Does the freshwater mussel Anodonta anatina remove the fish pathogen Flavobacterium columnare from water?

Global decline of freshwater mussels (Unionoida) is threatening biodiversity and the essential ecosystem services that mussels provide. As filter-feeding organisms, freshwater mussels remove phytoplankton and suspended particles from the water. By filtering bacteria, freshwater mussels also decrease pathogen loads in the water. The objective of this study was to evaluate whether the common freshwater bivalve Anodonta anatina (duck mussel) could remove the bacterial fish pathogen Flavobacterium columnare from the water. Mussels reduced bacteria in both of the two experiments performed, so that the bacterial concentration at the end of the 96-h monitoring in mussel treatments was only 0.3–0.5 times that of the controls. Surprisingly, mussels did not reduce algal cell concentration statistically significantly. Mussel behavior (shell openness, foot position, and movement) was not affected by the presence of bacteria or algae, except for biodeposition formation, which was greatest in algal-fed treatments, followed by bacterial-fed treatments and controls, respectively. The intestines of bacteria-incubated A. anatina harbored F. columnare, suggesting that mussels ingested the bacteria. Present results suggest that freshwater mussels may also have a potential to mitigate aquaculture pathogen problems, as well as play a role in water quality management.

Evolution of diverse host infection mechanisms delineates an adaptive radiation of lampsiline freshwater mussels centered on their larval ecology

North American watersheds contain a high diversity of freshwater mussels (Unionoida). During the long-lived, benthic phase of their life cycle, up to 40 species can co-occur in a single riffle and there is typically little evidence for major differences in their feeding ecology or microhabitat partitioning. In contrast, their brief parasitic larval phase involves the infection of a wide diversity of fish hosts and female mussels have evolved a spectrum of adaptations for infecting host fish with their offspring. Many species use a passive broadcast strategy: placing high numbers of larvae in the water column and relying on chance encounters with potential hosts. Many other species, including most members of the Lampsilini, have a proactive strategy that entails the use of prey-mimetic lures to change the behavior of the hosts, i.e., eliciting a feeding response through which they become infected. Two main lure types are collectively produced: mantle tissue lures (on the female’s body) and brood lures, containing infective larvae, that are released into the external environment. In this study, we used a phylogenomic approach (ddRAD-seq) to place the diversity of infection strategies used by 54 North American lampsiline mussels into an evolutionary context. Ancestral state reconstruction recovered evidence for the early evolution of mantle lures in this clade, with brood lures and broadcast infection strategies both being independently derived twice. The most common infection strategy, occurring in our largest ingroup clade, is a mixed one in which mimetic mantle lures are apparently the predominant infection mechanism, but gravid females also release simple, non-mimetic brood lures at the end of the season. This mixed infection strategy clade shows some evidence of an increase in diversification rate and most members use centrarchids (Micropterus & Lepomis spp.) as their predominant fish hosts. Broad linkage between infection strategies and predominant fish host genera is also seen in other lampsiline clades: worm-like mantle lures of Toxolasma spp. with sunfish (Lepomis spp.); insect larvae-like brood lures (Ptychobranchus spp.), or mantle lures (Medionidus spp., Obovaria spp.), or mantle lures combined with host capture (Epioblasma spp.) with a spectrum of darter (Etheostoma & Percina spp.) and sculpin (Cottus spp.) hosts, and tethered brood lures (Hamiota spp.) with bass (Micropterus spp.). Our phylogenetic results confirm that discrete lampsiline mussel clades exhibit considerable specialization in the primary fish host clades their larvae parasitize, and in the host infection strategies they employ to do so. They are also consistent with the hypothesis that larval resource partitioning of fish hosts is an important factor in maintaining species diversity in mussel assemblages. We conclude that, taking their larval ecology and host-infection mechanisms into account, lampsiline mussels may be legitimately viewed as an adaptive radiation.

Iron, Phosphorus and Trace Elements in Mussels’ Shells, Water, and Bottom Sediments from the Severnaya Dvina and the Onega River Basins (Northwestern Russia)

Trace elements in freshwater bivalve shells are widely used for reconstructing long-term changes in the riverine environments. However, Northern Eurasian regions, notably the European Russian North, susceptible to strong environmental impact via both local pollution and climate warming, are poorly studied. This work reports new data on trace elements accumulation by widespread species of freshwater mussels Unio spp. and Anodonta anatina in the Severnaya Dvina and the Onega River Basin, the two largest subarctic river basins in the Northeastern Europe. We revealed that iron and phosphorous accumulation in Unio spp. and Anodonta anatina shells have a strong relationship with a distance from the mouth of the studied river (the Severnaya Dvina). Based on multiparametric statistics comprising chemical composition of shells, water, and sediments, we demonstrated that the accumulation of elements in the shell depends on the environment of the biotope. Differences in the elemental composition of shells between different taxa are associated with ecological preferences of certain species to the substrate. The results set new constraints for the use of freshwater mussels’ shells for monitoring riverine environments and performing paleo-reconstructions.

