Survival Of Mussels Research Articles

Effects of epibiotic algae on the survival, biomass and recruitment of mussels, Mytilus L. (Bivalvia: Mollusca)

Habitats composed of living ‘ecosystem engineers’, such as mussels, are subject to direct and indirect interactions with organisms that live among them. These interactions may affect the presence and structure of habitat, and hence, the associated taxa. We examined the direct effects of epibiotic algae on the survival, biomass and recruitment of mussels ( Mytilus L.) on the west coast of Ireland. A field experiment showed that the presence of epibiotic fucoid algae reduced the likelihood of survival of mussels during storms. We also found that the strength of attachment of mussels did not increase in the presence of epibionts. Another in situ experiment revealed that the presence of ephemeral epibiotic algal mats had no effect on the biomass of host mussels, suggesting no effect on mussel growth or production. The abundance of small mussels (< 5 mm) covaried with cover of epibiotic algae at one location, but experimental results suggest no direct effect of the algae on recruitment unless through the action of chemical cues which linger after the removal of algae. We have identified a negative direct interaction between epibiotic algae and mussels on exposed rocky shores, which may often be characterised by bottom-up regulation. It is thought that positive interactions may be more important on more sheltered or sedimentary shores where top-down processes are more likely to dominate.

Factors Affecting Survival and Growth of Juvenile Freshwater Mussels Cultured in Recirculating Aquaculture Systems

AbstractSeasonal differences in glochidial maturity, substrate, and diet were studied to determine how these factors affect the survival and growth of juvenile freshwater mussels. Comparisons were made between juveniles produced in the fall and spring of the year; cultured in sediment, sand, or without substrate; and fed either of two species of small (5–10‐μm) green algae. The survival and growth of endangered juveniles of oyster mussel Epioblasma capsaeformis were compared with those of a common, seemingly more robust species, the rainbow mussel Villosa iris. The growth of rainbow mussel juveniles was significantly greater than that of oyster mussel juveniles (P &lt; 0.001). The survival and growth of oyster mussel juveniles were significantly greater when propagated in the spring, that is, when glochidia were mature and would normally be released, than in fall (P &lt; 0.001). Survival and growth of juveniles of both species were significantly greater when they were cultured in a sediment substratum rather than sand or no substratum (P &lt; 0.001). No differences (P &gt; 0.05) were observed in survival and growth of juveniles fed algal species Neochloris oleoabundans or Nannochloropsis oculata. In the spring of the year, juvenile oyster mussels achieved a survival of 29.6% and mean length of 664 μm at 60 d of age, whereas at the same age rainbow mussel juveniles exhibited a survival of 25.1% and a mean length of 1,447 μm.

Effects of seed size and density on growth, tissue-to-shell ratio and survival of cultivated mussels ( Mytilus edulis) in Prince Edward Island, Canada

In suspended aquaculture, the size of mussel seed and the density at which these mussels are placed in socks are two important factors affecting mussel production. However, the effect of these two factors has yet to be examined simultaneously. We conducted two large-scale field experiments to assess the effect of seed size and initial density on growth, tissue-to-shell ratio and survival of blue mussels ( Mytilus edulis) grown on longlines. Experimental mussel sites were set up during the autumn of two consecutive years in two bays on the north shore of Prince Edward Island, Canada. At each site, socks containing combinations of three seed sizes (small, medium and large) at two initial densities (low and high) were deployed and monitored over time. Small seed grew faster than large seed and often reached commercial size in the same time period. Furthermore, initial density generally did not affect shell growth. During the pre-spawning period following the autumn deployment, seed at low initial density had a higher tissue-to-shell ratio than seed at high initial density, especially for large seed. This effect of initial density disappeared in early summer. Early in the experiments (< about 10 months), mussel survival on socks was affected by seed size only: small seed generally had lower survival rates than larger seed. Late in the experiments (> 10 months), there appeared to be an interaction between seed size and initial density on mussel survival: survival of small seed generally decreased with increasing initial density, while survival of large seed was not affected by initial density. Since large seed tended to be packed at lower initial density than small seed, lack of crowding was likely responsible for the absence of density-dependent loss. Our study thus assessed different seeding strategies, and results were generally consistent across years and sites.

