Blue Carbon in Marine Protected Areas

A Guide to Understanding and Increasing Protection of Blue Carbon

Bull kelp in the ocean just below the surface.

This story map aims to broaden the reach and engagement of our recent reports on blue carbon in marine protected areas.

Three report covers on blue carbon, Part 1, Part 2 & Part 3. — *Download Part 1* *(left)* *Download Part 2* *(center)* *Download Part 3* *(right)*

Ultimately, we hope to encourage and promote discussions around blue carbon, including research priorities, and policy and management considerations.

What is Blue Carbon? Where is it found?

Coastal and oceanic ecosystems, and their habitats, species, and processes, play a significant role in the global carbon cycle . These valuable ecosystems sequester and store carbon over long timescales .

Coastal and open ocean "blue carbon” ecosystems help mitigate climate change and its impacts by facilitating the uptake of atmospheric carbon dioxide (CO2) into the ocean and transporting carbon into sediments or deep ocean waters , where it can remain indefinitely, if undisturbed [1].

History of Atmospheric Carbon Dioxide

Animation of a graph measuring atmospheric carbon dioxide from 800,000 years ago until January, 2019, from NOAA's Global Monitoring Laboratory.

https://gml.noaa.gov

A highly magnified phytoplankton sample. The magnified image shows a long chain with several spiky projections. — *Phytoplankton are microalgae that photosynthesize and convert atmospheric CO2 to organic carbon* (left). *Shorebirds flying and wading in salt marsh habitat, a blue carbon ecosystem* (center). *Mother and calf humpback whales traveling through clear blue water. Whales export significant amounts of carbon to the deep sea* (right).

Shorebirds flying and wading in salt marsh habitat. — *Phytoplankton are microalgae that photosynthesize and convert atmospheric CO2 to organic carbon* (left). *Shorebirds flying and wading in salt marsh habitat, a blue carbon ecosystem* (center). *Mother and calf humpback whales traveling through clear blue water. Whales export significant amounts of carbon to the deep sea* (right).

Fish swim around rocky coral. — *Cordell Bank National Marine Sanctuary* *protects rocky coral structures that supports diverse fish populations.*

The ocean is the largest carbon sink in the world, accumulating 20–35% of atmospheric CO2 [2].

It plays a significant role in the global carbon cycle by storing and cycling 93% of Earth’s CO2 and storing over half of the world’s biological carbon in living marine organisms [3].

Coastal Blue Carbon

Coastal blue carbon ecosystems (salt marsh, seagrass, and mangrove) are significant carbon sinks.

Toggle the buttons below to explore these habitats lining the shorelines of North America.

Use the + - to zoom into an area of interest. The button in the map's lower left is the legend.

Global means for soil organic carbon stocks up to one-meter depth and annual sequestration rates for mangrove, tidal salt marsh, and seagrass ecosystems. — *Global means for soil organic carbon stocks up to one-meter depth and annual sequestration rates for mangrove, tidal salt marsh, and seagrass ecosystems [14].*

Thriving blue carbon ecosystems store three to five times more carbon per unit area than tropical forests, and sequester carbon at a rate ten times greater than tropical forests [4].

Areas of salt marsh, seagrass and mangrove coverage in North America. Data shown are North American Blue Carbon (2021) from the Commission for Environmental Cooperation.

These vegetated coastal habitats remove carbon dioxide from the atmosphere (1), and fix it into organic carbon in the stems, branches, leaves, and roots of the plant.

Salt marsh habitat lining the shores of Bolinas Lagoon. — *Carbon-rich salt marsh habitat lining the shores of Bolinas Lagoon.*

Carbon storage occurs when kelp material (2) is exported from the subtidal rocky reefs to deep sea environments, where it may be buried in sediments.

An underwater rocky area with purple urchins and a few individual kelp plants. — *In the last six years, significant losses of bull kelp forests off Central and Northern California have greatly reduced carbon sequestration potential.*

For salt marsh and seagrass, dead plant material accumulates in the oxygen-free sediments (3) stabilized by the plants’ roots or rhizomes, accumulating considerable amounts of carbon over time.

