Selective feeding by three native North American freshwater mussels implies food competition with zebra mussels

The response of a benthic macroinvertebrate assemblage to whole-lake biomanipulation was studied in a small Finnish mesotrophic lake. From 1993 to 1997, over 200 kg ha^–1 of fish, mainly roach (Rutilus rutilus (L.)) and bream (Abramis brama (L.)) were caught and the fish biomass was reduced by nearly 80%. The biomass and density of benthic invertebrates were investigated during the years of fish removal and for the following three years. The decrease in benthivorous fish stock led to a higher biomass and density of all major groups of benthic invertebrates during the early years of fish removal. Non-biting midges (Chironomidae), water mites (Hydrachnellae), mayfly nymphs (Ephemeroptera), sphaeriid clams (Bivalvia: Sphaeridae) and biting midges (Ceratopogonidae) seemed to respond most profoundly to changes in fish biomass. The biomass of most invertebrate groups correlated negatively with the catch-per-unit-effort (CPUE). The total biomass and density of invertebrates had strong negative correlations with the CPUE (r= -0.85, p = 0.016, r = -0.84, p = 0.019, respectively), but they did not correlate significantly with total phosphorus, chlorophyll a, or temperature. However, the variation in total biomass that was not explained by the CPUE, was significantly associated with total phosphorus.The fish stock recovered to almost its initial level within three years after fish removal had been discontinued. As an apparent response to increased predation pressure, the biomasses of many invertebrate groups decreased again in the years 1999–2000. The strong relationship between macrozoobenthos and fish populations in the studied lake is likely to be a consequence of the open and sparsely vegetated bottom, which offers minimal shelter to invertebrate prey. An additional factor behind the recent low biomass levels may be changes in primary production. Phosphorus and chlorophyll a concentrations started to decrease markedly after three years of fishing and they have remained at a low level.     

Impending extinctions of North American freshwater mussels (Unionoida) following the zebra mussel (Dreissena polymorpha) invasion

1. Freshwater mussels (Order Unionoida) are the most imperiled faunal group in North America; 60% of described species are considered endangered or threatened, and 12% are presumed extinct. Widespread habitat degradation (including pollution, siltation, river channelization and impoundment) has been the primary cause of extinction during this century, but a new stress was added in the last decade by the introduction of the Eurasian zebra mussel, Dreissena polymorpha , a biofouling organism that smothers the shells of other molluscs and competes with other suspension feeders for food. Since the early 1990s, it has been spreading throughout the Mississippi River basin, which contains the largest number of endemic freshwater mussels in the world. In this report, we use an exponential decay model based on data from other invaded habitats to predict the long-term impact of D. polymorpha on mussel species richness in the basin.
2. In North American lakes and rivers that support high densities (>3000 m⁻²) of D. polymorpha , native mussel populations are extirpated within 4–8 years following invasion. Significant local declines in native mussel populations in the Illinois and Ohio rivers, concomitant with the establishment of dense populations of D. polymorpha , suggest that induced mortality is occurring in the Mississippi River basin.
3. A comparison of species loss at various sites before and after invasion indicates that D. polymorpha has accelerated regional extinction rates of North American freshwater mussels by 10-fold. If this trend persists, the regional extinction rate for Mississippi basin species will be 12% per decade. Over 60 endemic mussels in the Mississippi River basin are threatened with global extinction by the combined impacts of the D. polymorpha invasion and environmental degradation.     

Biodiversity conservation in cocoa production landscapes: an overview

Cocoa agroforests that retain a floristically diverse and structurally complex shade canopy have the potential to harbour significant levels of biodiversity, yet few studies have documented the plant and animal species occurring within these systems or within landscapes dominated by cocoa production. In this special issue, we bring together nine studies from Latin America, Africa and Asia that document the contribution of cocoa agroforestry systems to biodiversity conservation, and explore how the design, management and location of these systems within the broader landscape influence their value as habitats, resources and biological corridors. Tree diversity within the cocoa production systems is variable, depending on management, cultural differences, location and farm history, among other factors. Animal diversity is typically highest in those cocoa agroforests that have high plant diversity, structurally complex canopies, and abundant surrounding forest cover. In general, both plant and animal diversity within cocoa agroforests is greater than those of other agricultural land uses, but lower than in the original forest habitat. There are several emerging threats to biodiversity conservation within cocoa production landscapes, including the loss of remaining forest cover, the simplification of cocoa shade canopies and the conversion of cocoa agroforestry systems to other agricultural land uses with lower biodiversity value. To counter these threats and conserve biodiversity over the long-term, land management should focus on conserving native forest habitat within cocoa production landscapes, maintaining or restoring floristically diverse and structurally complex shade canopies within cocoa agroforests, and retaining other types of on-farm tree cover to enhance landscape connectivity and habitat availability.     