Effect of water flow and oxygen concentration on early settlement of the New Zealand green-lipped mussel, Perna canaliculus

Early settlement patterns of the mussel Perna canaliculus were investigated within water tanks exposed to different water flow regimes and oxygen concentrations. Hatchery-reared larvae and wild juvenile mussels (0.5–3.0 mm in maximum length) collected from the surf zone and subtidal habitats at Ninety Mile Beach, northern New Zealand, were used for the laboratory settlement experiments. Combinations of three water flow regimes (∼1, 5, and 10 cm/s) and three oxygen concentrations (∼6, 9, and 12 mg/L) were established within replicated tanks, each containing standardized, artificial filamentous substrata. The mortality and settlement of larvae and re-settlement of juveniles were recorded for each tank during a 24-h period. Mortality was highest at low water flows, and decreased consistently with increasing water flows for larvae (∼55–5%) and juvenile mussels (∼70–50% for subtidal, and 23–4% for surf zone mussels), but increasing oxygen concentration caused a decrease only in the mortality of the larvae, not the juveniles. For larvae, settlement increased with increasing water flow, both on the filaments and on the tank rims at the water surface, and higher oxygen concentrations appeared to enhance larval settlement. Hourly larval settlement counts within filaments suggest that exploratory behavior (i.e., settlement and re-settlement) takes place within low and medium water flows, but not under high water flows. However, settlement always was higher within filaments compared to the tank rims for larvae, and for juveniles collected from the surf zone and subtidal habitats. While oxygen concentration did not significantly affect settlement of juveniles, mussels collected from the surf zone had slightly higher settlement rates than those collected from subtidal habitats. This study further illustrates the complexity of larval and juvenile settlement and re-settlement processes for P. canaliculus. In particular, pre-harvesting history/environment, as well as the physical conditions present after harvesting, may determine survival and re-settlement of mussels within natural and farm conditions.

Effects of Water Level Fluctuations on Zebra Mussel Distribution in a Lake Erie Coastal Wetland

ABSTRACT In May–August 2002, we examined how seasonal water level changes and frequent wind-driven seiches limited the amount of habitat for zebra mussels (Dreissena polymorpha) in a Lake Erie coastal wetland. We counted numbers of veligers that colonized artificial substrates at different depths (1–17 cm, 18–34 cm and >34 cm below the water surface). Water levels decreased during the summer, and by August colonization plates set at 1–17 cm were exposed 85% of the time, plates set at 18–34 cm were exposed 15% of the time, but plates set at >34 cm were rarely exposed. The highest densities (numbers/m2) of colonization occurred in June (7176.1) and August (3119.5), and this bimodal pattern has been observed in other Great Lake habitats. Densities were highest at >34 cm depths (5552.7), intermediate at 18–34 cm (2802.1) and lowest at 1–17 cm (410.8). Veliger numbers on some plates in deep water levels were as high as 10,000/m2, which are similar to densities in the Great Lakes. We also measured survivorship of adult mussels in wire mesh cages from 28 July to 25 August. Most (~90%) adult zebra mussels survived in both 18–34 cm and >34 cm water levels, but only ~2% survived in 1–17 cm water levels. We determined the percent of Crane Creek Marsh in each of the three water depth zones and estimated that water level changes prevent zebra mussels from inhabiting 62% of this coastal wetland. The low survival of zebra mussels may be a reason why abundant unionids have recently been found in this and some other Great Lake coastal wetlands.

