Juvenile Mussels Research Articles

The Attachment of Juvenile Mussels via Byssus Weakened by Contaminated Polyethylene Fibers

In the process of mussel farming, the rope for attachment is indispensable, as it provides a stable attachment environment for mussel seedlings, directly affecting their survival rate and growth quality. The objective of this study is to examine the contamination of ropes, composed of polyethylene fibers, by heavy metals and polycyclic aromatic hydrocarbons (PAHs) after three years of deployment and to assess its influence on the attachment and locomotion behaviors of juvenile mussels. Utilizing a laboratory simulation of the seedling wrapping process, a comparative analysis was conducted to evaluate the number of juvenile mussels attached and their movement distances when exposed to contaminated old ropes versus uncontaminated new ropes. The findings indicated that the old ropes markedly diminished the attachment rate of juvenile mussels and heightened their movement distances. In particular, juvenile mussels utilizing old ropes exhibited a final attachment rate of 15.0% and an average movement distance of 0.86 cm, whereas those using new ropes achieved a final attachment rate of 96.7% with an average movement distance of 0.26 cm. Further inspection found that heavy metals and PAHs were present in the old rope, among which the concentrations of Zn (17.127 μg/g) and Pb (22.905 μg/g) in heavy metals were high, and the concentrations of Phe (5.53 μg/kg), Fla (6.35 μg/kg), and Pyr (5.17 μg/kg) in PAHs exceeded the detection limits, which were the main source of pollution. This research underscores the potential risk that heavy metal and PAHs contamination pose to the health of juvenile mussels and the profitability of aquaculture, emphasizing the critical need for the regular replacement of clean ropes.

Resilience of Juvenile Freshwater Pearl Mussels to ThermalStress.

Climate change poses a significant threat to freshwater ecosystems by causing increases of average water temperatures, and more frequent and extreme heating events. Freshwater mussels are declining globally, and the distribution of the freshwater pearl mussel (Margeritifera margeritifera) has decreased dramatically over the past century. Even though it is likely that climate change is contributing to the decline of the species, little is known about the specific mechanisms involved. Here, we test how short episodes of water temperatures above the known thermotolerance range affect the survival and growth of the early post parasitic juvenile phase of freshwater pearl mussels. We also test if previous experience with elevated water temperatures can modify survival and growth responses to subsequent high-temperatures exposure. Mortality was very low in all treatments (< 5%) and not affected by the temperature treatments, while growth rate was positively affected by temperature. Our results suggest that juvenile mussels can survive short periods of heat stress when other environmental conditions are favourable. Future studies should therefore address how heat stress affects survival in combination with other stressors, such as reduced availability of dissolved oxygen.

The role of substrata width and millimeter scale surface micro-structure in the attachment of juvenile mussels

The global mussel aquaculture industry is constrained by the unreliable supply of wild seed mussels and high losses of seed mussels shortly after they are seeded onto coastal farms. The success in the collection of the settling larvae of mussel in the wild and the subsequent on-growing of early seed mussels in aquaculture are largely determined by the settlement and attachment behaviour of the larval and juvenile mussels, which is strongly influenced by the physical structure of their attachment substrata, especially filamentous substrata. This study aimed to identify an ideal set of morphological characteristics of filamentous substrata that would promote the improved attachment of early mussels and contribute to reducing the shortage of seed mussels in the New Zealand green-lipped mussel (Perna canaliculus) aquaculture industry. Artificial filamentous substrata with varying branch width and textured surfaces were tested for their ability to promote the attachment of wild juvenile mussels. The attachment of early juvenile mussels to 1.6 mm wide filamentous substrate was six times higher than their wider counterparts (i.e., 3.7, 5.6, 7.4, and 9.5 mm). There was also a higher proportion of small-size mussels (<0.99 mm shell length) on the 1.6 mm substrata. Furthermore, the filamentous substrata with regularly ridged surface contours (1 mm spacings) tended to attract more juvenile mussels. However, this preference was not consistent for small-size mussels on filaments of thinner width (i.e., 0.4, 0.8, 1.6, and 3.7 mm). Overall, the dimensions of filamentous substrates identified through this study will be valuable for improving the design of artificial substrata used in mussel aquaculture for improving its effectiveness for the attachment of seed mussels.

