Seasonal variation in vertical and horizontal movement of the freshwater bivalve Elliptio complanata (Mollusca: Unionidae)

1. Vertical and horizontal movement were studied in the freshwater bivalve Elliptio complanata at a sandy site in an oligotrophic lake over 3 years. Mussel movement did not vary significantly between day and night. On average, between 2 and 8% of 527 mussels moved each month during the ice-free season and the distance travelled by moving mussels averaged 0.6 cm day^–1.
2. Mussels were endobenthic during the winter, emerged from the sandy substrate in mid-May, peaked in sediment surface abundance in July, and descended into the sediments for the winter in September–October. Vertical displacement of mussels was closely correlated with water temperature although daylength may play a role. Mussels apparently move very little beneath the sediment during the winter.
3. The number of mussels moving horizontally at any given time was linearly correlated with daylength, but the distance travelled during a sampling period was related to daylength in a non-linear fashion. Greatest horizontal displacement of epibenthic mussels was found during spring and early summer, coincident with spawning in E. complanata     

Locomotion in Elliptio complanata (Mollusca: Unionidae): a reproductive function?

1. Temporal variation in the spatial aggregation of the freshwater bivalve Elliptio complanata was studied at a sandy site in an oligotrophic lake over three years.
2. Epibenthic populations varied in aggregation over the season bringing animals closer together during spawning. The complex link between movements of mussels and aggregation dynamics suggested a functional reproductive role for horizontal locomotion of unionid mussels in lentic systems.
3. The rate of locomotion did not differ systematically among males, females or hermaphrodites, and was independent of gravidity, whether compared during spawning, after spawning or throughout the ice‐free season.
4. In spite of the high reproductive output of mussels and the energetic cost of locomotion, no relationship was found between the rate of movement of spawning gravid mussels and reproductive output.     

Internal shell annuli yield inaccurate growth estimates in the freshwater mussels Elliptio complanata and Lampsilis radiata

1. The objective of this study was to compare, in freshwater bivalves, growth rates inferred from the spacing of internal annuli to those obtained directly by measuring annual changes in shell length.
2. The unionid mussels studied were Elliptio complanata and Lampsilis radiata from a pond in the north-eastern U.S.A. Age was inferred from internal lines of 157 E. complanata and twenty-five L. radiata . Actual length change was determined from comparisons of annual remeasurements of marked E. complanata ( n = 520) in 1992–95 and L. radiata ( n = 81) in 1993–95.
3. High retrieval rates of painted mussels demonstrated the efficacy of the marking method.
4. Annual length changes determined by remeasurement were significantly lower than annual length changes predicted by length-at-age data from internal annuli. Should this be a common occurrence, past estimates of annual growth based on annuli are probably too large, and unionid mussels may be much older than previously assumed.     

Recruitment and distribution of Dreissena polymorpha (Bivalvia) on substrates of different shape and orientation

Dreissena polymorpha recruitment on artificial substrates was studied in the Włocławek Dam Reservoir (the Vistula River, Poland). Densities on downstream and upstream vertical surfaces of plastic plates differed significantly from each other, with the former settled by more individuals. Vertical and horizontal plates, as well as upper and lower horizontal surfaces were settled similarly. In another experiment mussels settled on flat, convex and concave glass surfaces, directed upstream or downstream. Among the upstream surfaces, the concave ones were the most densely settled. No significant differences in mussel recruitment on various downstream surfaces were found. Thus, substrate shape influenced mussels only when they were exposed to water flow. Mussels were aggregated (Lloyd index > 1) along all the edges of the horizontal plates and along the upper edge of the vertical ones. Such distribution was probably caused by the post‐settlement movement of metamorphosed individuals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Internal shell annuli yield inaccurate growth estimates in the freshwater mussels Elliptio complanata and Lampsilis radiata

1. The objective of this study was to compare, in freshwater bivalves, growth rates inferred from the spacing of internal annuli to those obtained directly by measuring annual changes in shell length.
2. The unionid mussels studied were Elliptio complanata and Lampsilis radiata from a pond in the north-eastern U.S.A. Age was inferred from internal lines of 157 E. complanata and twenty-five L. radiata . Actual length change was determined from comparisons of annual remeasurements of marked E. complanata ( n = 520) in 1992–95 and L. radiata ( n = 81) in 1993–95.
3. High retrieval rates of painted mussels demonstrated the efficacy of the marking method.
4. Annual length changes determined by remeasurement were significantly lower than annual length changes predicted by length-at-age data from internal annuli. Should this be a common occurrence, past estimates of annual growth based on annuli are probably too large, and unionid mussels may be much older than previously assumed.     