Population size and structure of three mussel species (Bivalvia: Unionidae) in a northeastern German river with special regard to influences of environmental factors

Unionid mussels are of great ecological importance in running and standing waters, however their populations declined continually during the 20th century. In order to collect more data on the situation of these mussels in running waters, the populations of Anodonta anatina, Anodonta cygnea, and Unio tumidus (Unionidae) were investigated in the northeastern German river Ryck from 1996 to 1998. At three sampling stations along the river, the mussel stocks as well as sediment and water properties were analyzed. In this river abundances of up to 138.7 indiv./m2 were detected. The average population densities varied from 10.9 to 34.9 indiv./m2. More critically however, the age structures showed significant signs of irregular reproductive success and overaging. Consequently, the mussel stocks are going to decline, and furthermore, U.tumidus should be listed as an endangered species in the Ryck river. Negative influences on bivalves can be expected from sporadically occurring low oxygen and high ion concentrations in the water. But after all, the conditions within the sediments seem to be decisive for the survival of juvenile mussels and thus for the age structure of the populations.

Scale‐Dependent Feedback and Regular Spatial Patterns in Young Mussel Beds

In the past decade, theoretical ecologists have emphasized that local interactions between predators and prey may invoke emergent spatial patterning at larger spatial scales. However, empirical evidence for the occurrence of emergent spatial patterning is scarce, which questions the relevance of the proposed mechanisms to ecological theory. We report on regular spatial patterns in young mussel beds on soft sediments in the Wadden Sea. We propose that scale-dependent feedback, resulting from short-range facilitation by mutual protection from waves and currents and long-range competition for algae, induces spatial self-organization, thereby providing a possible explanation for the observed patterning. The emergent self-organization affects the functioning of mussel bed ecosystems by enhancing productivity and resilience against disturbance. Moreover, self-organization allows mussels to persist at algal concentrations that would not permit survival of mussels in a homogeneous bed. Our results emphasize the importance of self-organization in affecting the emergent properties of natural systems at larger spatial scales.

Impact of an invader: epizootic American slipper limpet Crepidula fornicata reduces survival and growth in European mussels

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 286:13-19 (2005) - doi:10.3354/meps286013 Impact of an invader: epizootic American slipper limpet Crepidula fornicata reduces survival and growth in European mussels David W. Thieltges* Alfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt, Hafenstrasse 43, 25992 List, Germany *Email: dthieltges@awi-bremerhaven.de ABSTRACT: Worldwide introductions of species have raised concern about ecological and economic impacts. However, research on actual impacts of introduced species on native biota is rare. The American slipper limpet Crepidula fornicata (L.) was unintentionally introduced to Europe in the 1870s with oysters imported for farming purposes. Since C. fornicata is a filter-feeder, trophic competition and associated negative effects when epizootic on bivalves have been assumed. This study is the first to experimentally test in the field effects of the epizootic C. fornicata on survival and growth of its major basibiont in northern Europe, the blue mussel Mytilus edulis L. In 2 field experiments of 12 wk each, epigrowth by C. fornicata resulted in a 4- to 8-fold reduction in survival of mussels, equivalent to a mortality of 28 and 30%, respectively. Shell growth in surviving mussels with attached C. fornicata was 3 to 5 times lower compared to unfouled mussels, but similar to that with artificial limpets. As a causative agent, interference competition in the form of changes in small-scale hydrodynamics due to C. fornicata stacks is suggested. This may result in a high energy expenditure for byssus production of mussels. Trophic exploitation competition does not seem to be relevant. In general, interference and not exploitation competition is suggested to be the major impact of epizootic C. fornicata on its basibionts in Europe. However, the generality of this assumption has to be verified by investigating different C. fornicata-basibiont associations. This stresses the need for a species-by-species approach under diverse environmental settings in assessing impacts of introduced species. In the case of M. edulis, this study shows that C. fornicata has the potential to act as an important mortality factor. KEY WORDS: Crepidula fornicata · Mytilus edulis · Impact · Introduced species · Epibiosis · Interference competition · Mortality · Growth Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 286. Online publication date: February 02, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Evaluation of a nonlethal technique for hemolymph collection in Elliptio complanata, a freshwater bivalve (Mollusca: Unionidae)