Effect of mosquito killer insecticides on freshwater mussels

The effect of four insecticides (Fyfanon, K-Othrin, Unitox 7 and Unitox 20) was investigated on the freshwater mussels Anodonta cygnea L., Anodonta anatina L. and Unio pictorum L. The studies were performed in hard water (total salinity of 310 mg/l). The LC50 values for 24, 48, 72, 96 hr and 7 days were determined with a static test at 22 degrees C. All the three mussel species proved to be extremely tolerant against the insecticides tested. The effect of sublethal concentrations of these insecticides on the periodic activity of the mussels was also analyzed, comparing the changes of the active and resting periods. In a concentration of 0.1 microliter/l, all the four insecticides affected the periodic activity of U. pictorum, whereas in A. anatina three of them (Fyfanon, K-Othrin and Unitox 7) and in A. cygnea two of them (K-Othrin and Unitox 7) evoked alterations. This concentration is lower by three to five orders than those of the LC50 values of 96 hr.     

Importance of hybridization between indigenous and nonindigenous freshwater species: an overlooked threat to North American biodiversity

Biodiversity of North American freshwaters is among the greatest in the world. However, due to extensive habitat degradation, pollution, and introductions of nonindigenous species, this biodiversity is also among the most endangered. Unlike habitat degradation and pollution, nonindigenous species represent a permanent loss of biodiversity because their removal or control is often impossible. Most species introduced into nonnative North American ranges, however, are not from Eurasia but have been introduced from geographically isolated regions within North America. Although the ecological effects of introduced species have been widely documented, the effects of hybridization, especially between closely related species, represents an equally serious mechanism of extinction but is much less studied. Identification of which species are likely to hybridize after contact is of critical importance to prevent the further loss of native species. Molecular phylogenetics serves as a powerful tool to identify freshwater species at risk of introgression, if we can assume that genetic distance is a good predictor of the potential for hybridization. Although not a thorough review of all cases of hybridization, this article documents the extent and effects of hybridization in fishes, crayfishes, mussels, and other invertebrates in light of the currently accepted phylogenetic relationships. We suggest this approach may be the first step in addressing the potential threat of hybridization between many of the closely related species in North American fresh waters.     

Bivalves in a bottleneck: taxonomy,phylogeography and conservation of freshwater mussels (Bivalvia: Unionoida) in Australasia

The conservation biology of Australasian freshwater mussels is hindered by lack of a taxonomic framework that employs molecular data as a complement to shell characters, larval forms and internal anatomy. The fauna includes more than 32 known species (30+ Hyriidae, 2 Unionidae), but has not been revised for 55 years, despite minor amendments. The hyriids are relics of Gondwana, represented in Australia and New Guinea by the ancestral Velesunioninae and in Australia and New Zealand by the Hyriinae (Tribe Hyridellini). Many taxonomic and phylogeographic issues await resolution, including the relationships between Australasian and South American species, and between Australian and New Zealand species, and the status of species in New Guinea (including uncertain reports of Unionidae) and the Solomon Islands. Once these are clarified, it will be easier to identify threatened species and evaluate the conservation status of the fauna. At present, only seven taxa are named in the IUCN Red List or under national/state legislation, and these are not representative. Threatening processes include altered flow regimes, catchment disturbances, salinisation, pollution and invasive species. While the need for a taxonomic revision is paramount, progress in conservation may depend also upon involving the wider community.     

