CHALLENGES OF USING

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CHALLENGES OF USING BENTHIC ASSESSMENTS IN SAN
FRANCISCO ESTUARY
Bruce Thompson and Sarah Lowe San Francisco
Estuary Institute
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PURPOSE

• Summarize our understanding of benthic
  assemblages in the Estuary
• Relationships to key abiotic factors
• - Salinity
• - Sediment-type
• - Sediment contamination
• Conceptual models of benthic response
• Application of science to benthic assessments
• Information needs What does RMP need to do?

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WHAT IS AN ASSEMBLAGE ?

• The group of organisms collected within a
  common habitat-type aka community.
• Key attribute is relatively stable species
  composition and abundances within the assemblage
• Variations may be due to
• life histories
• ecological interactions
• disturbances

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IDENTIFICATION OF ASSEMBLAGES

• Multivariate methods were used to determine
  similarities in species composition and
  abundances among samples
• Principal Coordinates Analysis
• Relationships among samples along environmental
  gradients
• Classification (Cluster) Analysis
• Data was edited, transformed, and standardized
• Bray-Curtis Index ecological distance, etc.
• Clustered sites and species
• Produces a dendrogram, and two-way table

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DATA USED
Program Dates N. sites N.
samples RMP 1994 2001 12 80 BACWA LEMP 1994
1997 6 42 BPTCP 1992, 94, 97
22 24 DWR 1994 1998 15
436 CISNet 1999 2000 6 18 NOAA-EMAP
2000 2001 50 50
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Major Benthic Assemblages
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Major Assemblage Designations
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Most Common and Abundant Bay Benthos mean abund.
per sample (frequency)
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ABIOTIC VARIABLES THAT INFUENCE ASSEMBLAGES
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Main Mesohaline
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Oligohaline muddy
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CONCEPTUAL MODELS OFBENTHIC RESPONSE

• Expected field responses for response to
  contaminant mixtures by
• Number of Species, Abundances, Biomass
• Higher Taxa (e.g. amphipods)
• Sensitive and Tolerant Taxa
• Interactions of key abiotic factors
  (e.g.salinity, TOC, grain-size)
• Biological and ecological mechanisms
• Guides development of assessment methods

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CONCEPTUAL MODEL
Sensitive Tolerant taxa
Species, Abundances, Biomass Tolerant taxa,
Higher taxa
Sensitive taxa
Sediment Contamination / TOC Gradient

• Based on Pearson-Rosenberg response model
• Response to contamination is similar to TOC
• Position along gradient differs among
  assemblages

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HYPOTHESIZED MECHANISMS

• Interactions of toxicity and TOC enrichment
  affect taxa with varying tolerances, affects
  ecological interactions
• Contamination, TOC, and physical disturbance have
  similar effects on assemblages.
• Low contamination,TOC
• - Sensitive taxa abundant, few
  tolerant/opportunists (t-o)
• Moderate contamination,TOC
• - Sensitive taxa decrease due to toxicity
• - t-o taxa increase (persist) due to increased
  organic material, below most toxic thresholds
• High contamination TOC
• - Sensitive taxa absent due to acute toxicity
• - t-o taxa reduced, most effects thresholds
  exceeded
• Extremely high contamination
• - Acutely toxic to all organisms

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KEY ISSUES DEVELOPMENT OF BENTHIC ASSESSMENTS
METHODS

• Evaluation of benthic indicator metrics What do
  they indicate?
• Identification of reference samples
• 3. Evaluation of assessment results Do results
  properly reflect reference and impacted
  conditions?

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EVALUATION OF CANDIDATE INDICATOR METRICS
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REFERENCE SITES

• Reference samples
• Not toxic
• Mostly sensitive species
• Oligochaete proportion
• 2. Reference ranges
• Assessment Assemblage
• Indicator Polyhaline muddy
  Mesohaline
• No. Taxa 21 - 66 6 - 18
• Tot. Abund. 97 - 2931 20 -
  1090
• Molluscan Taxa 1 - 4
• Amphipod Taxa 2 - 11
• Oligochaete abund. 0 -
  47
• C. capitata 0 - 13
• Streblospio benedicti 0 - 38

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EXAMPLE OF BENTHIC ASSESSMENT Polyhaline Muddy
Assemblage
Site Date N. Taxa Total Abundance
Amphipod Taxa C. capitata
AV BB15 2/15/1994 24 81
0 1
2 EBMUD4 9/23/1994 60
4866 11 16
2 ZM-2 12/3/1997 0
0 0 0
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Example of Benthic Assessment Procedure
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EVALUATION OF ASSESSMENT METHOD
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CONCLUSIONS

• We know the species composition and abundances in
  the major benthic assemblages in the Estuary.
• We have a basic understanding of the spatial and
  temporal scales of change in these assemblages
• Benthic assessment methods exist and have been
  shown to accurately distinguish reference from
  impacted benthic conditions and reflect
  increasing sediment contamination
• Most benthic impacts in SF Estuary occur near the
  Estuary margins

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INFORMATION NEEDS

• Develop benthic assessment methods for other
  assemblages mesohaline, oligohaline Delta,
  wetlands
• Which contaminant(s) cause observed benthic
  impacts?
• Investigate contaminant specific responses in
  species composition
• Better links between sediment toxicity and
  benthic response

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SUGGESTED RMP PROPOSALS

• 1. Include benthos in RMP status and trends
  program in
• collaboration with other programs
• 2. Conduct special studies to identify causes of
  observed
• benthic impacts
• multivariate analysis of existing data
• lab, field, mesocosm experimental studies