Hemolymph, the circulatory fluid of bivalves, transports nutrients, respiratory gases, enzymes, metabolic wastes, and toxicants throughout the body. Hemolymph can provide information pertinent to health assessment of animals or populations, but is not commonly used in freshwater bivalves partly because of the lack of tested, practical techniques for its nonlethal collection. The objective of this study was to evaluate the effect of hemolymph collection on the growth and survival of Elliptio complanata, a freshwater bivalve (Unionidae). We describe a simple technique for the collection of hemolymph from the anterior adductor muscle sinus of E. complanata. To evaluate the effect of hemolymph sampling on mussel survival and growth, 30 mussels sampled using the technique and 30 unsampled controls were followed for 3 mo post collection. Nine animals were sampled 3 times over 7 mo to monitor effects of repeated sampling. No negative impacts on survival or growth were observed in either the singly or repeatedly sampled animals. We also compared the composition of hemolymph collected from the adductor muscle sinus with that collected from the ventricle of the heart. Calcium levels and cell count of hemolymph obtained from the adductor sinus and ventricle were significantly different. There was no significant difference between collection sites for magnesium, phosphorus, ammonia, protein, sodium, potassium, or chloride. We conclude that collection of hemolymph from the adductor sinus is safe for sampled E. complanata and should be explored as a relatively non-invasive, and potentially useful, approach to the evaluation of freshwater mussel health.

Drought Responses of Freshwater Mussels (Unionidae) in Coastal Plain Tributaries of the Flint River Basin, Georgia

ABSTRACT During extreme drought conditions, mussel survival and habitat conditions were monitored weekly at nine locations representing a gradient in stream size in the lower Flint River basin, Georgia, USA. Cumulative unionid mortality ranged from 13 to 93% among sites, and was associated with low flow velocity (below 0.01 m/s) and dissolved oxygen concentrations below 5 mg/L. Species assemblages demonstrated differential mortality under declining dissolved oxygen conditions. Riffle and medium-large stream mussel assemblages had greater mortality than generalist assemblages under reduced dissoloved oxygen (DO < 5 mg/L). Mussel community composition at medium-sized sites shifted toward greater dominance of generalist species and lower proportions of riffle and medium-large stream species. At other sites, community structure changed little, likely due to the dominance of drought-resilient species in small streams and less detrimental changes in stream habitat conditions in large streams. Low flow conditions and severe drought adversely affected mussel distributions and assemblages, particularly in high diversity, medium-sized streams.

Seasonal variations of physiological and cellular biomarkers and their use in the biomonitoring of north adriatic coastal waters (Croatia)

Lysosomal membrane stability, the content of neutral lipids and lipofuscin as cellular biomarkers were measured in the digestive gland of mussels, Mytilus galloprovincialis Lam., during a one year survey at selected sites along the coast of the northern Adriatic. The ability of mussels to survive in air as a general physiological response was tested at the same sites. Annual changes of sea temperature, salinity, O 2 saturation, pH and chlorophyll a concentration were measured and the effects of these environmental factors on the biomarkers selected for this study were determined. Survival of mussels after aerial exposure was significantly ( p<0.05) reduced in mussels collected from the contaminated harbors of Pula and Rijeka compared to clean control sites. Lysosomal membrane stability of mussels from urban and industrial areas was also lower indicating exposure to different environmental contaminants. At the same sites, the content of neutral lipids and lipofuscin in digestive cells was significantly higher compared to the reference sites, suggesting alterations in lipid metabolism and contaminant-induced peroxidation of cell membranes. The greatest influence of natural environmental factors was observed for the aerial survival of mussels and the neutral lipids and lipofuscin content in the digestive gland, indicating that the annual cycles of biomarker responses should be well understood for a correct interpretation of biomonitoring results.

