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Leaf litter decomposition plays an important role in nutrient cycling in both terrestrial and aquatic systems. Decay rates vary based on species, habitat, climate, and local environmental conditions. Invasive plants alter decomposition processes; however, there is a lack of research exploring patterns at regional and continental scales. In this study we examined the decomposition of both native and nonnative, invasive woody plant leaf litter and mixtures of the two, in both terrestrial and aquatic habitats at nine locations in the eastern and midwestern U.S.A. There was significant variation among locations, which was not clearly related 10 either average air temperature or precipitation. Unexpectedly, in locations with multiple years of data, there were higher rates of decomposition in years with lower temperatures and precipitation in both terrestrial and aquatic habitats. We found decay rates were generally higher in aquatic than terrestrial habitats and leaf litter from nonnative invasive species generally decayed faster than that of native species in both terrestrial and aquatic systems. Differences in litter decay rates among invasive species were significant in both terrestrial and aquatic habitats; whereas no differences were found among native species in either habitat. In mixed litter bags, decay rates were lower than what was predicted based on the relative amounts of native and invasive litter in each bag, possibly indicating the presence of native leaf litter slows the decomposition of invasive leaf litter. Additionally, there may have been threshold effects in the mixed litter bags, especially in aquatic systems. While this study supported several generalizations about leaf decomposition rates (invasive > native, aquatic > terrestrial), the variability in the decay rates from different locations and habitats indicates combinations of different species and local conditions may overshadow other general trends related to litter decomposition., INTRODUCTION Leaf litter decomposition is a critical process that mediates nutrient availability, accumulation of organic matter, and ecosystem carbon storage (Prescott, 2010; Gessner et al., 2010; Salinas et al., 2018). [...] more...

We conducted a series of studies to improve our understanding of pistolgrip life history and distribution in Minnesota and Wisconsin. In the St. Croix River, where this species is relatively abundant, we studied animals biweekly from May-Nov. 1997, Apr.-Oct. 1998 and nearly biweekly during May-Jul. 2004-2007 and observed gravid females between late Apr.-Jul. at water temperatures 13-25 C. Females held mature glochidia in a large mantle magazine that was significantly more inflated at night. Fifty-seven pistolgrip glochidia measured using scanning electron microscopy had an average height and length of 119 ± 6 Jam and 102 ± 4 µm (± 1 SD), respectively. Of 65 fish species (18 families) exposed to pistolgrip glochidia only flathead catfish (Pylodictis olivaris) and brown (Ameiurus nebulosus) and yellow (A. natalis) bullheads were suitable hosts, with flathead catfish showing the strongest host response. Glochidia grew 422 ± 17% while attached to fish. Pistolgrip is found in central and southeastern U.S. but is declining in several locations. Surveys conducted between 1980 and 2009 show the geographic range of pistolgrip has decreased in Minnesota and Wisconsin. It is extirpated from the Minnesota River and nearly so in the Mississippi River. However, we see evidence of a recovering population in a once heavily polluted reach of the Mississippi River downstream of Minneapolis-St. Paul. The largest populations are in the lower reaches of the St. Croix (MN, WI), Chippewa, Black, Wolf and Wisconsin rivers (WI). In light of the apparent close association between pistolgrip and flathead catfish, we recommend pistolgrip conservation efforts include sustainable flathead catfish management and habitat improvement to support expansion of remaining pistolgrip populations., INTRODUCTION 'The heavy waves will break many of the fine strings on which the young clams are fastened and wash them to the shore. Millions of such little tiny shells [...] more...

It has been hypothesized that variation in shell shape and sculpture in freshwater mussels from streams is related to hydrologic variability. Using quantitative sampling, we found smooth-shelled species were more common in upstream portions of the St. Croix River, Minnesota and Wisconsin, which has coarser substrate while species with sculptured shells were more common downstream and in finer substrate. For four species distributed throughout the length of the river, individuals tended to have shells that increase in obesity (width/length) and relative height (height/length) downstream. These results support suggestions that mussels with sculptured or obese shells may have an anchoring advantage in areas of high discharge while smooth-shelled or slim forms may reburrow more readily after dislodgement in hydraulically flashy environments. One species that showed increased obesity downstream had juveniles with similar shell shape at all locations suggesting phenotypic plasticity in shell shape. The juvenile and adult valve shape for the other three species examined varied among locations making it is less clear whether the differences noted are genetically fixed or phenotypically plastic. Understanding the complex interplay between shell shape and sculpture and disturbance regimes in rivers may provide useful information when developing conservation plans for these vulnerable animals. While both shell ornamentation and shape vary along river length, and may be correlated with substrate anchoring and stream flow, other factors such as behavior and physiology also contribute to mussels' success in maintaining their location in a river., INTRODUCTION Freshwater mussels (unionids) are among the most endangered animals in the U.S. (Wilcove and Master, 2005), and are important to many lotic ecosystems. They are threatened by a number [...] more...

We compared the physiological rates and biochemical composition of dreissenid mussels (Dreissena polymorpha) from a riverine population that were attached to unionid mussels (Amblema plicata) or to rocks. Specimens were collected from Lake Pepin, Mississippi River, Wisconsin and Minnesota. Unionid-attached specimens had greater oxygen uptake and ammonia excretion rates than did rock-attached specimens. However, unionidattached specimens also had lower carbohydrate and lipid contents. Our results indicate that there are physiological costs of attaching to unionids, at least under some circumstances. Interspecific competition for a limited food resource may negatively impact not only the unionids, but the attached dreissenids as well. This conclusion challenges the assumption that dreissenids benefit from attaching to unionid mussels., INTRODUCTION The zebra mussel, Dreissena polymorpha, is a dramatically successful aquatic invader in both Europe and North America. This introduced bivalve has had major impacts on freshwater ecosystem function. Impacts [...] more...