Bloom Forming and Toxic Cyanobacteria in New Zealand Species Diversity and Distribution, Cyanotoxin Production and Accumulation of Microcystins in Selected Freshwater Organisms

<p>The objective of this doctoral study was to identify waterbodies in New Zealand containing cyanobacterial blooms and mats, to assess the species composition and to establish types and concentrations of cyanotoxins in samples obtained. A total of 271 water and cyanobacterial mat samples from 147 different waterbodies around New Zealand were collected or received between January 2001 and December 2004. Sixty seven percent were found to contain cyanobacteria and 4l% of the samples contained cyanobacteria in sufficiently high concentrations to be termed a bloom. A total of 54 different cyanobacteria species were recorded. Prior to 1987, 33 lakes in New Zealand were recorded as having experienced cyanobacterial blooms. In the present study an additional 18 lakes were recorded as having experienced blooms. Eight bloom forming cyanobacteria species not previously identified in New Zealand (Anabaena planktonica, Cylindrospermopsis raciborskii, Microcystis botrys, M. panniformis, M. icthtyoblabe, M. wesenbergii, Planktothrix peronata f. attenuata and Sphaerocavum brasiliense) were found to be dominant or co-dominant in at least some cyanobacterial blooms. In addition to these species, three non-dominant species were identified that were also new records for New Zealand. The water and cyanobacterial mat samples were analysed using ELISA's, LC/MS, HPLC and neuroblastoma assays for cyanotoxins and identified; microcystins/nodularins (102 samples from 54 different locations), anatoxin-a (3 samples from 3 different locations), cylindrospermopsins (l sample) and saxitoxins (48 santples from 4l different locations). Species from the genera Microcystis, Anabaena, Cylindrospermopsis, Nostoc, Planktothrix, Oscillatoria and Phormidium produce these cyanotoxins. An in-depth study in Lakes Rotoehu and Rotoiti investigated the relationship between cyanobacteria species composition and levels of microcystins over a six month period and examined accumulation of microcystins in rainbow trout (Oncorhynchtts mykiss) and freshwater mussels (Hydridella menziesi). Weekly water samples collected from both lakes showed that cyanobacteria species and levels of microcystins can vary over time during a bloom event. When phytoplankton samples were dominated by very high cell concentration of Microcystis spp. they were found to contain microcystins. Generally cell counts were found to be a poor indicator of levels of microcystins in the water samples, suggesting that cell counts alone are not a satisfactory way of identifying human health dangers in waterbodies containing cyanobacteria. Microcystins were detected in rainbow trout liver and muscle tissue, and in freshwater mussels. The Total Daily Intake of microcystins recommended by the World Health Organisation for humans is 0.04 pg kg-1 tdoy-1. A 70kg human consuming 300g of muscle tissue would have exceeded this level in 50% (Lake Rotoiti) and 7l% (Lake Rotoehu) of the samples. Health problems could result if more than 300 g of trout muscle tissue was consumed on a regular basis over an extended period. This study has demonstrated that the prevalence of freshwater cyanotoxin-producing cyanobacteria is widespread in New Zealand waterbodies and these cyanotoxins pose a potential health risk to both humans and animals either directly or indirectly.</p>

Bloom Forming and Toxic Cyanobacteria in New Zealand Species Diversity and Distribution, Cyanotoxin Production and Accumulation of Microcystins in Selected Freshwater Organisms

