In some agricultural regions, natural wetlands are scarce, and constructed agricultural ponds may represent important alternative breeding habitats for amphibians. Properly managed, these agricultural ponds may effectively increase the total amount of breeding habitat and help to sustain populations. We studied small, constructed agricultural ponds in southeastern Minnesota to assess their value as amphibian breeding sites. Our study examined habitat factors associated with amphibian reproduction at two spatial scales: the pond and the landscape surrounding the pond. We found that small agricultural ponds in southeastern Minnesota provided breeding habitat for at least 10 species of amphibians. Species richness and multispecies reproductive success were more closely associated with characteristics of the pond (water quality, vegetation, and predators) compared with characteristics of the surrounding landscape, but individual species were associated with both pond and landscape variables. Ponds surrounded by row crops had similar species richness and reproductive success compared with natural wetlands and ponds surrounded by nongrazed pasture. Ponds used for watering livestock had elevated concentrations of phosphorus, higher turbidity, and a trend toward reduced amphibian reproductive success. Species richness was highest in small ponds, ponds with lower total nitrogen concentrations, tiger salamanders (Ambystoma tigrinum) present, and lacking fish. Multispecies reproductive success was best in ponds with lower total nitrogen concentrations, less emergent vegetation, and lacking fish. Habitat factors associated with higher reproductive success varied among individual species. We conclude that small, constructed farm ponds, properly managed, may help sustain amphibian populations in landscapes where natural wetland habitat is rare. We recommend management actions such as limiting livestock access to the pond to improve water quality, reducing nitrogen input, and avoiding the introduction of fish.

We conducted a dose-response laboratory study to quantify the level of exposure to dietary Hg, delivered as methylmercury chloride (CH3HgCl), that is associated with suppressed immune function in captive-reared common loon (Gavia immer) chicks. We used the phytohemagglutinin (PHA) skin test to assess T-lymphocyte function and the sheep red blood cell (SRBC) hemagglutination test to measure antibody-mediated immunity. The PHA stimulation index among chicks receiving dietary Hg treatment did not differ significantly from those of chicks on the control diet (p = 0.15). Total antibody (immunoglobulin [Ig] M [primary antibody] + IgG [secondary response]) production to the SRBC antigen in chicks treated with dietary methylmercury (MeHg), however, was suppressed (p = 0.04) relative to chicks on control diets. Analysis indicated suppression of total Ig production (p = 0.025 with comparisonwise alpha level = 0.017) between control and 0.4 microg Hg/g wet food intake treatment groups. Furthermore, the control group exhibited a higher degree of variability in antibody response compared to the Hg groups, suggesting that in addition to reducing the mean response, Hg treatment reduced the normal variation attributable to other biological factors. We observed bursal lymphoid depletion in chicks receiving the 1.2 microg Hg/g treatment (p = 0.017) and a marginally significant effect (p = 0.025) in chicks receiving the 0.4 microg Hg/g diet. These findings suggest that common loon chick immune systems may be compromised at an ecologically relevant dietary exposure concentration (0.4 microg Hg/g wet wt food intake). We also found that chicks hatched from eggs collected from low-pH lakes exhibited higher levels of lymphoid depletion in bursa tissue relative to chicks hatched from eggs collected from neutral-pH lakes.

ABSTRACT1. Despite a heightened global concern for native mussels, fundamental research on mussel ecology in large rivers is lacking. These gaps in knowledge about where mussels occur, and why, are limiting habitat restoration activities.2. Large-scale systematic surveys for native mussels in three reaches of the Upper Mississippi River documented mussel communities composed of 16-23 species and ranging from 2.9-4.5 live mussels m À2 that were actively recruiting new cohorts into their populations (87-100% of the species were found as juveniles p5 years old). Estimates of mean tissue biomass and production in these reaches ranged from 2.1-3.1 g C m À2 and 0.4-0.6 g C m À2 year À1 , respectively. 3. Mussels filtered a significant amount of water (range, 0.05-0.07 m 3 m À2 d À1) over a 480 km reach of the Upper Mississippi River -amounting to a filtration rate of 53.1 million m 3 day À1 . The filtration rate of mussels as a percentage of river discharge ranged from 0.5-1.4% at high flows (5% exceedance), from 1.5-4.4% at moderate flows (50% exceedance) and from 4.4-12.2% during low flows (95% exceedance).4. Collectively, these data suggest that native mussels play an integral role in this ecosystem by sequestering suspended materials that can be used by other benthic organisms.

1. Managers in the Upper Mississippi River (UMR) are using reductions in the River's water levels during summer to mimic historical water regimes and rehabilitate habitats for vegetation and other species. Concerns for the unintended effects of these actions on mussel populations threatened to halt these projects. 2. Our objective was to characterise the survival and movement of two mussel species in the UMR associated with a water level drawdown. During 2009 (no drawdown) and 2010 (0.3 m summer drawdown), we glued passive integrated transponder tags to 10 Amblema plicata and 10 Lampsilis cardium at each of 11 sites. Five sites were in shallow areas expected to be minimally affected by the drawdown (reference sites), and six sites were in shallow areas expected to be directly affected by the drawdown (treatment sites). About equal numbers of sites within both the reference and treatment areas had low and high slopes. Tagged mussels were randomly allocated across sites (within years). 3. Recovery of tagged mussels was >88% in 2009 and 2010. Mortality was similar and low (mean, c. 5% in both species) among reference sites but was variable and relatively high (means, c. 27% in L. cardium and c. 52% in A. plicata) among treatment sites; variation in mortality among treatment sites appeared related to slope. 4. The study found evidence of drawdown associations with net horizontal movements in A. plicata but not L. cardium. Weekly horizontal movements in both species were significantly correlated with changes in water elevation. We observed significant slope associations related to the drawdown for mortality and net horizontal movement in A. plicata. 5. There were strong species-specific differences in the effects of the drawdown on mortality, vertical movement and horizontal movement. These results suggest that A. plicata responded to the drawdown by vertical movement into the substratum, whereas L. cardium responded by horizontal movement to deeper water. No directionality of movement was observed in either species. 6. Collectively, these data suggest that drawdowns can influence the mortality, movement and behaviour of mussels in the UMR. However, more information on spatial and temporal distributions of mussels is needed to better understand the magnitude of these effects. Results from this study are being used by resource managers to better evaluate the effects of this management tool on native mussel assemblages.

Abstract-Based on the need for a test to evaluate chronic sublethal toxicity in estuarine sediments, a 28-d sediment bioassay with the estuarine amphipod Leptocheirus plumulosus (Shoemaker) was developed. The test was initiated with animals less than 2 weeks old (i.e., 425-600 m sieved size class). Test endpoints included survival, growth (g dry weight/d), and reproduction (number of neonates/surviving female). Factors with the potential to influence test animal performance (i.e., nontreatment factors) such as artificial sea salts, salinity, food ration, size at test initiation, intraspecific density, sediment grain size, and diet were evaluated. For example, intraspecific densities between 10 and 60 animals/beaker (i.e., 0.18-1.4 animals/cm 2 ) did not affect survival, growth, or reproduction. Similarly, L. plumulosus were tolerant of a wide range of sediment grain sizes with only extremely fine grained (e.g., Ͼ75% clay) or coarse grained (e.g., Ͼ75% sand) material significantly affecting survival, growth, and reproduction. Test performance criteria included control survival (Ͼ80%) and reproduction (production of offspring in all control replicates), and response to a reference toxicant test with cadmium chloride in a control chart format.