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Management of fish populations for conservation in thermally variable systems requires an understanding of the fish's underlying physiology and responses to thermal stress. Physiological research at the organismal level provides information on the overall effects of stressors such as extreme temperature fluctuations. While experiments with whole organisms provide information as to the overall effects of temperature fluctuations, biochemical assays of thermal stress provide direct results of exposure that are both sensitive and specific. Electron transport system (ETS; Complex III) assays quantify a rate-limiting step of respiratory enzymes. Parameters that can be estimated via this approach include optimum thermal temperature (T

We describe demographics of young-of-year (YOY) Pondmussels (Ligumia subrostrata) and Giant Floaters (Pyganodon grandis) in ponds during 2009 and 2011. YOY attained large size by approximately 6 months (Pondmussel, mean = 48.5 mm; Floater = 57.5), most individuals were sexually mature, and most females were gravid. Size and sex ratios varied among ponds. Pondmussel size was negatively related to mussel density, suggesting food competition; Floater size was not related to density. Size was not related to glochidial infestation pressure on fishes, suggesting that acquired immunity did not affect YOY performance. The percentage of gravid female Pondmussels varied between years from 27 to 100%, and 91% of female Floaters were gravid in 2011. Mean fecundity was high (Pondmussel = 34,311; Floater = 38,873). The proportion of gravid females and mean fecundity were not related to male density, showing that fertilization was efficient. Variation in size, sex ratios, and gravidity among ponds suggests that small differences in environmental conditions or demographic stochasticity can have large effects on populations. Rapid growth, early maturity, efficient fertilization, and high fecundity of YOY are contrary to traditional views of mussel life history, but these traits may allow Pondmussels and Floaters to rapidly colonize disturbed, unstable habitats.

Benthic organisms may be exposed to polycyclic aromatic hydrocarbons (PAHs) in marine sediments as the result of oil spills. PAH photoinduced toxicity, which has been documented in a wide range of early life stage (ELS) aquatic biota, is a phenomenon by which ultraviolet (UV) radiation potentiates the toxicity of photodynamic PAHs (often leading to mortality). Fiddler crabs (Uca longisignalis) are important ecosystem engineers that influence biogeochemical cycles via burrowing. As gravid females burrow, their eggs may bioaccumulate PAHs from contaminated sediments, leading to in ovo exposure. Consequently, free-swimming larvae exposed to intense UV may be at risk for photoinduced toxicity. In the present study, mature fiddler crabs were bred on oiled sediments contaminated via simulated tidal flux. Gravid females were transferred to clean water after 10 days, and larvae were collected at hatch. While in ovo exposures to oil alone did not affect survival, offspring that were subsequently exposed to full spectrum sunlight in clean water experienced significant mortality that corresponded with in ovo exposures to sediments containing ≥1455 μg/kg tPAH50. Results presented here provide evidence for the potential of photoinduced toxicity to occur in benthic organisms with free-swimming early life stages.

Burrowing is a common trait among crayfish thought to help species deal with adverse environmental challenges. Here we used in-vivo experimental data and in-silico modelling of oxygen saturation in a virtual burrow inhabited by crayfish. Except for the entrance 200 mm region, the burrow microenvironment becomes anoxic, on average, within 8 hours, and 12-hour day-night multiple cycles were not sufficient for refreshing the burrow microenvironment even with temporary lack of crayfish. We asked whether the ecological category of crayfish burrowing activity is reflected in the physiological ability to cope with hypoxia and anoxia. As dissolved oxygen declined, respiration patterns of primary burrowers differed from those of secondary and tertiary burrowers, showing also the highest variability in anoxia tolerance. Secondary burrowers showed consistent tolerance with all species exhibiting a mean survival of > 3h anoxic conditions. Tertiary burrowers were variable, exhibiting moderate to zero tolerance of anoxia. The adaptive mechanisms to cope with hypoxia might be a basal legacy from the crayfish monophyletic ancestors – lobsters, traveller crustaceans often reaching deep depths in the ocean. These results challenge the current understanding of crayfish ecology, opening an evolutionary ecological perspective which might be relevant for the next generation of phylogenetical approaches.

Most crayfish species are capable of constructing underground burrows. Burrow construction provides crayfishes the potential to actively engineer microhabitat and optimize local environmental conditions. Little attention, however, has been paid to quantifying the environmental outcomes of burrow morphology. We examined the potential of chimneys to ventilate burrows via wind-assisted buoyancy ventilation. We first conducted proof-of-concept trials in the field using smoke tracers. We then used a wind tunnel to quantify effects of wind velocity, chimney height, burrow orientation, and tunnel angle on model burrow ventilation rates. We developed a predictive model to predict burrow airflow based on endogenous and exogenous factors, and proofed the model with field measurements from a natural burrow. Proof-of-concept trials showed that during breezy conditions (i.e., 8–16 km−h wind gusts), smoke generated near a natural burrow was rapidly drawn into the non-chimney entry, through the burrow, and out the chimney. Wind-tunnel trials revealed significant effects of chimney height and wind velocity on burrow airflow, but no significant effects of burrow orientation towards the prevailing wind direction, nor of the angle of the burrow beneath the chimney. A model developed from wind-tunnel trials predicted air velocities exiting a theoretical chimney that were within 85% of observed velocities exiting natural chimney-burrow complexes. We conclude that crayfish chimneys can serve as passive ventilation systems for crayfish burrows, with chimney height and wind velocity exerting particularly strong effects on airflow. Costs and benefits associated with chimney construction and ventilation are still speculative but should comprise a productive line of research for future studies focused on burrowing crayfish ecology and conservation.

