Research - Category II: Aquatic Ecosystems

Freshwater Mussels in California's North Coastal Streams; Current Status and Geomorphologic Controls
(Funded 2000-2001)

Principal Investigator: Kurt Cuffey
Department of Geography
UC Berkeley
(510) 643-1641
kcuffey@socrates.berkeley.edu

Executive Summary:
Problem Statement: At present, freshwater mussel populations are declining rapidly in many regions of the United States, yet the current status of California's freshwater mussel populations is poorly documented, and controls on their distribution and abundance are poorly understood. To assess and interpret changes in these mussel populations it is necessary to establish a benchmark for future studies by documenting current populations. Further, it is necessary to understand how physical variability of the river bed habitat affects variability of mussel populations in California's streams.

In addition to substantial population declines, several factors make freshwater mussels a particularly interesting subject for research, and such studies may yield unique insight into the health of California's aquatic ecosystems. Through their dependence on suitable riverine habitat, mussel populations are potentially sensitive to environmental changes throughout a watershed. They also depend on fish hosts (including salmonids) for one essential state in their reproductive cycle. Mussel individuals are also long-lived, with life spans of up to one century. The age distribution of active mussel populations therefore may reveal information about the timing and causes of population changes.

Research Approach: The proposed research focuses strictly on three streams in the northern Coast Ranges, which currently have host fish and where our preliminary investigations have found mussel beds. Here we wish to establish field sites, along six separate reaches, for which we will document and characterize current mussel populations in terms of density and spatial distribution, and statistical distribution of individuals' species, size and age. The interrelations of these variables will be quantified. Further, for one of the streams (South Fork Eel) we propose to place this information in its proper geomorphologic context by also measuring and mapping river channel physical properties which may be important habitat-limiting variables (including substrate type, turbidity and near-bed velocity gradients). Statistical analyses will be used to demonstrate co-variation of populations traits and physical habitat (or lack thereof), and process-based hypotheses for such links will be offered.

Expected Results: The proposed study will improve methods for evaluating stream ecosystem health in the northern Coastal Ranges by introducing a new and potentially informative metric, the status and characteristics of freshwater mussel populations. This study will provide a benchmark from which future changes in mussel population health and age distribution can be inferred and analyzed. Furthermore, the proposed study will illuminate how the large variability of the river bed physical environment causes variability in the distribution and character of mussel beds. This understanding will assist designs for meaningful monitoring programs for these populations, will contribute to interpretations of populations changes, and may ultimately proved important in efforts to preserve these organisms in California streams.