To better determine the ecological role of motility in pennate diatoms, we quantitatively characterized several motility and adhesion properties of four species of motile pennate diatoms (Craticula sp., Pinnularia sp., Nitzschia sp., and Stauroneis sp.) isolated from the same freshwater pond. Using computer‐assisted video microscopy, we measured speed, size/shape, functional adhesion, path curvature, and light sensitivity for these species, each of which shows a distinctive set of motile behaviors. The average speeds of Stauroneis, Pinnularia, Nitzschia, and Craticula cells are 4.6, 5.3, 10.4, and 10.0 μm · s−1, respectively. Craticula and Nitzschia cells move in a relatively straight path (<4 degrees rotation per 100 μm movement), Stauroneis exhibits minor rotation (about 7 degrees per 100 μm movement), and Pinnularia rotates considerably during movement (about 22 degrees per 100 μm moved). Functional adhesion (as measured by the release rate of attached cells from the underside of an inverted coverslip) shows a half time for cell release of approximately 50 min for Craticula, 192 min for Pinnularia, and >1 day for Nitzschia and Stauroneis. Direction reversal at light/dark boundaries, which appears to be the main contributor to diatom Phototaxis, is most responsive for Craticula, Pinnularia, and Nitzschia at wavelengths around 500 nm. Craticula and Nitzschia cells are the most sensitive in the photophobic response, with over 60% of these cells responding to a 30‐1x light/dark boundary at 500 nm, whereas Pinnularia cells are only moderately responsive at this irradiance, showing a maximal response of approximately 30% of cells at 450 nm. Stauroneis cells, in contrast, had a maximal photosensitive response at 700 nm, suggesting that this cell type may use a different response mechanism than the other three cell types. In addition, Craticula and Pinnularia show a net movement out of the light spot when illuminated at 650 nm, whereas Stauroneis shows a net movement out of the light spot when illuminated at 450 nm. Such quantitative characterizations of species‐specific responses to environmental stimuli should give us a firm foundation for future studies analyzing the behavior of interspecies diatom competition for limited light or nutrient resources.

Stream conductivity reflects both landscape and anthropogenic interactions, although increasing chloride inputs from road salt in eastern North America is also important. Employing a spatially extensive database derived from the Maryland Biological Stream Survey (MBSS), we examined relationships of stream conductivity to landscape attributes and determined relationships between stream MBSS fish metrics, abundance, and biomass as well as fish assemblages by means of conductivity (as a chloride surrogate) to estimate potential effects. Background stream conductivity for the MBSS strata and Maryland L3 ecoregions ranged from 51 to 150 μS/cm, with the Piedmont having the highest background conductivity (145–160 μS/cm). For MBSS sites there were strong relationships of stream conductivity and chloride with both impervious surface and road density, and 0.26% of the MBSS sites exceeded the U.S. Environmental Protection Agency's acute chloride criterion and 1.5% the chronic chloride criterion. For the Maryland Piedmont species assemblage, observed conductivity values between 230 and 540 μS/cm caused important alterations in the biotic community as measured by the series of fish metrics, and thus affected fish species assemblages associated with chloride concentrations between 33 and 108 mg/L. Maryland coastal, coldwater, and highland species assemblages displayed variable responses of conductivity to fish metrics, abundance, and biomass. If regional conductivity and chloride levels continue to increase or remain high from road deicing owing to an increase in urbanization in a watershed or climatic changes, differences in stream fish assemblages and therefore fish diversity may become more apparent. Because of the linkage between salt usage and impervious road surfaces resulting from urbanization, it is important to manage effectively the use of road salt to protect biotic resources. Received January 24, 2012; accepted June 5, 2012

1. We identified priority sites for freshwater conservation in the Upper Mississippi River (UMR) basin using a coarse-and fine-filter approach to defining biodiversity elements as building blocks. Fine-filter species included federally listed threatened and endangered, imperilled, declining, endemic, disjunct and wide-ranging species. We had species data for over 1300 individual occurrences of species and communities identified as fine-filter elements. The coarse-filter elements are ecosystems ('Aquatic Ecological Systems') defined using physical attributes of streams and lakes, and stratified to represent key zoogeographical and physiographical gradients. 2. We used relative ecosystem integrity, species population viability and expert opinion to generate an initial 'portfolio' of 600 freshwater areas of biodiversity significance representing the best examples of the species and ecosystem elements. Representation targets were met for all ecosystem types and for an average of 45% for species groups. 3. The application of a coarse-and fine-filter approach to identify biodiversity conservation priorities in the UMR demonstrates the contribution of each component -even in an area with relatively rich fine-filter data. For a large assessment area, data, even if plentiful, will be uneven, and community-level diversity is not catalogued. Thus, the coarse filter allows for greater confidence that a broad suite of species and key environmental gradients are captured in a conservation portfolio, while fine-filter data provide greater confidence that species of conservation and management interest are addressed adequately.

Four species of biraphid pennate diatoms (Craticula cuspidata (Kiitzing) D.G. Mann, Stauroneis phoenicenteron (Nitzsch) Ehrenberg, Nitzschia linearis (Agardh) W. Smith, and Pinnularia viridis (Nitzsch) Ehrenberg) were studied to determine the effect of temperature changes on their motility and adhesion to the substratum. The pattern of cell movement in response to temperature was similar in all species; the average cell speed increased with temperature, with a maximal speed at 30-35°C. Temperatures > 35OC caused a rapid decrease in cell speed, with cells showing little movement at 40°C; the shape of the temperature profile was nearly identical in all species. The loss of motility above the threshold was not due to cell death as cells exposed to 42°C could recover movement when cooled. In contrast to temperature effects on cell movement, its effect on adhesion for all four species showed distinct qualitative differences. The adhesion of P. viridis and S. phoenicenteron to a glass substrate decreased from 20°C to 35"C, but increased slightly at 45OC. The loss of adhesion in S. phoenicenteron was not quite as severe as in P. viridis, with the latter showing little ability to remain adhered at higher temperatures. Nitzschia linearis demonstrated a higher degree of cell adhesion between 5 and 45°C than C. cuspidata, with both species showing little change in adhesion over the temperature range. Flume studies also demonstrated that P. viridis decreased its adhesion as temperature increased, while S. phoenicenteron maintained or slightly increased its adhesion. The lack of correlation between the adhesion and speed responses to temperature changes and the uniformity in the shape of the temperature/speed profile for all four species suggest that alterations in adhesion characteristics are not directly responsible for regulating cell speed. Both cell speed and adhesion were sensitive to the presence of a second species. Pinnularia viridis displayed lower adhesion in dual-species test samples, and exhibited significantly reduced average speed in the presence of S. phoenicenteron, but not when co-incubated with C. cuspidata. In contrast, S. phoenicenteron showed no change in adhesion in the presence of P. viridis. Additional species had no effect on the cell speed of either C. cuspidata or S. phoenicenteron, while C. cuspidata did show reduced adhesion in the presence of P. viridis. Our results suggest that ecologically important behaviours such as movement and adhesion can respond not only to environmental factors such as temperature, but also to the presence or absence of other diatom species.