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CHALLENGES OF USING

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Summarize our understanding of benthic assemblages in the Estuary ... Bray-Curtis Index: ecological distance, etc. Clustered sites and species ... – PowerPoint PPT presentation

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Title: CHALLENGES OF USING


1
CHALLENGES OF USING BENTHIC ASSESSMENTS IN SAN
FRANCISCO ESTUARY
Bruce Thompson and Sarah Lowe San Francisco
Estuary Institute
2
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?


3
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

4
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

5
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
6
(No Transcript)
7
Major Benthic Assemblages
8
Major Assemblage Designations
9
Most Common and Abundant Bay Benthos mean abund.
per sample (frequency)
10
ABIOTIC VARIABLES THAT INFUENCE ASSEMBLAGES
11
Main Mesohaline
12
Oligohaline muddy
13
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

14
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

15
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

16
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?

17
EVALUATION OF CANDIDATE INDICATOR METRICS
18
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

19
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
4
Example of Benthic Assessment Procedure
20
EVALUATION OF ASSESSMENT METHOD
21
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

22
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

23
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
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