For both (2) and (3), carbon can remain captured indefinitely if undisturbed.

A heron wades in seagrass habitat in Tomales Bay. — A heron wades in seagrass (eelgrass) habitat in Tomales Bay, within Greater Farallones National Marine Sanctuary. Eelgrass forms extensive underwater meadows with dense belowground networks of rhizomes that stabilize carbon-rich sediments.

Explore Coastal Blue Carbon Habitats

Salt Marsh

Salt marshes are the largest coastal blue carbon storage ecosystem in the United States, occupying over 19,000 sq. km [5] and comprising 1–2% of the total estimated yearly carbon sink in the U.S. [6].

Use arrows on right to explore more.

Salt Marsh

Since the early 1600s, the United States has lost more than 110 million acres of wetlands.

From 2004–2009, this loss has occurred at an average rate of 80,000 acres per year [7].

The West Coast of the United States alone has lost up to 90% of its salt marshes since the 1900s [8] [9].

Salt Marsh

Threats to the remaining salt marsh include habitat conversion, poor water quality, and erosion from sea level rise and increasing storm activity.

Muddy shoreline alongside eroded shoreline vegetation

Salt Marsh

Marine protected areas (MPAs) can ensure that salt marshes are protected from development and disturbance, which is critical for maintaining the carbon sequestration benefits provided by this coastal habitat [10].

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Seagrass

Seagrass forms extensive underwater meadows with dense belowground networks of rhizomes. These rhizomes hold sediment in place [11], which is where the long-term carbon storage occurs.

Use arrows on right to explore more.

Seagrass

Approximately 20% of the United States’ seagrass extent is protected in national marine sanctuaries [12].

Seagrass covers large areas of Florida Keys National Marine Sanctuary and provides important habitat for many species.

Seagrass

The majority of seagrass meadows in the U.S. have experienced rapid decline since 1980 [13].

Seagrass

Protection of seagrass beds and restoration of damaged or lost beds is imperative, not only to increase carbon sequestration and storage, but also to maintain important direct and indirect benefits for society.

Seagrass

Societal benefits include coastal protection, water purification, maintenance of fisheries, tourism, recreation, research, and education [8].

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Mangroves

Mangroves are salt-tolerant, viviparous shrubs and trees that grow in coastal, brackish waters.

Use arrows on right to explore more.

Forest of mangrove trees, showing the roots under the water.

Mangroves

Mangrove systems sequester carbon through the entrapment and burial of sediments by roots and pneumatophores , and through the net growth of forest biomass [10] [14].

Mangroves

Mangroves are in decline globally. In the United States, mangroves are most impacted by erosion and extreme weather events (e.g., tropical storms and hurricanes).

Just 10% of U.S. mangrove extent is protected by the Florida Keys National Marine Sanctuary [15].

Use the + - to explore mangrove habitat.

Mangroves

Evaluating and mitigating climate-driven impacts to protected mangroves is vital for U.S. MPA managers.

This will ensure carbon stores within mangrove ecosystems remain in place, and that carbon sequestration continues.

Oceanic Blue Carbon

Oceanic blue carbon is the sinking or export of carbon from surface waters to the deep sea via marine animals and vegetation.

For all oceanic carbon sequestration [1], seafloor sediments are often the final destination for carbon immobilization or long-term storage.

A larvatian inside its gelatinous house hover above the ocean seafloor that is scattered with fragile pink urchins and bioturbated holes housing small fish and invertebrates. — *A larvatian inside its elaborately shaped gelatinous house hovers over carbon-rich seafloor sediments that are scattered with fragile pink urchins.*

These sediments hold vast amounts of carbon on geologic timescales, from thousands to millions of years, if left undisturbed [16].

These types of sediments are the largest non-fossil pool of organic carbon on the planet.