Assessing new microalgae species as potential feed for bivalve spat in nursery culture

ABSTRACT Microalgae remains a primary food source for hatchery and nursery culture of juvenile bivalves. However, there is a mismatch between the characteristics of the microalgae currently used in nursery culture and the feeding abilities and nutritional requirements of juveniles of some bivalve species, such as the green-lipped mussel, Perna canaliculus. Therefore, there is a need to identify new species of microalgae for this purpose that have favourable cell size, good growth performance under culture conditions and appropriate nutritional content for juvenile bivalves by using these characteristics as primary selection criteria. In this study, the growth performance under standard culture conditions of four microalgae species (Chrysochromulina camella, Gymnodinium simplex, Pyramimonas parkeae and Stephanodiscus niagarae) which are of a sufficiently large cell size to meet the needs of juvenile mussels (i.e. 10–20 µm size range) were tested in comparison to three commonly cultured commercial species (Chaetoceros muelleri, Diacronema lutheri and Tisochrysis lutea). Results show that G. simplex, S. niagarae and the two strains of P. parkeae (P. parkeae (C) and P. parkeae (I)) can achieve similar biomass as the reference species in the intermediate (1 L) culture stages despite the large difference in cell densities. The poor growth of C. camella in F/2 media indicates a necessity of determining its appropriate culture conditions before further assessing its suitability as a nursery feed for juvenile bivalves. The proximate analysis of S. niagarae, G. simplex and P. parkeae (I) reveals nutritional profiles conducive to spat development. However, the P. parkeae (C) strain contained low carbohydrate content, suggesting inferior nutritional value compared to the P. parkeae (I) strain, showing that variants of the same species can have different biochemical composition and suggesting the former might have limited suitability for feeding in nursery culture. The findings indicate that G. simplex, S. niagarae and P. parkeae (C) hold sufficient promise as spat feed in nursery culture to warrant further testing to confirm their efficacy as live microalgal feed for bivalve spat.

Still waters and deep: Habitat characteristics, density and distribution of a lake-dwelling population of the freshwater pearl mussel Margaritifera margaritifera

The freshwater pearl mussel, Margaritifera margaritifera is widely considered to be confined to fast-flowing, near-pristine rivers, and is highly endangered throughout its Holartic range. Here we describe a large population of some 150–200,000 individuals of the freshwater pearl mussel living in an oligotrophic Irish lake.Employing underwater photographic techniques and snorkel diving, mussels were found in two separate locations in the lake. In the first location, 200 m from the shore, mussels were found at a maximum density of 43 m−2, in a largely random distribution in the sandy bed substrate of the lake, up to 9.5 m deep. In the second shoreline location, mussels were observed in dense aggregations up to 118 individuals m−2, in sandy pockets in between boulders and bedrock, in waters 1–2 m deep. In both locations, mussels were found associated with macrophytes – the charophyte Nitella sp. in the deeper location and the quillwort Isoetes lacustris in the shallower shoreline location. Juvenile mussels (>1.5 cm length) were observed lying exposed on the sediment surface in the shallow littoral location, indicating that recruitment occurs in this population, although no estimates of juvenile density were obtained.The discovery of a large population of lentic Margaritifera margaritifera has significant implications for the species’ conservation and indicates that there may be substantial lentic populations of the species elsewhere. The environmental envelope of the species is clearly much wider than thought and our discovery challenges assumptions about the fundamental feeding and reproductive biology of this endangered species.

