Title: CHALLENGES OF USING
1CHALLENGES OF USING BENTHIC ASSESSMENTS IN SAN
FRANCISCO ESTUARY
Bruce Thompson and Sarah Lowe San Francisco
Estuary Institute
2PURPOSE
- 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?
3WHAT 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
4IDENTIFICATION 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
5DATA 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)
7Major Benthic Assemblages
8Major Assemblage Designations
9Most Common and Abundant Bay Benthos mean abund.
per sample (frequency)
10ABIOTIC VARIABLES THAT INFUENCE ASSEMBLAGES
11Main Mesohaline
12Oligohaline muddy
13CONCEPTUAL 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
14CONCEPTUAL 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
15HYPOTHESIZED 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
16KEY 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?
17EVALUATION OF CANDIDATE INDICATOR METRICS
18REFERENCE 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
19EXAMPLE 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
20EVALUATION OF ASSESSMENT METHOD
21CONCLUSIONS
- 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
22INFORMATION 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
23SUGGESTED 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