Explore Different Methods of Oceanic Carbon Sequestration

Phytoplankton

Global phytoplankton populations capture 37 billion metric tons of CO2 from the atmosphere annually.

This is equivalent to 40% of annual global emissions, or the amount of CO2 captured by four Amazon Rainforests annually [17] [3].

Use arrows on right to explore more.

Phytoplankton

Phytoplankton absorb dissolved CO2, convert it to biomass, and then facilitate deep-sea carbon transport through two main mechanisms:

1) Phytoplankton that are not consumed die and sink to the seafloor, and

2) Phytoplankton that are grazed upon are secreted in fecal pellets, which sink to the seafloor [18].

Microscopic diatom dominant phytoplankton community.

Kelp

Kelp, large brown algae in the order Laminariales, are commonly found attached to rocky substrates and form dense forests in temperate zones worldwide.

Use arrows on right to explore more.

Kelp

These macroalgae have remarkably high productivity, and fix carbon much more rapidly than terrestrial plants.

Kelp growth rates reach up to 2 feet in a 24-hour period during the summer months.

Kelp

Kelp ecosystems are recognized as significant contributors to global carbon sequestration.

These ecosystems act as “carbon donors” to “receiver sites” by exporting carbon to deep-sea environments [19].

Kelp

Carbon is exported from kelp forests by way of blade erosion or detachment of an entire plant.

It is estimated that approximately 11% of kelp primary productivity is exported and sequestered each year, which is equivalent to 600 million metric tons globally [20].

Fish

Fish mediate an average of 16% of the carbon exported from the euphotic zone [21].

Use arrows on right to explore more.

Fish

Mesopelagic fish inhabit intermediate depths of the ocean between approximately 200 and 1,000 meters.

At night these fish move vertically into the euphotic zone in search of food.

Fish

This vertical movement mediates carbon export from the euphotic zone to the deep sea, where carbon is released via defecation, respiration, excretion, and mortality.

School of Bar jack near the ocean surface.

Fish

These actions effectively remove carbon from the atmospheric carbon cycle, and some of it can become immobilized through deposition and burial [22].

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Whales

There are three mechanisms by which whales facilitate carbon sequestration: 1) the “whale pump,” 2) the “whale conveyor belt,” and 3) whale falls [1].

Use arrows on right to explore more.

Whales

The "whale pump" and "whale conveyor belt" are indirect processes that result in carbon sequestration.

These processes are driven by whale defecation, which stimulates local phytoplankton growth.

A whale feeding at the ocean surface surrounded by birds.

Whales

The "whale pump" is characterized by the vertical movement of whales, such as sperm whales, from deep-sea feeding grounds to surface waters, where nutrients are dispersed at the surface through defecation, which stimulates phytoplankton growth [37].

Whales

The "whale conveyor belt" also functions to sequester carbon via nutrient dispersion from defecation.

This process involves the latitudinal movement of whales from nutrient-rich feeding grounds, often in temperate and polar waters, to nutrient-poor calving grounds, often in the tropics [23] [24].

Whales

Direct carbon sequestration via whale falls occurs when whales die and sink to the ocean floor.

Carbon stored in whale tissues can be immobilized in the deep sea for millennia.

Whales

Large whales are efficient at fixing and storing vast amounts of carbon due to their relatively high metabolic efficiency [25]. This is called “marine vertebrate” or “fish” carbon.

An estimated 33 tons of CO2 equivalent is stored in each great whale [17].

Whales

If global whale populations are restored to historic levels, an additional 160,000 tons of carbon could be sequestered, annually, through increased whale falls.

This would be equivalent to preserving over 2,000 acres of forest annually [25].

Guiding Principles

Principles for Preserving Blue Carbon Habitats and Processes

*Panel at COP25, presenting on global climate action in marine protected areas.*

Marine protected areas are a critical component of global and national mitigation and adaptation responses to climate change.