Genetics and ontogeny are key factors influencing thermal resilience in a culturally and economically important bivalve

Increasing seawater temperatures coupled with more intense and frequent heatwaves pose an increasing threat to marine species. In this study, the New Zealand green-lipped mussel, Perna canaliculus, was used to investigate the effect of genetics and ontogeny on thermal resilience. The culturally and economically significant mussel P. canaliculus (Gmelin, 1971) has been selectively-bred in New Zealand for two decades, making it a unique biological resource to investigate genetic interactions in a temperate bivalve species. Six selectively-bred full sibling families and four different ages, from early juveniles (6, 8, 10 weeks post-fertilisation) to sub-adults (52 weeks post-fertilisation), were used for experimentation. At each age, each family was exposed to a three-hour heat challenge, followed by recovery, and survival assessments. The shell lengths of live and dead juvenile mussels were also measured. Gill tissue samples from sub-adults were collected after the thermal challenge to quantify the 70 kDa heat shock protein gene (hsp70). Results showed that genetics, ontogeny and size influence thermal resilience in P. canaliculus, with LT50 values ranging between 31.3 and 34.4 °C for all studied families and ages. Juveniles showed greater thermotolerance compared to sub-adults, while the largest individuals within each family/age class tended to be more heat sensitive than their siblings. Sub-adults differentially upregulated hsp70 in a pattern that correlated with net family survival following heat challenge, reinforcing the perceived role of inducible HSP70 protein in molluscs. This study provides insights into the complex interactions of age and genotype in determining heat tolerance of a key mussel species. As marine temperatures increase, equally complex selection pressure responses may therefore occur. Future research should focus on transcriptomic and genomic approaches for key species such as P. canaliculus to further understand and predict the effect of genetic variation and ontogeny on their survival in the context of climate change.

Sulfate sensitivity of early life stages of freshwater mussels Unio crassus and Margaritifera margaritifera

Sulfate is increasingly found in elevated concentrations in freshwater ecosystems due to anthropogenic activities. Chronic exposure to sulfate has been reported to cause sublethal effects on freshwater invertebrates. Previous sulfate toxicity tests have mostly been conducted in hard or moderately hard waters, and research on species inhabiting soft water is needed, given that freshwater organisms face heightened sensitivity to toxicants in water of lower hardness. In the present study, we examined sulfate sensitivity of two endangered freshwater mussel species, Unio crassus, and Margaritifera margaritifera. Glochidia and juveniles of both species were subjected to acute and/or chronic sulfate exposures in soft water to compare sulfate sensitivity across age groups, and effective concentrations (EC)/lethal concentrations (LC) values were estimated. Mussels were individually exposed to allow relatively larger numbers of replicates per treatment. Chronic sulfate exposure significantly reduced growth, foot movement, and relative water content (RWC) in juvenile mussels of M. margaritifera. Mussels at younger stages were not necessarily more sensitive to sulfate. In the acute tests, LC50 of glochidia of M. margaritifera and U. crassus was 1301 and 857 mg/L, respectively. Chronic LC10 was 843 mg/L for 3-week-old U. crassus juveniles, 1051 mg/L for 7-week-old M. margaritifera juveniles, and 683 mg/L for 2-year-old M. margaritifera juveniles. True chronic Lowest Effective Concentration for 7-week-old M. margaritifera may be within the 95% interval of EC10 based on RWC (EC10 = 446 mg/L, 95%CI = 265–626 mg/L). Our study contributed to the understanding of sulfate toxicity to endangered freshwater mussel species in soft water.

