Submerged Aquatic Vegetation

1. Submerged Aquatic Vegetation Biology 561 Barrier Island Ecology

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 10-15 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. Common US Pacific Seagrasses Scouler’s Seagrass Phyllospadix scouleri Surfgrass Phyllospadix serrulatus Torrey’s Seagrass Phyllospadix torreyi

10. Northeast (ME-NJ) Zostera marina Ruppia maritima Mid-Atlantic (DE-NC) Halodule wrightii Ruppia maritima Southeast and Gulf (FL-Mexico, Caribbean Halodule wrightii Halophila decipiens Halophila engelmanii Halophila johnsonni Ruppia maritima Syringodium filiforme Thalassia testudinum Seagrass Species Distribution

11. West Coast of US (CA – WA) Phyllospadix scouleri Phyllospadix serralatus Phyllospadix torreyi Ruppia maritima Zostera japonica Zostera marina Alaska Zostera marina Phyllospadix serralatus Hawaii Halophila hawaiiana Seagrass Species Distribution

12. 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 Causes of Decline in Seagrasses

13. 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.

14. 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

15. “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

16. The Chesapeake Bay Experience • Bay possesses 10 major species of submerged grasses • Seagrasses serve as primary indicators of water quality in the bay • Eel Grass, Zostera marina, had massive die-off in 1927-33 • Another major die-off of all species in the 1960s and 1970s • Half of acreage of seagrasses disappeared • Species dependent upon seagrasses also declined (blue crabs, canvasback ducks, and others)

17. The Chesapeake Bay Experience • 1960-70 decline included all species • Suspects for decline include: • Overgrazing by animals (European Carp, cownose carp, mute swans) • Hurricanes (Agnes, 1972) • Warming trend • Natural diseases (Labyrinthula) • Point and non-point pollution • Turbidity • Excessive nutrients • Herbicides • Petrochemicals • Dredging and boat traffic • No one of these factors can be determined as responsible for the general decline of seagrasses

18. The Chesapeake Bay Experience • The most important factor in determining growth and survival in Chesapeake Bay is the amount of light reaching the plants • Total suspended solids • Algae (phytoplankton) • Epiphytes • Nutrients/dissolved organics (color) • Sediment in water column

19. 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