Development of Benthic Community Indices for Mesohaline Environments
Benthic community assessment is often used as an indicator of ecosystem condition and has become a central element of regulatory programs such as the California’s sediment quality objectives for bays and estuaries. Benthos are the indicators of choice for monitoring and assessment for several reasons, including:
1. Limited mobility makes them indicative of impacts at the site where they are collected.
2. Several animal phyla and classes are sensitive to impacts to their environments and can be used to differentiate certain types of effects.
3. Life-histories are short enough that the effects of one-time impacts disappear within a year but long enough to integrate the effects of multiple impacts occurring within seasonal time scales.
4. Living in the bottom sediments, benthos have high exposure to common anthropogenic impacts, such as sediment contamination, high sediment organic carbon, and low bottom dissolved oxygen.
5. They are important components of aquatic food webs, transferring carbon and nutrients from suspended particulates in the water column to the sediments by filter feeding and serving as forage for bottom-feeding fishes.
For benthic data to be useful in a regulatory context, they must be interpreted in relation to scientifically valid criteria or thresholds that distinguish “healthy” from “unhealthy” benthic communities. While reducing complex biological data to index values has disadvantages, the resulting indices remove much of the subjectivity associated with data interpretation. Such indices also provide a simple means of communicating complex information to managers, tracking trends over time, and correlating benthic responses with stressor data.
To date, benthic indices have been calibrated and validated for two nearshore habitats in California, 1) southern California marine bays, and 2) polyhaline (high salinity) portions of San Francisco Bay. Indices have not been developed for other habitats such as the low salinity mesohaline and tidal freshwater environments. These habitats are particularly challenging because they are naturally subject to relatively broad ranges of conditions (e.g. salinity and dissolved oxygen) and hence the resident organisms are adapted to tolerate environmental stress.
These challenges can be addressed through compilation of robust data sets, careful identification of reference conditions to anchor indices and development of multiple indices that can be used to increase overall sensitivity to detect change in condition.The objective of this project is to develop and calibrate a minimum of three benthic indices for the mesohaline environments of San Francisco Bay. To the extent possible, we will use the initial consultations with experts to provide a foundation for future work on developing an index for the tidal fresh environment.
The objective of this effort is to develop an index for the mesohaline portions of the Bay. This study would assist in our ability to answer the following priority questions for benthos:
1. What are the spatial and temporal patterns of impacts of sediment contamination?
2. Which pollutants are responsible for observed impacts?
3. Are the toxicity tests, benthic community assessment approaches,
Programs and Focus Areas:
Clean Water Program