Blue Carbon

Mangroves, Salt Marshes, Kelp Forests, and Seagrass Beds are recognized as effective sinks for carbon also know as Blue Carbon.

Four Types of Coastal Habitats and Why They Matter – By: Simon Reddy

Mangroves, seagrass, salt marshes, Kelp Forests, and coral reefs sustain ocean life and help mitigate climate change.

Coastal habitats—areas both along and close to marine shorelines—are vital ecosystems. They help mitigate the impacts of climate change, for example by storing carbon and buffering the effects of floods and storms, and provide a range of other services, including serving as nurseries for a range of species and absorbing runoff from farming.

Conserving these habitats is vital for protecting shorelines, feeding and sheltering marine life, and lessening the effects of climate change, an effort that must also include reducing global carbon emissions. Here’s a deeper dive into four types of coastal habitat: mangroves, salt marshes, seagrass meadows, and coral reefs.



A recognizable feature of some mangrove trees are their roots—tangled, clumped together, and growing above the shorelines. These roots buffer coastlines from storm surges, tides, waves, and currents; make ideal nursery grounds for groupers, snapper, and some species of sharks; and provide protection for smaller fish from their predators. Mangrove forests can store three to five times more carbon in their soil than tropical rainforests. All 80 or so species of mangrove trees are found in tropical and subtropical equatorial regions. 

Seagrass Meadows

Seagrass Meadows
Seagrass Meadows

Seagrass is exactly what its name suggest—plants growing underwater, with roots, stems, and leaves.  There are 72 species, and one or more of them grows in nearly every coastal ecosystem, from the Arctic Circle to the tropics. These critical habitats also serve as nursery grounds for many valuable fish and wildlife species, and play a key role in maintaining water quality. Similar to mangrove forests, seagrass also helps lessen the impacts of severe weather, reduces erosion, and mitigates the effects of climate change by absorbing about 10 percent of the total estimated organic carbon sequestered in the oceans each year.

Salt Marsh

Salt Marshes
Salt Marshes

Salt marshes are found worldwide, most commonly in temperate regions. These unique coastal areas are often flooded by saltwater as tides come in and are home to a range of species from fish to invertebrates and birds. Many species of shrimp, crab, and fish also use these areas as nursery habitat, making marshes an important contributor to fisheries and local economies. By absorbing rainwater and reducing flooding, marshes also serve as natural infrastructure to protect coastal communities. Salt marshes are also recognized as effective sinks for carbon, a characteristic they share with mangroves and seagrass.

Coral Reef

Coral Reef
Coral Reef

When most people hear “coral reef” they think of the tropics, but these habitats are found throughout the ocean, even in the Antarctic. The most recognizable corals are those that form hard calcium carbonate skeletons using the chemicals found in seawater. However, there are soft coral species such as sea whips and sea fans. The biggest coral reefs are thousands of years old and usually thrive in warm, shallow water where they receive plenty of sunlight. Much like seagrass meadows, mangrove forests, and salt marshes, coral reefs are home to numerous species. In addition to providing critical nursery and rich feeding grounds for a wealth of marine species, they also help to buffer coastlines from severe storms and flooding. 

Simon Reddy directs The Pew Charitable Trusts’ coastal wetlands and coral reefs project.

Kelp Forests

Kelp Forests
Kelp near Anacapa Island, Calif., in May. (Tristin McHugh/The Nature Conservancy)

The scientists fighting to save the ocean’s most important carbon capture system

The population of kelp forests, which help clean the air, has fallen dramatically. That has environmentalists worried.

By Lucy SherriffJuly 5, 2021 at 1:42 p.m. EDT Washington Post

ANACAPA ISLAND, Calif. — Frank Hurd gently parted the curtains of giant kelp that reached upward through the cold waters of the North Pacific, looking for signs of life.

Kelp forests cover a quarter of the world’s coastlines, stretching from Antarctica to Australia, Mexico to Alaska, providing food and shelter for thousands of species, while sucking carbon from the atmosphere. But over the past decade, thanks to warming waters and overfishing, they’re disappearing.

