X2 reflects many ecosystem factors

X2

Physical Habitat changes

Water Quality

Contaminant effects

Larval dispersal

Adult migration and spawning

X32

X2

X22 X12

1967-871988-2000

1982-2000 (DS)All Years

Fish- X2

RelationshipsFrom Kimmerer 2002 1

2

3

4

1

2

3

4

0

1

2

3

2

3

4

5

0

1

2

3

2

3

4

5

50 60 70 80 90

0

1

2

3

50 60 70 80 90

-2

-1

0

1

Bay Shrimp

Striped BassSplittail

Longfin smeltDelta smelt

Herring Am. Shad

Flounder

Lo

g A

bu

nd

an

ce

or

Su

rviv

al

X2 (km)

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

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)

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

• 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