Allozyme Loci Selection in the Pacific Mussel Mytilus trossulus under Stressful Conditions

The allozyme variability for 15 loci in two samples of the Pacific mussel Mytilus trossulus collected from a single giant cluster was investigated using the method of gel electrophoresis. One sample was subjected to short-term anaerobic stress and then to a longer aerobic stress, leading to the death of about 85% of the individuals. At some of the loci, significant differences in the genotypic and allele frequencies were found between the samples. The results are suggestive of the differential survival of mussels with different genotypes and alleles at some of the surveyed loci under stress. Our data are in agreement with the hypothesis of the adaptive significance of allozyme polymorphism.

Estimating Survival and Recruitment in a Freshwater Mussel Population Using Mark-recapture Techniques

We used a mark-recapture method and model averaging to estimate apparent survival, recruitment and rate of population growth in a native freshwater mussel population at a site on the Cacapon River, which is a tributary to the Potomac River. Over 2200 Elliptio complanata, E. fisheriana and Lampsilis cariosa were uniquely tagged over a period of 4 y. Recapture probabilities were higher in spring and summer than in winter except for L. cariosa which had a low probability of recapture regardless of time of year. All three species had high annual adult survival rates (>90%) with lower estimated survival of small (≤55 mm) mussels (43%–69%). The variation in apparent survival over time was similar for all three species. This suggests that whatever environmental variables affect survival of mussels in this site affected all three species the same. Recruitment rates were low (1–4%) for both E. complanata and L. cariosa, with E. fisheriana having several periods of high (15–23%) recruitment. Distribution within the site was affected by both downstream and upstream movement, though movement rates were generally <1%. Average population growth rates for E. complanata (λ = 0.996, se = 0.053), L. cariosa (λ = 0.993, se = 0.076) and E. fisheriana (λ = 1.084, se = 0.276) indicated static populations. Population growth rate approximating 1.0 suggests this site supports a stable freshwater mussel population through a life history strategy of low but constant recruitment and high annual adult survival.

Effects of hypoxia on predator-prey interactions between juvenile Carcinus aestuarii and Musculista senhousia

The impact of hypoxia upon predator-prey interactions between juvenile Mediterranean shore crabs Carcinus aestuarii and the mytilid Musculista senhousia was investigated in laboratory and mesocosm experiments. These species are among the most abundant macrobenthic organisms in the Sacca di Goro, a lagoon in the Po River deltaic system (Adriatic Sea, Italy). The effect of normoxia and hypoxia on juvenile C. aestuarii predatory behaviour was examined in laboratory experiments; factors were prey size (small, medium and large) and oxygen level (normoxic: >6.0 mg O 2 l -1 ; moderately hypoxic: 3.0 to 1.5 mg O 2 l -1 ; severely hypoxic: 6.0 mg O 2 l -1 ; severely hypoxic: <1.5 mg O 2 l -1 ). Consumption rates of C. aestuarii were lower under hypoxia, resulting in reduced mortality rates of mussels. Predation was inversely dependent. Short-term hypoxia, therefore, reduced the ability of crabs to forage on mussels efficiently and increased mussel survival, probably reducing the transfer of bivalve prey to predatory crabs.

Effect of additions of dietary triacylglycerol microspheres on growth, survival, and settlement of mussel ( Mytilus sp.) larvae

This study reports the effect of additions of dietary microspheres of triacylglycerol (TAG, extracted from the diatom Chaetoceros muelleri) on larval development and settlement of Mytilus sp. The first experiment showed that mussel larvae successfully ingested TAG microspheres as soon as they acquired the ability to feed from exogenous sources. In a second experiment, larvae were fed for 28 days on diets consisting of 0, 1, 20, or 50% TAG microspheres (based on the cell concentration of a full algal ration) added as partial replacements for a ration of Isochrysis sp. (T-ISO). Lipid content and growth of larvae fed on a diet composed of 20% TAG were higher than those of the control groups, whereas survival was negatively affected. No growth or survival effect was detected with larvae fed on a diet composed of 1% TAG, whereas high mortality after 14 days was observed for larvae fed on a diet composed of 50% TAG microspheres. In a third experiment, 22-day-old larvae were fed on rations of Isochrysis sp. supplemented with 0, 1, 10, 20, 50, and 100% TAG for 2 days and allowed to settle for a 7-day period. TAG content of the larvae increased with TAG added to the diet until a saturation threshold was reached between a 20 and 50% supplementation level. Similarly, free fatty acid (FFA) content increased with TAG level in the diet and was linearly correlated with TAG content of larvae. Increased levels of FFA in larvae were attributed to digestion of TAG supplements. Settlement success and survival of larvae were not affected by diet; however, regression analysis revealed that TAG level in pre-metamorphic larvae explained 28% of survival variability among cultures.