Mussels are at particular risk from thermal stress and hypoxia due to limited range and mobility. Of interest to managers is whether sensitivity is uniform or varies among species and subpopulations. We used respirometry to investigate effects of temperature on energy demand and hypoxia tolerance of two narrowly distributed species (Cyclonaias petrina, Colorado River; C. necki, Guadalupe River), and two subpopulations of a widely distributed species (C. pustulosa: Colorado and Navasota rivers) in central Texas. We observed zero mortality during acclimation and respirometry runs even when mussels were exposed to hypoxic conditions for several hours at 36 °C. However, type and magnitude of sublethal effects varied across species and subpopulations as temperatures increased. C. pustulosa (Colorado River) exhibited the greatest increase in energy demand, C. petrina exhibited a decreasing ability to regulate oxygen consumption and an increase in critical dissolved oxygen concentration, C. pustulosa (Navasota River) exhibited metabolic depression, and both C. petrina and C. necki exhibited increasing frequency of valve closure. Results suggest that effects of increasing temperature on energetic requirements are more important than effects on hypoxia tolerance. Management strategies considering physiological differences among species and/or subpopulations are likely to be more effective than a simple “one-size-fits-all” approach.

We used in situ exposures of juvenile mussels (96-d average, May–September) to investigate the causes of mussel declines. We measured survival and growth of mussels exposed to ambient condi...

Freshwater biodiversity of the United States has long been recognized for its high level of species richness. The US crayfish fauna is richer than that found in any other country or continent in the world. Crayfishes are critically important members of freshwater ecosystems and have long been utilized for human consumption. Combined, these factors argue for effective conservation. When compared to other diverse aquatic groups such as fishes or unionid mussels, conservation efforts for US crayfishes are lacking. We review here, knowledge gaps that prevent effective conservation and past and ongoing crayfish conservation and management activities. We conclude by proposing a strategy of actions to improve the conservation standing of this important group of organisms. These action items include improved outreach efforts, funding and research to fill numerous knowledge gaps, and the inclusion of crayfishes in broader scale aquatic conservation activities.

Ecologists require standardized, ecologically relevant information on the thermal ecology of aquatic ectotherms to address growing concerns related to changing climates, altered habitats, and introduced species. We measured multiple thermal endpoints to investigate potential for establishment of the invasive Ringed Crayfish (Faxonius neglectus) in thermally heterogeneous habitat of the narrowly distributed endemic Coldwater Crayfish (Faxonius eupunctus). For each species, we examined the relationships between thermal endpoints at the cellular and organismal levels. We then compared results between the two species to gain insight as to the generality of linkages between cellular and organismal-level endpoints, as well as the potential for thermal niche separation between the native and potential invader. At the cellular level, we found no differences in the temperature for maximum activity of electron transport system enzymes (ETSmax) between species. At the organismal level, F. neglectus preferred significantly warmer temperatures than F. eupunctus, but this difference was small (1.3 °C) and likely to have only limited biological significance. The critical thermal maximum (CTM) did not differ between species. For both species, the thermal performance curve for ETS enzyme activity served as a useful framework to link thermal endpoints and estimate the transition from optimal to stressful temperatures — organismal thermal preference and optimal temperature estimates consistently fell below ETSmax whereas CTM estimates fell above ETSmax. Taken together, the strong similarities in thermal endpoint patterns between the two species suggest habitats thermally suitable for the native F. eupunctus will also be thermally available to expanding populations of F. neglectus, thereby increasing the opportunity for negative interactions and population effects if F. neglectus invades one of the few remaining, uninvaded, critical habitats of F. eupunctus.

Benthic organisms may be exposed to polycyclic aromatic hydrocarbons (PAHs) in marine sediments as the result of oil spills. PAH photoinduced toxicity, which has been documented in a wide range of early life stage (ELS) aquatic biota, is a phenomenon by which ultraviolet (UV) radiation potentiates the toxicity of photodynamic PAHs (often leading to mortality). Fiddler crabs

Skipjack Herring (Alosa chrysochloris) has long been proposed as the sole host for Reginaia ebenus (Ebonyshell) and Elliptio crassidens (Elephantear), but these relationships were unconfirmed because of difficulties with maintaining this fish species in captivity. We confirmed the suitability of Skipjack Herring as host for both mussel species, and we also showed that Alabama Shad (Alosa alabamae) is an additional suitable host for E. crassidens; both fish species produced large numbers of juvenile mussels. No other fish species tested (n = 12) were suitable hosts for either mussel species. Our results, combined with results from other studies, suggest these mussel species are specialists on genus Alosa. Traditional methods for host identification were problematic for herrings because of their sensitivity to handling and the large volumes of water required to maintain them in captivity. In addition to traditional methods, we confirmed the suitability of these fishes as hosts using a novel technique in which fish gills infected with glochidia were excised from sacrificed fishes and held in recirculating holding tanks with flow until metamorphosis was complete. Completion of metamorphosis on excised gills required glochidia spend at least 11–17 d encapsulated on live fishes before gill excision. This technique may be useful for other large or sensitive fishes that do not lend themselves well to traditional methods for host identification. Confirmation of Alosa spp. as primary hosts for R. ebenus and E. crassidens supports the idea that dams and other river modifications that disrupt migrations of these fishes are key factors in the range restrictions of these mussel species.

