Chesapeake Bay Program

Bay Grasses

Wild celery and coontail are two species of bay grasses that grow in the shallow waters of the

Chesapeake Bay. (Chesapeake Bay Program)

Overview

Bay grasses are plants that grow underwater. They are found in the shallow waters of the Chesapeake Bay and its

streams, creeks and rivers.

Bay grasses are also known as submerged aquatic vegetation or SAV.

Bay grasses are a critical part of the Chesapeake Bay ecosystem. They provide underwater life with food and

habitat, absorb nutrients, trap sediment, reduce erosion, and add oxygen to the water.

Bay grasses are an excellent measure of the Bay’s overall condition because their health is closely linked with the

Bay’s health.

Pollution and extreme weather conditions are two factors that hinder bay grass growth.

Improving water clarity is the most important part of bay grass restoration because bay grasses need sunlight to

grow.

What are bay grasses?

Bay grasses are plants that grow underwater. They are found in the shallow waters of the Chesapeake Bay and its

streams, creeks and rivers.

Bay grasses are also known as submerged aquatic vegetation or SAV.

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Why are bay grasses important?

Bay grasses are a critical part of the Chesapeake Bay ecosystem because they provide food and habitat for numerous

species. They also help keep the water clear and healthy by absorbing nutrients, trapping sediment, reducing erosion and

adding oxygen.

Bay grasses provide food and habitat

Bay grass beds form habitats that provide food and shelter for many species. A bay grass community is an excellent

example of a food web because of the many species that depend on each other for food.

Tiny zooplankton feed on decaying bay grasses. In turn, zooplankton are food for larger creatures.

Many small invertebrates – including barnacles, sponges, sea slugs and sea squirts – feed on and attach

themselves to bay grass stems and leaves.

Small fish dart between grasses as they graze on smaller prey and hide from larger fish and crabs.

Molting blue crabs seek refuge from predators within bay grass beds because their soft shells make them very

vulnerable.

Bay grass beds are protective nurseries for young crabs and fish such as spot, croakers, weakfish, menhaden,

white perch and American shad. Scientists have found 30 times more juvenile blue crabs in bay grass beds than in

areas with no grasses.

Migratory waterfowl eat bay grasses and the animals that live in bay grass communities.

Bay grasses help keep the water clear and healthy

Healthy bay grass beds help keep the Chesapeake Bay clean and healthy. Bay grasses absorb excess nutrients, trap

sediment, reduce erosion and add oxygen to the water.

Bay grasses absorb nitrogen and phosphorus – major Bay pollutants – and convert them into organic matter that

other aquatic life can use.

Bay grass beds reduce erosion by slowing water currents, anchoring bottom sediments and softening waves that

break along the shoreline. Bay grasses also trap sediment particles suspended in the water.

As bay grasses go through photosynthesis, they release oxygen into the water. All life in the Bay needs oxygen to

survive.

Although bay grasses are sensitive to pollution, they respond fairly quickly to improvements in the Bay’s condition. This

makes bay grasses an excellent measure of overall Bay health.

How do bay grasses grow?

Just like any other plant, bay grasses go through photosynthesis. This means they need sunlight to grow. Sunlight is the

single most important factor determining bay grass survival. The water must be clear enough for the sun’s rays to pass

through and reach bay grasses growing at the bottom.

How does pollution affect bay grasses?

Bay grass growth is hindered mostly by pollutants that block sunlight. Suspended sediment particles and dense algae

blooms fueled by excess nutrients cause the water to become cloudy.

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Healthy bay grass beds are able to trap and absorb some of this pollution, but too much pollution blocks out sunlight and

kills bay grasses.

How does weather affect bay grasses?

Extreme weather events, such as very high temperatures or lots of precipitation, can also harm bay grasses.

Temperature

Some bay grasses, such as eelgrass, cannot grow in water that is too warm. In 2005, very high temperatures caused

large eelgrass beds in the lower Chesapeake Bay to die. It takes several years for bay grass beds to recover from these

types of large-scale losses.

Precipitation

Precipitation – and the water-clouding pollution it carries into the Chesapeake Bay – is a major influence on bay grass

growth.

Higher-than-average rainfall washes too much pollution into the Bay and its rivers. In 2003 – a year with many

rainstorms, including Tropical Storm Isabel – scientists recorded a 30 percent decrease in bay grass acreage.

Lower-than-average rainfall usually results in clearer water, allowing bay grasses to grow better.

How are the Chesapeake Bay’s bay grasses being restored?

Today’s science allows researchers to target bay grass restoration efforts in areas where grasses once grew. However, the

Bay’s continuing poor health, irregular weather conditions, and lack of funding have slowed progress toward restoring bay

grasses.

Bay Program partners focus on four major initiatives to restore bay grass beds and keep them healthy: improving water

clarity, planting bay grasses, protecting existing bay grass beds, and enhancing education and outreach about bay

grasses.

Improving water clarity

Improving water clarity is a critical part of bay grass restoration because sunlight is the single most important factor

influencing bay grass growth and survival. When the water is clearer, new bay grasses can grow and existing bay grass

beds can expand.