Substratum patch selection in the lacustrine mussels Elliptio complanata and Pyganodon grandis grandis

1. Sediment selection was investigated under controlled conditions in two common lake-dwelling species of freshwater mussels (Bivalvia: Unionidae), Elliptio complanata and Pyganodon grandis grandis .
2. Sediment choice was determined in six independent experiments under controlled conditions by distributing mussels randomly or evenly in tanks containing patches of sand and mud, and following their movement among sediment patches in experiments lasting between 30 and 45 days.
3. In all experiments, both species were found most frequently in muddy sediment patches. Movement toward muddy patches occurred rapidly: an average of nearly 80% of Pyganodon grandis grandis were found in mud after 30 days. Elliptio complanata moved rapidly to patches of mud at the start of experiments, but occupation of muddy sediments appeared to decrease after about 30 days.
4. Our results contrast with many field studies that suggest populations of lake-dwelling freshwater mussels infrequently inhabit mud and silt. We therefore postulate that large-scale mussel distribution in lakes is influenced most strongly by factors other than sediment composition.     

DNA adducts as indicators of genotoxic exposure in indigenous and transplanted mussels, Mytilus edulis L. from Icelandic coastal sites

Indigenous mussels, Mytilus edulis, were collected at sites with supposed different amounts of pollution; Reykjavík harbour, Keflavík harbour, Grafarvogur and Hvalfj?rdur (reference), along the south-western coast of Iceland in March 2000. Mussels from Hvalfj?rdur and Reykjavík harbour were also collected in August the same year. Additionally, mussels were transplanted from the reference site to Reykjavík harbour for 6 weeks during both winter and summer for comparison. DNA adducts were analysed by 32P-post-labelling in gills and digestive gland. Highest adduct levels were found in gill tissue from indigenous mussels collected in Reykjavík harbour. Adduct levels in both tissues from mussels collected at the reference site were below or very close to the detection limit during winter, but seemed to increase a little during summer. Mussels from sites with supposed intermediate pollution had intermediate levels of DNA adducts in gills but did not differ from Reykjavík harbour in digestive gland. No increase in adduct levels was observed in mussels transplanted from the reference site to Reykjavík harbour, except for a slight increase in digestive gland during winter. This study shows that 32P-post-labelling analysis of DNA adducts is sensitive enough to be used on indigenous mussels from relatively pristine areas and that adduct levels are increased in harbours/urban sites. However, transplantation of mussels from a clean site to the harbour for 6 weeks did not result in increased adduct levels in gills, the tissue with the highest adduct levels. The results also indicate that seasonal variation in adduct levels may occur.     

Winter movements and activity of signal crayfish Pacifastacus leniusculus in an upland river,determined by radio telemetry

Radio-telemetry was used to study the late autumn and winter movements of twenty adult signal crayfish Pacifastacus leniusculus (32.9–63.8 mm carapace length) an introduced exotic crayfish species, in the upland River Wharfe, northern England. The distances moved during the study varied greatly between individuals (0–328 m). Movements were generally sporadic; crayfish would remain in one position for several weeks and make occasional movements to new locations. Total distances travelled, linear range and ranging area did not differ significantly between males and females. The distance travelled in upstream and downstream directions did not differ significantly and there was no correlation between distance travelled and crayfish size. Several high flow events occurred during the study, but these did not cause any mortality or apparent displacement of crayfish downstream, suggesting that this is not a significant factor in downstream dispersal or mortality of adults of this invasive crayfish species in winter. A marked reduction in large-scale movements occurred in mid-December which coincided with a decline in water temperature. There was a less distinct pattern in local activity which was strongly correlated with water temperature and varied before and after mid-December.     