Linking fisheries management and conservation in bioengineering species: the case of South American mussels (Mytilidae)

We examined a complete list of South American mussels (Mytilidae) to identify species with current or potential needs for management and conservation actions. Based on ecological/ecosystem (aggregations, beds or banks affecting ecosystem functioning) and socio-economic (artisanal fisheries or aquaculture systems) attributes species with high relevance were identified. At least 14 species exhibited large ecosystem level effects at local scales. Further, most of them also sustain important fisheries: nearly one/third of these fisheries showed characteristics that may contribute to their lack of sustainability and overexploitation, while half are either in the initial exploitation phase or in the stabilization of extraction and institutionalization phase. Invading species are modifying the structure of mussel habitats. Allocation of spatially explicit management tools, notably Territorial User Rights in Fisheries and Marine Reserves, together with co-management initiatives, are suggested as relevant tools to fulfill management and conservation objectives for these key bioengineering species.     

Biodiversity, phylogeography, biogeography and conservation: lemurs as an example

The lemurs of Madagascar represent a spectacular example of adaptive radiation among primates. Given the special setting under which they evolved (i.e. long isolation, geographical location, geological relief), they provide excellent models for study in many realms, and at different levels and scales, including diversity. At the same time, they occur in a 'hottest hot spot' region for biodiversity conservation. Although there is no single definition of biodiversity, the most commonly used units to measure biodiversity are species-species richness, species abundance and, for conservation purposes in particular, species endemism. However, what a species actually is or how, precisely, it should be defined are unresolved issues. Many species concepts have been proposed and several have been used in primatology in recent years. Nowadays, one of the more common approaches to measuring diversity, and eventually inferring species status, is to look at genetic diversity as reflected by mitochondrial DNA differences. Not enough attention has been paid, however, to the different levels at which genetic differences may occur. Lemurs provide instructive examples to highlight the questions involved in species recognition and definition. Using lemurs as examples, I will highlight the strengths and limitations of some analytical tools, including phylogeography and cladistic biogeography and, I will, in particular, emphasize the questions arising at the interface of scientific and conservation perceptions, both of which influence decisions in the field of biodiversity preservation.     

Neurochemical effects of benzodiazepine and morphine on freshwater mussels

The purpose of this study was to examine the neurochemical effects of morphine, diazepam, a common benzodiazepine, and an effluent concentrate on the endemic freshwater mussel Elliptio complanata. Mussels were exposed to the drugs and to the solid-phase concentrate of a municipal effluent and left to stand at 15 °C for 48 h. Neurochemical effects were determined by monitoring changes in dopamine, serotonin, glutamate and γ-aminobutyric acid (GABA) levels in the visceral mass (containing the nerve ganglia) of mussels. The activities of acetylcholinesterase (AChE), dopamine and serotonin-dependent adenylyl cyclase (ADC) were also determined in the mussels. Oxidative stress was determined by tracking changes in lipid peroxidation (LPO) in the mitochondrial and post-mitochondrial fractions. The results revealed that the drugs and the effluent extract were biologically active in mussels. Morphine reduced serotonin and increased dopamine in mussel tissues while reducing AChE activity and increasing GABA levels. This suggests the induction of a relaxation state in mussels. Diazepam also reduced serotonin levels but produced no change in dopamine levels. However, dopamine-sensitive ADC activity was readily activated, indicating the potential effect on opiate signaling. Diazepam increased glutamate levels slightly, but AChE remained stable. The increase in both dopamine ADC activity and glutamate concentrations was also associated with greater oxidative stress on the mitochondrial and post-mitochondrial fractions in cells. A comparison of the global response pattern of these drugs with those of the effluent extract revealed only a relative proximity to morphine. In conclusion, the data warrant more studies on the analysis of opiates and benzodiazepines in municipal effluents to better address the potential environmental hazard of these neuroactive drug classes to aquatic organisms.     

