Seagrass
Seagrasses
are submerged flowering plants, found mostly along the coastline, covering an
estimated global area of 300,000-600,000 km2. Healthy seagrasses
protect the shore, promote biodiversity, store carbon, cycle nutrients, and
help support numerous industries (e.g. fishing, tourism).
Seagrasses are threatened by reductions in water clarity caused by eutrophication, erosion, and increased concentrations of particulate matter.
There are 72 known species of seagrass, of which 10 are at risk of extinction and 3 are endangered (Short 2011).
Seagrasses have declined in area by about 29% since the beginning of the twentieth century, at an annual rate of about 1.5% and faster in recent years, replaced with unvegetated, mud and sand soils (Fourqurean et al. 2012).
Seagrasses are threatened by reductions in water clarity caused by eutrophication, erosion, and increased concentrations of particulate matter.
There are 72 known species of seagrass, of which 10 are at risk of extinction and 3 are endangered (Short 2011).
Seagrasses have declined in area by about 29% since the beginning of the twentieth century, at an annual rate of about 1.5% and faster in recent years, replaced with unvegetated, mud and sand soils (Fourqurean et al. 2012).
Seagrass Ecosystem: Loss of Habitat
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Which Goals Does This Affect?
How Was It Measured?
No globally complete
databases or maps of seagrass extent currently exist, so seagrass extent was
calculated from vector-based data obtained from the Global Distribution of
Seagrasses database maintained by United Nations Environmental Program’s World
Conservation Monitoring Center (UNEP-WCMC).
Seagrass Status and Trend data were calculated on a per-site basis using data from Waycott et al. 2009 and Short et al. 2011, which provide annual seagrass habitat extent data for several sites around the world.
When possible, the reference condition was calculated as the mean of the three oldest years between 1975-1985; alternative methods are described in Halpern et al. 2012.
Seagrass Status and Trend data were calculated on a per-site basis using data from Waycott et al. 2009 and Short et al. 2011, which provide annual seagrass habitat extent data for several sites around the world.
When possible, the reference condition was calculated as the mean of the three oldest years between 1975-1985; alternative methods are described in Halpern et al. 2012.
What Are the Impacts?
ECOLOGICAL IMPACT
Seagrasses
uptake carbon dioxide from the atmosphere in a process known as
‘sequestration’. Two-thirds of seagrass biomass is buried as
rhizomes and roots. If undisturbed, these structures, as well as seagrass
litter in surrounding soil, are capable of storing carbon for centuries. When seagrass beds are damaged
or destroyed, carbon is released back into the atmosphere.
Changes or disturbances to seagrass beds and meadows are often warning signs of increasing pressure from human activities. Seagrass’ sensitivity to these changes makes it an 'indicator species', acting as a barometer for the health of the surrounding ecosystem.
Seagrass beds occupy less than 0.2% of the area of the world's oceans, but bury between 4.2 and 8.4 Gt (1 GT = 1 billion metric tonnes) of organic carbon per year.
Rapid loss of seagrass habitat not only decreases carbon sequestration by seagrass ecosystems, but also releases stored carbon from the disturbed soils, contributing as much as 10% of the 0.5-2.7 Gt C per year released from changes in land use.
Seagrasses store approximately twice the amount of organic carbon per hectare as terrestrial soils. Though seagrass biomass is small compared with forests, the amount of carbon they store in soils may be nearly as high as that stored by terrestrial systems and mangroves.
Most terrestrial forests eventually return stored carbon to the atmosphere during forest fires, but seagrass soils can accumulate to depths of meters over millennia if undisturbed.
Over the last century, drainage of 1,800 km2 of wetlands for agricultural use in the San Joaquin Delta has released 4,000 years worth of carbon dioxide into the atmosphere, an amount of nearly 1 billion tons. Each year, between 5 and 7.5 million tons of CO2 continue to seep from the Delta, an amount equivalent to 1-1.5% of California’s annual greenhouse gas emissions.