Freshwater unionid mussel diversity is decreasing because of species extirpation or extinction. While little can be done to recover lost species, there is an opportunity to develop techniques to save other species. This can be facilitated through gene banking and assisted reproduction. Unfortunately, limited information is available on mussel reproduction, especially relating to sperm quality. Objectives, therefore, were to quantify seasonal changes in sperm concentration and morphology for two unionid mussels, Ligumia subrostrata and Lampsilisstraminea, measure intraspecific heterogeneity for sperm morphometry, and develop an efficient method to quantify sperm concentration using a microspectrophotometer. There were no differences in sperm concentration when cells were extracted from the center or at a half centimeter on either side of the visceral mass, during the spawning season. There was a seasonal change in sperm concentration, such that concentration for L. subrostrata ranged from 1.1 × 109 to 19.60 × 109 cells/mL with there being the largest counts between 26 September to 7 November. L. straminea sperm concentration was greatest (20.0 × 109 cells/mL) on 13 September and subsequently decreased. Sperm were uniflagellated and SEM results for L. subrostrata and L. straminea showed mean head length and width (mid-spawning) were 3.38 ± 0.04 μm and 1.61 ± 0.01 μm and 3.37 ± 0.04 μm and 1.61 ± 0.01 μm, respectively. There were close (R2 ≥ 0.85) quadratic associations between hemocytometer counts and absorbance (300, 600, 700 nm). These results provide baseline information to further investigate sperm quality, fertilizing capacity, and cryopreservation for freshwater mussels.

Environmental cues contain critical information for individuals while searching for mates and suitable habitat. Crayfish have well-developed chemosensory abilities for detecting environmental cues in water; much less is known about these abilities on land. The Devil crayfish (Cambarus diogenes) is a burrowing crayfish often found in dense floodplain colonies as adults. Juveniles however are released in surface water and must navigate overland to burrow. Previous work demonstrates juveniles use cues from conspecific adults, and to a lesser extent, soil cues, for burrow site selection. Using mesocosms, we build on this by examining burrowing cues associated with (1) congeneric adults, (2) excavated burrow material and (3) other juveniles. In contrast to conspecific adults, cues provided by congeneric adults did not override cues associated with soil type. Similarly, juveniles burrowed closer to conspecific adult burrow mounds than to congeneric and human-built mounds. Juveniles also showed significant grouping behaviour in the absence of all other cues. These results suggest juvenile crayfish integrate multiple terrestrial cues for burrow site selection.

Crayfish and their ectosymbiotic worms may be a valuable model system for studying strategies to maintain symbiotic relationships strained by host-induced environmental shifts. Ectosymbiotic branchiobdellidan worms are thought to be dependent on crayfish hosts for reproduction. However, many crayfish species leave surface waters to excavate and reside in subterranean burrows. During this semi-terrestrial phase, crayfish are frequently out of water, subjecting their associated worms to desiccation. Water balance characteristics of Cambarincola mesochoreus, an ectosymbiont of Procambarus clarkii, were examined to elucidate strategies for surviving emersion while maintaining host associations. Emersed worms were characterized by a high water loss rate and low tolerance for dehydration. A lack of direct water contact eventually prompted a coiled, immobile dormant state where water loss was temporarily suppressed. This dormant state was broken by addition of water and re-entered by subsequent emersion. Neither group effects by clustering of many worms, nor water vapor absorption were utilized as mechanisms to increase desiccation hardiness. When crayfish leave surface or subterranean water, worm survival while maintaining host contact is likely facilitated by facultative quiescence. However, this strategy only allows for survival during relatively short-term, cyclic bouts of emersion. Survival of longer-term emersion periods would require worms to leave hosts and remain behind in surface or subterranean water. These strategies likely incur counterbalancing trade-offs: increased mortality but maintenance of host association versus increased survival but temporary or permanent loss of host association and sites for reproduction.

The 2010 explosion of the Deepwater Horizon (DWH) oil rig led to the release of millions of barrels of oil in the Gulf of Mexico. Oil in aquatic ecosystems exerts toxicity through multiple mechanisms, including photo-induced toxicity following co-exposure with UV radiation. The timing and location of the spill coincided with both fiddler crab reproduction and peak yearly UV intensities, putting early life stage fiddler crabs at risk of injury due to photo-induced toxicity. The present study assessed sensitivity of fiddler crab larvae to photo-induced toxicity during co-exposure to a range of environmentally relevant dilutions of high-energy water accommodated fractions of DWH oil, and either10, 50, or 100% ambient sunlight, achieved with filters that allowed for variable UV penetration. Solar exposures (duration: 7-h per day) were conducted for two consecutive days, with a dark recovery period (duration: 17-h) in between. Survival was significantly decreased in treatments the presence of10% UV and relatively low concentrations of oil. Results of the present study indicate fiddler crab larvae are sensitive to photo-induced toxicity in the presence of DWH oil. These results are of concern, as fiddler crabs play an important role as ecosystem engineers, modulating sediment biogeochemical processes via burrowing action. Furthermore, they occupy an important place in the food web in the Gulf of Mexico.

