X2 reflects many ecosystem factors
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X2 reflects many ecosystem factors
X2
Physical Habitat changes
Water Quality
Contaminant effects
Larval dispersal
Adult migration and spawning
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X32
X2
X22 X12
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1967-871988-2000
1982-2000 (DS)All Years
Fish- X2
RelationshipsFrom Kimmerer 2002 1
2
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0
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50 60 70 80 90
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50 60 70 80 90
-2
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Bay Shrimp
Striped BassSplittail
Longfin smeltDelta smelt
Herring Am. Shad
Flounder
Log
Abu
ndan
ce o
r S
urvi
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X2 (km)
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X2 observations
Fish:X2 Relationships maintained across 35 years of data
Massive change in food web had little impact on relationships
Mechanisms remain unclear and probably diverse
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Future Directions
• Research strategy under development (CBDA grant to Kimmerer and Bennett)– Limited ability to test mechanisms– Reduced funding likely to restrict studies
• Discussion with local biologists suggest that, for many possible mechanisms, variability is likely important (Estuarine Ecology Team July 2004)
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Conclusions
• X2 seems to be working to protect aquatic resources from reductions in estuarine habitat quality
• Protecting both mean and variance of X2 seem important
• Unlikely that more effective ways to protect resources will be found soon
• Continued data collection is vital for meaningful review
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• Kimmerer, W.J. 2002. Physical, biological, and management responses to variable freshwater flow into the San Francisco estuary. Estuaries 25:1275-1290
• Jassby, A.D., W. J. Kimmerer, S.G. Monismith, C. Armor, J.E. Cloern, T.M. Powell, J.R. Schubel, and T.J. Vendlinski. 1995. Isohaline position as a habitat indicator for estuarine populations. Ecological Applications 5:272-289
Main references