Effects of pore-water ammonia on in situ survival and growth of juvenile mussels (Lampsilis cardium) in the St. Croix Riverway, Wisconsin, USA.

We conducted a series of in situ tests to evaluate the effects of pore-water ammonia on juvenile Lampsilis cardium in the St. Croix River (WI, USA). Threats to this river and its associated unionid fauna have accelerated in recent years because of its proximity to Minneapolis-St. Paul, Minnesota, USA. In 2000, caged juveniles were exposed to sediments and overlying water at 12 sites for 10 d. Survival and growth of juveniles was significantly different between sediment (mean, 47%) and water column (mean, 86%) exposures; however, these effects were unrelated to pore-water ammonia. During 2001, juveniles were exposed to sediments for 4, 10, and 28 d. Pore-water ammonia concentrations ranged from 0.3 to 62.0 microg NH3-N/L in sediments and from 0.5 to 140.8 microg NH3-N/L within exposure chambers. Survival (mean, 45, 28, and 41% at 4, 10, and 28 d, respectively) and growth (range, 3-45 microm/d) of juveniles were highly variable and generally unrelated to ammonia concentrations. Although laboratory studies have shown unionids to be quite sensitive to ammonia, further research is needed to identify the route(s) of ammonia exposure in unionids and to understand the factors that contribute to the spatial variability of ammonia in rivers.

Effect of temperature on the development, growth, survival and settlement of green musselPerna viridis(Linnaeus, 1758)

The eiect of temperature on the development, growth, survival and settlement of Perna viridis was studied under controlled conditions to provide information needed for the development of commercial hatchery technology for green mussel P. viridis. Total mortality of the larvae occurred after 24 h at temperatures of 33 1C and 35 1C. At 24 1C, larvae took longer to settle than at temperatures of 27 1C, 29 1C and 31 1C. For optimum larval development (8^13 h), growth (17.270.84 mmday^1) and survival (55.27 0.84%), a hatchery rearing temperature of 31 1C is required. For settlement no signi¢cant diierence was seen between the percentage settlement at 29 1C (49.373.34%) and 31 1C (45.871.76%). However, the process of settlement began and ended earlier at 29 1C (from15 to18 days) thanat 31 1C (from18 to 20 days). Thus for larval settlement a temperature of 29 1C is recommended.