Life-history studies have been published for only a small proportion of crayfish species native to the southeastern United States. The Southeastern Crayfish Biologist Working Group was formed to help meet this deficit by coordinating life-history research efforts. We used a combination of field sampling and computer modeling to evaluate a basic core sampling protocol and assess sample size issues. We focused on a locally abundant species, Procambarus versutus, and followed the protocol for 5 months at two sites in Alabama. Results showed a monthly sample size of 10 juvenile males plus 10 adult males could be met consistently and provided a = 85% probability of detecting seasonal shifts in proportion of Form I males under a range of scenarios. Weaknesses of the effort included inconsistent determination of sex in juveniles and form of adult males among sampling crews. More importantly, female life-history information was rarely obtainable due to an inability to collect sufficient numbers of glaired or berried adults. We suggest several priorities to address before implementation of coordinated, large-scale sampling efforts. These include development of sampling techniques to increase captures of glaired and berried females, and assessment of non-lethal gamete extraction techniques to track reproductive state of males and females.

Host-parasite theory makes predictions about the influence of host abundance, competition for hosts, and parasite transmission on parasite population size, but many of these predictions are not well tested empirically. We experimentally examined these factors in ponds using two species of freshwater mussels with parasitic larvae that infect host fishes via different infection strategies. For both species, recruitment and larval survival were positively related to host abundance, but there was no apparent minimum host threshold and positive population growth occurred when an average of one fish per mussel was present. Recruitment increased rapidly with an initial increase in host abundance but appeared to approach an asymptote at moderate host abundance. Recruitment and larval survival did not differ according to whether mussel species occurred alone or in combination, providing no evidence for competition for hosts via acquired immunity. However, larval survival of the species that attracts hosts with a lure was higher than the species that infects hosts passively, but lower survival of the latter strategy was offset by higher fecundity, which resulted in comparable recruitment between the two species. The lack of evidence for competition for hosts or host saturation suggests that mussel recruitment is limited primarily by fecundity and larval transmission efficiency. Despite the lack of a minimum host abundance threshold, high variation in recruitment in all treatments suggests that population growth at low host abundance is limited by stochasticity. These results show that host-parasite interactions in natural situations may differ substantially from predictions based on models or laboratory findings.

Summary Branchiobdellidans are small, symbiotic annelids (Clitellata) that can have positive effects on the survival and growth of the crayfish host. We hypothesised that branchiobdellidans would be particularly beneficial to crayfish that move to underground burrows (characterised by poor water quality) as surface waters recede. In surface water mesocosms, the symbioses were mutualistic, with worm (Cambarincola barbarae.) density increasing over time and crayfish (Procambarus clarkii) growing faster when worms were present. Contrary to previous studies, the outcome did not shift from mutualism to parasitism at high worm densities. In burrowing chambers in the laboratory, the symbiotic relationship was lost, as worm density decreased by 92% and crayfish growth ceased. Similarly, in burrows excavated in field experiments, worm density decreased by 84%. Rather than the symbiotic relationship increasing survival when crayfish moved underground, this crayfish species may be faced with a trade-off between the benefits of a mutualism with worms while on the surface and protection from heat stress and desiccation by burrowing when water levels are low.

The Deepwater Horizon (DWH) oil spill resulted in the release of millions of barrels of oil into the Gulf of Mexico, and some marsh shorelines experienced heavy oiling including vegetation laid over under the weight of oil. Periwinkle snails (Littoraria irrorata) are a critical component of these impacted habitats, and population declines following oil spills, including DWH, have been documented. This study determined the effects of oil on marsh periwinkle movement and survivorship following exposure to oil. Snails were placed in chambers containing either unoiled or oiled laid over vegetation to represent a heavily impacted marsh habitat, with unoiled vertical structure at one end. In the first movement assay, snail movement to standing unoiled vegetation was significantly lower in oiled chambers (oil thickness ≈ 1 cm) compared to unoiled chambers, as the majority (∼75%) of snails in oiled habitats never reached standing unoiled vegetation after 72 h. In a second movement assay, there was no snail movement standing unoiled structure in chambers with oil thicknesses of 0.1 and 0.5 cm, while 73% of snails moved in unoiled chambers after 4h. A toxicity assay was then conducted by exposing snails to oil coated Spartina stems in chambers for periods up to 72 h, and mortality was monitored for 7 days post exposure. Snail survival decreased with increasing exposure time, and significant mortality (∼35%) was observed following an oil exposure of less than 24 h. Here, we have shown that oil impeded snail movement to clean habitat over a short distance and resulted in oil-exposure times that decreased survival. Taken together, along with declines documented by others in field surveys, these results suggest that marsh periwinkle snails may have been adversely affected following exposure to DWH oil.

