fish and chickens. 

Fisheries have introduced new species to local places where mollusks are fished for food—for example, an oyster that grows faster. Typically, the new species of oyster also introduces new diseases and other problems that are hard for the native species to win against.


Drilling and shipping oil and gas in the oceans and on coasts have harmed the habitats of marine animals, including seabirds and sea otters. For example, air guns are used to explore the ocean floor for oil and gas drilling. The very loud sound of the air guns can harm animals’ hearing, make their brains bleed, and keep them from talking to each other. The impact of the air gun blast has been found to kill tiny marine animals.

Miners of gems, metals, and minerals in the sea and on the coasts also see their waste end up in the ocean, which also harms life on the coasts. When coal is burned, for example, it releases mercury into the air. Paints used to protect the bottom of ships can be toxic to sea life as well. Crustaceans have to rely on their chemical senses and when they are directly exposed to metals like cadmium, for example, their nervous systems can be almost entirely damaged. 

Most animals also eat less food in response to contaminants. With less food, an animal will often have less energy for what they normally do day-to-day, including finding more food that they need to survive. 

Finally, the bottom of the ocean is covered with sand and gravel that was used to construct buildings. Dredging the bottom of the ocean also damages the homes of marine animals.

Global Warming       

Too much carbon dioxide can trap heat in the air. it changes how the ocean works and shortens the lives of marine animals. For example, on the coast of Britain, the type of sea plants now growing in the water are the type you would normally find in warmer waters. As a result, there have been fewer crustaceans living nearby and much fewer codfish than usual. 

In 2017, researchers found that the ocean had lost two percent of its oxygen between 1960 and 2010. The loss syncs with climate change models predicting habitat loss for marine animals as a result of global warming. 

Habitat Loss and Degradation       

Humans have destroyed the homes of marine animals in many ways, including overfishing, releasing nutrients, pathogens, and other toxic materials into the ocean from land. Pollutants can result in stress from noise, reduced oxygen, and making the waters more acidic. Examples of human activities that cause habitat loss and degradation include chemical industries, sewage treatment, and farming. Acidification is the result of increased levels of carbon dioxide, which is linked to climate change.

When there is too much fertilizer flowing from the land and rivers into the ocean, too many of the same type of plant grow in the run-off area, and fewer species of fish and coral can live there. When there are too many nutrients running off from the land or rivers to the ocean, a dead zone may form. In a dead zone, there is no oxygen and too many other gases (hydrogen sulfide and methane), making it very difficult for marine animals to live there. 

Mangroves are trees that grow in a mixture of saltwater and freshwater. More than half of the mangrove forests that used to cover three-quarters of tropical coasts are now gone due to human destruction—including prawn farming and urbanization. Mangroves attract many animals, including seahorses and fish. Mangrove forests protect humans from tropical storms and tsunamis. 


Military exercises in the air and in the sea have created noise pollution that is harmful to marine animals. Whales, dolphins, and other fish often leave an area in response to loud noises. Read more about why indigenous people oppose the U.S. Navy’s threats to marine life in the Pacific Northwest here.

Ocean Traffic and Fisheries

Noise from ship traffic, fishing boats, military ships, surveyors, ships using sonar, and pile driving stress marine animals and could lead to future oceans where marine animals will have fewer places to live.

Large ships meant to bring oil and other bulk goods—known as bulk carriers—can also carry new species to their destinations. Marine animals that are new to an area may become unexpected predators of indigenous species. 

Lost fishing gear—nets, lines, recreational or commercial equipment—contribute to the approximately 14 billion pounds of litter or debris released into the ocean per year. Fishing boats often catch marine animals in their nets. This process is known as bycatch, and it takes the lives of billions of sea creatures every year.

Marine Life Facts and Statistics

How Many Marine Animals Die from Plastic

According to UNESCO, “more than a million seabirds every year, as well as more than 100,000 marine animals” die each year from plastic debris. 

Most Popular Sea Creatures

According to Positive Travel, the most popular marine animals on Instagram are the following: polar bear, orca, whale shark, humpback whale, great white shark, manta ray, sailfish, angelfish, pufferfish, and narwhal. 

In popular culture, UW360 found the following species at the center of major blockbuster films: red Jamaican crab, sponges, giant squid, Pacific regal blue tang, clownfish, starfish, and bottlenose dolphin.

What Is the Importance of Marine Life?

“Oceans play a fundamental role for life on earth, providing over 70 percent of the oxygen we breathe and over 97 percent of the world’s water supply, not to mention being a source of food,” writes Joshua Cooper at Cultural Survival.

What Is the Most Important Marine Animal?

As theorist Syl Ko writes in “By ‘Human,’ Everybody Just Means ‘White,’” a chapter in a book connecting Black liberation and animal liberation, she explains how the term animal is usually posed as distinct from the term human. When we talk about animals, we are usually excluding homo sapiens. It is activities of homo sapiens that have directly led to harm in marine life. Homo sapiens can take action to protect marine life by reducing the harms we have inflicted through overfishing, pollution, and exploitation

What Is the Depth of the Ocean?

According to NOAA, the average depth of the ocean is 12,000 feet, or 3,700 meters. 

How Can We Save Marine Life?

One way to save marine life would be to reduce the harm from climate change. United Nations Sustainable Development Goal 13: Climate Action focuses on giving more power to local communities and communities with less power, including women and youth, in island states and low-income countries. For example, according to Duke Lankard, the Native Conservancy plans to farm kelp in a way that helps Native communities, the ocean, and the planet.

The Road Ahead

Now you have a brief overview of marine animals based on their descriptions and different ways that homo sapiens have harmed them. People have learned a lot about how marine animals have responded to stress in their environments—and the benefits of removing these sources of stress. You can learn more about how each type of animal responds to these stressors, including how people like you are resisting threats to marine life, here.

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