Quantifying and protecting blue carbon sequestration processes is an essential component to achieving the Biden Administration’s climate mitigation goal — 50% reduction of greenhouse gasses from 2005 levels — by 2030. There is also a clear nexus with the administration’s goal of conserving 30% of the nation’s lands and 30% of ocean areas by 2030 ( Executive Order 14008, 2021 ).

These guiding principles are critical to advance the assessment, protection, and restoration of valuable blue carbon habitats and processes in marine protected areas.

Aerial view of Elkhorn Slough National Estuarine Research Reserve. — *Elkhorn Slough National Estuarine Research Reserve* *winds seven miles inland from Monterey Bay. This salt marsh is second in size to San Francisco Bay in the State of California.*

Blue carbon assessments provide a foundation for improved management. Managers can't protect what they don't know. Conducting a Tier 1 assessment is a simple calculation that can give a rough estimate of the climate mitigation services provided by the coastal habitats in a marine protected area.

Ecosystem-based management is blue carbon management. Within MPA networks, predator-prey interactions are inherently protected, which helps control herbivore populations. Decreased grazing allows plants and algae to continue to grow, increasing their carbon sequestration capacities and the preservation of carbon stocks.

Blue crab siting in sand in seagrass. — *The presence of predators, like blue crabs, contributes to enhanced carbon cycling, accumulation, and storage.*

Incorporate blue carbon into marine spatial planning and consider it as a factor in MPA designation and management decisions. To ensure that nationally significant blue carbon habitats and processes continue to sequester carbon, rather than become sources of emissions, it is critical that marine spatial planning and the designation of new MPAs consider the presence of blue carbon [26].

Reducing impacts leads to significant sequestration gains. Reducing erosion of existing blue carbon habitats produces sequestration benefits that far exceed those resulting from restoration alone [27].

Panel presentation at COP25: Global climate action in marine protected areas. — *Panel presentation at COP25: global climate action in marine protected areas.*

Managers should understand how to leverage blue carbon to finance MPAs. MPAs are increasingly financed because of their blue carbon potential, including through participation in carbon markets, the use of blue bonds, and mitigation banking, among others. Managers should understand and consider these mechanisms.

Blue carbon management is not just coastal. Currently, restoration and protection of blue carbon is fairly limited to coastal blue carbon — seagrasses, salt marshes, and mangroves — but the largest carbon reserves on Earth are found in the open ocean and within seafloor sediments, an enormous area with massive carbon sequestration potential.

Climate policies must include blue carbon. From sub-national management to international climate policies and agreements, blue carbon as a mitigation tool has not yet been fully realized.

Case Study: Greater Farallones

Close-up of bull kelp taken underwater near Del Mar Landing in the northern portion of Greater Farallones National Marine Sanctuary. — *Bull kelp (Nereocystis luetkeana) near Del Mar Landing in the northern portion of Greater Farallones National Marine Sanctuary.*

Greater Farallones Association conducted a Tier 2 blue carbon analysis for two coastal habitats and two oceanic processes in Greater Farallones National Marine Sanctuary.

This is the first assessment of multiple blue carbon sequestration processes in a U.S. federal MPA.

The habitats and processes assessed have the potential to sequester:

Salt Marsh

Salt marsh in GFNMS covers an area of 3.6 square kilometers (1.4 square miles) within , , and .

Dominant species include: saltgrass (Distichlis spicata), pickleweed (Sarconia pacifica), with Pacific cordgrass (Spartina foliosa) [28] and alkali bulrush lining the more shallowly sloped edges.

Use the + - to explore salt marsh habitat of Greater Farallones National Marine Sanctuary.

*Breakdown of salt marsh species within Greater Farallones National Marine Sanctuary.*

Salt marsh extent data were sourced from the Marin Countywide Fine Scale Vegetation Map , which includes tidal wetlands mapped in 2019 using light detection and ranging (LiDAR, a remote sensing method) to a 0.1 hectare minimum mapping unit. The tidal wetlands map should be considered an approximation of tidal wetland extent due to the wide spectral variation within species groups, the influence of substrate on spectral signature, and other factors.