Effects of different culture methods on growth, meat yield, and nutritional composition of Mediterranean mussels (Mytilus galloprovincialis), south side of Marmara Sea, Türkiye

This study, conducted between February 2016 and October 2017 on the coast of Erdek in the Marmara Sea, established two longline systems (buoy and pipe). Monthly growth rates of juvenile mussels placed in polyethylene and polyamide nets within these systems were monitored. The monthly chemical composition and meat yield of mussels that reached harvest size were analyzed in both systems. Environmental parameters were measured monthly to assess environmental conditions. The highest meat yield of harvested mussels was recorded in January, with values of 36.99 ± 0.72% for mussels cultured in the pipe system and 31.43 ± 1.82% for those cultured in the buoy system. The highest growth in mussels was achieved in the group cultured in the pipe system within polyamide nets. The December sample showed the highest moisture content of 83.98% and the highest ash content of 2.34%. The highest crude fat content was found in the September sample. The June sample had the highest protein content. The Black Sea, Sea of Marmara, and Aegean Sea offer suitable areas for mussel cultivation. Currently, mussel farming is conducted in these areas, producing tens of thousands of tons annually. This publication contributes to the expansion of the production process.

Population status and host fishes of the freshwater pearl mussel in the eastern part of the Onega Peninsula, Northern European Russia

Four populations of freshwater pearl mussel Margaritifera margaritifera were studied at lower sections of three river basins of the eastern part of the Onega Peninsula, Northern European Russia: the Bol’shaya Syarta, the Ust’-Yaren’ga and the Lopshen’ga (including Kamenny Stream). One of the populations from the Lopshen’ga River was discovered for the first time. Here we present preliminary data on the population status of M. margaritifera, its host fishes and glochidia infestation in the studied river basins. Living juvenile mussels and fishes infested by glochidia were recorded only in two waterbodies, i.e., the Bol’shaya Syarta and Ust’-Yaren’ga rivers. The pearl mussel population from the Bol’shaya Syarta River seems to represent the most prosperous among studied ones. The average density of visible mussels was small in the lower section of the river, but the proportion of young mussels was rather high (33.1 %) and intensity of glochidia infection reached 865 glochidia per fish. The highest average density was recorded in the pearl mussel population from the Kamenny Stream, Lopshen’ga River basin. However, only one juvenile mussel and none of host fishes infested by glochidia were recorded in this watercourse that may indicate the population aging and decrease of reproduction. Morphological analyses revealed significant differences between four studied populations of M. margaritifera towards the shell convexity index (SCI) and shell elongation index (SEI). In all studied basins, salmonid fishes were also infested by other parasites, mainly flatworms and their cysts. This factor may negatively impact the salmonid host fish populations that require monitoring of the current situation. The data obtained and future studies will allow to develop a system for protecting and monitoring of populations of a rare species such as the freshwater pearl mussel M. margaritifera.

First observation of a spawning mantle display in a European unionid mussel.

Freshwater bivalve mussels in the order Unionida are highly endangered ecosystem engineers with a parasitic lifecycle necessitating a fish host to metamorphose from larval glochidia to juvenile mussel. While many species are broadcast spawners and release a large number of glochidia into the water column, many other species have a variety of highly evolved lure mechanisms and mantle displays to attract hosts to ensure a more targeted infestation. Almost all lure mussels are found exclusively in North America, with only one European species (Unio crassus) occasionally displaying a host attraction behaviour referred to as larval spurting. Here, I present evidence that the depressed river mussel (Pseudanodonta complanata) exhibits mantle displays to attract fish to gravid mussels for a targeted infestation, the first description of mantle displays in Europe.

Evaluation of Short-Term Mussel Test for Estimating Toxicity.

Effect concentrations of ammonia, nickel, sodium chloride, and potassium chloride from short-term 7-day tests were compared to those from standard chronic 28-day toxicity tests with juvenile mussels (fatmucket, Lampsilis siliquoidea) to evaluate the sensitivities of the 7-day tests. The effect concentrations for nickel (59 µg Ni/L), chloride (316-519 mg Cl/L, a range from multiple tests), and potassium (15 mg K/L) obtained from the 7-day tests were within a range of effect concentrations for each corresponding chemical in the 28-day tests (41-91 µg Ni/L, 251->676 mg Cl/L, 15-23 mg K/L), whereas the 7-day ammonia effect concentration (0.40 mg/L total ammonia nitrogen; TAN) was up to 3.3-fold greater than the 28-day effect concentrations (0.12-0.36 mg TAN/L) but with overlapped 95% confidence limits. These results indicate that the 7-day tests produced similar estimates compared to the 28-day tests. Further studies are needed to evaluate the 7-day test sensitivity using additional chemicals with different modes of toxic action. Environ Toxicol Chem 2024;43:2020-2025. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Boosting efficiency of mussel spat collection for ecological sustainability: Identifying critical drivers and informing management

