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Seagrasses 2

Seagrasses 2. Light, Eutrophication & Foodwebs = Why seagrasses are used to indicate coastal/estuarine system stability. Light Limitation is the Principal Determinant of SAV Distribution. Water causes light attenuation

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Seagrasses 2

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  1. Seagrasses 2 Light, Eutrophication & Foodwebs = Why seagrasses are used to indicate coastal/estuarine system stability.

  2. Light Limitation is the Principal Determinant of SAV Distribution

  3. Water causes light attenuation Due to: suspended particles (turbidity) and color (CDOM). Turbidity a fnt of phytoplankton and other “particles” (TSS) K = attenuation coefficient Beer-Lambert Law:Iz = Io e-zK Msr with secchi disk or PAR sensors PAR vs PUR Light Environment I Z

  4. IOP AOP • AOP = Secchi depth (m) or attenuation coefficient (Kd) in 1/m • Kd (AOP) depends on inherent optical properties (IOP’s) • IOP’s depend on water quality • IOP’s are a based on absorption (a) and scattering (b) of water+TSS+color+chl a • Radiative transfer modeling provides the link between AOP and IOP’s of the 3 components of attenuation (TSS + color + chl a) • From this relationship a direct link between water quality and light available to SAV can be made. TSS Light Limitation is the Principal Determinant of SAV Distribution Apparent Optical Properties vs Inherent OP’s

  5. Eutrophication • Eutrophication reduces light (phytoplankton and epiphytes), • and increases sulfide-toxicity

  6. WHY SEAGRASS ONLY FOUND IN SHALLOW WATER? 15-25% of Surface Light (Io)

  7. Seagrass loss causes sediments to be resuspended. Sediment resuspension causes water quality to decline -> less light Less light means seagrasses are further prone to sulfide toxicity Results in ongoing losses of remaining seagrasses

  8. (TMDL) $$$ Importance of WQ to SAVConceptual Model (Virnstein et al. 2000)

  9. Food Webs

  10. Fewer Critters if no Grass Shrimp feed in Grassbeds

  11. Reef Halos

  12. Parrotfish and Surgeons

  13. FLORIDA BAY 1997

  14. American wigeon Green-winged teal Redheads CONSUMERS OF SAV • Migrating waterfowl • Important food source • e.g. 5000 seeds in 1 duck • Anatini (dabbling ducks) • Aythyini (diving ducks) • Cygnini (swans)

  15. TOP-DOWN - pred fish Trophic cascade + small fish - mesograzers Eutrophication? BOTTOM-UP + Nutrients • TROPHIC CASCADES: • Jackson et al, Nature 2001 • Heck and Valentine, JEMBE 2006 + algae/p’plankton - light - seagrass

  16. Top-down and bottom-up control

  17. Why we are concerned

  18. 3 papers to read • William C. Dennison; Robert J. Orth; et al. 1993.Assessing Water Quality with Submersed Aquatic Vegetation BioScience, Vol. 43, pp. 86-94. • Kenneth L. Heck Jr, John F. Valentine. 2006. Plant–herbivore interactions in seagrass meadows. Journal of Experimental Marine Biology and Ecology 330: 420–436 • Michelle Waycott, Carlos M. Duarte, et al. 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proceedings of the Natural Academy of Sciences (PNAS) vol. 106 pp. 12377–12381

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