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

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?

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 V ariations may be due to: –life histories –ecological interactions –disturbances

IDENTIFICATION OF ASSEMBLAGES Multivariate methods were used to determine similarities in species composition and abundances among samples 1.Principal Coordinates Analysis –Relationships among samples along environmental gradients 2.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

DATA USED Program Dates N. sites N. samples RMP1994 – BACWA LEMP1994 – BPTCP1992, 94, DWR1994 – CISNet1999 – NOAA-EMAP 2000 –

Oligohaline (muddy) Oligohaline-Mesohaline (transition) Mesohaline (muddy) Polyhaline (muddy) Major Benthic Assemblages

Oligohaline (muddy) Oligohaline (sandy) Oligohaline-Mesohaline (transition) Mesohaline (muddy) Mesohaline (margin) Polyhaline (muddy) Polyhaline (sandy) Major Assemblage Designations

Most Common and Abundant Bay Benthos mean abund. per sample (frequency)

ABIOTIC VARIABLES THAT INFUENCE ASSEMBLAGES

Main Mesohaline

Oligohaline muddy

CONCEPTUAL MODELS OF BENTHIC 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

Sediment Contamination / TOC Gradient Sensitive & Tolerant taxa CONCEPTUAL MODEL Based on Pearson-Rosenberg response model Response to contamination is similar to TOC Position along gradient differs among assemblages Sensitive taxa Species, Abundances, Biomass Tolerant taxa, Higher taxa

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

1.Evaluation of benthic indicator metrics: What do they indicate? 2.Identification of reference samples 3. Evaluation of assessment results: Do results properly reflect reference and impacted conditions? KEY ISSUES DEVELOPMENT OF BENTHIC ASSESSMENTS METHODS

EVALUATION OF CANDIDATE INDICATOR METRICS

REFERENCE SITES 1.Reference samples Not toxic Mostly sensitive species Oligochaete proportion 2. Reference ranges Assessment Assemblage Indicator Polyhaline muddy Mesohaline No. Taxa Tot. Abund Molluscan Taxa Amphipod Taxa Oligochaete abund C. capitata Streblospio benedicti

Example of Benthic Assessment Procedure Site Date N. Taxa Total Abundance Amphipod Taxa C. capitata AV BB152/15/ EBMUD4 9/23/ ZM-2 12/3/ * EXAMPLE OF BENTHIC ASSESSMENT Polyhaline Muddy Assemblage

EVALUATION OF ASSESSMENT METHOD

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

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

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