Marine habitat

A marine habitat is a special place in the sea where different kinds of marine life live. The word marine comes from the Latin word mare, which means sea or ocean. These habitats are places where animals and plants can survive, and they all need the saltwater found in the ocean.

Marine habitats can be divided into two main types: coastal and open ocean habitats. Coastal habitats are near the shore, stretching from where the tide reaches up to the edge of the continental shelf. Most sea creatures live in these areas, even though they are only a small part of the ocean. Open ocean habitats are far from shore, in the deep parts of the ocean beyond the continental shelf.

Another way to look at marine habitats is by dividing them into pelagic and demersal zones. Pelagic habitats are near the ocean’s surface or in the open water column, while demersal habitats are close to or on the ocean floor. Some sea creatures, like corals, kelp, mangroves, and seagrasses, change their environment to create new homes for other animals. The ocean gives us the most space for life on our planet.

Overview

Marine habitats are special places in the ocean where sea creatures live. Unlike land habitats, ocean habitats can change a lot. Fish and other swimming animals like areas near the edge of the continental shelf, but only when lots of food comes up from deep water. Shellfish live on sandy beaches, but storms and waves keep changing these places.

All marine habitats have seawater, but many things decide what kind of life can live there. The temperature, how much sunlight reaches the water, the amount of food, and even the shape of the ocean floor all play a role. There are five big oceans, with the Pacific Ocean being the largest. The ocean covers most of Earth’s surface and holds almost all of our planet’s liquid water.

Marine habitats can be divided into two main types: pelagic and demersal. Pelagic habitats are in the open water far from the bottom, while demersal habitats are near or on the ocean floor. Each type supports different kinds of sea creatures.

Ocean currents

Main article: Ocean current

In the ocean, ocean currents help create homes for sea creatures. These currents carry nutrients that help tiny plants called phytoplankton grow. Phytoplankton are the start of the food chain in the ocean. When phytoplankton grow, they feed tiny animals called zooplankton, which include baby fish and small sea animals. When there is enough zooplankton, small fish called forage fish come, and then larger predatory fish and other sea animals can arrive.

Ocean currents are made by changes in how salty or warm the water is. Colder, saltier water sinks, while warmer, less salty water rises. Winds and the pull of the sun and moon also help make currents and waves. The way the Earth spins changes the direction of currents, causing them to curve in a pattern called the Coriolis effect.

Topography

A marine habitat is a special place in the ocean where plants and animals live. The word "marine" comes from an old word for the sea, called "mare". Every place in the sea where living things can stay is called a habitat. These habitats help sea creatures survive in their watery homes.

Biomass

See also: Marine biomass

One way to learn about how important different parts of the ocean are is to look at how fast they make living material. This material is called biomass. It helps us know which places support more sea life.

Coastal

Main article: Marine coastal ecosystems

Marine coasts are areas that change a lot because of the ocean. Weather and sea level changes shape the land, creating continental shelves and drowned river valleys.

The main forces that shape coasts are waves, tides, and currents. The type of rock also matters — harder rocks stay the same longer.

Tides affect how far sediment moves on the shore. High tides let waves reach farther, while low tides leave sediment in a smaller area. Tides don’t usually cause erosion, but tidal bores can wear away river estuaries.

Waves break on shore and move sediment from cliffs along the coast. Rivers add sediment too, which ends up on the shore.

The scientist Francis Shepard divided coasts into two types:

• Primary coasts are shaped by land. If a coast looks the same as it did after the last ice age, it’s a primary coast. These coasts form through erosion, adding new soil, or movement of the earth. An example is a river delta, where a river drops soil into the sea.
• Secondary coasts are shaped by the ocean or sea creatures. Examples include sea cliffs, barrier islands, mud flats, coral reefs, mangrove swamps, and salt marshes.

Continental coasts usually have a continental shelf, a shallow area that stretches from the land. These shelves cover part of the ocean and support many plants and animals, from tidal pools to fjords and estuaries. Coastal fish live here because there is lots of food from nutrients brought by rivers and ocean currents.

Coastal habitats are full of life but cover only a small part of the ocean. They are important because they support many kinds of animals and plants.

Intertidal

Main article: Intertidal zone

Intertidal zones are areas near shore that are covered and uncovered by tides. Many animals live here, from small creatures that eat sea life to birds and land animals that visit the shore.