Infographic — Sediments underlying salt marsh habitat within Greater Farallones National Marine Sanctuary contain approximately 99,268 megagrams of carbon. If destroyed, this would release the equivalent emissions of 79,159 passenger vehicles (assuming a fuel economy of 22 mpg and 11,500 miles driven per year) or 41 million gallons of gasoline [31]. These services are valued at approximately $129,859 per year [32].

Seagrass

Seagrass meadows, composed of eelgrass (Zostera marina), cover an area of 7.2 square kilometers (2.8 square miles) in Greater Farallones National Marine Sanctuary, with 99% of the extent solely located in , with patchy extent in .

Use the + - to explore seagrass habitat of Greater Farallones National Marine Sanctuary.

Maximum extent data were used to estimate the carbon stored in estuarine sediments. Seagrass extent data were collected from the California Department of Fish and Wildlife for the years 1992, 2000–2002, and 2013 and Merkel and Associates, Inc. for 2015 and 2017 using side-scan sonar. Data were mapped in ArcGIS and clipped to sanctuary boundaries for analysis.

Sediments underlying seagrass habitat within Greater Farallones National Marine Sanctuary contain approximately 75,880 megagrams of carbon. If destroyed, this would release the equivalent emissions of 60,509 passenger vehicles (assuming a fuel economy of 22 mpg and 11,500 miles driven per year) or 31 million gallons of gasoline [31]. These services are valued at approximately $139,000 per year [32].

Kelp

The bull kelp, Nereocystis luetkeana, is the dominant canopy-forming kelp in Greater Farallones National Marine Sanctuary.

Extensive kelp forests occur along the Sonoma and Mendocino County coasts [29].

Bull kelp floating at the ocean surface. — Bull kelp along the rocky shoreline.

Due to compounding environmental factors, the kelp forests throughout Greater Farallones National Marine Sanctuary have drastically decreased since 2014, with an estimated decline of 90% in bull kelp extent during that time [30].

Prior to the significant kelp loss that first occurred in 2014, bull kelp covered an area of nearly 2.5 million square meters in the sanctuary in a typical year of highly productive growth.

This analysis compares the carbon capture and export by sanctuary kelp beds in a relatively high kelp growth year (2008, left), prior to the 2014 decline, with a low kelp growth year (2019, right), following the decline.

Landsat imagery provides the longest, most consistent and complete historical data set to determine bull kelp canopy in the sanctuary. Using cloud-free Landsat 5, 7, and 8 imagery, the spectral signature of kelp was identified during the peak growth period in 2008 and 2019. Layers for kelp cover for each of these years were clipped to the borders of Greater Farallones National Marine Sanctuary. Kelp area was determined at a resolution of 30 x 30 m.

Kelp carbon stored within Greater Farallones National Marine Sanctuary amounts to 5,577 megagrams of carbon per year during a relatively high kelp growth year and only 16 megagrams of carbon per year in years with low productivity. These services are valued at approximately $114,735 per year and $337 per year, respectively [32].

Whales

This assessment focuses on the most reliably estimated process — the direct carbon export of whales dying and sinking to the seafloor — whale falls .

Carbon stored in whale tissues can remain in the deep sea for millennia.

Deteriorating whale carcass on the seafloor. — *Whale fall discovered in 2019 near Davidson Seamount within Monterey Bay National Marine Sanctuary.*

Decaying whale carcass on the seafloor. — *Returning to the whale fall in 2020 showed noticeable decay of bones, cartilage, and tissues, which hold carbon, and will remain at the seafloor, if undisturbed.*

Whales

Abundant baleen whale populations feed in and migrate through sanctuary waters.

Modeled data from at-sea surveys demonstrate the abundance of two of the whale species included in this analysis — and whales.

