James A. Stoeckel

Artificial light at night is an emerging environmental stressor with significant implications for aquatic ecosystems, influencing species’ behaviour and physiological processes. We examined the effects of artificial light at night on the routine metabolic rate of two widespread, invasive crayfish species, red swamp, Procambarus clarkii (Girard, 1852) and signal, Pacifastacus leniusculus (Dana, 1852). Crayfishes were exposed to light intensities mimicking urban nighttime lighting (20 lux) and natural daylight (1000 lux) to assess species-specific metabolic responses to artificial light at night. The results revealed distinct patterns: P. clarkii displayed no significant metabolic change (P = 0.331), suggesting a lower sensitivity to artificial light at night, whereas P. leniusculus showed a significant (P < 0.0001) reduction in routine metabolic rate under artificial light at night, likely due to behavioural adaptations related to reduced activity. Both species exhibited higher nocturnal routine metabolic rate compared to diurnal measurements, regardless of treatment, with routine metabolic rate of P. clarkii remaining elevated longer than that of P. leniusculus. These findings underscore the species-specific metabolic responses to artificial light at night, with potential ecological implications for their roles within aquatic ecosystems. The study enhances our understanding of invasion ecology by demonstrating how species-specific responses to environmental stressors like artificial light at night may influence their competitive dynamics and ecological impacts.

The exopolysaccharide (EPS) produced by Rhizobium tropici ATCC 49672® has been modified to create a stable salt solution and applied as a soil amendment to reduce erosion. We assessed the ecotoxicity of R. tropici-produced EPS on Procambarus clarkii (Girard 1852), the red swamp crayfish. Artificial maternal burrowing chambers were used to monitor behavioral responses to biopolymers in the soil and to observe possible effects on oviposition and hatch rates. The study consisted of post-mated mature females held individually in burrowing chambers containing either control soil or soil amended with 1% EPS. For each treatment, five artificial burrows were placed within each of six bins (n = 3 per treatment) and maintained for 4 mo. The EPS treatment resulted in complete reproductive inhibition, with no oviposition in any of the treated bin chambers compared to 47% ± 23% (mean ± SD) of crayfish producing eggs in the control bin chambers. Control crayfish produced a total of 1,519 hatchlings compared to no hatchlings by crayfish exposed to EPS. Given the potential for soil stabilizers to control P. clarkii populations, a biopolymer salt derived from R. tropici represents a promising management tool that combines ecological benefits with the control of invasive crayfishes.

Predicting effects of rising temperatures on the health and physiology of aquatic organisms is receiving increasing attention, particularly in arid regions with limited freshwater habitat. One approach to estimating energetic health of aquatic ectotherms is scope for growth (SFG)—the net energy available for reproduction and growth after meeting basic maintenance costs. We examined the relationships between temperature, clearance rates, respiration rates, and other physiological parameters to estimate SFG of Popenaias popeii—a federally endangered mussel native to the semi-arid Rio Grande basin of the southwestern USA and Mexico. Scope for growth followed a three-phase pattern with values remaining stable but negative from 16 to 24°C, increasing and becoming positive from 24 to 28°C, and decreasing back down to negative values from 28 to 32°C. In New Mexico’s Black River, a last stronghold for P. popeii, seasonal thermal regimes show that maximum investment in growth and reproduction likely occurs from May to October, when positive SFG values are most common. Within this critical period, mid-summer increases from 28 to 32°C may temporarily dampen or eliminate growth and reproduction in P. popeii as SFG decreases from peak to negative values. Management of flow to minimize thermal stress during mid-summer appears critical to maximizing growth and reproduction of remaining populations.

Freshwater mussel populations are declining worldwide, but the causes and mechanisms of these declines are poorly understood. Biomarkers that reflect the health or fitness of individual mussels are needed for understanding causes of mussel declines, but existing approaches each have weaknesses. We conducted two laboratory experiments to examine the utility of the cellular energy allocation (CEA) model for assessing juvenile mussel responses to stress induced by food limitation. The CEA assesses the energetic status of an organism as CEA = Ea/Ec, where Ea is available energy reserves (total carbohydrates, protein, and lipids) and Ec is energy consumption, estimated using electron transport system (ETS) activity as a proxy for respiration rate and metabolic demands. Experiment 1 evaluated the effects of food abundance (fed and unfed) on CEA and its component biomarkers at a single temperature (mean = 26.8°C) over 23 days. Experiment 2 evaluated the response of ETS activity to food abundance (unfed, low food, high food) in relation to temperature (20, 25, 30°C) over 27 days. In Experiment 1, most constituent biomarkers were lower in unfed mussels, but CEA did not differ between treatments because Ea and Ec declined by similar magnitudes. In Experiment 2, ETS declined with decreasing food abundance, but only at 25 and 30°C, and ETS was affected by temperature only in the unfed treatment. The ETS enzyme assay can be an informative biomarker of stress, but it requires accounting for confounding factors such as food, temperature, and species identity, as well as the lag time in response of ETS relative to respiration rate. Despite its value as a robust, holistic stress biomarker in other organisms, CEA may have limited usefulness for bivalves because of their tendency to reduce feeding and energy consumption under stress, which results in a simultaneous decline in Ea and Ec.

