Seagrass and Salt Marsh: Critical Coastal Habitats

South Slough National

Estuarine Research Reserve

What is a Salt Marsh?

Salt marshes are transitional areas between land and water, occurring along the intertidal shore of estuaries and sounds where salinity (salt content) ranges from near ocean strength to near fresh in upriver marshes.

What is a Seagrass Bed? Seagrasses are flowering plants that have adapted

to living in salt water. Seagrasses are found mostly on soft sediment in estuaries and shallow coastal waters and are frequently found growing in dense beds.

In Pacific Northwest estuaries, the common species of seagrass is called eelgrass (Zostera marina), which grows in soft sediments of intertidal and subtidal zones.

Where are seagrass and salt marsh communities located?

Salt marshes

Estuarine Habitats:Salt marshes Tidal channels:

Estuarine Habitats:Salt marshes Tidal channels:

1. Open Water- Subtidal

Eelgrass beds

Estuarine Habitats:Salt marshes Tidal channels:

1. Open Water- Subtidal2. Intertidal mudflat

Intertidal mudflatEelgrass beds

High Salt MarshLow and Mid Salt Marsh

Mudflat and/or Seagrass

Transitional Zone

Elevation is a primary determinant of seagrass and salt marsh location

Tidal Inundation Period:

High Marsh- Short

Low Marsh- Long

Low Tide MLLW

Mainstem Tidal Channel

High Tide MHHW

Extreme High Tide

Why are seagrass and salt marsh communities important?

What roles do they play in the coastal ecosystem?

In ecological and economic value, they rival tropical rainforests and the world’s richest farmlands!

• Primary Production

• Fish and Wildlife Habitat (including “nursery” role)

• Sediment sink

• Shoreline protection

• Water Quality

Seagrass and Salt Marsh Functions

Primary Production

• Production• Shredding• Colonization/decomposition • Consumption by small

organisms (“grazers”)• Consumption by larger

organisms (“predators”)• Defecation/Nutrient

transformation

Eelgrass and Salt Marsh provide the critical foundation to the “detrital food web”

• Juvenile Salmon rearing habitat

• Foraging

• Physiological transitions

• Refuge from predators

Fish and Wildlife Habitat Example

• Resident and migratory bird habitat

• Shorebirds – feed on insects, fish, invertebrates

• Ducks and geese graze on vegetation – Ex. Black Brant / eelgrass

Fish and Wildlife Habitat Example

Water Quality• Nutrient uptake • Sediment trapping and baffling of wave energy• Oxygen production

Natural Variability of Salt Marsh and Seagrass Habitats

Plant distribution, species diversity, and density can vary substantially over seasons and years in response to:

– Precipitation, water table

– Light availability

– Temperature

– Nutrient availability

– Plant competition/succession

– Sediment characteristics

– Oceanic cycles (El NIÑO, PDO)

– Sea level rise

Human Impacts on Salt Marsh and Seagrass

Direct Impacts:• Dredging• Diking• Draining• Filling

Indirect Impacts:• Pollution – toxics, nutrients, sediments• Water diversions• Shading – i.e. docks, piers, bridges, boats, high water turbidity• Invasive species

HISTORIC CHANGES OF COOS BAY TIDAL WETLANDS, FILLED AGRICULTURAL LANDS, AND

RESIDENTIAL COMMUNITIES (1892-1995)

1892

1901

1937

1942

1971

1987

1995

0

1000

2000

3000

4000

5000

6000

7000

8000

900018

92

1901

1937

1942

1971

1987

1995

TIDALWETLANDS

WETLANDCONVERTED TOAGRICULTURE

WETLANDFILLED FORRESIDENCES

AC

RE

S

YEAR

Coos Bay 1900

Why Monitor Salt Marsh and Seagrass Habitat?

• To further our understanding of coastal ecology

• To document changes over time as an indicator of estuarine health

• To assess changes in sensitive estuarine habitats from long term trends in sea level rise and climate change

• To alert us to declines in key habitats and guide corrective action

• To motivate the public to protect existing habitat, restore degraded habitat, and improve upstream land use practices

South Slough’s Monitoring Strategy

South Slough National Estuarine Research Reserve (SSNERR) currently monitors a variety of physical and chemical measures as part of a nationwide effort to track the status and trends of estuarine resources in the United States.

Monitoring of eelgrass and salt marsh serve as biological indicators of ecosystem health.

A key advantage of biological indicators of estuary health is that they respond to a broad variety of environmental variables (temperature, salinity, light, pollution, etc), and therefore provide an integrated measure of how the ecosystem is functioning.

The “Big Picture” Questions:

• Within salt marshes and eelgrass beds, how are species composition, abundance, and distribution changing over time?

• What might be causing these changes?

Questions about short-term variability in these habitats:

• How closely linked are the seasonal ecological characteristics of these habitats along the estuarine gradient?

• How does the location of a habitat along the estuarine gradient affect species diversity, spatial cover, and biomass?

Questions about long-term variability in these habitats:

• How are changes in eelgrass and salt marsh habitats related to longer-term changes in the nearshore Pacific Ocean and/or freshwater inputs from the local watershed?

Guiding Concepts of Our Monitoring Approach:

• Establish monitoring sites along estuarine gradient (marine freshwater)

• Conduct representative sampling using transects and plots

• Repeatable measures• Measure both plant community attributes and

environmental variables• Testing both national (NERRS) and International

(SeagrassNet) protocols• Sample quarterly (4x per year) to assess seasonal

variability

Transects and Plots

Water Table HeightWater Table Height

Sediment elevation changesSediment elevation changes

Sediment grain size Sediment grain size

Light using loggersLight using loggers

Water temperature using loggersWater temperature using loggers

Water depthWater depth

Water salinity (salt content)Water salinity (salt content)

What do we measure at each site?

Canopy height / Blade widthCanopy height / Blade width

Shoot densityShoot density

Flowers & fruitsFlowers & fruits

Sediment descriptionSediment description

Biomass core (0.0035mBiomass core (0.0035m22))

Seagrass % cover Seagrass % cover

Species composition Species composition

PhotographPhotograph

What do we measure at each quadrat plot?

Monitoring sediment elevation changes

SeagrassNet Sites

Current project status?

• First year of project – 3 seasons of data collected

• Data analysis this Fall

• Ongoing long term monitoring to reveal trends