Transcript Submerged Aquatic Vegetation

Submerged
Aquatic
Vegetation
Introduction to
Coastal
Management
Submerged Aquatic
Vegetation
• Typically composed of
seagrasses
– Marine flowering plants
– 13 genera; 58 species
worldwide
• Grow in shallow subtidal
or intertidal water on soft
muds and sandy
sediments (some on
rocky substrates)
• Evolved from terrestrial
grasses
Turtle Grass,
Thalassia testudinum
Lifestyle Requirements for
Seagrasses
• Must be adapted to saline waters (true halophyte)
• Must be able to grow completely submerged
• Must be securely anchored in the substrate
(some species are anchored to rocky substrates)
• Must be able to flower, fruit and produce seeds in
water
• Leaves and stems lack waxy cuticle typical of
terrestrial plants
• Typically possess aerenchyma tissue for
bouyancy
Occurrence
• Worldwide in distribution
• In US, found on Atlantic, Pacific, and Gulf
coasts
• 90% of seagrasses in US are in Gulf of
Mexico
– Major beds in Chesapeake Bay, Florida, Texas
and California
• Occur primarily in “beds,” typically patchy
in nature
• Grasses typically found in 10-15 m of
water, but have been found down to 130
Ecology of Seagrass Beds
• Seagrass beds are important to:
– Grazers—manatees, ducks, etc.
– Epiphyte grazers—feed on seagrass
epiphytes—sea urchins, fish, etc.
– Detritus feeders—feed on decaying
organic matter
– Shelter for conch, starfish, sand
dollars, etc
• Substrate and food for bay barnacles,
sea squirts, sponges, isopods,
amphipods, snails, seahorses,
anchovies, silversides, shrimp, blue
crabs, waterfowl and others
Ecology of Seagrass Beds
• Bind sediments with extensive rhizomes
and roots
• Baffle waves and currents
• Trap sediments/clear the water column
• Improve water quality by taking up
nutrients (epiphytes do the same)
• Important in oxygenating water
• Seagrass systems protected under federal
“no-net-loss” policy for wetlands
Vulnerability of Seagrass
Beds
• Conditions resulting in reduction of
seagrass beds
– Nutrient loading
– Light reduction
– Physical destruction
• Rate of loss: weeks to months
Propeller scars on seagrass
• Rate of recovery: years
beds near Windley Key,
– Vegetatively slow recovery
Florida Keys
– Seeding shows more rapid recovery
Common Seagrasses of the
Eastern and Gulf US
Turtle Grass
Thalassia testudinum
Shoal Grass
Halodule wrightii
Eel Grass
Zostera marina
Manatee Grass
Syringodium filiforme
Paddle Grass Halophila decipiens
Widgeon Grass
Ruppia maritima
Causes of Decline in
Seagrasses
• Dredge and fill
operations
• Mooring scars
• Propeller scars
• Vessel wakes
• Jet skis
• Fish and shellfish
harvesting
techniques
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Sewage outfalls
Thermal pollution
Disease
Storms
Ice scour
Epiphyte load
Burrowing shrimp
Green algae
Seagrass Diseases
• “Wasting Disease” of
Zostera marina in the
North Atlantic Ocean
• Massive die-off of
Thalassia testudinum in
Florida Bay
• Suspect in both cases is
marine slime mold
Labyrinthula
Photomicrograph of
Labyrinthula sp.
Florida Bay Seagrass
Diseases
South Florida, Florida Bay and
Keys
• Massive die-off of
Thalassia testudinum
in Florida Bay in 1987
• Preceded by year of
low freshwater runoff
from the everglades
• Labyrinthula thrives in
high salinity
• Restoration of
Everglades freshwater
flows may help
seagrasses
“Wasting Disease”
• Started in 1927; eelgrass
virtually wiped out by 1933 in
all of North Atlantic Ocean
• Suspect factors
– Salinity extremes
– Waterfowl grazing (Brant
populations plummented)
– Storms
– Increasing turbidity,
eutrophication
– Slime mold, Labyrinthula
– Increased water temperatures
Eelgrass, Zostera
marina
Restoration of Seagrass
Beds
• Methods of transplantation
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Plugs
Cans
Direct seeding
Mats
-- Sprig
-- Peatpot
-- Seedlings
-- Boulder
• Costs: estimates are $2,000/acre in 3-ft
water; $200,000 in 8-ft water
• More emphasis on impact avoidance and
minimization rather than mitigation or
restoration