Context-dependent effects of freshwater mussels on stream benthic communities

1. We asked whether unionid mussels influence the distribution and abundance of co‐occurring benthic algae and invertebrates. In a yearlong field enclosure experiment in a south‐central U.S. river, we examined the effects of living mussels versus sham mussels (shells filled with sand) on periphyton and invertebrates in both the surrounding sediment and on mussel shells. We also examined differences between two common unionid species, Actinonaias ligamentina (Lamarck 1819) and Amblema plicata (Say 1817). 2. Organic matter concentrations and invertebrate densities in the sediment surrounding mussels were significantly higher in treatments with live mussels than treatments with sham mussels or sediment alone. Organic matter was significantly higher in the sediment surrounding Actinonaias than that surrounding Amblema. Actinonaias was more active than Amblema and may have increased benthic organic matter through bioturbation. 3. Living mussels increased the abundance of periphyton on shells and the abundance and richness of invertebrates on shells, whereas effects of sham mussels were similar to sediment alone. Differences in the amount of periphyton growing on the shells of the two mussel species reflected differences in mussel activity and shell morphology. 4. Differences between living and sham mussel treatments indicate that biological activities of mussels provide ecosystem services to the benthic community beyond the physical habitat provided by shells alone. In treatments containing live mussels we found significant correlations between organic matter and chlorophyll a concentrations in the sediment, organic matter concentrations and invertebrate abundance in the sediment and the amount of chlorophyll a on the sediment and invertebrate abundance. There were no significant correlations among these response variables in control treatments. Thus, in addition to providing biogenic structure as habitat, mussels likely facilitate benthic invertebrates by altering the availability of resources (algae and organic matter) through nutrient excretion and biodeposition. 5. Effects of mussels on sediment and shell periphyton concentrations, organic matter concentrations and invertebrate abundance, varied seasonally, and were strongest in late summer during periods of low water volume, low flow, and high water temperature. 6. Our study demonstrates that freshwater mussels can strongly influence the co‐occurring benthic community, but that effects of mussels are context‐dependent and may vary among species.     

Molecular systematics of Scaphirhynchinae: an assessment of North American and Central Asian Freshwater Sturgeon Species

The sturgeon subfamily Scaphirhynchinae contains two genera of obligate freshwater sturgeon: Scaphirhynchus and Pseudoscaphirhynchus, from North America and Central Asia, respectively. Both genera contain morphologically variable species. A novel data set containing multiple individuals representing four diagnosable morphological variants for two species of Pseudoscaphirhynchus, P. hermanni and P. kaufmanni, was generated. These data were used to test taxonomic hypotheses of monophyly for the subfamily Scaphirhynchinae, monophyly of both Scaphirhynchus and Pseudoscaphirhynchus, monophyly of P. hermanni and P. kaufmanni, and monophyly of the recognized morphological variants. Monophyly of the subfamily Scaphirhynchinae is consistently rejected by all phylogenetic reconstruction methodologies with the molecular character set while monophyly of both river sturgeon genera is robustly supported. The molecular data set also rejects hypotheses of monophyly for sampled species of Pseudoscaphirhynchus as well as monophyly for the recognized intraspecific morphological variants. Interestingly both Scaphirhynchus and Pseudoscaphirhynchus demonstrate the same general pattern in reconstructed topologies; a lack of phylogenetic structure in the clade with respect to recognized diversity. Despite rejection of monophyly for the subfamily Scaphirhynchinae with molecular data, reconstructed hypotheses from morphological character sets consistently support monophyly for this subfamily. Disparities among the data sets, as well as reasons for rejection of monophyly for Scaphirhynchinae and species of Scaphirhynchus and Pseudoscaphirhynchus with molecular characters are examined and a decreased rate of molecular evolution is found to be most consistent with the data.     

Biodiversity: bridging the gap between condition and conservation

The aim of this study is to create a two-tiered assessment combining restoration and conservation, both needed for biodiversity management. The first tier of this approach assesses the condition of a site using a standard bioassessment method, AUSRIVAS, to determine whether significant loss of biodiversity has occurred because of human activity. The second tier assesses the conservation value of sites that were determined to be unimpacted in the first step against a reference database. This ensures maximum complementarity without having to set a priori target areas. Using the reference database, we assign site-specific and comparable coefficients for both restoration (Observed/Expected taxa with >50% probability of occurrence) and conservation values (O/E taxa with <50%, rare taxa). In a trial on 75 sites on rivers around Sydney, NSW, Australia we were able to identify three regions: (1) an area that may need restoration; (2) an area that had a high conservation value and; (3) a region that was identified as having significant biodiversity loss but with high potential to respond to rehabilitation and become a biodiversity hotspot. These examples highlight the use of the new framework as a comprehensive system for biodiversity assessment.     