SUMMARY 1. Small or sparse populations can experience Allee effects if egg fertilisation is reduced because of a shortage of sperm. 2. Freshwater mussels are spermcasters that often occur as sparse, patchy populations. Previous studies suggested that sperm shortage limits these populations unless facultative hermaphroditism and selffertilisation occur at low density. We conducted experiments in ponds to examine fertilisation in the mussel, Lampsilis straminea, in response to flow, presence of and distance from males, male density, and the presence of upstream females that could compete for sperm with downstream females. 3. Self-fertilisation in the absence of males did not occur in either experiment. Female fertilisation success was uniformly high in most treatments and was not related to flow or distance from males (1–25 m). Fertilisation success was significantly lower at low male density (0.02 m 2 , compared with 0.16 m 2 ) but remained relatively high even in most low male density treatments. The proportion of females that became gravid was higher in the presence of upstream females, but fecundity was significantly lower when upstream females were present; these conflicting results made it difficult to assess the role of competition among females for sperm. 4. Overall, high fertilisation success occurred at densities three orders of magnitude lower than previously proposed thresholds for mussels. Sperm dispersal and acquisition and egg fertilisation appear to be complex processes associated with adaptations for spermcasting. These adaptations are likely to facilitate persistence at low population density and buffer mussels from reproductive Allee effects.

Burrowing crayfish are potentially important ecological links between terrestrial and aquatic systems, but little is known about what drives their local distribution patterns. We investigated potential mechanisms underlying the patchy local distribution of the devil crayfish (Cambarus diogenes Girard) in a stream floodplain ecosystem of the coastal plain of Alabama. We used a series of field surveys and laboratory trials to: 1) quantify local distributions and soil-type associations, 2) identify soil preferences of juveniles and adults, 3) examine the effects of biotic (adult occupancy) and abiotic (soil compaction) factors on juvenile burrowing preferences, and 4) investigate the role of floodplain connectivity on burrow density. Juvenile crayfish were more abundant in sandy streamside soils, whereas adults were more abundant in clay-based floodplain soils. In laboratory preference trials in artificial burrowing chambers, adults and juveniles showed affinity for floodplain over streamside soils, ...

Elevated suspended solids are a widespread stressor of aquatic ecosystems, but their effects on growth and reproduction in freshwater mussels are largely unknown. We fertilized experimental ponds to create a gradient in total suspended solids (TSS) and examined the effects of TSS on growth, nutritional status, reproduction, and clearance rate in Ligumia subrostrata. The number of females that became gravid declined sharply with increasing TSS, and no gravid females were found in the highest TSS treatments. The proportion of gravid females was not related to the TSS organic∶inorganic ratio. Fertilization was an all-or-nothing phenomenon. In all females that did become gravid, 98 to 99% of eggs were fertilized regardless of TSS, and total fecundity was unrelated to TSS. Clearance rates declined sharply as TSS increased but showed a threshold relationship in which clearance was uniformly low at TSS > ∼8 mg/L. Reproductive failure probably was not caused by poor body condition or nutritional status be...

Cambarus (Depressicambarus) harti (Piedmont Blue Burrower) is a state-endangered primary burrowing crayfish found in highly organic soils associated with seepage areas only in Meriwether County, GA. As is the case with many native burrowing crayfishes, virtually nothing is known about the biology and ecology of this species. To help fill this gap, the current study provides information on population demographics, environmental correlates of activity, burrowing behavior, and habitat fidelity of C. harti. Field surveys from the type locality revealed that crayfish could be found throughout the year, with a near 3:1 ratio of female to male adults captured, an ovigerous female found in June, and the highest number of small juveniles found in August. Adults were not found together in burrows; however, juveniles were often found sharing the burrows of females. Burrowing activity was generally higher in the summer than winter, and also increased with receding groundwater levels. Based on observations and experiments with artificial burrowing chambers (ABCs), the burrows of C. harti followed a predictable form and were often capped with at least one chimney of seemingly deliberate construction. Total burrow area and mean chimney pellet diameter increased with crayfish size. It appeared that C. harti will burrow in other soils, but displays a strong affinity to its type-locality soils, particularly below groundwater level. Observations from a communal ABC revealed that adults use burrows to brood young and will share burrows with other adults for a period of time, possibly during burrow construction and/or times of disturbance, but eventually tend to segregate to solitary occupancy. Taken together, these data offer insight into the biology and ecology of this highly endemic and elusive animal that will be useful for management and conservation efforts and provide much-needed scientific information about burrowing crayfishes in general.

Summary 1. Droughts have become prevalent in the south-eastern U.S.A. and are predicted to become more common in the future. Drought conditions have particularly strong negative effects on sessile aquatic organisms with limited dispersal ability. This study explored the linkages between physiological tolerance, behavioural response and survival of three species of freshwater mussels subjected to drought. 2. To assess physiological tolerance, we measured survival under desiccation at 25, 35 and 45 °C in the laboratory. To assess behavioural responses, we tracked horizontal and vertical movement of mussels in a drying stream reach. 3. Uniomerus tetralasmus showed the greatest desiccation tolerance, Lampsilis straminea was intermediate, and Pyganodon grandis had the lowest tolerance at all temperatures. 4. In the drying stream reach, U. tetralasmus showed little horizontal movement and quickly became stranded. The other two species tracked the receding water. It was not until the pool had been reduced to c. 10% of its original size that ≥50% of P. grandis and L. straminea became stranded. 5. Uniomerus tetralasmus and L. straminea burrowed in response to becoming stranded; however, both species burrowed only shallowly (3–4 cm), presumably because burrowing to greater depths did not convey increasing thermal refuge. Pyganodon grandis rarely burrowed. No P. grandis survived the 15-week drought, while 45% of L. straminea and 77% of U. tetralasmus survived. 6. Three strategies emerged for freshwater mussels to cope with drought conditions: tracking (intolerant), track then burrow (semi-tolerant) and burrowing (tolerant). Results suggest that drought poses the greatest threat to intolerant trackers, while tolerant burrowers are the most resistant to drought conditions.

