Seagrasses 2

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Seagrasses 2

• Light, Eutrophication Foodwebs
• Why seagrasses are used to indicate
  coastal/estuarine system stability.

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Light Limitation is the Principal Determinant of
SAV Distribution
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Light Environment
I

• 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 LawIz Io e-zK
• Msr with secchi disk or PAR sensors
• PAR vs PUR

Z
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Light Limitation is the Principal Determinant of
SAV Distribution Apparent Optical Properties vs
Inherent OPs
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Profiles (0.5m surface to bottom)
YSI 6600
LiCor 4?
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Beer-Lambert Law Applied
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Why the Deep edge is important
Tidal range
0.5m
1m
2m
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Why the Deep edge is important
Tidal range
0.5m
1m
2m
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Why the Deep edge is important
22 light _at_ 0.5m depth
Tidal range
0.5m
1m
20 area
20
2m
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Eutrophication

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

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WHY SEAGRASS ONLY FOUND IN SHALLOW WATER?
15-25 of Surface Light (Io)
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Seagrass loss causes sediments to be resuspended.
Sediment resuspension causes water quality to
decline -gt less light Less light means seagrasses
are further prone to sulfide toxicity Results in
ongoing losses of remaining seagrasses
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Importance of WQ to SAVConceptual Model
(Virnstein et al. 2000)
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Food Webs
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Fewer Critters if no Grass
Shrimp feed in Grassbeds
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Reef Halos
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Parrotfish and Surgeons
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FLORIDA BAY 1997
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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)

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Eutrophication?
BOTTOM-UP
Nutrients

• TROPHIC CASCADES
• Jackson et al, Nature 2001
• Heck and Valentine, JEMBE 2006

algae/pplankton
- light
- seagrass
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Top-down and bottom-up control
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Why we are concerned
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