The cyanotoxin, microcystin (MC), is known to accumulate in the tissues of diverse aquatic biota although factors influencing exposure, such as feeding habits and seasonal patterns in toxin production, are poorly known. We analyzed seasonal variation in the MC content of primary and secondary consumers, and used dietary analysis (gut contents and stable isotopes) to improve understanding of cyanotoxin transport in food webs. Periods of elevated toxin concentration were associated with peaks in the abundance of genes specific to Microcystis and MC toxin production (mcyD). Peak toxin levels in consumer tissues coincided with peak MC concentrations in seston. However, toxins in tissues persisted in overwintering populations suggesting that potential health impacts may not be limited to bloom periods. Interspecific differences in tissue MC concentrations were related to feeding habits and organic matter sources as pelagic fishes ingested a greater proportion of algae in their diet, which resulted in greater MC content in liver and muscle tissues. Sediments contained a greater proportion of allochthonous (terrestrial) organic matter and lower concentrations of MC, resulting in lower toxin concentrations among benthic detritivores. Among shellfish, the benthic suspension feeder Rangia cuneata (wedge clam) showed seasonal avoidance of toxin ingestion due to low feeding rates during periods of elevated MC. Among predators, adult Blue Catfish had low MC concentrations, whereas Blue Crabs exhibited high levels of MC in both muscle and viscera.

Primary consumers may mitigate or exacerbate the effects of nutrient enrichment by grazing on plant matter and recycling nutrients. Few studies have quantified these effects for a suite of consumers and in the context of other processes regulating plant standing crop and nutrient supply. We quantified the abundance, feeding and diet of zooplankton, benthic filterfeeders, and planktivorous and detritivorous fish in the James River Estuary and found that consumer-mediated fluxes of CHLa and N were small in comparison to other fluxes regulating phytoplankton abundance (production, respiration, advection) and N availability (external inputs, internal recycling). Chlorophyll-a ingestion by consumers was equivalent to 15% of daily phytoplankton production and N recycling by consumers corresponded to 29% of phytoplankton N demand. The bulk of phytoplankton production (74%) was lost to autotrophic and heterotrophic respiration. Recycling of N contained in autochthonous and allochthonous organic matter was sufficient to meet 100% of phytoplankton N demand with external inputs corresponding to 39% of phytoplankton N demand. Experiments using 2000 L outdoor mesocosms with natural plankton communities showed that the presence of consumers (shad) resulted in higher N availability, elevated CHLa and reduced macrozooplankton abundance. Overall, our study showed that the direct effect of consumers on fluxes of CHLa and N was small as the bulk of phytoplankton biomass and N passed to microbial decomposers. However selective grazing by planktivorous fishes reduced zooplankton densities resulting in greater phytoplankton yield at lower nutrient concentrations.

have contributed greatly to this effort through their field work and program responsibilities. Staff at the HRSD Laboratory performed the nutrient and total suspended solids analyses for the large number of samples collected. Their efforts to accommodate unpredictable sample collection schedules are greatly appreciated. The support of the Hampton Roads Planning District Commission, specifically that of K.C. Filippino and Whitney Katchmark, has been instrumental to the success of the program.This study was designed by John Jastram and Kenneth Hyer of the U.S. Geological Survey (USGS), who contributed to the success of the effort by sharing their expertise in waterresources monitoring and data analysis. Chelsea Delsack, James Duda, and numerous USGS hydrologic technicians have spent substantial amounts of time in the field maintaining instrumentation and collecting data, and their efforts are greatly appreciated. Additional thanks are extended to Charles Stillwell and Douglas Chambers for thoughtful and insightful reviews.

Ecologists with the Fairfax County Department of Public Works and Environmental Services, primarily Shannon Curtis and Joe Sanchirico, have contributed greatly to this effort through field work and program responsibilities. Their dedication to the success of this effort has been vital in the progress toward the achievement of program objectives. Staff at the Fairfax County Environmental Services Laboratory performed the nutrient analyses for the large number of samples collected. Their efforts to accommodate unpredictable sample collection schedules are greatly appreciated. This study was designed by Doug Moyer and Ken Hyer of the U.S. Geological Survey (USGS), who continue to contribute to the success of the effort by sharing expertise in water-resources monitoring and data analysis. Alyssa Thornton and numerous USGS hydrologic technicians have spent substantial amounts of time in the field maintaining instrumentation and collecting data, and their efforts are greatly appreciated. We would also like to thank Guoxiang Yang for his analysis of long-term trends in continuously collected specific conductance data.

contributed greatly to this study. Their program coordination, field expertise, and scientific insights have been critical to the success of this effort and will continue to be relied upon in future study years. Staff at the Fairfax County Environmental Services Laboratory performed the nutrient analyses for most samples collected; their work is sincerely appreciated. Many U.S. Geological Survey (USGS) staff have contributed to the design, operation, and interpretation of this study since its inception in 2007. These combined efforts have produced years of consistent data collection and foundational knowledge that greatly benefited this report. Technical reviews by Doug Chambers of the USGS and Jonathan Duncan of the Pennsylvania State University strengthened this report and are greatly appreciated. The authors also thank Kaycee Faunce of the USGS for helping identify and communicate the findings of this research.