Evaluation of estrogenic effects of municipal effluents to the freshwater mussel Elliptio complanata

Municipal effluents are an important source of estrogens to the aquatic environment. The purpose of this study was to examine the estrogenicity of municipal effluents to the indigenous freshwater mussel, Elliptio complanata. First, estradiol-binding sites in gonad homogenates were characterized to determine the binding affinity and specificity of estrogens. Mussels were exposed to increasing concentrations of a municipal effluent for 96 h at 15 degrees C. In another experiment, mussels were placed in cages and submerged for 62 days at 1.5 km upstream and 5 km downstream of a municipal effluent plume in the St. Lawrence River. Mussels were harvested for assessment of vitellogenin-like proteins in the hemolymph and determination of total lipid, carbohydrate and protein in the gonad. The presence of specific estrogen-binding sites was found in both male and female gonads. Binding of estradiol to cytosol proteins reached saturation, yielding a dissociation constant of 0.4 nM. Vitellogenin (Vg) levels increased significantly in both the hemolymph and the gonad after exposure to the effluent. Moreover, females appeared to be more sensitive than males to producing Vg. Mussels exposed in situ to contaminated surface waters had higher levels of Vg at the downstream site, again, females had higher levels of Vg than did males. On the other hand, lipid and sugar levels in male gonads were significantly increased at the downstream site. Moreover, mussels at the downstream site had decreased shell growth length and increased total and soft tissue weights. We conclude that municipal effluents contain bio-available xenoestrogens at levels sufficient to elicit effects in freshwater mussels.     

Length‐specific growth rates in freshwater mussels (Bivalvia: Unionidae): extreme longevity or generalized growth cessation?

1. North American lacustrine freshwater mussels (Bivalvia: Unionidae) are one of the world's most imperilled groups of organisms. Knowledge of their age structure and longevity is needed for the understanding and management of mussels. Current methods for age estimation in freshwater mussels are insufficient and may have resulted in an erroneous view of the ages of lacustrine freshwater mussels.
2. We collected growth data through mark-recapture in Minnesota and Rhode Island, U.S.A., examining four lentic populations of three of the most common species of freshwater mussels, Elliptio complanata , Lampsilis siliquoidea , and Pyganodon grandis . Using an inversion of the von Bertalanffy growth equation, we estimated age at length from length-specific growth relationships.
3. In some populations, lacustrine mussels may be much older than previously predicted. Ages predicted from actual growth rates suggest that individuals in some populations frequently reach ages in excess of a century, placing unionid mussels among the Earth's longest-lived animals. Alternatively, if growth has only recently slowed in these populations, generalized growth cessation may be occurring over a broad distributional range of some common North American lacustrine mussels.     

Alterations in DNA metabolism in Elliptio complanata mussels after exposure to municipal effluents

This study sought to examine the genotoxic potential in Elliptio complanata freshwater mussels exposed to a physically and chemically treated municipal effluent before and after ozone treatment. Mussels were continuously exposed to increasing concentrations of the effluents for 14 days. Genotoxicity was determined by tracking changes in key enzymes for purine and pyrimidine synthesis (dehydrofolate reductase and aspartate transcarbamoylase), catabolism of purines (xanthine oxido-reductase) and DNA strand-break levels as determined by the alkaline precipitation assay. Other biomarkers related to xenobiotic biotransformation (cytochrome P4503A and glutathione S-transferase activities), metal metabolism (labile zinc and redox state of metathioneins) and oxidative stress (superoxide dismutase activity) were also determined in the mussels. The data revealed that dehydrofolate reductase activity was reduced by the initial effluent and increased by the ozonated effluent. Aspartate transcarbamoylase activity was significantly induced only with the ozonated effluent. The levels of DNA strand breaks responded in a biphasic manner in mussels exposed to the physically and chemically treated effluent where an initial decrease was observed at a low effluent concentration (3% v/v) followed by an increase in DNA strand breaks at a higher effluent concentration (20%). This response pattern was lost in the ozonated effluent, where only a decrease in DNA breaks was found. Xanthine oxidoreductase activity was not significantly affected but did correlate significantly with dehydrofolate reductase activity. Multivariate factorial and canonical analyses revealed that oxidative stress and metal/xenobiotic metabolism markers were strongly correlated with DNA strand breaks in mussels, suggesting that the presence of metals (zinc) and planar hydroxylated hydrocarbons present in these effluents were strong contributors to the observed response. We conclude that municipal effluents contain a complex mixture of pollutants that could modulate DNA synthesis and repair mechanisms in mussels.     