Freshwater mussels use an array of strategies to transfer their parasitic larvae (glochidia) to fish hosts. We examined the effects of temperature, photoperiod, and female gravidity on mantle lure display and conglutinate release by Ligumia subrostrata (Say, 1831) in 2 laboratory experiments. In the 1 st experiment, we examined the use of these strategies in 4 temperature treatments (5, 15, 25, 35uC) and 3 photoperiods (10:14, 12:12, and 14:10 h light: dark). In the 2 nd experiment, we observed infection strategies under ambient conditions with flow-through pond water. Water temperature appeared to be the primary cue governing use of these strategies. Lure display occurred over a protracted period, but the highest display frequency occurred between ,11 and 20uC. Lure display declined rapidly above this range and ceased altogether .28uC. Release of conglutinates increased coincident with the decrease in lure display but, at ambient temperatures, occurred over a protracted period similar in duration to lure display. Females that were not gravid at the beginning of the experiment did not display lures, and gravid females whose gills were flushed of glochidia displayed for only a short period during which frequency of display was much lower than gravid individuals. Ligumia subrostrata exhibits a temperature-mediated switch between alternate host strategies. We present evidence that lure display is a primary strategy for host infection and conglutinate release is a secondary, bet-hedging strategy to reduce wastage of glochidia that ultimately must be cleared from the gills at the end of the reproductive season.

Stoeckel, James A., Jade Morris, Elizabeth Ames, David C. Glover, Michael J. Vanni, William Renwick, and Maria J. Gonzalez, 2012. Exposure Times to the Spring Atrazine Flush Along a Stream-Reservoir System. Journal of the American Water Resources Association (JAWRA) 48(3): 616-634. DOI: 10.1111/j.1752-1688.2011.00633.x Abstract: We used enzyme-linked immunosorbent assay to examine reservoir-mediated shifts in spring to fall exposure of aquatic organisms to the spring atrazine pulse over four years in a Midwestern stream-reservoir system. Peak atrazine concentrations in the major inflowing stream exceeded 10 μg/l in all four years. The reservoir had a beneficial effect in two of four years by diluting atrazine below the 10 μg/l threshold. However, during the other two years, exposure times above 10 μg/l were approximately doubled in the reservoir compared to the major inflowing stream. Thresholds of 3 and 5 μg/l were exceeded during all four years in the reservoir. The uplake and downlake reservoir sites were four to five times more likely to exceed these thresholds and aquatic organisms were subjected to longer exposure times above these thresholds compared to the inflowing stream. Release of elevated atrazine concentrations from the reservoir extended exposure times in the outflowing stream. This effect was most pronounced just below the dam. Aquatic organisms upstream of the reservoir were most likely to experience acute exposures whereas organisms within and immediately downstream of the reservoir were more likely to experience chronic exposures. The ubiquity of reservoirs and the annual spring herbicide flush highlight the importance of considering the presence and relative location of reservoirs when assessing risk to aquatic communities as well as locations of drinking water intakes.

Crayfish are a highly diverse group of freshwater crustaceans with great ecological and economic importance. Many species construct terrestrial burrows within which they reproduce, overwinter, and/or avoid desiccation. Basic life-history and environmental tolerance information is still lacking for many species, particularly in regards to terrestrial portion(s) of their life cycle. In this paper we present and evaluate a design for a crayfish burrowing chamber that allows for experimental control of burrowing conditions, including substrate, groundwater height and flow, as well as direct observation of burrow construction and measurement of groundwater quality. Results of evaluation assays with Cambarus striatus, a widespread secondary burrower native to the southeastern United States show that chambers are amenable to studies examining burrowing behavior, survivorship, growth and water quality. Water table height was easily manipulated in chambers. Seepage rates were strongly affected by substrat...

Summary 1. Although large cladocerans are usually uncommon in large rivers, Daphnia lumholtzi (an exotic species in North America) is widespread and occasionally abundant. We collected zooplankton on the Illinois River (Illinois, U.S.A.) in 1995 and 1996 and found that the peak density of D. lumholtzi (25 L−1) typically exceeded that of all native species combined. Maximum density occurred during warm periods (up to 27 °C) when concentrations of inorganic suspended sediments were high (>50 mg L−1). 2. Using a life table experiment, we examined the effects of variation in suspended sediment (0 and 80 mg L−1) and food (104 and 105Ankistrodesmus cells mL−1) on fitness of D. lumholtzi and the native Daphnia parvula. Daphnia lumholtzi had greater survivorship than D. parvula in most treatments and higher life-time fertility than D. parvula in all treatments. Both species achieved their fastest intrinsic rates of growth in treatments with high food, but their responses to suspended solids differed. The growth rate of D. lumholtzi in high food was slightly increased by higher turbidity, whereas that of D. parvula was depressed. 3. Results suggest that the ability of D. lumholtzi to tolerate suspended solids is an important factor contributing to its success in invading North American rivers.