Sandy shores

See also: Beach

Sandy shores, or beaches, are where sand builds up. Waves and currents move the sand, forming features like spits, barrier islands, and tombolos. Sandy beaches are full of life, from tiny diatoms and bacteria in the sand to fish, turtles, birds, and animals like clams and crabs.

Rocky shores

See also: Rocky shore and Tidal pool

Rocky shores seem more stable than sandy shores because the rocks don’t move easily. Plants and animals can attach to the rocks, though they still compete for space.

Mudflats

See also: Bay mud

Mudflats are wet areas where mud settles, often in protected spots like bays and estuaries. They are covered and uncovered by tides about twice a day.

Mangrove forests and salt marshes

See also: Mangrove forest, Ecological values of mangroves, and Salt marsh

Mangrove swamps and salt marshes are important coastal habitats. Mangroves are trees and shrubs that grow in salty coastal areas, forming forests that protect coastlines and support many animals.

Estuaries

Main article: Estuaries

An estuary is where rivers meet the sea, creating a mix of fresh and salt water. These areas support many fish, birds, and other animals.

Kelp forests

Further information: Kelp forest

Kelp forests are areas underwater filled with tall kelp plants. They provide homes for many sea creatures and are very important for ocean life.

Seagrass meadows

Main article: Seagrass meadows

Seagrasses are flowering plants that grow in shallow coastal waters. They form meadows that give shelter and food to many animals, help protect coastlines, and store carbon.

Reefs

Main article: Reef

A reef is a ridge of rock or coral under the water’s surface. Coral reefs are especially rich in life, but they can be harmed by changes in water temperature.

Surface waters

See also: Ocean surface ecosystem

Surface microlayer

The surface microlayer of the ocean is the thin layer where the sea meets the air. It covers most of Earth because oceans are almost everywhere. This special layer has its own tiny plants and animals.

The microlayer is not just water; it is like a gel with lots of nutrients. It helps protect the ocean from harmful sunlight and is a safe place for tiny fish eggs to grow. Sometimes, too much dust or pollution can make the tiny plants grow too fast.

Epipelagic zone

The surface waters get sunlight, and this area down to about 200 metres is called the epipelagic zone. Here, tiny plants called phytoplankton can make food from sunlight. But these waters often don’t have many nutrients because when plants and animals die, they sink down.

In some places, like near land, extra nutrients from deep water or rivers can make the phytoplankton grow very fast. These areas are important for many sea animals. Tiny plants are eaten by even tinier animals, which are then eaten by bigger animals like fish, whales, and birds.

Open ocean

See also: Pelagic fish

The open ocean may not have a lot of food, but because it is so big, it makes more food for plants and tiny animals than any other sea home. Only about 10 percent of sea animals live here, but some of the biggest, fastest, deepest-diving, and longest-traveling sea animals do. In the dark deep parts, we find animals that look very strange to us.

Deep sea

See also: Deep sea and Deep sea communities

The deep sea begins where sunlight almost disappears. Many animals here can make their own light, a special skill called bio-luminescence.

In the deep ocean, the water goes far below the top layer and holds very different sea animals that have learned to live there. Much of the food for these deep places comes from the open ocean in the form of bits of dead plants and animals falling down. This "marine snow" starts near the top where there is light and travels down, feeding deep-sea animals that cannot see sunlight.

Some deep-sea fish, like lanternfish, are more common near special underwater structures. These fish and their food are drawn to these places.

Different deep-sea fish have special ways of living and looking. Some deep-sea fish have very big mouths to catch food bigger than themselves.

Sea floor

See also: Benthic zone, benthos, and Marine sediment

Special places in the ocean, like hydrothermal vents and cold seeps, help many tiny sea creatures live.

The deepest part of the ocean is the Mariana Trench near the Philippines in the Pacific Ocean. Even in the deep, dark water, some sea creatures like a white flatfish, a shrimp, and a jellyfish have been seen there. Underwater mountains called seamounts attract fish and other sea life.

Anthropogenic impacts

See also: Human impact on marine life

Coastal areas like mudflats are important for many animals, especially birds that travel long distances. These areas give animals a place to have babies and find food.

Human activities have changed parts of the ocean floor. For example, a fishing method called bottom trawling drags equipment across the sea floor, changing its shape. Pollution from tiny pieces of plastic and harmful chemicals from industrial waste hurt sea creatures and change the water where they live.

Plastic pollution is a problem in the ocean. Large piles of plastic have been found deep in the ocean, and these pieces can be eaten by small sea animals. Old fishing nets and traps left in the water can catch and trap sea animals.