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Major Marine Habitats

Environments in Which Marine Plants and Animals Live

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About 70% of our planet is covered with water. Earth has been nicknamed 'the blue planet' because it looks blue from space. About 96% of this water is marine, or salt water, made up of the oceans covering the Earth. Within these oceans, there are many different types of habitat, or environments in which plants and animals live, ranging from freezing polar ice to tropical coral reefs. These habitats all come with their unique challenges and are inhabited by a wide variety of organisms. You can find more information about the major marine habitats below, along with some information on two major geographic areas.

Mangroves

Pean Krasop Mangrove Sancturay. Cambodia.
Eitan Simanor/Photodisc/Getty Images

The term “mangrove” refers to a habitat comprised of a number of halophytic (salt-tolerant) plant species, of which there are more than 12 families and 50 species worldwide. Mangroves grow in intertidal or estuarine areas. Mangrove plants have a tangle of roots which are often exposed above water, leading to the nickname “walking trees.” The roots of mangrove plants are adapted to filter salt water, and their leaves can excrete salt, allowing them to survive where other land plants cannot.

Mangroves are an important habitat, providing food, shelter and nursery areas for fish, birds, crustaceans and other marine life.

Seagrasses

Eelgrass off Plum Island, Massachusetts
© Blue Ocean Society

Seagrass is an angiosperm (flowering plant) that lives in a marine or brackish environment. There are about 50 species of true seagrasses worldwide. Seagrasses are found in protected coastal waters such as bays, lagoons, and estuaries and in both temperate and tropical regions. Seagrasses attach to the ocean bottom by thick roots and rhizomes, horizontal stems with shoots pointing upward and roots pointing downward. Their roots help stabilize the ocean bottom.

Seagrasses provide an important habitat to a number of organisms. Some use seagrass beds as nursery areas, others seek shelter there their whole lives. Larger animals such as manatees and sea turtles feed on animals that live in the seagrass beds.

Intertidal Zone

Tide pooling along the rocky Atlantic coast of New Hampshire.
Blue Ocean Society

The intertidal zone is the area where land and sea meet. This zone is covered with water at high tide, and exposed to air at low tide. The land in this zone can be rocky, sandy or covered in mudflats. Within the intertidal, there are several zones, starting near dry land with the splash zone, an area that is usually dry, and moving down to the littoral zone, which is usually underwater. Within the intertidal zone, you’ll find tide pools, puddles left in the rocks as water recedes when the tide goes out.

The intertidal is home to a wide variety of organisms. Organisms in this zone have many adaptations that allow them to survive in this challenging, ever-changing environment.

Reefs

Coral bleached at St. Croix (NOAA photo)
NOAA

There are hundreds of coral species found in the world’s oceans. There are two types of corals – stony (hard) corals, and soft corals. Only hard corals build reefs.  

While the majority of coral reefs are found in tropical and sub-tropical water within the latitudes of 30 degrees north and 30 degrees south, there are also deep water corals in colder regions. A flourishing tropical reef is made up of many different plant and animal communities. It is estimated that 800 different coral species are involved in building tropical reefs.

Coral reefs are complex ecosystems supporting a wide array of marine species. The largest and most well-known example of a tropical reef is the Great Barrier Reef in Australia.

The Open Ocean (Pelagic Zone)

Bluefin Tuna (Thunnus thynnus), NOAA photo
NOAA

The open ocean, or pelagic zone, is the area of the ocean outside of coastal areas, and where you’ll find some of the biggest marine life species. The pelagic zone is separated into several subzones depending on water depth, and each provide habitat for a variety of marine life. Marine life you’ll find in the pelagic zone includes wide-ranging animals such as cetaceans, large fish such as bluefin tuna and invertebrates such as jellyfish.

The Deep Sea

NOAA DeepWorker submersible vessel image.
NOAA

The deep sea includes the deepest, darkest, coldest parts of the ocean. Eighty percent of the ocean consists of waters greater than 1,000 meters in depth. Parts of the deep sea described here are also included in the pelagic zone, but these areas in the deepest reaches of the ocean have their own special characteristics. Most areas are cold, dark, and inhospitable to us humans, but support a surprising number of species that thrive in this environment.

Hydrothermal Vents

Black Smoker Hydrothermal Vent
NOAA PMEL Vents Program / www.pmel.noaa.gov

Hydrothermal vents, also in the deep sea, were unknown until about 30 years ago, when they were discovered in the submersible Alvin. Hydrothermal vents are found at an average depth of about 7,000 feet and are essentially underwater geysers created by tectonic plates. These huge plates in the Earth’s crust move and create cracks in the ocean floor. Ocean water enters these cracks, is heated up by the Earth’s magma, and then released through the hydrothermal vents, along with minerals such as hydrogen sulfide. The water coming out of the vents can reach incredible temperatures of up to 750 degrees F. Despite their intimidating description, hundreds of species of marine life thrive in this habitat.

Gulf of Mexico

Gulf of Mexico Map / NOAA
Courtesy of NOAA

The Gulf of Mexico covers about 600,000 square miles off the coast of the southeastern U.S. and a portion of Mexico. It is home to different types of marine habitat, from deep canyons to shallow intertidal areas. It is also a haven for a wide variety of marine life, from huge whales to tiny invertebrates. The importance of the Gulf of Mexico to marine life has received attention in recent years due to the presence of Dead Zones and the major oil spill that occurred in April 2010.

Gulf of Maine

The Gulf of Maine covers over 30,000 square miles and is a semi-enclosed sea next to the Atlantic Ocean. It lies off the U.S. states of Massachusetts, New Hampshire, and Maine, and the Canadian Provinces of New Brunswick and Nova Scotia.  The cold, nutrient-rich waters of the Gulf of Maine provide a rich feeding ground for a variety of marine life, particularly in the months from the spring through late fall.

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