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Animals That Live in Estuaries (9 Examples)

Estuaries are a vital part of the ecosystem. An estuary is an area of land where freshwater rivers and streams meet the ocean. The water there is brackish, slightly salty but not as much salt as ocean water. In this post we will list 9 examples of animals that live in estuaries and are able to thrive in this unique environment.

Animals that live in estuaries

Estuaries are also important for humans, as they protect our coastlines from storms and floods. Humans have long used estuaries for fishing, but they are also important places for recreation and tourism. Estuaries are some of the most productive ecosystems on Earth and play a vital role in the global food web. Only certain types of plants, birds and animals can thrive in this slightly salty environment.

Let’s look at 9 examples of animals that live in estuaries.


1. River Otter

Northern river Otter | image: GlacierNPS

Scientific name: Lontra canadensis

The river otter is a carnivorous mammal that can be found in estuaries all over the world. They can grow up to four feet long and weigh up to twenty-five pounds. River otters are able to swim and hunt in freshwater, saltwater and brackish water.

They are semi-aquatic animals, meaning they spend time in the water and on land. River otters are excellent swimmers, and they use their webbed feet to help them move through the water. They are also very good at catching fish.

River otters have a thick coat of fur that keeps them warm in the coldest waters. They also have a long, muscular body that helps them move quickly through the water and on land.

River otters are very social animals and live in groups of up to twelve animals. These groups are called “rafts,” and they help the river otters travel, hunt, and protect themselves from predators.


2. American Alligator

American Alligator

Scientific name: Alligator mississippiensis

The American alligator is a giant reptile found in the southeastern United States. It’s an apex predator, meaning it has no natural predators.

These animals are typically found in areas with freshwater, such as marshes and swamps. However, scientists have found that American alligators can “commute” from freshwater into the brackish water and back again. This travel between separate freshwater and estuarine habitats can facilitate transfer of nutrients between the two regions.

They swim to estuaries because the salt water helps regulate their body temperature. They can also find food such as crabs, shellfish, and fish in the estuaries.

While most animals avoid salt water because it can harm them, the American alligator can adapt to this environment. That’s because they have special glands in their bodies that remove excess salt from their blood.


3. Sea Mullet

Sea Mullet | image by Roberto Pillon via Wikimedia Commons | CC BY 3.0

Scientific name: Mugil cephalus

Sea mullets are a type of fish that you can find in both salt water and fresh water. They are known for their silver scales and ability to jump out of the water and skip vigorously across the surface. Hence, their nick names “happy mullet” or “jumping mullet.”

Scientists and researchers believe that this jumping behavior increases the oxygen in the mullet’s body and helps them avoid predators. Sea mullets are a popular food fish and are often caught by anglers. They typically eat small invertebrates, such as shrimp, crabs, and squid.

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They can be found in estuarine and marine habitats and often congregate near shore in large schools when they travel to colder habitats after spawning. Sea mullets do not have many predators but can sometimes be eaten by larger fish or birds.


4. Harbor Seal

Harbor Seal laying in the sand
Harbor Seal | image by Amanda Boyd / USFWS via Flickr

Scientific name: Phoca vitulina

Harbor seals are found in both the Atlantic and Pacific oceans. In the Pacific, you can find harbor seals on the shores of Baja California and Alaska. They are brown, gray, or white with dark spots. They can grow to be six feet long and weigh up to three hundred pounds.

Harbor seals eat fish, squid, and crustaceans and can stay underwater for up to thirty minutes. They live in groups of up to one hundred seals called pods. Predators of the harbor seal include orcas, sharks, and humans.

They are also affected by pollution and climate change and are protected by the Marine Mammal Protection Act of 1972. This protection act makes it illegal to harass or hunt marine mammals, especially seals, in American waters.


5. Sunflower Sea Star

sunflower star on coral
Sunflower star | image by Ed Bierman via Wikimedia Commons | CC BY 2.0

Scientific name: Pycnopodia helianthoides

The sunflower sea star is a type of starfish that can be found in coastal and estuarine areas in the northeast Pacific.  Sunflower sea stars can be many colors, have between 16 – 24 arms and can grow as large as 3 feet across! This multitude of arms connected to a central round body makes this sea star look like the a large sunflower.

Sea urchins are their favorite food, and they also eat clams, abalone and snails. If large fish or other sea stars try and attack it, they can shed one of their arms to get away, and regenerate it later.

Unfortunately, warming water temperatures and climate change are negatively affecting their habitat and places such as California and Oregon have seen dramatic population declines.


6. Stalked Jellyfish

stalked jellyfish attached to plant
Stalked Jellyfish | image by G.Mannaerts via Wikimedia Commons | CC BY-SA 4.0

Scientific name: Stauromedusae

A stalked jellyfish is a type of jellyfish that has long, thin arms that they use to capture prey. Unlike other jellyfish that are free floating, the stalked jellyfish attaches itself to rocks and plants. They can fire toxic darts to slow down their prey, then grab the organism with their tentacles.

Stalked jellyfish are usually a dark color, like brown or black, and can grow up to eight inches long. These animals are not harmful to humans, but their sting can be quite painful.

In the U.S., you can find stalked jellyfish in the Chesapeake Bay and the Gulf of Mexico. If you’re ever in these areas, be sure to keep an eye out for these fascinating creatures!


7. Hermit crabs

hermit crab in a shell
Hermit Crab | image by Conall via Flickr | CC BY 2.0

Superfamily: Paguroidea

With over 800 known species, hermit crabs can be found all over the world, including the United States, along beaches and estuaries. Some spend their life in the water while some species live completely on land.

Unlike true crabs, hermit crabs don’t have a fully hard protective shell across their whole body. Their body resembles lobsters and shrimp, with a long, curved, soft abdomen. This soft abdomen has no protection of its own, so hermit crabs seek empty shells made by other species, usually snails, for their shelter.  As they grow larger, they will continue to trade their shells for larger ones.

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Their diet is diverse, including small fish, plankton, worms, invertebrates and any food particles they come across.


8. Bull Sharks

bull shark
Bull shark | image by Albert Kok~enwiki via Wikimedia Commons | CC BY-SA 4.0

Scientific name: Carcharhinus leucas

While you may think of sharks as exclusively open ocean creatures, and many are, the bull shark has the ability to live in both saltwater and freshwater environments. These sharks can be found in coastal waters and often travel through estuaries and up freshwater rivers. In fact, female bull sharks like to birth their young in low-salinity or freshwater nursery areas.

Bull sharks are gray on top and white on the bottom They get their name from their stocky build and a broad, flat snout. They eat mainly bony fish, stingrays and other small sharks, but also animals like turtles, dolphins and birds. They use murky water to sneak up on their prey.


9. The Estuarine Crocodile

saltwater crocodile on bank
Estuarine / Saltwater Crocodile | image by Djambalawa via Wikimedia Commons

Scientific name: Crocodylus porosus

The Estuarine crocodile, also known as the saltwater crocodile, is the largest living reptile in the world, and they make their home in estuaries. These massive creatures can grow up to 23 feet long and weigh over 2,000 pounds.

Estuarine crocodiles are excellent swimmers and can stay submerged for up to an hour at a time. They are carnivores, and their diet consists of fish, crustaceans, reptiles, and mammals. Estuarine crocodiles are solitary animals, and they only come together to mate.

Females lay up to 60 eggs at a time, which she incubates for around three months. The young hatchlings are about two feet long and are extremely vulnerable to predators. They will spend the first few years of their life in freshwater rivers and ponds before moving into estuarine habitats as they mature.

The saltwater crocodile can be found in places like India, the Philippines and Australia.