Abstract The long‐term sustainability of natural and bottom‐cultured mussel beds relies on the availability of spat (i.e. juvenile mussels). Traditional spat collection methods, which disrupt the donor population and its habitat, have prompted the adoption of suspended mussel spat collectors (SMCs) as an ecologically sustainable alternative. However, practical experience has demonstrated that SMC efficiency is subject to significant spatiotemporal variability, with the underlying biotic and abiotic drivers remaining unresolved. Based on 11‐year SMC practices in the Dutch Wadden Sea, we first validated, through field experiments, the inference that larval abundance and settlement rate in seawater are the primary determinants of SMC efficiency. Secondly, we screened the key factors driving variation in SMC efficiency using an integrated dataset that includes both management options (i.e. user‐defined factors, like SMC types) and environmental conditions (i.e. site‐specific factors, such as hydrodynamics). Lastly, we developed a predictive model to explore the sensitivity of SMC efficiency to these key factors. The efficiency of SMCs was not affected by larval abundance and settlement rate, but rather regulated by management options and environmental conditions, with the key factors identified as SMC type, substrate size, mean wave height and starfish abundance. Rope‐based SMCs outperform net‐based SMCs in terms of harvest efficiency. Both types of SMCs exhibit consistent sensitivity to environmental conditions, with harvest efficiency higher in areas with lower mean wave height and fewer starfish. Increasing substrate size (i.e. rope length and net area) in these areas has the potential to further improve SMC efficiency. Synthesis and applications: Our study highlights the importance of environmental conditions over life cycle‐related factors in regulating SMC efficiency. This offers optimistic prospects for investment in larger‐scale deployment of SMCs and maximizing efficiency through site suitability assessments beforehand. The predictive model we developed can provide information for this purpose. Furthermore, strategically adjusting management options would further optimize SMC efficiency, but it is necessary to balance the associated benefits and costs. Overall, our study underscores the predictability and controllability of SMC efficiency and informs management to maximize sustainable spat supply in both mussel culture and restoration.

Impacts of seeding density on the abundance and size of juvenile mussels and biofouling accumulation in Greenshell™ mussel aquaculture

Growth of the Greenshell™ mussel (Perna canaliculus) industry, New Zealand's most significant aquaculture sector, is limited by spat abundance in the early stages of the aquaculture cycle. However, there are few management techniques to improve spat production. Here, we tested the effects of seeding density (low: 257, mid: 515, and high: 1030 mussels per 10 cm of culture rope) – a putative method to manage spat seeding efficiency and yield – on the abundance and size of P. canaliculus spat at four depths at two sites in the Marlborough Sounds. We also recorded the abundance and size of blue mussels, Mytilus galloprovincialis, which are a problematic biofouling species, as well as the biomass and composition of the biofouling accumulating on mussel culture ropes under the same experimental treatments. Although the abundance of P. canaliculus was greatest at the highest seeding density (∼200 mussels per 10 cm of rope at 87 days), this seeding density also experienced the greatest losses. However, while fewer spat were lost from the low-density seeding treatment, the overall number of spat per 10 cm was significantly reduced, resulting in few operational gains in terms of biofouling reduction or spat size. Overall, the seeding density of suggesting that seeding density of ∼1030 spat per 10 cm of rope was the optimal density tested in this study and could be a useful target density for mussel farmers.