Population numbers were sourced from NOAA Fisheries marine mammal stock assessments for either California/Oregon/Washington (CA/OR/WA) or Eastern North Pacific (ENP) stocks of five baleen whale species — humpback, gray, fin, blue, and minke.

Whale populations were used to calculate the amount of carbon that is currently exported from the euphotic zone to the deep-sea every year via whale falls.

Click the buttons below to explore sighting locations of each species (1991-2014).

Modeled data: Rockwood R.C., M.L. Elliott, B. Saenz, N. Nur, J. Jahncke. 2020. Modeling predator and prey hotspots: Management implications of baleen whale co-occurrence with krill in Central California. PLoS ONE 15: e0235603

Whale populations: Marine Mammal Stock Assessment Reports by Species/Stock

Whale sightings data downloaded from OBIS-SEAMAP: Halpin, P.N., A.J. Read, E. Fujioka, B.D. Best, B. Donnelly, L.J. Hazen, C. Kot, K. Urian, E. LaBrecque, A. Dimatteo, J. Cleary, C. Good, L.B. Crowder, and K.D. Hyrenbach. 2009. OBIS-SEAMAP: The world data center for marine mammal, sea bird, and sea turtle distributions. Oceanography 22(2):104-115 .

Whale falls of five species export approximately 2,899 megagrams of carbon per year, which is equivalent to removing 2,312 vehicles from the road each year or preventing 1 million gallons of gasoline from burning. The societal value of this service is approximately half a million dollars [32].

Salt marsh and seagrass habitats in the sanctuary currently store approximately 175,148 megagrams of carbon in their sediments, which is equivalent to 642,000 metric tons of CO2 or 140,000 vehicles driving for one year [31].

Case Study: Sediment Carbon

Greater Farallones Association, in partnership with NOAA’s Office for Coastal Management, conducted the first systematic evaluation of marine sedimentary carbon stocks in North-Central California. This included a first-order estimate of the marine sedimentary carbon stock within the top 10 centimeters (surficial) of marine sediments in Greater Farallones, Cordell Bank, and the northern portion of Monterey Bay national marine sanctuaries.

Results show surficial (top 10 centimeters of) sediments in these sanctuaries, which accumulated over hundreds to thousands of years, hold approximately 9 ± 3.4 million metric tons of carbon (32 million metric tons of CO2), which is equivalent to the emissions from burning 3.5 billion gallons of gasoline.

Sediments of Greater Farallones and Cordell Bank National Marine Sanctuaries, which have accumulated over many years, hold approximately 9 ± 3.4 million metric tons of carbon, which is equivalent to the emissions from burning 3.5 billion gallons of gasoline.

Areas of high carbon content include a mid-shelf mud belt spanning approximately 100 km (63 miles) from Gualala to Point Reyes, 5 km (3 miles) offshore of California, and a large mud swath west of the shelf in the northern portion of Greater Farallones National Marine Sanctuary.

This interactive map displays the data referenced in Blue Carbon in Marine Protected Areas Part 3: An Evaluation of Sedimentary Carbon Stocks in Greater Farallones and Cordell Bank National Marine Sanctuaries.

Activities that disturb or alter the surficial (top 10 centimeters of the seafloor) seabed, such as mining, oil and gas exploration, and bottom-contact fishing, resuspend carbon-rich sediments, potentially re-mineralizing the carbon into CO2, decreasing the pH of the surrounding waters, and reducing the ocean’s capacity to absorb atmospheric carbon dioxide.

These findings can be applied to spatial planning and management of the seabed to ensure adequate protection of carbon sinks in sanctuaries.

Moving Forward

Marine protected areas protect valuable blue carbon habitats and processes, and must be part of the climate solution.

Greater Farallones and Cordell Bank National Marine Sanctuaries will continue to demonstrate national and global leadership by leveraging staff expertise, synthesizing available data, and developing guidance to protect and restore blue carbon habitats and processes within marine protected areas.