The ellipse, Venustaconcha ellipsiformis (Bivalvia: Unionidae), was first recorded in Minnesota from the Straight River in 1987, but we knew little of its distribution in the state, brooding behavior, glochidial host fish relationships or status. To examine these questions, we followed standard procedures to conduct an extensive, qualitative statewide mussel survey, described mantle flapping behavior from field and laboratory observations and identified suitable glochidia hosts in the laboratory and from naturally infested fishes. We found extant populations in five Mississippi River tributaries in southeastern Minnesota: the Cannon, Cedar, Root, Upper Iowa and Zumbro rivers. This appears to be the extent of its historic range in Minnesota as no valid records were found elsewhere. Among these, the largest population occurred in the headwaters of the Root River drainage, which was also the only drainage where we observed recent recruitment. Brooding V. ellipsiformis quickly flap a small mantle extension, often in response to passing shadows or jarring of the substrate, or their mantle extensions may be slowly undulated. We identified 11 fish species as suitable hosts for V. ellipsiformis glochidia in the laboratory: brook stickleback (Culaea inconstans), mottled sculpin (Cottus bairdii), slimy sculpin (C. cognatus), logperch (Percina caprodes), mud darter (Etheostoma asprigene), rainbow darter (E. caeruleum), Iowa darter (E. exile), fantail darter (E. flabbelare), Johnny darter (E. nigrum), banded darter (E. zonale) and blackside darter (P. maculata). Rainbow darter, fantail darter and blackside darter were also found naturally infested with V. ellipsiformis glochidia. Venustaconcha ellipsiformis should remain classified as a 'Threatened' species in Minnesota and management should include conserving populations within drainages due to its restricted range and likely low dispersal ability. more...

Size limited brood capacity is common among species with hard exoskeletons or shells. In these species, brood size is limited by the physical capacity to hold offspring. Here we present evidence that brood size is limited by physical constraints in Sphaerium striatinum, a small brooding bivalve. Sphaerium striatinum is a sequential brooder and produces offspring throughout the year. Offspring are brooded in marsupial sacs located on the inner demibranch. In an unconstrained brooder one would predict that brood size would increase as a function of adult length cubed, a volumetric relationship. In S. striatinum, brood size increases as less than a function of adult length squared. We demonstrate that brood size is limited by two general constraints: marsupial sacs and the retention of extra-marsupial offspring. The number of marsupial sacs increases as less than a function of adult length squared. This relationship may be a result of physiological process such as feeding and respiration. Offspring size at independence is a crucial factor in determining offspring survivorship. The retention of extra-marsupial offspring promotes growth inside a safe environment and increases survivorship upon independence. However, the exponent relating brood size to adult length is significantly less for adults that contain extra-marsupial offspring than compared to adults that do not contain extra-marsupial offspring. Although the evolution of brooding in S. striatinum has resulted in severe constraints on brood size, the benefits of brooding outweigh the cost of limited brood capacity. We discuss our results in relation to brooding strategies and size limited brood capacity in other brooding bivalves. more...

We examined physical and biological factors that may influence the distribution of the endangered winged mapleleaf mussel Quadrula fragosa (Conrad, 1835). Quantitative sampling of the mussel community was undertaken at two sites in the St. Croix River known to harbor Q. fragosa. Additional searches were conducted specifically for Q. fragosa individuals. For each quantitative sample of mussels, substrate composition, water velocity and depth were assessed and mussels were identified and measured. In general, Q. fragosa does not have habitat requirements different from the rest of the mussel community, although Q. fragosa occurred in shallower areas with lower bottom current velocity compared to the overall mussel community. There was no difference in substrate composition in areas with and without Q. fragosa. Mussel community density and richness were higher in areas where Q. fragosa was found. The mussel community associated with Q. fragosa was not significantly different from the general mussel community in the area. However three species (Truncilla truncata, Truncilla donaciformis and Quadrula metanevra) were significantly associated with Q. fragosa. Due to its association with dense and diverse mussel communities, management that benefits the entire mussel community should be effective in protecting this endangered species., INTRODUCTION North America has the largest number of species of fresh water mussels in the world. Unfortunately, of the 297 species and subspecies of freshwater mussels found in North America, [...] more...

Monthly collections of Corbicula fluminea were taken for 1 yr from a small river (depth range 0.1-1.1 m) near Charlottesville, Virginia. Mean densities ranged from 173-2990 clams[multiplied by][m.sup.-2], With an annual mean of 677 clams[multiplied by][m.sup.-2]. shell-length frequency distributions and from dissections of adults, it appeared that them was one generation produced per year with the first detectable newborns (shell length [nearly equal 0.4 mm) settling in the substrate during july. Maximum lifespan was 2-3 yr during which clams reached average shell lengths of 11.1 mm in the 1st yr and 17.6 mm in the 2nd yr of life. Other studies have most often reported two generations produced per year with lifespans of 2-4 yr and maximal shell lengths of 30-60 mm. It is suggested that much of the variation in life history displayed by this introduced species in phenotypic. more...