The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary

The Sargasso Sea is a vast patch of ocean is named for a genus of free-floating seaweed called Sargassum. While there are many different
types of algae found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagic' — this means that the algae not only freely floats
around the ocean, but it reproduces vegetatively on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.

Sargassum provides a home to an amazing variety of marine species. Turtles use sargassum mats as nurseries where hatchlings have food and shelter. Sargassum also provides essential habitat for marine species,such as shrimp, crab, and fish, that have adapted specifically to this floating algae. The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Commercial fish, such as tuna, and birds also migrate through the Sargasso Sea and depend on it for food.

While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined only by ocean currents. It lies within the Northern Atlantic Subtropical Gyre. The Gulf Stream establishes the Sargasso Sea's western boundary, while the Sea is further defined to the north by the North Atlantic Current, to the east by the Canary Current, and to the south by the North Atlantic Equatorial Current. Since this area is defined by boundary currents, it's borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.

For more information:
What's the difference between an ocean and a sea? (Ocean Fact)

Sargassum: A Complex 'Island' Community at Sea (NOAA's Ocean Explorer)

Sampling the Sargassum Community: Dip Nets and Green-Light Lures (NOAA's Ocean Explorer)

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Sea cucumbers are animals, not vegetables. Found only in salt water, more than a thousand species of sea cucumbers exist around the world. These squishy invertebrates are echinoderms, making them distant relatives to starfish and urchins. Unlike starfish or sea urchins, the bodies of sea cucumbers are covered with soft, leathery skin instead of hard spines.

If you ever encounter a sea cuke and he feels threatened, you could be in for a surprise. Some sea cucumbers shoot sticky threads at their enemies, entangling and confusing predators. Others can violently contract their muscles and shoot some of their internal organs out of their rear ends. The missing body parts are quickly regenerated.

Most sea cucumbers are scavengers, moving along the seafloor and feeding on tiny particles of algae or microscopic marine animals collected with tube feet that surround their mouths. The particles they grind down to smaller pieces are further broken down by bacteria and become part of the ocean’s nutrient cycle. This is a similar role to that which earthworms perform on land.

Sea cucumbers are enjoyed as meals for other critters such as fish and crabs. In some places, especially Asia, sea cucumbers are considered a delicacy and are enjoyed by humans.

Sea cukes are certainly a little odd, and definitely not something you’d ever find in your garden.


For more information:
Weird Fins: Sea cucumbers, NOAA’s National Marine Fisheries Service

Weird Animals: Sea Cucumbers, Ocean Today



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The health of submerged aquatic vegetation is an important environmental indicator of overall ocean and estuary health.

Seagrasses in bays and lagoons, for instance, are vital to the success of small invertebrates and fish. These small creatures are a food source for commercial and recreational fish.

Seagrasses also stabilize sediments, generate organic material needed by small invertebrates, and add oxygen to the surrounding water.

Underwater vegetation in shallow coastal waters also supports a wide diversity of marine creatures by providing spawning, nursery, refuge, and foraging grounds for many species.

For more information:
Benthic Habitat Mapping, NOAA Coastal Services Center (CSC)
Benthic Habitat Data, CSC

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Some seaweeds are microscopic, such as the phytoplankton that live suspended in the water column and provide the base for most marine food chains. Some are enormous, like the giant kelp that grow in abundant “forests” and tower like underwater redwoods from their roots at the bottom of the sea. Most are medium-sized, come in colors of red, green, brown, and black, and randomly wash up on beaches and shorelines just about everywhere.


The vernacular “seaweed” is a bona-fide misnomer, because a weed is a plant that spreads so profusely it can harm the habitat where it takes hold. (Consider kudzu, the infamous “mile-a-minute vine” that chokes waterways throughout the U.S. Southeast). Not only are the fixed and free-floating “weeds” of the sea utterly essential to innumerable marine creatures, both as food and as habitat, they also provide many benefits to land-dwellers, notably those of the human variety.

Seaweed is chock-full of vitamins, minerals, and fiber, and can be tasty. For at least 1,500 years, the Japanese have enrobed a mixture of raw fish, sticky rice, and other ingredients in a seaweed called nori. The delectable result is a sushi roll. Many seaweeds contain anti-inflammatory and anti-microbial agents. Their known medicinal effects have been legion for thousands of years; the ancient Romans used them to treat wounds, burns, and rashes. Anecdotal evidence also suggests that the ancient Egyptians may have used them as a treatment for breast cancer. Certain seaweeds do, in fact, possess powerful cancer-fighting agents that researchers hope will eventually prove effective in the treatment of malignant tumors and leukemia in people. While dietary soy was long credited for the low rate of cancer in Japan, this indicator of robust health is now attributed to dietary seaweed. These versatile marine plants and algae have also contributed to economic growth. Among their many uses in manufacturing, they are effective binding agents (emulsifiers) in such commercial goods as toothpaste and fruit jelly, and popular softeners (emollients) in organic cosmetics and skin-care products. All across our ocean wafts a wonderful “weed,” indeed.

For more information:
Seaweeds, Olympic Coast National Marine Sanctuary |Kelp Forests, Office of National Marine Sanctuaries

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In kelp forests, the most commonly found invertebrates are bristle worms, scud, prawn, snails, and brittle stars. These animals feed on the holdfasts that keep kelp anchored to the bottom of the ocean and algae that are abundant in kelp forests. Sea urchins will often completely remove kelp plants by eating through their holdfasts. Other invertebrates found in kelp forests are sea stars, anemones, crabs, and jellyfish.

A wide range of fish can be found in kelp forests, many of which are important to commercial fishermen. For example, many types of rockfish such as black rockfish, blue rockfish, olive rockfish, and kelp rockfish are found in kelp forests and are important to fishermen.