Seagrasses provide an abundance of food and nutrients for surrounding species and neighboring habitats. They also offer protection from predators, and serve as nursery grounds for many young vertebrate and invertebrate species.
Seagrasses provide an essential habitat for culturally important species such as manatees, dugongs, and green turtles. Certain sea birds, such as ducks, geese and swans, rely upon seagrass as a food source.
Changes or disturbances to seagrass beds and meadows are often warning signs of increasing pressure from human activities. Seagrass’ sensitivity to these changes makes it an 'indicator species', acting as a barometer for the health of the surrounding ecosystem.
Seagrass beds occupy less than 0.2% of the area of the world's oceans, but bury between 4.2 and 8.4 Gt (1 GT = 1 billion metric tonnes) of organic carbon per year.
Rapid loss of seagrass habitat not only decreases carbon sequestration by seagrass ecosystems, but also releases stored carbon from the disturbed soils, contributing as much as 10% of the 0.5-2.7 Gt C per year released from changes in land use.
Seagrasses store approximately twice the amount of organic carbon per hectare as terrestrial soils. Though seagrass biomass is small compared with forests, the amount of carbon they store in soils may be nearly as high as that stored by terrestrial systems and mangroves.
Most terrestrial forests eventually return stored carbon to the atmosphere during forest fires, but seagrass soils can accumulate to depths of meters over millennia if undisturbed.
Over the last century, drainage of 1,800 km2 of wetlands for agricultural use in the San Joaquin Delta has released 4,000 years worth of carbon dioxide into the atmosphere, an amount of nearly 1 billion tons. Each year, between 5 and 7.5 million tons of CO2 continue to seep from the Delta, an amount equivalent to 1-1.5% of California’s annual greenhouse gas emissions.
Seagrasses provide an abundance of food and nutrients for surrounding species and neighboring habitats. They also offer protection from predators, and serve as nursery grounds for many young vertebrate and invertebrate species.
Seagrasses provide an essential habitat for culturally important species such as manatees, dugongs, and green turtles. Certain sea birds, such as ducks, geese and swans, rely upon seagrass as a food source.
HUMAN HEALTH IMPACT
Seagrasses
stabilize coastal sediments and prevent them from eroding.
Seagrasses provide shoreline protection by absorbing the impact of waves, although protection potential can be limited in extreme weather events, such as hurricanes and tsunamis.
Seagrasses provide shoreline protection by absorbing the impact of waves, although protection potential can be limited in extreme weather events, such as hurricanes and tsunamis.
ECONOMIC IMPACT
Seagrasses
use and recycle nutrients found in water, providing services for which people
would normally pay US $19,002 per hectare per year.
Seagrasses are important habitats or nursery areas for many commercially important species of fish, crustaceans (e.g. shrimp, spiny lobster) and shellfish (e.g. queen conch).
Seagrasses are important habitats or nursery areas for many commercially important species of fish, crustaceans (e.g. shrimp, spiny lobster) and shellfish (e.g. queen conch).
What Has Been Done?
On Virginia’s Eastern Shore, Efforts to Restore Seagrass Revive the Scallop Industry (VIDEO)
On
Virginia’s Eastern Shore, an industry worth US $2.8 million (adjusted) in 1929 all
but disappeared when disease and extreme weather hit the region in the 1930s,
wiping out the population of seagrass that had been home to a diverse array of
species, including the valued bay scallop.
In
1997, the Virginia Institute of Marine Science and the Nature Conservancy came
together to form the Virginia Coastal Zone Management program, which aimed to
restore seagrass to the areas by planting seeds. In the past decade, over 38
million seeds have been distributed, generating the growth of over 4,200 acres
of seagrass, and in 2009, the bay scallop harvest generated US $1.9 million.
National Geographic
Combined Efforts of Legislators and Community Organizers Restore Seagrass in Tampa Bay, Florida
In
the last century, seagrass meadows in Tampa Bay, Florida declined nearly 75%
because of pollution from industrial and municipal waste. Thanks to a federal
grant from the US Environmental Protection Agency to upgrade sewage treatment
plants, state legislation requiring higher standards of sewage treatment, and
the community-based efforts of the Tampa Bay National Estuary Program, the loss
of seagrass has been reversed. The flow of excess nitrogen from industrial and
domestic sources was reduced by 90%, and between 1982 and 1994, the abundance
of seagrass increased 23%.