Genotype by environment interactions for growth and inner shell color disparity in Hyriopsis cumingii under different light conditions

The light plays a pivotal role in influencing the growth and body color for aquaculture animals. The freshwater pearl mussel Hyriopsis cumingii, inhabiting benthic environments naturally, is predominantly cultivated by hanging methods. This aquaculture method altersmutiple environmental factors, with light being one of the maximum variationfactor. In order to comprehend the impact of light change on the growth and inner shell color of H. cumingii, a total of 14 full-sibling families were established and cultivated separately under natural light and dim light conditions for a period of 13 months in this study. The results revealed that under natural light conditions, juvenile mussel exhibited accelerated growth rates, while dim light conditions expedited purple pigmentation in the inner shell. Genetic analysis indicated general heritability range for the entire experimental population falls between 0.07 and 0.28. heritability estimates for all traits under natural light conditions (NL) ranged from 0.33 to 0.72, indicating consistently high heritability. However, heritability estimates for all traits under dim light conditions (DL) ranged from 0.05 to 0.16. The growth and inner shell color traits showed significant G × E interactions under different light conditions. The anal angle radial rib length (AARRL) trait exhibited a significantly higher correlation with body weight (BW) compared to shell height (SH) and total shell height (TSH). Furthermore, the growth and inner shell color traits of different families were compared and evaluated under the two environmental conditions in this study. Families 1 and 6 excelled in various traits under both conditions, making them promising candidates for genetic improvement breeding. In this study, pronounced influences of light exposure on the growth of pearl mussels were identified, emphasizing the need for tailored breeding strategies for both bottom seeding and suspended cultivation methods.

Potential for juvenile freshwater mussels to settle onto riverbeds from field investigation

Freshwater mussel populations have been declining at an alarming rate around the world. Herein, we investigate whether changing flow conditions, as they affect juvenile freshwater mussel settling, could be a potential causative factor for this decline in the Dan River, North Carolina, USA. We deployed two uplooking velocity sensors on the riverbed between May and November 2019: one where mussels reside and another where they do not. From this data, we calculated shear velocity, which is a measure of the turbulence that acts to lift particles into suspension and acts against particle settling. We determined that a shear velocity less than 0.66 cm/s would be required to settle relatively large and dense juvenile mussels onto the riverbed; however, the lowest shear velocity we measured was 0.9 cm/s. Additionally, we estimated that juvenile freshwater mussels as large as 280-510 µm could always be suspended and not be able to settle onto the riverbed at these two locations. Therefore, the flow during May-November 2019 was high enough to prohibit recruitment of juvenile freshwater mussels at the sensor locations. Furthermore, we have identified that the magnitude of the lowest flows has increased since 2000, which may be exacerbating the decline in freshwater mussels.

Dislodgement and mortality challenges when restoring shallow mussel beds (Mytilus edulis) in a Danish estuary

In recent decades, mussel beds in the northern Atlantic and Scandinavia have declined rapidly in extent due to anthropogenic impacts, similar to many other marine habitats. In this study, a large‐scale restoration experiment was conducted to identify major challenges that arise during restoration efforts on shallow subtidal mussel beds. Suspension‐grown mussels (Mytilus edulis) were relayed in two different treatments either directly on bare bottom sandy sediments, or on coir nets (Net), used as a proxy for suitable byssal attachment substrate. The treatments were monitored for 1.5 years and coverage (%), biomass (WW), and population dynamics were quantified. Two main challenges of shallow bed restoration were identified: (1) Lack of suitable attachment substrate resulting in dislodgment of individuals during storm events. The Net treatment had significantly higher coverage and biomass of Mytilus at the end of the monitoring period, clearly demonstrating the importance of suitable substrate at physically exposed locations. (2) High mortality of juvenile mussels. Population dynamics revealed a high mortality of juvenile Mytilus, which resulted in almost complete loss of relayed Mytilus individuals less than 30 mm within the first season. This was most likely due to high meso‐predator densities, as a result of declining top‐predator populations. The high mortality of juvenile Mytilus prevented successful annual recruitment, thereby making the population unsustainable long‐term. Both challenges need to be addressed to create stable beds during restoration. Additionally, the experiment demonstrated the viability of using suspension‐grown Mytilus as a seed‐source when restoring mussel beds.

