1. Submerged Aquatic Vegetation
Introduction to Coastal Management

2. 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

3. 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

4. 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 m of water, but have been found down to 130 feet

5. 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

6. 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

7. Vulnerability of Seagrass Beds
Conditions resulting in reduction of seagrass beds
Nutrient loading
Light reduction
Physical destruction
Rate of loss: weeks to months
Rate of recovery: years
Vegetatively slow recovery
Seeding shows more rapid recovery
Propeller scars on seagrass beds near Windley Key, Florida Keys

8. Common Seagrasses of the Eastern and Gulf US
Turtle Grass
Thalassia testudinum
Shoal Grass
Halodule wrightii
Eel Grass
Zostera marina
Manatee Grass
Syringodium filiforme
Widgeon Grass
Ruppia maritima
Paddle Grass Halophila decipiens

9. Causes of Decline in Seagrasses
Dredge and fill operations
Mooring scars
Propeller scars
Vessel wakes
Jet skis
Fish and shellfish harvesting techniques
Sewage outfalls
Thermal pollution
Disease
Storms
Ice scour
Epiphyte load
Burrowing shrimp
Green algae
Takes 3-5 years to heal a scar from propellers
Thermal pollution Turkey Point Nuclear plant in Miami is goodexample (biscayne Bay)
Various fishing techniques drag chains and net along the bottome distrubing the bottom.
Green algae cover the surface of the leaves and reduce photosynthses on the plants
Sewage outfalls increase nutrients and increased phytoplankoton until the plans die

10. 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.

11. Florida Bay Seagrass Diseases
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
South Florida, Florida Bay and Keys

12. “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

13. Restoration of Seagrass Beds
Methods of transplantation
Plugs -- Sprig
Cans -- Peatpot
Direct seeding -- Seedlings
Mats -- 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