National Geographic
In Peam Krosaup, Cambodia, Seagrass is Key to Food Security
In
the last century, seagrass meadows in Tampa Bay, Florida declined nearly 75%
because of pollution from industrial and municipal waste. Thanks to a federal
grant from the US Environmental Protection Agency to upgrade sewage treatment
plants, state legislation requiring higher standards of sewage treatment, and
the community-based efforts of the Tampa Bay National Estuary Program, the loss
of seagrass has been reversed. The flow of excess nitrogen from industrial and
domestic sources was reduced by 90%, and between 1982 and 1994, the abundance
of seagrass increased 23%.
National Geographic
In Peam Krosaup, Cambodia, Seagrass is the Key to Food Security
In
the Peam Krosaup wildlife sanctuary in Cambodia, food security depends on the
health of seagrass beds and the species they support. By 2000, overfishing and
illegal fishing with pushing boats had damaged the seagrass beds and heavily
exploited the food supply, threatening the well-being of the five villages in
Pream Krosaup. In 2006, the Federation of Community Coastal National Resources
Management instituted an 18-month program to protect 20 hectares of seagrass
beds across the region. The program helped community member install 330
concrete poles to prevent pushing boats from entering protected areas, as well
as plant mangroves, place artificial fish shelters, and install four patrol
boats to curb illegal fishing. The result: more fish, crabs and shrimp for the
villages, more seagrass, and increased community awareness of ways to protect
and support a thriving ecosystem.
National Geographic
Artificial Seagrass Boosts Fish Populations in New Zealand, and Inspires a Collaboration to Restore the Real Thing
Seagrasses
used to cover about 14 km2 in Whangarei Harbor, New Zealand, but by
1970, they had nearly all disappeared.
When Dr. Mark Morrison of the National Institute of Water and
Atmospheric Research (NIWA) successfully transplanted seagrass into areas of the bay, local
organizations took notice. Inspired by the dramatic regeneration of fish stocks
because of the transplanted seagrass, the Northland Regional Council, the NIWA,
and the Whangarei Harbour Kaitiaki Roopu, a caretaker group, got together to
reduce contamination of the waters and bring new seagrass beds to the region.
By improving water quality, they created conditions that enabled the growth of
new seagrass, which they had transplanted in small patches from donor sites.
Since 2004, the seagrass has thrived, and now covers an area of over 1,200
square meters.
National Geographic
Get More Information
Seagrass Recovery
A
Unites States based organization dedicated to preserving seagrass through
patented inventions and services for replanting and restoring damaged seagrass
beds.
SeagrassNet
A
global ecological monitoring program that “investigates and documents the
status of seagrass resources and the threats to this important and imperiled
marine ecosystem”.
References
Crooks, S., Herr, D., Tamelander, Jerker, Laffoley, Dan & Vandever, Justin Mitigating climate change through restoration and management of coatsal wetlands and near-shore marine ecosystems: challenges and opportunities. (The World Bank: Washington D.C., 2011).
Fourqurean, J. W. et al. Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience 5, 505–509 (2012).
Heck
Jr, K. L. H., Hays, G. & Orth, R. J. Critical evaluation of the nursery role hypothesis for seagrass meadows. Mar Ecol Prog Ser 253, 123–136 (2003).
McArthur, L. C. & Boland, J. W. The economic contribution of seagrass to secondary production in South Australia. Ecological Modelling 196, 163–172 (2006).
Watson, R., Coles, R. & Lee Long, W. Simulation estimates of annual yield and landed value for commercial penaeid prawns from a tropical seagrass habitat, Northern Queensland, Australia. Mar. Freshwater Res. 44, 211–219 (1993).
PHOTO(S): © Keith A. Ellenbogen