Predicting zebra mussel fouling on native mussels from physicochemical variables

1. Predictive models of impact are needed for the risk assessment of invasive species. One such species is the Eurasian zebra mussel ( Dreissena polymorpha ), a fouling bivalve that overgrows and kills native mussels (Unionidae) in many North American lakes and rivers. The level of mortality in a native mussel population increases with the fouling intensity – i.e. the mean number of zebra mussels attached to each native mussel.
2. We conducted a multi-site survey within the St Lawrence and Richelieu rivers (Quebec, Canada) to determine whether zebra mussel fouling intensity can be predicted from environmental variables. We found fouling intensity to be positively correlated with calcium concentration [Ca²⁺] and negatively correlated with sediment size, but not affected by local macrophyte cover.
3. A multiple regression model that includes calcium concentration and sediment size explains 86% of variation in fouling intensity across all sites.
4. Analysis of data from invaded sites in North America and Europe revealed a nonlinear relationship in which fouling intensity increases with calcium concentration up to an asymptotic threshold of 24 mg L⁻¹ Ca²⁺.
5. Our results suggest that the community-level impacts of zebra mussels are mediated by abiotic environmental variables and gradients in these variables may provide local habitat refugia for native mussels.     

Seasonal dynamics, movements and the effects of experimentally increased female densities on a population of imaginal Calopteryx aequabilis (Odonata: Calopterygidae)

Abstract. 1. A population of Calopteryx aequabilis Say was sampled daily on a tributary of Canard River, Kings County, Nova Scotia, for the entire flight season in 1983 (29 May to 13 August), using capture–mark–recapture techniques.
2. 2701 sightings of 678 individuals were obtained along a 635 m segment of the stream. A maximum daily count of 174 imagines was reached on 11 June, after which the population gradually declined.
3. More females than males were marked but sexually mature males outnumbered females at the water on all but four days.
4. Immigration rather than local emergence accounted for a large proportion of the population after 20 June.
5. Females were consistently vagile; males were site–specific but occasionally moved long distances between captures.
6. Males and females first marked as tenerals became reproductively mature after about 5 days.
7. We experimentally increased female density on a partially isolated section of the study stream to see how increased female numbers affected the demographics and movement patterns of the population.
8. Residence times for introduced and resident females were similar. In contrast, during a similar introduction of males a year earlier, most introduced males disappeared quickly.
9. Males decreased the distance they travelled daily between captures, their total distance travelled and their range following the introduction, and females showed a tendency (not statistically significant) toward increased movements and dispersal, as predicted.     

Shoals ofDreissena polymorpha as bio-processor of seston

Mussels ofD. polymorpha were collected from mesotrophic lake Partęczyny in which it occurs in form of narrow but very dense shoal. Having transported them to the laboratory live specimens were sorted with respect to size and placed in lake water on artificial substrata made with plexi plates. During the night most of mussels reattached to substrate with byssus threads. The plates covered with mussels were transported to shallow, eutrophic lake Druzno in whichD. polymorpha has not been present in recent years. A set of plates and separate plates were exposed in lake water to which a fine fraction of sediment was added. The resulting concentration of suspension was slightly higher than those found during intensive sediment resuspension. It was observed that during first 10–30 minutes of exposure to suspension mussels kept their valves closed, but after this time they were able to continue filtration. The obtained results showed that the relatively high concentration of sediment added to lake seston did not affect clearance capacity of suspension inD. polymorpha and even enhanced it.     

Hierarchical spatial structure in soft-bottom mussel beds

Mussels (Mytilus edulis L.) are unusual because they thrive in both rocky shore and soft-bottom habitats. Despite their ecological and economic importance, little is known about their spatial structure. Mussels do not generally recruit to bare soft substrate because larvae and postlarvae cannot attach to a bottom of small sediment particles. They attach to hard objects on the sediment surface (especially other mussels), so soft-bottom mussel beds may be spatially organized in ways that are fundamentally different from those on rocky shores. The purpose of our study was to characterize the scales of spatial variability for several mussel abundance parameters in soft-bottom, intertidal M. edulis beds in coastal Maine. We used a random factor nested-ANOVA design of 200 cm² Cores within 1 m² Quadrats within 6 m Transects within Positions within bed Sites along 70 km (euclidean distance) of the Maine coast. Based on the literature and our field observations, we hypothesized that Sites and Positions account for most of the spatial variance in soft-botttom mussel beds. We rejected this hypothesis. Sites and Positions were not important in explaining variation in total mussel density, density of new recruits, or density of larger mussels. Although most of the variance in surface silt-clay fraction did occur at these levels, most mussel variation occurred at smaller spatial scales, specifically at the Quadrat scale for new recruits and total mussels and at the Transect scale for larger mussels. Variance in mussel parameters was not closely linked to the silt-clay fraction of surface sediment or to Site rankings of wind exposure and tidal flow. Variance in total mussel density was due primarily to variance in recruitment. No single scale explained more than about half the mussel variance, and no single scale was best at explaining all the mussel parameters. Greater knowledge about mussel bed spatial variability would be useful because it can help direct scale-dependent sampling regimes, field experiments, and coastal management practices.     