<p>The objective of this doctoral study was to identify waterbodies in New Zealand containing cyanobacterial blooms and mats, to assess the species composition and to establish types and concentrations of cyanotoxins in samples obtained. A total of 271 water and cyanobacterial mat samples from 147 different waterbodies around New Zealand were collected or received between January 2001 and December 2004. Sixty seven percent were found to contain cyanobacteria and 4l% of the samples contained cyanobacteria in sufficiently high concentrations to be termed a bloom. A total of 54 different cyanobacteria species were recorded. Prior to 1987, 33 lakes in New Zealand were recorded as having experienced cyanobacterial blooms. In the present study an additional 18 lakes were recorded as having experienced blooms. Eight bloom forming cyanobacteria species not previously identified in New Zealand (Anabaena planktonica, Cylindrospermopsis raciborskii, Microcystis botrys, M. panniformis, M. icthtyoblabe, M. wesenbergii, Planktothrix peronata f. attenuata and Sphaerocavum brasiliense) were found to be dominant or co-dominant in at least some cyanobacterial blooms. In addition to these species, three non-dominant species were identified that were also new records for New Zealand. The water and cyanobacterial mat samples were analysed using ELISA's, LC/MS, HPLC and neuroblastoma assays for cyanotoxins and identified; microcystins/nodularins (102 samples from 54 different locations), anatoxin-a (3 samples from 3 different locations), cylindrospermopsins (l sample) and saxitoxins (48 santples from 4l different locations). Species from the genera Microcystis, Anabaena, Cylindrospermopsis, Nostoc, Planktothrix, Oscillatoria and Phormidium produce these cyanotoxins. An in-depth study in Lakes Rotoehu and Rotoiti investigated the relationship between cyanobacteria species composition and levels of microcystins over a six month period and examined accumulation of microcystins in rainbow trout (Oncorhynchtts mykiss) and freshwater mussels (Hydridella menziesi). Weekly water samples collected from both lakes showed that cyanobacteria species and levels of microcystins can vary over time during a bloom event. When phytoplankton samples were dominated by very high cell concentration of Microcystis spp. they were found to contain microcystins. Generally cell counts were found to be a poor indicator of levels of microcystins in the water samples, suggesting that cell counts alone are not a satisfactory way of identifying human health dangers in waterbodies containing cyanobacteria. Microcystins were detected in rainbow trout liver and muscle tissue, and in freshwater mussels. The Total Daily Intake of microcystins recommended by the World Health Organisation for humans is 0.04 pg kg-1 tdoy-1. A 70kg human consuming 300g of muscle tissue would have exceeded this level in 50% (Lake Rotoiti) and 7l% (Lake Rotoehu) of the samples. Health problems could result if more than 300 g of trout muscle tissue was consumed on a regular basis over an extended period. This study has demonstrated that the prevalence of freshwater cyanotoxin-producing cyanobacteria is widespread in New Zealand waterbodies and these cyanotoxins pose a potential health risk to both humans and animals either directly or indirectly.</p>

Status of Freshwater Mussels (Unionidae) in the French Creek Watershed, USA at the Onset of Invasion by Round Goby, Neogobius melanostomus

Freshwater mussels are an imperiled group of organisms that are vital to aquatic ecosystems. Services performed by freshwater mussels, coupled with their use for biomonitoring, make them an invaluable asset. Neogobius melanostomus (Round Goby), a recently introduced invasive species to the French Creek watershed, was once restricted to the watershed of Lake Erie in Pennsylvania. The Round Goby’s propensity to consume Dreissena polymorpha (Zebra Mussel) and Dreissena bugensis (Quagga Mussel) in their native habitat raises concerns about this recent introduction into Pennsylvania’s Allegheny River watershed. Since the discovery of their introduction within the watershed, we have followed the range expansion and dispersal rate of Round Gobies, which makes this study unique. The objectives of this study were to quantify baseline data on the contemporary diversity and abundance of unionid mussels in the upper French Creek watershed, and to explore potential habitat factors that influence or limit the size of the mussel populations. We gathered baseline data on freshwater mussel diversity and abundances across eight sites in the French Creek watershed and examined substrate particle size and host availability as potential limiting factors of the freshwater mussel distribution. Freshwater mussel surveys were conducted during the summer months (July–September) of 2017 using area-constrained surveys. Results showed a significant relationship between mussel diversity and substrate particle size (p < 0.05). From the data collected, we were able to calculate population estimates for the species found across the sample sites. Our results regarding the locations of native mussel populations and characteristics of their habitat provide the needed insight for establishing priority areas for the conservation of freshwater mussels, facilitating planning for protection, mitigation, and adaptation as the invasive Round Goby continues its spread.

Molecular phylogeny reveals a new genus of freshwater mussels from the Mekong River Basin (Bivalvia: Unionidae)

A new genus of freshwater mussels (Bivalvia: Unionidae) is described from the Mekong River Basin as Namkongnaia gen. nov. The validity of the new genus is supported by its unique conchological characteristics, namely the lack of hinge dentition and elongated shells, together with its evolutionary distinctiveness as estimated by multi-locus phylogenetic analyses (mitochondrial COI and 16S, and nuclear 28S genes). The new genus includes two lineages with deep divergence, shown by 5.10% uncorrected COI p-distance. One lineage is a type species described herein as Namkongnaia inkhavilayi gen. et sp. nov. The other is a recognized species under the name ‘Pilsbryoconcha lemeslei (Morelet, 1875)’. Molecular phylogenetic analysis further shows that the new genus belongs to the tribe Pseudodontini, and evolutionarily is closely related to the genus Monodontina Conrad, 1853. However, its conchology is similar to the genus Pilsbryoconcha Simpson, 1900. Time-calibrated phylogeny suggests that the main radiation events of the tribe Pseudodontini occurred during the Late Cretaceous to the Eocene, with the divergence between the new genus and Monodontina placed in the Miocene. The discovery of new freshwater mussel taxa in this study highlights the importance of the Mekong River Basin as one of the world’s biodiversity hotspots for freshwater fauna.