A wide range of marine mammals inhabit kelp forests for protection and food. Sea lions and seals feed on the fish that live in kelp forests. Grey whales have also been observed in kelp forests, most likely using the forest as a safe haven from the predatory killer whale. The grey whale will eat the abundant invertebrates and crustaceans in kelp forests. One of the most important mammals in a kelp forest is the sea otter, who takes refuge from sharks and storms in these forests. The sea otter eats the red sea urchin that can destroy a kelp forest if left to multiply freely.

Kelp forests are a natural buffet for birds such as crows, warblers, starlings, and black phoebes which feed on flies, maggots, and small crustaceans that are abundant in kelp forests. Gulls, terns, egrets, great blue herons, and cormorants dine on the many fish and invertebrates living in the kelp. Kelp forests also provide birds with a refuge from storms.

For more information:


Ecosystems: Kelp Forests, Office of National Marine Sanctuaries
Invertebrate and Vertebrate Assemblages Associated with Kelp Forests, Monterey Bay National Marine Sanctuary
Kelp Forest, Olympic Coast National Marine Sanctuary

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Phytoplankton, also known as microalgae, are similar to terrestrial plants in that they contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean, where sunlight penetrates the water. Phytoplankton also require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert into proteins, fats, and carbohydrates.

The two main classes of phytoplankton are dinoflagellates and diatoms. Dinoflagellates use a whip-like tail, or flagella, to move through the water and their bodies are covered with complex shells. Diatoms also have shells, but they are made of a different substance and their structure is rigid and made of interlocking parts. Diatoms do not rely on flagella to move through the water and instead rely on ocean currents to travel through the water.

In a balanced ecosystem, phytoplankton provide food for a wide range of sea creatures including whales, shrimp, snails, and jellyfish. When too many nutrients are available, phytoplankton may grow out of control and form harmful algal blooms (HABs). These blooms can produce extremely toxic compounds that have harmful effects on fish, shellfish, mammals, birds, and even people.

The National Centers for Coastal Ocean Science conduct extensive research on harmful algal blooms. Scientists use a range of technologies to predict where and when HABs are likely to form and how they will affect the areas where they occur. Scientists use this information to inform coastal authorities on how to best respond in order to minimize negative impacts.

For more information:
NOAA's National Centers for Coastal Ocean Science
Phytoplankton -- What Are They?, Northwest Fisheries Science Center
Phytoplankton Monitoring Network
Harmful Algal Blooms

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Algin, an emulsifying and bonding agent, is extracted from kelp and used in these products. Kelp is also used as food on mollusk farms. Between 100,000 and 170,000 wet tons of kelp are harvested from California waters each year.

Kelp forests are extremely biologically productive habitats for a huge range of sea creatures including fish, urchins, sea otters, sea lions, and even some whales. Because of this, kelp forests are critical for fishing and recreation industries.

Sadly, overfishing disrupts the balance of kelp forests by removing predators and allowing plant-eating populations to explode and overeat the kelp, destroying the forests. Pollution, such as sediment runoff and industrial waste, also contributes to the destruction of kelp forests.

Today, many kelp forests are located in marine protected areas and are studied by NOAA scientists. Kelp forests are monitored for kelp size and distribution, physical oceanic conditions, and associated life. The more that we discover about these amazing habitats, the better they can be preserved and strengthened.

For more information:
Ecosystems: Impacts on Kelp Forests, National Marine Sanctuaries
Kelp Forests, Olympic Coast National Marine Sanctuary
Kelp Forest and Rocky Subtidal Habitats, Monterey Bay National Marine Sanctuary

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Kelp forests can be seen along much of the west coast of North America. Kelp are large brown algae that live in cool, relatively shallow waters close to the shore. They grow in dense groupings much like a forest on land. These underwater towers of kelp provide food and shelter for thousands of fish, invertebrates, and marine mammal species.

Kelp forests harbor a greater variety and higher diversity of plants and animals than almost any other ocean community. Many organisms use the thick blades as a safe shelter for their young from predators or even rough storms.

Among the many mammals and birds that use kelp forests for protection or feeding include seals, sea lions, whales, sea otters, gulls, terns, snowy egrets, great blue herons, cormorants, and shore birds.

These dense canopies of algae generally occur in cold, nutrient-rich waters. Because of their dependency upon light for photosynthesis, kelp forests form in shallow open waters and are rarely found deeper than 15-40 meters (49-131 feet).

NOAA scientists study kelp forests by visiting the same locations over and over to assess the presence and abundance of a variety of organisms. Monitoring allows marine scientists to determine if the kelp forest is changing over time and to identify the cause of those changes, whether natural or human.

For more information:


Kelp Forests, National Marine Sanctuaries

Kelp Forest and Rocky Subtidal Habitats, Monterey Bay National Marine Sanctuary

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There are about 80 different species of mangrove trees. All of these trees grow in areas with low-oxygen soil, where slow-moving waters allow fine sediments to accumulate. Mangrove forests only grow at tropical and subtropical latitudes near the equator because they cannot withstand freezing temperatures.

Many mangrove forests can be recognized by their dense tangle of prop roots that make the trees appear to be standing on stilts above the water. This tangle of roots allows the trees to handle the daily rise and fall of tides, which means that most mangroves get flooded at least twice per day.  The roots also slow the movement of tidal waters, causing sediments to settle out of the water and build up the muddy bottom.

Mangrove forests stabilize the coastline, reducing erosion from storm surges, currents, waves, and tides. The intricate root system of mangroves also makes these forests attractive to fishes and other organisms seeking food and shelter from predators.

For more information:
Mangrove Forests, NOS Education
Habitat Types: Mangrove Forests, NOAA Fisheries

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