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Marine Anthophytes
Seagrasses
What…Where
Seagrasses are submerged flowering plants
found in shallow marine waters in bays,
lagoons, and along the continental shelf in
the Gulf of Mexico.
Seagrasses provide food, habitat, and
nursery areas for thousands of species.
Seagrasses perform numerous functions:
Stabilization:
Ocean bottom areas without seagrass are
vulnerable to intense wave action from
currents and storms. The extensive root
system in seagrasses, which extends both
vertically and horizontally, helps stabilize
the sea bottom in a manner similar to the
way land grasses prevent soil erosion. With
no seagrasses to diminish the force of the
currents along the bottom, our Gulf
coastline, businesses, and homes can be
subject to greater damage from storms.
Ecosystem support:
Seagrasses provide food, shelter, and
essential nursery areas to commercial and
recreational fishery species and to
countless invertebrates living in seagrass
communities. Again, our grouper, redfish,
trout and many, many other important
species rely on healthy seagrass beds.
Food:
While some animals, like the Florida
manatee and green sea turtle, graze
directly on seagrass leaves, others use
seagrasses indirectly to provide nutrients.
Detritus from seagrasses feed the worms,
crabs, and filter feeders that serve as the
base for our area's rich food chain.
Nursery areas:
The relative safety of seagrass meadows
provides an ideal environment for juvenile
fish and invertebrates to conceal themselves
from predators. Seagrass leaves are also
ideal for the attachment of larvae and eggs,
including those of the sea squirt and mollusk.
Much of the Gulf’s recreationally and
commercially important marine life can be
found in seagrass meadows during at least
one early life stage.
Habitat:
While seagrasses are ideal for juvenile and small
adult fish for escape from larger predators, many
infaunal organisms (animals living in soft sea
bottom sediments) also live within seagrass
meadows. Species such as clams, worms, crabs,
and echinoderms, like starfishes, sea cucumbers,
and sea urchins, use the buffering capabilities of
seagrasses to provide a refuge from strong
currents. The dense network of roots established
by seagrasses also helps deter predators from
digging through the substratum to find infaunal prey
organisms. Seagrass leaves provide a place of
anchor for seaweeds and for filter-feeding animals
like bryozoans, sponges, and forams.
Water Quality:
Seagrasses help trap fine sediments and
particles that are suspended in the water
column, which increases water clarity. When a
sea floor area lacks seagrass communities, the
sediments are more frequently stirred by wind
and waves, decreasing water clarity, affecting
marine animal behavior, and generally
decreasing the recreational quality of coastal
areas. Seagrasses also work to filter nutrients
that come from land-based industrial discharge
and stormwater runoff before these nutrients are
washed out to sea and to other sensitive
habitats such as coral reefs.
Economics:
Although seagrass is not a commodity that is
directly cultivated along the Gulf Coast, its
economic value can be measured through other
industries, such as commercial and recreational
fisheries and nature and wildlife tourism, which
rely on this habitat to survive. Since most of the
fishery species (approximately 70%) spend at
least part of their life cycle within seagrass
communities, seagrasses are vital to the survival
of these fishing industries.
Some facts
Seagrasses grow in lush beds throughout the
bay wherever conditions are favorable and
there is enough bottom sediment for the
seagrasses to take root. Like the grasses of
your lawn at home, seagrasses are flowering
plants. They have roots, stems, and flowers.
They produce oxygen. And without
exceptionally clear water that allows the
sunlight to reach them, seagrasses will die off
just as your lawn at home would if it were
deprived of sunlight.
Micro-world in the seagrass bed
Seagrass beds are typical for shallow estuarine and
coastal zones where the light can penetrate to the
sea floor. Depending on size and density, the sea
grass beds interact more or less intensively with the
boundary layer currents. The reduction of water
flow within the canopy permits the settlement of
suspended materials that provide nutrients to the
seagrasses. Likewise, the limited water exchange
between the seagrass bed and the overlying water
generates a microclimate that has positive effects
on the growth of the sea grasses.
Kinds
Turtle-grass,
Thalassia testudinum,
the most common
seagrass, has wide
leaf blades and a
deep root structure,
and forms most of the
large, lush seagrass
meadows.
• Shooting photos of
seahorses in the
turtle grass
another…
• Manatee grass, Syringodium
filiforme, is a shallow subtidal
species that thrives at a depth
of approximately 2 -3 feet, but
also occurs to depth of 60
feet. It forms monospecific
beds or can be found in mixed
beds, where it intermingles
with grass, Thalassia
testudinum. Preferred
substrate is sand or fine mud.
• Manatee grass ranges
throughout the tropical western
Atlantic from eastern Florida
through the Gulf of Mexico,
Caribbean, Bermuda, and the
Bahamas.
Eelgrass
Zostera
• Seagrasses found in
sheltered bays and
inlets are dominated
by species of
Zosteraceae,
commonly known as
eelgrass.
Sampling seagrasses
Not just Florida…It is Alabama’s, too
Seagrasses support over 70% of Florida's
fisheries by providing food and critical habitat,
but since the turn of the century, Florida has
lost over half of its seagrass beds due to
development, dredging, pollution and
increased boating activity. It is our choices that
decide whether this trend continues or if
healthy seagrasses serve to nurture our trout,
redfish, flounder, grouper, numerous types of
baitfishes, and many, many more important
ocean species.
What can you do to protect the
seagrasses?
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Be Aware
Read the Waters
Know Your Boating Signs and Markers
Know Your Depth and Draft
Be On the Lookout
Study Your Charts
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Be Aware: If you live near the coast or along a river, be careful when applying
fertilizers and pesticides to your lawn. Use only the amount of fertilizer required
and consider using a slow-release fertilizer. Gutters and storm drains transport
excess lawn chemicals to the water.
Read the Waters: Wear polarized sunglasses when boating to reduce the surface
glare to help you see shallow areas and seagrass beds. Polarized sunglasses can
also help you see and avoid manatees and underwater hazards.
Know Your Boating Signs and Markers: Operate your boat in marked channels
to prevent running aground and damaging your boat and seagrass beds. Know the
correct side to stay on when approaching channel markers. Learn the shapes and
markings of signs warning boaters of dangerous shallows and areas where boats
are prohibited by law.
Know Your Depth and Draft: When in doubt about the depth, slow down and idle.
If you are leaving a muddy trail behind your boat, you are probably cutting
seagrass. Tilt or stop your engine if necessary. If you run aground, pole or walk
your boat to deeper water. Never try to motor your way out. This will cause
extensive damage to seagrass and may harm your motor. Know the times for your
low and high tides.
Be On the Lookout: Docks, boathouses, and even boats can block sunlight from
reaching the seagrass below. When building or repairing a dock, consider building
the dock five feet above the water and using grating rather than planks. Extend the
dock to deeper water so your boat does not shade seagrass.
Study Your Charts: Use navigational charts, fishing maps, or local boating guides
to become familiar with waterways. These nautical charts alert you to shallow
areas so you don’t run aground and damage seagrass. Know before you go.