Mussels as bioindicators of trace metal pollution in the Danube Delta of Romania

Specimens of mussels species Anodonta anatina, Unio pictorum, U. tumidus and surfical sediment samples were collected in the summers of 1994 and 1995 from twelve lakes in the Danube Delta, Romania. Whole mussel tissues were analyzed for metals (Ag, As, Cd, Co, Cu, Cr, Ni, Pb, Se and Zn), and sediment samples were subjected to weak acid extraction and to a sequential extraction procedure, and analyzed for Cr, Cu, Ni and Zn. Total mean Cu and Ag concentrations were statistically greater in Unio species than in Anodonta species, but other metal levels did not significantly differ between mussel species. There was a ten fold variation for Cd and Pb and five fold variation for Zn, Ag and Co concentrations in mussels among lakes. Mean concentrations of As, Cu, Se and Zn in mussel tissues varied two fold among lakes. Zn, Co and Cd concentrations in mussels were significantly negatively correlated with distance gradients from the origin of the Delta and with distance from main channels of the Danube. Other metal concentrations in mussels did not correlate with either distance gradient. Trace metal levels in mussel tissues were correlated with those in weak acid and in sequential extractions of sediment. Zn concentrations in the carbonate fraction was the best predictor of Zn concentrations in mussels. Cu and Ni levels in the organic matter and sulfide fraction were the best estimators of Cu and Ni concentrations in mussels. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of the effects of current velocity on mussel feeding and mussel bed stability using an annular flume

An annular flume was used to measure the effect of increasing current velocity on mussel (Mytilus edulis) feeding rate and the stability of mussel beds sampled from the mouth of the Exe estuary (SW England). It was found that, in contrast to earlier flume studies, the feeding rates of mussels from open coast sites were unaffected by current velocities up to 0.8 m s^–1. Algal cell depletion in the water column above mussels was a function of current velocity, increasing with declining currents below 0.05 m s^–1. The erodability/stability of the mussel bed, measured in terms of critical erosion velocity, sediment mass eroded and mean erosion rate, was found to be a function of the nature of the substrate and the density of the mussels. Erosion of mussel beds on sandy substrate showed a non-linear relationship with mussel bed density. In comparison with the sand (0% mussel cover), sediment resuspension was about five and four times higher for 25% and 50% cover, respectively. This was due to the increased turbulence and scouring around the clumps of mussels in low-density parts of the bed, and this resulted in some mussels detaching from the bed. At ~100% mussel cover, the sandy bed was more protected by the dense surface layer of mussels, and none became detached during erosion due to the high number of byssal attachments between individuals. The sediment resuspension from the 100% mussel cover was about three times lower than the 0% cover. Erosion of the bed with 50% cover resulted in burial of a large proportion of the mussels, with a 6 cm increase in sediment level. However, the mussels returned to the surface and recovered in 1–2 days, due to a combination of migration upwards and substrate settlement. Channels on the edge of the main Exmouth mussel bed were characterised by a more stable substrate comprising pebbles and sand with varying mussel densities. At these sites, where mussels experience high current velocities on spring tides (up to 0.9 m s^–1), there was no difference between the erodability of pebble/sand substrate with 0% and 100% mussel cover. The sediment erosion was also lower than the 100% mussel cover on the sandy substrate, particularly at currents >0.4 m s^–1. Sampling of different parts of the mussel bed at Exmouth showed mussels at low densities were made up of smaller clumps with a lower mass ratio of mussels to attached substrate (pebbles/sand), thus providing a greater degree of anchorage. Electronic Publication     

The influence of preceding dive cycles on the foraging decisions of Antarctic fur seals