Freshwater mussels are globally imperilled, which is attributed to their sensitivity to changes in streamflow and temperature. The Black River in south‐eastern New Mexico, USA, harbours a stronghold population of the federally endangered unionid Popenaias popeii (Texas hornshell). Decreasing discharge and elevated water temperatures are considered the primary factors responsible for the species’ decline. However, the impact of these factors has not been quantified directly, which may hinder conservation efforts. The upper thermal tolerances (LT₀₅ and LT₅₀) of Black River P. popeii larvae (glochidia) and newly transformed juveniles were evaluated. Individuals were acclimated to 27°C and then immersed at five experimental temperatures (28, 30, 32, 34 and 36°C) for 24 h (glochidia) or 96 h (juveniles). The thermal tolerances of P. popeii and its presumed host fishes were then overlain onto in situ water temperature and discharge data to determine thermal exceedances in the past 15 years. Temperature was hindcast back to 2007 using machine learning (random forest model) and coupled with discharge. For glochidia, LT₀₅ was exceeded frequently (41%) and LT₅₀ was exceeded occasionally (13%) during spring and summer periods, whereas juvenile thresholds were never exceeded. Upper continuous duration above threshold (UCAT) analysis revealed periods of catastrophic high temperature, which were used to determine discharge bottlenecks. This study demonstrates how laboratory‐derived physiological thresholds can be used in conjunction with environmental data to evaluate the hydrological needs of aquatic organisms, which is useful in efforts to maintain flow regimes that protect native ecosystems.

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding the potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO₂), ability to regulate oxygen consumption (regulation index (RI)), and/or critical dissolved oxygen concentration (DO_crit). We then examined the effects of temperature on MO₂, RI, and DO_crit. The results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DO_crit with increasing temperatures. Glochidial respiration temperature coefficient ( Q₁₀) values were approximately 2–3× those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing the hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand.

Freshwater mussels of the order Unionida are currently one of the most imperiled groups of organisms in the North American faunal region. Accurate risk assessments and development of effective management strategies for remaining populations require knowledge of thermal limits in the face of increasing surface water temperature due to climate change and various anthropogenic factors. We conducted a systematic literature review of unionid mussels (order Unionida, families Margaritiferidae and Unionidae) in the North American faunal region to (1) summarize lethal thermal tolerance data by life stage and taxonomy, (2) discuss ecological and climate change implications of existing lethal tolerance data, and (3) identify needs for future research. We identified lethal tolerance estimates for only 28 of 302 species in the families Unionidae and Margaritiferidae. The mean acute median lethal temperatures were 32.8 °C for glochidia (19 species), 35.0 °C for juveniles (13 species), and 36.3 °C for adults (4 species). Generally, glochidia were less tolerant than juveniles or adults of the same species—but there were several exceptions. Generally, Amblemini had the highest acute and chronic thermal tolerance of all tribes followed by Anodontini, Pleurobemini, Lampsilini, and Quadrilini. Acclimation temperature affected lethal tolerance endpoints in less than half (52 of 145) of comparisons within species. Lethal tolerance data for additional species, combined with a comprehensive database of in situ surface water temperatures, would be useful for modeling the frequency and duration of lethal limit exceedance in North America and identifying populations currently living at or near their upper lethal limits.

Nearly half of the over 400 North American crayfish species are imperiled and need some level of protection to ensure sustainable populations, but the detailed life histories of only about 12% of these crayfishes have been published. We provide needed baseline information on the reproductive biology of the Sly Crayfish, Procambarus versutus (Hagen, 1870), through sampling a small stream monthly (N = 23 samples) in the Choctawhatchee River watershed, southeastern Alabama, USA for two years. We collected data on 2,026 individuals (mean 88 sample–1) over the duration of the study and found minimum size at sexual maturity to be 18.3 mm for both males and females. Life cycles were consistent across both years with a major peak in reproductively active males in June and reproductively active females in July. Reproductively-active males and females were nevertheless collected nearly year-round, suggesting continuous low levels of reproduction throughout a given year, with three peaks in reproduction that vary in magnitude. Only three ovigerous females were collected over the study period, possibly because ovigerous females become reclusive and inactive, therefore difficult to collect. The maximum brood size sampled was 242 eggs female–1. There was no evidence for distinct age classes, likely due to year-round reproduction. Similar regional species with detailed information on reproductive biology available have reproduction patterns similar to those in our data. The information herein contributes to the largely lacking information on the life history of North American crayfishes and emphasizes the need to further evaluate the reproductive biology of species lacking sufficient data to aid conservation efforts.

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.