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Seagrasses

Seagrasses. Support abundant life Provide complex habitat Trophic support Refuge Recruitment Nursery. Characteristics and Distribution. Approximately 48 species Family Hydrocharitaceae – Thalassia testudinum Family Cymodoceaceae – Halodule , Cymodocea filiforme

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Seagrasses

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  1. Seagrasses • Support abundant life • Provide complex habitat • Trophic support • Refuge • Recruitment • Nursery

  2. Characteristics and Distribution • Approximately 48 species Family Hydrocharitaceae – Thalassia testudinum Family Cymodoceaceae – Halodule, Cymodocea filiforme • Distribution is limited to temperate and tropical waters worldwide • Requirements for survival: salt tolerance submergence anchoring system in turbulent environment hydrophilous pollination

  3. Cymodocea filiforme Manatee Grass

  4. Thalassia testudinum Turtle-grass

  5. Halodule sp. Shoalgrass

  6. Morphological Adaptations • Flattened, strap-like leaves • Extensive root/rhizome system • Halophytic • Light sensitive • Nutrient uptake through roots and leaves • Reproduction: sexual (pollination) and asexual through prolific vegetative propagation • Hydrophilic pollination pollen transported on water surface (Halodule, Ruppia) pollen transported beneath water surface (Thalassia)

  7. Seagrasses-Anatomical Adaptations Leaves • Lack stomata; thin cuticle to allows gas and nutrient exchange • Large thin-walled aerenchyma facilitate gas diffusion within the leaf & provides buoyancy to the leaves Roots and Rhizomes • Oxygen transport to the roots creates an oxic environment around the roots, facilitating nutrient uptake • All produce root hairs

  8. Ecophysiology and Productivity • Wide temperature tolerance 0-36 degrees C (tolerance), 0-30 degrees C (growth) • Wide salinity tolerance 0-90 ppt (tolerance) 0-56 ppt (growth) • Minimum 18% surface irradiance PAR requirements • Blade productivity: 0.2-18.7 g C/m2/day • Biomass up to 8,000 g drywt/m2

  9. Factors affecting species composition & zonation • Substrate composition • Mud or muddy sand • Wave energy • low • Water depth • 11-25% SI • Intertidal to 10-12 m • Salinity tolerance • Optimal vs tolerance • Successional stage • Latitude

  10. ECOSYSTEM DEVELOPMENT SANDY SUBSTRATE Halodule/Halophila Thalassia Cymodocea MUDDY SUBSTRATE STABLE ENVIRONMENTAL CONDITION DISTURBANCE Succession

  11. Trophic Support • Large amounts of primary productivity • Supports detrital food webs • Large amount exported to adjacent habitats & ecosystems • Supports some grazing food webs • Direct grazing on roots & rhizomes • Epiphytes grazed

  12. Trophic Interactions • Herbivore/predator control • Distribution & abundance • Population biology • Sexual reproduction • Subtle interactions between producers & consumers • Epiphyte removal & control by grazers • Overfishing of top predators & release of epiphyte grazing pressure

  13. Increased nutrient loading Remineralized seagrass nutrients Epiphyte & phytoplankton increase Seagrass decomposition Seagrass loss Overfishing Decreased recruitment Large predator decline Seagrass loss Small predators increase Epiphytes increase Grazers decrease

  14. Nursery & Refuge • Support more animals than adjacent unvegetated areas • Many animals present as juveniles • Provide protection: increased vegetation = increased protection • Not much evidence for greater growth rates • Role as nursery probably greatest in tropical & subtropical areas • Some species may compete for habitat & refuge

  15. Influence of Habitat Structure • Complex, at several levels of spatial scale • Above & belowground complexity • Macroalgae & epiphytes • Gaps

  16. Spatial Scales • Individual leaf shoots (mm) • Gradient of epiphytic cover (biomass) • Centimeters • Changes in seagrass & algal species • Meters • Patchy distribution & gaps • Kilometers • Patch configuration

  17. Animal Response • Amphipods preferred high SA/volume ratios • Pipefish preferred long leaves & dense meadows • Heterogeneity in meadows increases numbers & species • Mobile predators found along edges

  18. Linkages • Animal movements • Migration to and from beds • Export of detritus

  19. Human Influences • Algal overgrowth due to eutrophication or top predator removal • Introduction of non-native plants & animals • Dredging & filling • Propeller scarring

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