The foraging strategy of many animals is thought to be determined by their past experiences. However, few empirical studies have investigated whether this is true in diving animals. We recorded three-dimensional movements and mouth-opening events from three Antarctic fur seals during their foraging trips to examine how they adapt their behaviour based on past experience—continuing to search for prey in the same area or moving to search in a different place. Each dive cycle was divided into a transit phase and a feeding phase. The linear horizontal distance travelled after feeding phases in each dive was affected by the mouth-opening rate during the previous 244 s, which typically covered two to three dive cycles. The linear distance travelled tended to be shorter when the mouth-opening rate in the previous 244 s was higher, i.e. seals tended to stay in the same areas with high prey-encounter rates. These results indicate that Antarctic fur seals follow decision-making strategies based on the past foraging experience over time periods longer than the immediately preceding dive.     

The distances travelled by downstream-moving trout fry, Salmo trutta, in a Lake District stream

SUMMARY. 1. Field experiments were performed in the day and night at six modal water velocities (range 10–52cm s⁻¹), using: (i) newly- emerged fry without neutral buoyancy; (ii) older fry in poor condition (weight well below that expected for resident fry); (iii) older fry in good condition (weight similar to that of resident fry); (iv) dead fry.
2. An exponential model described the return rate of fry to the stream bottom; the mean distance travelled downstream varied considerably between the four fry categories, but always increased linearly with increasing water velocity.
3. Results were similar for dead fry and newly-emerged fry released at night; 50% of the fry returned to the bottom in 10–11 s and nearly all returned in c . 70s, the maximum distance travelled ranging from c . 7 m at 10 cm s⁻¹ to c . 37m at 52cm s⁻¹, Newly-emerged fry released in the day returned slightly faster (54s for 99% return to bottom).
4. Older fry in poor condition returned to the bottom slightly faster in the day than at night, but took about 2 min and travelled about twice the distance covered by dead fry. Older fry in good condition returned to the bottom at the fastest rate (3–6s for 50% and c . 30s for the rest), and travelled only about half (at night) or a third (in day) of the distance covered by dead fry.
5. The implications of this investigation are discussed and it is concluded that, apart from water velocity, the age and condition of the fry were the two most important factors affecting their downstream movement.     

Endocrine disruption and health effects of caged mussels, Elliptio complanata, placed downstream from a primary-treated municipal effluent plume for 1 year

Freshwater mussels, Elliptio complanata, were caged in special benthic pens and were immersed at one upstream (Ups) site and two downstream sites (8 and 11 km) of a primary-treated municipal effluent plume for 1 year. The levels of metallothionein-like proteins (MT), lipid peroxidation, protein-free DNA strands and glutathione S-transferase (GST) activity were assayed in digestive gland, gill and gonad tissues to evaluate biological effects and damage. The levels of monoamines (serotonin and dopamine) in nerve ganglia, ATP-dependent transport activity and monoamine oxidase (MAO) activity were also investigated in the homogenates, synaptosomes and mitochondria, respectively. Results showed that significant amounts of sediment accumulated in cages and 82% of mussels survived the yearlong exposure period at the downstream sites. MT-like proteins were induced in all tissues with the following response intensity: gill (3-fold), digestive gland (1.4-fold) and gonad tissues (1.3-fold). Lipid peroxidation decreased (2.5-fold) in digestive gland but increased in gill (1.6-fold) and in gonad tissues (1.5-fold). GST activity was readily increased in digestive gland (2.5-fold), suggesting the presence of organic contaminants in the plume. Levels of protein-free DNA strands did not vary significantly in digestive gland and gill tissues but were significantly reduced in gonad tissues (2.5-fold) relative to the upstream site. In visceral nerve ganglia, both serotonin and ATP-dependent serotonin transport decreased 1.7-fold with a 4-fold increase of 5-hydroxyindole acetate (5-HIAA, a serotonin metabolite) level relative to the upstream site. However, MAO activity was somewhat reduced at downstream sites (0.7- to 0.9-fold of the activity at the upstream site). Dopamine levels were found to be decreased (1.5-fold), but dopamine ATP-dependent transport activity was increased 1.8-fold, suggesting reduced dopaminergic activity. These results indicate that estrogenic chemicals are likely at play, and the increased dopamine and decreased serotonin ATP-dependent transport suggest that the municipal plume was serotonergic for mussels located at the downstream sites. Mussels exposed for 1 year display a complex but characteristic pattern of responses that could lead to harmful health effects including neuroendocrine disruption of reproduction.