EVALUATION OF RELOCATION OF UNIONID MUSSELS TO IN SITU REFUGIA

The aim of this study was to evaluate the recovery and survival of four species of unionid mussles [pimpleback, Quadrula pustulosa pustulosa (I. Lea, 1831); spike, Elliptio dilatata (Rafinesque, 1820); Higgins eye, Lampsilis higginsii (I. Lea, 1857); and pocketbook, Lampsilis cardium (Rafinesque, 1820)] that were experimentally relocated to in situ refugia in the St Croix River of Minnesota and Wisconsin, USA. In 1996, 150 mussels of each of the first three species (450 total) were relocated to three 5 � 5 m study grids (Site A), one near Lakeland, Minnesota, which served as a source-site control, and two in the experimental refuge 48 km upstream, near Franconia, Minnesota. In a second relocation in 1997, L. cardium was substituted for L. higginsii and 150 mussels of this and each of the other two species (450 total), were relocated to two study grids (Site B). The source site control was near Sunrise, Minnesota and the experimental refuge was 14 km downstream near Almelund, Minnesota. Mussel recovery, survival and substratum characteristics were evaluated annually at Site A for 2 years and for 3 years at Site B. Mean annual recovery of all three species ranged from 90 to 100% at Site A, and from 34 to 70% at site B. The mean annual survival of recaptured mussels ranged from 85 to 100% at Site A, and from 88 to 100% at Site B. The textural characteristics of the substratum differed significantly between the control and the two refuge locations at the beginning of the study, but did not differ from this initial status among subsequent years at Site A. At Site B, there was a significant shift in textural characteristics from large to smaller fractions over the four years. The relatively high survival of mussels during this study demonstrates the importance of proper handling and transport protocols when relocating mussels and the selection of suitable relocation habitat with stable substratum. When established correctly, in situ refugia may be a viable tool for preserving unionid mussels.

Native eelgrass Zostera marina controls growth and reproduction of an invasive mussel through food limitation

In southern California, native eelgrass Zostera marina L. and the invasive non-native mussel Musculista senhousia have dynamic complex interactions. Although high densities of M. sen- housia inhibit the growth of eelgrass, mussel survival and growth decline with increasing eelgrass shoot density and patch size. The correlation of these eelgrass attributes with local concentrations of chlorophyll a and water flow speeds suggested that the mussels, which feed on phytoplankton deliv- ered by water currents, might suffer food limitation inside large eelgrass beds. By supplementing phytoplankton to M. senhousia living in eelgrass, we confirmed this hypothesis: mussels grew 50% faster when food availability was enhanced. Lab and field experiments investigating the effects of food limitation on growth and reproduction of M. senhousia showed that mussels respond by reduc- ing shell growth, and subsequently fecundity. We found no evidence that mussels reallocated resources preferentially to reproduction when food was limited. Our results highlight how the effects of anthropogenic perturbations that currently threaten eelgrass populations directly could be magni- fied by interactions with a non-native species. Eelgrass habitat fragmentation and increasingly frequent phytoplankton blooms resulting from coastal development and eutrophication have well- described direct negative effects on eelgrass. By increasing phytoplankton availability to M. sen- housia, such perturbations also indirectly affect eelgrass by acting to enhance mussel survival and growth, magnifying the negative effects of the mussel on Z. marina.

Support of Science-Based Decisions Concerning the Evaluation of the Toxicology of Mixtures: A New Beginning

The Clinch River contains one of the most diverse freshwater mussel assemblages in the United States, with 46 extant species, 20 of which are listed as federally endangered. In a 91 km section of the Clinch River, mussel densities have severely declined at key sites from 1979 to 2014 (zone of decline), compared to other river sections that support high density and stable mussel populations (zone of stability). Coal mining has occurred in tributary watersheds that drain to the zone of decline since the late nineteenth century. To determine differences in survival, growth, and organ (gills, digestive glands, kidneys, and gonads) tissue health between the river zones, laboratory-propagated mussels were deployed to cages for one year at four sites each within the zones of mussel stability and decline. Means of growth and survival of mussels in the zone of stability were significantly greater than in the zone of decline, and mean fractions of kidney lipofuscin in mussels in the zone of decline was significantly greater than in the zone of stability. Water concentrations of K+, Na+, Al, and Mn were significantly greater in the zone of decline than in the zone of stability. Statistical correlation results indicated that mussel survival was positively associated with concentrations of Mn in water, and kidney lipofuscin was negatively associated with concentrations of dissolved K+, SO42−, and Mg2+. Most concentrations of contaminants were below published benchmark criteria, yet our results suggest that conditions continue to exist in the zone of decline that promote impacts to mussels that are at least partially associated with low concentration coal-related contaminants. More research is needed to determine the additive, synergistic, or antagonistic effects of these complex ionic mixtures on freshwater mussels from river environments, such as in the Clinch River, where constituent concentrations are relatively low.