Evaluation of Chronic Effects of Potassium Chloride and Nickel on Survival, Growth, and Reproduction of a Unionid Mussel (Lampsilis siliquoidea).

The ASTM International standard test method for freshwater mussels (E2455-13) recommends 4-week toxicity testing with juveniles to evaluate chronic effects on survival and growth. However, concerns remain that the method may not adequately address the sensitivity of mussels to longer term exposures (>4 weeks), particularly in relation to potential reproductive impairments. No standard method directly evaluates toxicant effects on mussel reproduction. The objectives of the present study were to (1) evaluate toxicity endpoints related to reproduction in fatmucket (Lampsilis siliquoidea) using two common reference toxicants, potassium chloride (KCl) and nickel (Ni); (2) evaluate the survival and growth of juvenile fatmucket in standard 4-week and longer term (12-week) KCl and Ni tests following a method refined from the standard method; and (3) compare the sensitivity of the reproductive endpoints with the endpoints obtained from the juvenile mussel tests. Reproductive toxicity tests were conducted by first exposing female fatmucket brooding mature larvae (glochidia) to five test concentrations of KCl and Ni for 6 weeks. Subsamples of the glochidia were then removed from the adults to determine three reproductive endpoints: (1) the viability of brooded glochidia; (2) the viability of free glochidia in a 24-h exposure to the same toxicant concentrations as their mother; and (3) the success of glochidia parasitism on host fish. Mean viability of brooded glochidia was significantly reduced in the high KCl concentration (26 mg K/L) relative to the control, with a 20% effect concentration (EC20) of 14 mg K/L, but there were no significant differences between the control and any Ni treatment (EC20 > 95 µg Ni/L). The EC20s for viability of free glochidia after the additional 24-h exposure and parasitism success were similar to the EC20s of brooded glochidia. The EC20s based on the most sensitive biomass endpoint in the 4-week juvenile tests were 15 mg K/L and 91 µg Ni/L, similar to or greater than the EC20s from the reproductive KCl and Ni tests, respectively. When exposure duration in the juvenile tests was extended from 4 to 12 weeks, the EC20s decreased by more than 50% in the KCl test but by only 8% in the Ni test. Overall, these results indicate that a standard 4-week test with juvenile mussels can prove effective for estimating effects in chronic exposures with different life stages although a longer term 12-week exposure with juvenile mussels may reveal higher sensitivity of mussels to some toxicants, such as KCl. Environ Toxicol Chem 2024;43:1097-1111. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

High‐volume plankton tow net sampling improves eDNA detection of invasive zebra mussels (Dreissena polymorpha) in recently infested lakes

AbstractAquatic invasive species are a serious and growing threat to biodiversity. Zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) are freshwater invaders causing substantial ecological and economic damage across Europe and North America. Early detection of invasive mussels and other non‐indigenous species is increasingly needed to prevent their establishment and spread. Environmental DNA (eDNA) techniques potentially offer higher sensitivity monitoring tools to complement more conventional methods for surveying adult and juvenile mussels and veliger larvae. eDNA assays are typically performed on small‐volume (0.5–5 L) water samples that are concentrated by filtration prior to extraction and downstream processing. Sampling using a towed plankton net of a larger (64 μm) pore size can process orders of magnitude larger water volumes with the potential for increasing eDNA detection sensitivity. We compared the sensitivities of high‐volume plankton tow net water sampling to filter sampling in three recently infested lakes in Canada and Minnesota, USA. Paired filtration and tow net samples were analyzed for Dreissena DNA using an established quantitative polymerase chain reaction assay for the genus. Higher yields of Dreissena eDNA (more DNA copies) were recovered from plankton tow than from filtered samples in all 33 paired comparisons. In some cases, plankton tow samples were positive for Dreissena eDNA while lower‐volume filtering produced a false negative detection. Our results demonstrate the effectiveness of plankton tow net sampling for eDNA early detection of invasive mussels, a method that can be used exclusively or as a supplement to filter sampling. Our results further suggest that eDNA testing could be incorporated into monitoring programs that routinely use plankton tows for visual detection of invasive mollusk larvae, as well as other aquatic invasive and non‐invasive species ranging from plankton to metazoans, including many fish.

