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

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 Rate of recovery: years –Vegetatively slow recovery –Seeding shows more rapid recovery Propeller scars on seagrass beds near Windley Key, Florida Keys

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

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

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 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

“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 –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