Seagrasses 2
Light, Eutrophication & Foodwebs =
Why seagrasses are used to indicate coastal/estuarine system stability.
Light Limitation is the Principal Determinant of SAV Distribution
Light Environment
• 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
Z
I
Light Limitation is the Principal Determinant of SAV Distribution
Apparent Optical Properties vs Inherent OP’s
• 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
AOPIOP
•Eutrophication reduces light (phytoplankton and epiphytes),
•and increases sulfide-toxicity
Eutrophication
WHY SEAGRASS ONLY FOUND IN SHALLOW WATER?
15-25% of Surface Light (Io)
Seagrass loss causes sediments to be resuspended. Sediment resuspension causes water quality to decline -> less lightLess light means seagrasses are further prone to sulfide toxicityResults in ongoing losses of remaining seagrasses
Importance of WQ to SAVConceptual Model (Virnstein et al. 2000)
(TMDL)
$$$
Food Webs
Fewer Critters if no Grass Shrimp feed in Grassbeds
Reef Halos
FLORIDA BAY 1997
Green-winged teal American wigeon
Redheads
• Migrating waterfowl• Important food sourcee.g. 5000 seeds in 1 duck Anatini (dabbling ducks) Aythyini (diving ducks) Cygnini (swans)
CONSUMERS OF SAV
Eutrophication?
+ Nutrients
BOTTOM-UP
+ algae/p’plankton
- seagrass
- light
TOP-DOWN
- mesograzers
+ small fish
- pred fishTrophicTrophiccascadecascade
TROPHIC CASCADES:•Jackson et al, Nature 2001
•Heck and Valentine, JEMBE 2006
Top-down and bottom-up control
Why we are concerned
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