Maryland, Virginia and the District of Columbia have specific water clarity criteria for shallow waters where bay grasses

grow or once grew. The criteria list exact amounts of sunlight that must be able to pass through the water and reach bay

grasses at the bottom.

Large pollution reduction efforts aim to slow the flow of nutrients and sediment into the Bay and its local waterways.

Programs to upgrade wastewater treatment plants and implement agricultural conservation practices are expected to

improve water clarity, which will help bay grass restoration.

Planting bay grasses

Planting bay grasses enhances the natural expansion of grass beds that comes with reducing pollution and increasing

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protection. However, improving water clarity is the main focus of bay grass restoration because grasses can naturally

colonize an area at a much faster rate than can be achieved through planting.

The Maryland Department of Natural Resources, a Bay Program partner, led a large-scale eelgrass restoration project on

the Patuxent and Potomac rivers from 2004 to 2008. Scientists with the project have concluded that using seeds is a

practical way to restore eelgrass. However, scientists need sustained funding, adequate supplies of plants and seeds, and

sufficient data to identify the best places to plant eelgrass.

Protecting existing bay grass beds

Bay grass beds can be physically damaged by a number of factors, including human activities, invasive species and

climate change.

Human activities

Clam dredging and boat propellers tear bay grasses out of the Bay’s bottom. In many shallow areas, you can see large

“scars” across grass beds from these human activities.

Regulations exist to help prevent this damage, but boaters need to do their part to protect bay grasses. Always follow

posted speed limits and no-wake laws to avoid harming bay grasses. Also, steer clear of bay grass beds growing in

shallow waters.

Invasive species

Invasive species such as mute swans and water chestnut also threaten existing bay grass beds.

Mute swans eat significant amounts of bay grasses and can deplete entire beds in localized areas.

Water chestnut, an aquatic plant, floats on the water’s surface and completely blocks sunlight from reaching the

bottom.

Ongoing efforts to control these invasive species also help protect bay grasses.

Climate change

Scientists are increasingly concerned about the potential effects of climate change and sea level rise on bay grasses.

Rising temperatures may make the Bay unsuitable for certain bay grass species, such as eelgrass.

Flooding and shoreline erosion could make the water even cloudier and more polluted.

Scientists are monitoring bay grasses to better understand how they respond to climate change and rising sea levels.

Enhancing bay grass education and outreach

Another critical part of bay grass restoration is helping citizens understand why bay grasses are so important.

Many organizations lead programs that teach citizens about bay grasses. For example:

Students are studying, growing and planting bay grasses through Maryland DNR’s Bay Grasses in Classes.

The Chesapeake Bay Foundation helps Virginia residents grow wild celery in their homes through a program called

Grasses for the Masses. The grasses are eventually planted in Virginia freshwater rivers that flow to the Bay.

Many people volunteer with small watershed groups to help plant and monitor bay grasses in their local rivers.

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From Around the Web

Submerged Aquatic Vegetation (SAV) in Chesapeake Bay - Virginia Institute of Marine Science

Bay Grasses - Maryland Department of Natural Resources

Submerged Aquatic Vegetation - NOAA Chesapeake Bay Office

Restoring SAV - Maryland Sea Grant

Chesapeake Bay News

2011 dissolved oxygen levels lowest in four years - June 12, 2012

34% of Bay waters met standards for dissolved oxygen; some oyster and grass beds healthy despite conditions.

Chesapeake Bay underwater grasses decrease 21 percent in 2011 - March 28, 2012

Extreme weather conditions in 2010 and 2011 led to a substantial decrease in bay grasses throughout the Bay

and its rivers.

Susquehanna Flats bay grass beds survive late summer hurricanes, rain storms -

December 15, 2011

The vast underwater grass beds of the Susquehanna Flats are in much better condition than scientists expected.

Monitoring results show little effect of late summer storms on Susquehanna Flats bay

grasses - November 18, 2011

Aerial photos show the upper Bay’s grasses mostly survived muddy plumes.

Mid-year bay monitoring update shows bay grasses up in some areas, down in others -

September 02, 2011

Scientists with the Virginia Institute of Marine Science have released a mid-year update on bay grass monitoring

in the Bay.

More Chesapeake Bay News » »

In The Headlines

Blog: Maryland coastal bays losing sea grasses - Baltimore (Md.) Sun 5/24/2012

Seagrasses Decline Significantly in Maryland's Coastal Bays - Southern Maryland Newspapers 5/24/2012

Study: Seagrass stores more carbon than forests - Reuters 5/23/2012

Seagrasses drop sharply in Md., Va. coastal bays - Associated Press 5/23/2012

Seagrasses drop sharply in Md., Va. coastal bays - Salisbury (Md.) Daily Times 5/23/2012

The Forest Below: Underwater Grass Planting Along the Potomac - Patch.com 5/22/2012

Homegrown Underwater Grass To Replenish Potomac - WAMU (D.C.) Radio 5/9/2012

More Bay News » »

News Progress Video Publications Maps

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