Genetic structure of American black bears in the desert southwest of North America: conservation implications for recolonization

American black bears (Ursus americanus) have recolonized parts of their former range in the Trans-Pecos region of western Texas after a >40-year absence. Assessment of genetic variation, structuring, gene flow, and dispersal among bear populations along the borderlands of Mexico and Texas is important to gain a better understanding of recolonization by large carnivores. We evaluated aspects of genetic diversity and gene flow for 6 sampling areas of black bears in southwestern North America using genotypic data from 7 microsatellite loci. Our results indicated that genetic diversity generally was high in the metapopulation of black bears in northern Mexico and western Texas. The episodic gene flow occurring via desert corridors between populations in northern Mexico and those in western Texas has permitted the establishment of only moderate levels of genetic structuring. Bayesian clustering analyses and assignment testing depicted the presence of 3 subpopulations among our 6 sampling areas and attested to the generally panmictic nature of bear populations in the borderlands region. The potentially ephemeral nature of the small populations in western Texas and genotypic characteristics of bears recolonizing these habitats attest to the importance of linkages along this portion of the borderlands of the United States and Mexico to effectively conserve and manage the species in this part of its range.     

Biodiversity conservation and the extinction of experience

Biodiversity loss is a matter of great concern among conservation scientists, but the wherewithal to reverse this trend is generally lacking. One reason is that nearly half of the world's people live in urban areas and are increasingly disconnected from nature. If there is to be broad-based public support for biodiversity conservation, the places where people live and work should be designed so as to provide opportunities for meaningful interactions with the natural world. Doing so has the potential not only to engender support for protecting native species, but also to enhance human well-being. Accomplishing these goals will necessitate conservation scientists forging new collaborations with design professionals, health practitioners and social scientists, as well as encouraging the participation of the general public.     

Non-biting midges in biodiversity conservation and environmental assessment: Findings from boreal freshwater ecosystems

Non-biting midges (Diptera: Chironomidae) are frequently overlooked in freshwater biodiversity surveys and environmental assessment, yet they are commonly the most abundant and the most diverse taxon in freshwater ecosystems. We reviewed the diversity patterns and assemblage–environment relationships of non-dipterans and chironomids mainly in boreal freshwater ecosystems building on previously reported findings. Although generally the same environmental gradients are correlated with assemblage structure, their relative importance varies between chironomids and non-dipterans. Chironomid assemblage response to and recovery from human impacts are also likely to differ from that of other common benthic taxa. Thus, environmental assessments may be biased if chironomids are not included. Different surrogacy approaches have thus far shown little success in accounting for chironomid species richness and assemblage structure, and there appears to be no easy short-cut for the examination of chironomids as part of freshwater surveys. However, we show that genus-level identification of pupal exuviae provides a reliable and rapid way of estimating chironomid species richness at least in boreal freshwater ecosystems. In addition, we demonstrate that the inclusion of chironomids may increase the signal-to-noise ratio in bioassessment data sets, and that this information can be obtained with modest increases in costs.     

A synthetic phylogeny of freshwater crayfish: insights for conservation

Phylogenetic systematics is heading for a renaissance where we shift from considering our phylogenetic estimates as a static image in a published paper and taxonomies as a hardcopy checklist to treating both the phylogenetic estimate and dynamic taxonomies as metadata for further analyses. The Open Tree of Life project (opentreeoflife.org) is developing synthesis tools for harnessing the power of phylogenetic inference and robust taxonomy to develop a synthetic tree of life. We capitalize on this approach to estimate a synthesis tree for the freshwater crayfish. The crayfish make an exceptional group to demonstrate the utility of the synthesis approach, as there recently have been a number of phylogenetic studies on the crayfishes along with a robust underlying taxonomic framework. Importantly, the crayfish have also been extensively assessed by an IUCN Red List team and therefore have accurate and up-to-date area and conservation status data available for analysis within a phylogenetic context. Here, we develop a synthesis phylogeny for the world''s freshwater crayfish and examine the phylogenetic distribution of threat. We also estimate a molecular phylogeny based on all available GenBank crayfish sequences and use this tree to estimate divergence times and test for divergence rate variation. Finally, we conduct EDGE and HEDGE analyses and identify a number of species of freshwater crayfish of highest priority in conservation efforts.