Kelp are essentially the ocean’s equivalent of trees. They absorb carbon dioxide and nitrogen compounds, helping clean the atmosphere while capturing up to 20 times more carbon per acre than land forests.

On this afternoon, Hurd, a marine biologist at the Nature Conservancy, said he was relieved to find thick kelp canopies surrounding an unpolluted patch off Anacapa Island, part of the Channel Islands National Park in California. But, he says, such refuges are becoming harder to find. “The scale of this problem is dire,” Hurd said.

The fate of the world’s kelp forests may depend on controlling its sworn enemy — sea urchins — and the Nature Conservancy, an Arlington-based environmental group, says it has a plan. It is touting urchins as a culinary cuisine, hoping to appeal to commercial fishermen who could scoop them out of the ocean. It is also attempting to increase the population of their natural predators, sea stars and growing kelp in controlled environments before releasing the algae back into the sea.

“There really is no single silver bullet option to solve this problem. We need to invest in comprehensive solutions to reestablish healthy, resilient ecosystems,” Hurd said.

ut the size of kelp forests off the coast of Northern California has shrunk by more than 95 percent since 2014, according to satellite data analyzed by the Nature Conservancy. Other regions have had similar losses: Tasmania’s canopies have decreased by 95 percent, as have Chile’s. Globally, kelp forests along coastlines have declined by a third over the past decade, according to a paper published in the American Institute of Biological Sciences journal BioScience.

“There’s been a catastrophic loss,” said Tom Dempsey, the Nature Conservancy’s California Oceans Program director. “And it’s been all but completely ignored.”

The problem was exacerbated along the California coast by a 2013 heat wave. The average kelp canopy cover off the coasts of Mendocino and Sonoma counties in Northern California fell from 2 million square meters to 60,000 square meters over the course of two years, according to the Nature Conservancy. This marine heat wave, known as “the Blob,” along with a fast-spreading marine virus, all but wiped out the sunflower sea star, the main predator of urchins.

“It’s like this endless parking lot, stretching for miles in every direction, covered in purple urchins,” Dempsey said. With few starfish, the urchin population “exploded to up to 100 times their previous numbers.”

The Nature Conservancy began looking for ways to get the urchin population under control in 2018. Traditionally, efforts to cull the spread of urchins — the purple, rather than the marketable red or green species — consisted of volunteer divers swimming out to sea and smashing the spiky echinoderms with a hammer.

But that would take too long, they decided, and the group began testing some alternatives.

First, they hoped to increase commercial demand for sea urchins, noting that their shells contain calcium carbonate that could be made into fertilizer or be used in cosmetics. They also hoped to popularize uni, the reproductive organs of the urchins, as a restaurant cuisine. But the type typically considered a cuisine are not the invasive purple variety that eat at the roots of kelp.

“Purple urchin is definitely the less desired species in the seafood market,” Dempsey added.

The organization is also trying to find ways to revive the sea urchins’ predator — the sea star. The sea star population has fallen victim to warming waters, too, allowing the urchin population to skyrocket.

“Sea stars are sorely missed in our near-shore environment, and having them back is critical,” said Scott Groth, head of the marine resources program at Oregon’s Department of Fish and Wildlife, which has reported a sharp decline in sea stars.

Coral Reef
Coral Reef

Over the last 200 years or so

Systems do not stay the same – when one part is changed, other parts respond and change to restore a balance. Over the last 200 years or so, there has been a detectable change in the carbon cycle. Humans have been burning carbon-rich fossil fuels, releasing carbon dioxide into the atmosphere. This has been releasing carbon that would normally be stored in the geosphere. Even the carbon dioxide put into the atmosphere by all the volcanoes that erupt in a year is only a hundredth of that released by human activity.

The Carbon Cycle

The ocean and the carbon cycle

The ocean plays an important role in the global carbon cycle. Carbon moves in and out of the ocean daily, but it is also stored there for thousands of years.