Population viability analysis (PVA) provides a mechanism for analyzing extinction risk by considering processes, such as random fluctuation in demographic features, loss of genetic variation, environmental stochasticity, and the occurrence of catastrophes. Freshwater mussels (Unionoidea) are candidates for PVA because of elevated risk of extinction from anthropogenic activities. We designed a stage-based conceptual model summarizing demographic and genetic changes throughout the mussel life cycle that are associated with changes in population size. We discuss what is known about these stages and the processes that affect transitions between stages. Considerably more information is known about adults than other life stages. Much more work must be done on nonadult life stages because they are potentially vulnerable to disruption via environmental degradation, habitat fragmentation, and loss of vertebrate hosts. New approaches, such as development of molecular identification keys, use of microsatellite markers, and assignment tests to measure dispersal, promise to increase our understanding of nonadult life stages, breeding systems, and linkages among populations. Few studies have attempted to use theory from population biology and conservation genetics to gain insight into strategies for effective conservation. We suggest that more work must be done with species that are not yet critically imperiled because study of such species is likely to yield useful data for PVAs and insight into the mechanisms regulating freshwater mussel populations.

Though a great deal of research focuses on the range expansion and presence of adult zebra mussels, there is still a need to understand the processes of larval settlement and how that relates to adult populations. There is evidence that marine bivalves preferentially settle on filamentous substrates such as hydroid colonies and algae; however, similar studies are rare in freshwater systems. We examined the importance of filamentous substrate for the settlement of the zebra mussel (Dreissena polymorpha) larvae by deploying PVC settlement plates with and without polypropylene filaments in the Bark River for a 6-week period. Larval supply was monitored weekly. Our results suggest that artificial filaments facilitated recruitment, primarily by increasing surface area available for attachment. Mussels on artificial filaments were significantly smaller in size than mussels attached to filamentous or control plate surfaces, providing some evidence that mussels may detach from filamentous substrate after initial settlement. This study adds to our general understanding about the role of filamentous substrates in the process of larval settlement and suggests that substrates colonized by filamentous epibionts may face increased risk of fouling by zebra mussels.

Brian Helms, Zachary J. Loughman, Bryan L. Brown, AND James Stoeckel 1 Department of Biological Sciences, Auburn University, Auburn, Alabama 36849 USA 2 Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia 26074 USA 3 Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 USA 4 School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University, Auburn, Alabama 36849 USA

Embayments and tidal flow can affect the population structure of organisms, such as the zebra mussel (Dreissena polymorpha), that have a planktonic larval phase. To examine the potential retention of larvae in embayments in tidal rivers and predict the effect of embayments on transport in the river, a field experiment was conducted and a quasi one-dimensional model was developed. Dye was injected into North Tivoli Bay, which is adjacent to the tidal portion of the Hudson River, at the start of a flood tide, and measurements of concentration, stage, and velocity over 1.5 tidal cycles were used in a mass balance to estimate the fraction of dye mass in the bay. After the first ebb, 27% of the dye remained in the bay, and during the following flood the dye that returned increased the mass in the bay to 42% of the injection mass. The field measurements were used to calibrate a quasi one-dimensional model consisting of a series of well-mixed cells with a well-mixed bay adjacent to one of the river cells. The model predicts that a small fraction of larvae would be retained in the bay by the time larvae were competent to settle, but self-recruitment may be possible due to large numbers of larvae. If enough larvae are initially produced, recruitment in the river near the spawning site is possible because the small net southward flow typical of the spawning season provides little downstream transport of the peak of the dye cloud.

Previous work has suggested that zebra mussel populations differ in temperature tolerance and researchers have hypothesized that these differences have been caused by natural selection. For selection to act on a phenotypic character such as heat tolerance, there must be additive genetic variation for the character within populations. Individuals must have different alleles at loci that contribute to measurable differences in the phenotypic character of interest. We tested the hypothesis that heat tolerance of zebra mussel veligers has an additive genetic component and is therefore heritable. We used a full-sib, half-sib design with a large number of full-sib families (20), half-sib families (5), and offspring (averaging 41) per family (estimated power, β = 0.75). We exposed family groups to a lethal temperature of 34°C and determined individual time-to-death. Our best estimate of heritability (which can range from 0 to 1) was −0.125 (±0.095), which implies that heritability of heat tolerance among veligers was extremely low. These results are surprising given the high genetic diversity reported for North American zebra mussel populations. A lack of additive genetic variation for heat tolerance within the studied population means that heat tolerance of the veliger stage is not likely to increase further via natural selection. Further studies examining both the veliger and adult stages, and examining populations in different watersheds are required to show whether this lack of variation is widespread among North American zebra mussel populations.