The role of adaptive resistance in a widespread freshwater mussel species

Abstract Organism features, such as size, weight, sex and age, among others, can influence the success of parasitism. For species that depend on a host to complete their life cycle, such as freshwater mussels (Bivalvia, Unionida), understanding how these traits influence parasitism can help guide management actions aimed at improving their reproductive success, ultimately benefitting their conservation. In this study, the physiological compatibility between the duck mussel Anodonta anatina and its host fish was investigated in a simultaneous infestation experiment on four (three native and one non‐native) fish species using sympatric and allopatric host strains. The success of glochidia metamorphosis in juvenile mussels was evaluated as a function of host species, strain and fish length. Successful metamorphosis was achieved in almost all fish species tested and differences were detected between allopatric and sympatric strains, with higher values found in allopatric hosts. Allopatric strains of primary hosts produce more juveniles than marginal hosts and non‐native species. In addition, larger fish have lower rates of metamorphosis. The results confirm recent findings showing high variation in the metamorphosis success of A. anatina glochidia among different native and non‐native hosts, both in the natural environment and in artificial laboratory infestations. Allopatric hosts were more suitable for encystment, demonstrating potential adaptive immunity, not yet observed in A. anatina. Nevertheless, A. anatina may temporarily exploit the naivety of smaller fish regardless of strain. Overall, the results suggest that mussel propagation, reproduction and reintroduction efforts should consider the mechanisms that influence adaptive immunity in fish, including differences in compatibility within and between populations of sympatric and allopatric host strains. This situation should be taken into account, as successful metamorphosis is an important factor in the selection of hosts for juvenile development, especially in efforts to propagate endangered mussel species.

Oxidative Damage and Antioxidants as Markers for the Selection of Emersion Hardening Treatments in GreenshellTM Mussel Juveniles (Perna canaliculus).

Transport out of the water is one of the most challenging events for juvenile Perna canaliculus and can be a highly inefficient process, with many juveniles subsequently being lost following extended periods of emersion. Hardening techniques offer a possible method for reducing transport-related stress. In this study, different hardening treatments (short, long and intermittent sub-lethal emersion) were used to prepare ~1.2 mm P.canaliculus for transport (20 h) and subsequent reoxygenation stress during re-immersion (i.e., recovery). The oxidative stress responses, resettlement behaviour, respiration rates and survival of the mussels after transport and during recovery were all assessed. Short emersion (1 h) as a hardening treatment prior to transport did not cause major stress to the mussels, which maintained respiration at control levels, showed significantly stimulated antioxidant defences during recovery, showed greater resettlement behaviour and remained viable after 24 h of recovery. In comparison, the long and intermittent emersion treatments negatively impacted oxidative stress responses and affected the viability of the mussels after 24 h of recovery. This study showed that exposing juvenile P.canaliculus to a mild stress prior to transport may stimulate protective mechanisms, therefore eliciting a hardening response, but care must be taken to avoid overstressing the mussels. Improving the management of stress during the transport of juvenile mussels may be key to minimising mussel losses and increasing harvest production, and biomarkers associated with oxidative stress/antioxidant metabolism could be valuable tools to ensure emersion hardening does not overstress the mussels and reduce survival.