Small-scale turbulence can increase the mortality of zebra mussel (Dreissena polymorpha) veligers. Laboratory experiments were conducted in which veligers were subjected to turbulence due to a bubble plume and the rate of dissipation of turbulent kinetic energy was measured directly. The ratio d* of the shell size and the Kolmogorov length, the size of the smallest eddy in the velocity field, is introduced to quantitatively assess whether turbulence can affect larvae. The laboratory experiments show that mortality increases when d* exceeds 0.9, that is, when the size of the larvae is comparable with or larger than the smallest eddy. The laboratory results are used to show that turbulence can increase veliger mortality in streams and to evaluate the possibility of using bubble screens as a dispersal barrier to control zebra mussels in rivers. If the mortality is due to acute effects of turbulence (taken to be exposure on the order of minutes), the control scheme would work, but if the mortality is due to longer-term exposure, using bubble screens would not be practical.

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid- to late-summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm LT juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid- to late-summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.

We found evidence for a critical population bottleneck at a developmental-stage transition in larvae of the zebra mussel Dreissena polymorpha Pallas from field estimates of mortality. Identification of this critical period in the field was made possible by closely tracking cohorts of larvae over 5 days of development as they dispersed 128 km in a river system. The presence of a survival bottleneck during development was confirmed in laboratory studies of zebra mussel larvae. Development-specific mortality has important implications for spatial population dynamics of the zebra mussel in particular, and all species with indirect development in general. Marine reserves that do not take development-specific mortality into account may dramatically underestimate reserve size needed to protect rare and/or exploited marine populations. Conversely, for the zebra mussel, the lower contribution of dispersing individuals to population growth downstream of reserves can lead to more feasible control through the blocking of dispersal.

Feeding processes and energetic balance of zebra mussels were both related to the quantity and quality of natural seston. Filtration rate and pseudofeces production increased while clearance rate remained constant with increasing seston concentration. Ingestion rate, assimilation efficiency, and assimilation rate all increased with increasing food quality, measured as the ratio of organic to inorganic material in the seston. Respiration rate did not change with either food quantity or quality. As a result, scope for growth declined with decreasing food quality, and fell below 0 cal mg−1 h−1 at an organic:inorganic ratio of 0.5. The association between feeding processes and food quality appears related to a breakdown in the ability of zebra mussels to selectively ingest high-quality organic particles when the organic content of the seston is low. Ingestion, assimilation efficiency, assimilation rate and scope for growth were all higher when seston was amended with an addition of a natural assemblage of algae. Food quality may be a better indicator of environmental conditions suitable for growth than food quantity. These results suggest that the conditions of high suspended inorganic sediment concentrations in large turbid rivers represent a difficult growth environment for the zebra mussel.

In situ oxygen consumption rates can be used to evaluate respiratory costs of organisms in the natural environment. We determined the in situ oxygen consumption rates of freshwater gastropods by using an assay of the coenzymes involved in the electron transport system (ETS). This assay may be used to estimate in situ and in vitro metabolic rates of individuals when direct monitoring of oxygen consumption is not practical. The relationship between ETS activity and measured oxygen consumption was determined for individuals of 3 common Lake Michigan snail species: Elimia livescens, Stagnicola woodruffi, and Physella integra. The snails were exposed to various temperature conditions to stimulate a wide range of oxygen consumption. After 14 d of acclimation to the experimental conditions, oxygen consumption rates were measured daily. After 5 d, the snail tissue was removed from the shells, flash frozen, and stored in liquid nitrogen until the ETS assay could be performed. Oxygen consumption was highly correlat...

We examined the effects of inorganic suspended sediment (0, 1, 10, and 100 mg ·L-1) and food concentrations (0.1, 0.5, and 2.0 mg particulate organic matter (POM) ·L-1) on clearance, ingestion, respiration, feces, and pseudofeces production rates and assimilation efficiencies of adult zebra mussels (Dreissena polymorpha) under laboratory conditions at 20 ± 1°C. Food quality indices (the proportion of inorganic to organic material in feeding suspensions = IO ratios) ranged from 0.304 to 63.04. Suspended inorganic sediment above 1 mg ·L-1greatly reduced clearance rates, ingestion rates, and assimilation efficiencies of zebra mussels, and ingestion of POM was maintained only at high food concentrations. Pseudofeces were produced copiously by zebra mussels in the 100 mg ·L-1sediment treatment, and there appeared to be an increased metabolic cost associated with pseudofeces production. Declining food quality caused exponential declines in clearance, ingestion, and absorption rates, water processing potential, and assimilation efficiencies, with the sharpest declines between IO ratios of 0.304 and 5.0. IO ratios in turbid rivers often exceed 1.71, our experimental threshold where scope for growth for zebra mussels was zero. We contend that zebra mussels in turbid rivers may exhibit low growth potential and may not stabilize at the high population densities seen in their lake counterparts.

Zebra mussels (Dreissena polymorpha) in the Illinois River are likely to function as a metapopulation (a system of local populations connected by dispersal). River currents reduce or eliminate internal recruitment by local populations, making them dependent upon external recruitment from propagules (larvae) produced by upriver populations. Because of the importance of external recruitment, understanding the population dynamics of riverine zebra mussels requires knowledge of larval flux. In 1994 and 1995, larval drift past a fixed site on the Illinois River was characterized by pulses of similar-sized individuals. These pulses were composed primarily of D-stage (straight hinge) larvae, not yet competent to settle. The continual passage of pulses of young larvae suggests that the upriver source population(s) spawned in frequent distinct bursts throughout the summer months rather than spawning only once or twice. Overall larval abundance was a poor predictor of availability of competent larvae. Although larv...