Description:    The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment behaviors contribute to the persistence of Pomacea canaliculata in lotic environments . This invasive apple snail is commonly considered a lentic dweller. In a first series of trials in a laboratory flume, current velocity was gradually increased until snails’ detachment. Detachment velocity was highly variable, with some snails able to withstand strong currents during short periods. Sexually undifferentiated snails were the most resistant to detachment; most of the snails that resisted high velocities were facing flow before detachment. In a second series of trials, snails’ net displacement was estimated at three fixed velocities (0, 0.15, and 0.30 m s −1 ). Current velocity did not influence mean net displacement, which was not different from zero. Marked snails were released in a stream and recaptured 24 h later estimating their net displacement. Most recovered snails dispersed a short distance from the release point and crawled through sites with very low current velocities. A small proportion of snails drifted downstream, indicating the existence of different dispersal mechanisms. Snails were able to resist current velocities that are among the highest recorded in streams in the Pampas region. P. canaliculata did not show a positive rheotactic response; in flowing water, snails crawl more often upstream, but at a slower pace than downstream. At the population level, a slow upstream spread seems possible in plain’s streams, probably being enough to compensate drift, but not to colonize headwaters. Irrigation systems are feasible pathways for the spread of this species in invaded regions. Content Type Journal Article Pages 1-14 DOI 10.1007/s10452-011-9386-4 Authors María E. Seuffert, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina Pablo R. Martín, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Organism growth and reproduction are often limited by nutrient availability in freshwater ecosystems where, in some cases, food webs are primarily supported by allochthonous organic matter. Therefore, we hypothesized that the composition of riparian vegetation would influence the variability of N, P, and fatty acid content of in-stream consumers. Specifically, we predicted that organisms living in alder streams would have higher levels of N, P, and polyunsaturated fatty acids than organisms in coniferous streams. To determine this, we sampled fresh and aged leaf litter, periphyton, invertebrates, and cutthroat trout ( Oncorhynchus clarki ) from 6 streams in western Washington state: 3 streams had high densities of nitrogen-fixing red alder ( Alnus rubra ) in the riparian zone, whereas 3 had high densities of conifers. We found fresh alder litter had twice the total polyunsaturated fatty acid concentrations of hemlock vegetation while there were few statistical differences among aged alder and aged hemlock vegetation. Multidimensional plots showed fatty acid profiles were unique to vegetation and fish while periphyton and invertebrates shared the same multidimensional space. We used a mixed model to determine the relative importance of vegetation type (fixed factor: conifer or alder), trophic levels (fixed factor: periphyton, primary consumer, or fish), and streams (random factor) on individual fatty acid concentrations. Total polyunsaturated fatty acids, 16:0, 20:1, 20:3n6 and total n3 were the only fatty acids influenced by stream vegetation (vegetation + stream model or full model). 67% of the fatty acids were best supported by the trophic + stream model. Nitrogen, P, Ca, Fe, C:N, N:P, and C:N:P were all best supported by the trophic level + stream model, and Zn was the only nutrient supported best by the full model. Correlations of n3 and n6 fatty acid concentrations between periphyton and primary consumers, and primary consumers with trout indicated several fatty acid metrics, such as n3:n6, showed food resources may affect relative fatty acid abundances of consumers. Although vegetation type did not influence relative fatty acids of stream organisms, the importance of trophic level likely indicates organisms have different physical requirements for fatty acids. The significance of a random factor, ‘stream,’ suggests that the relative abundances of fatty acids in periphyton, invertebrates, and trout are stream-specific and are responding to local environmental or communal variables. Content Type Journal Article Pages 1-15 DOI 10.1007/s10452-011-9383-7 Authors Carol Volk, South Fork Research, Inc., 44842 SE 145th St, North Bend, WA 98045, USA Peter Kiffney, NOAA-Fisheries, National Marine Fisheries Service, Fish Ecology Division, Mukilteo Biological Field Station, Northwest Fisheries Science Center, 10 Park Avenue, Building B, Mukilteo, WA 98275, USA Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Scales collected during a maximum of seven fish population surveys over a 25-year period (1983–2008) in the River Wensum, a lowland river in Eastern England, enabled temporal analysis of the growth rates of roach Rutilus rutilus , dace Leuciscus leuciscus and chub Leuciscus cephalus . Across the study period, all species showed temporal variability in their growth patterns. Roach showed a significant temporal decrease in their growth, where rates recorded in surveys in 2005 and 2008 were significantly slower those recorded in surveys between 1983 and 1994. This change in growth rate was significantly associated with the implementation of phosphate stripping in the catchment’s sewage treatment works that reduced nutrient inputs (specifically orthophosphate). Prior to the implementation, temperature patterns explained most of the annual growth variability; following implementation and a consequent shift to the less eutrophic conditions, this relationship was lost, with changes in annual phosphate loadings now explaining most of the annual growth variation. This suggests that the changes in roach growth rates were related to shifts in river productivity resulting from water quality improvements. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-011-9387-3 Authors Helen Beardsley, Environment Agency Anglian Region Eastern Area, Norwich, UK J. Robert Britton, Centre for Conservation Ecology and Environmental Sciences, School of Applied Sciences, Bournemouth University, Poole, Dorset BH12 5BB, UK Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata , were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods. Content Type Journal Article Pages 1-9 DOI 10.1007/s10452-011-9385-5 Authors Valter Amaral, Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugal Henrique N. Cabral, Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugal Melanie J. Bishop, Department of Biological Sciences & Climate Risk CoRE, Macquarie University, North Ryde, NSW 2109, Australia Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Phytoplankton stoichiometry or nutrient content has been shown to vary in a number of dimensions (species, condition, time, space), but the heterogeneity within a species at a given time and location, and the underlying mechanisms and importance have not been explored. There are a number of mechanisms that can create intraspecific heterogeneity, and theory suggests it can affect the population growth rate. We studied heterogeneity in P content of the freshwater diatom Cyclotella meneghiniana in the Charles River in Boston. Single-cell observations using synchrotron-based X-ray fluorescence show that the nutrient status varies from P-starved to P-replete. We simulate individual cells using an agent-based model that accounts for a number of mechanisms that can create heterogeneity, including surface area–based uptake, mortality differentiation, stochastic biological variability in states and behavior, macroscale mixing, and microscale nutrient patch encounter. By performing a number of simulations with various mechanisms turned on/off and comparing to data, we conclude that the heterogeneity is mostly due to microscale patchiness (85%). We explore the importance of accounting for heterogeneity in models by performing a simulation with the growth rate based on the population-average internal nutrient, as is done in conventional population-level models. This shows that ignoring heterogeneity increases the population growth rate by a factor of 1.47. To account for different heterogeneity in the laboratory and field, population-level ecosystem models should reduce maximum growth rates. The magnitude of this correction depends on local conditions, and in our case, it is a factor of 0.72. Content Type Journal Article Pages 1-18 DOI 10.1007/s10452-011-9384-6 Authors Vanni Bucci, Civil and Environmental Engineering Department, Northeastern University, Boston, MA 02115, USA Daliangelis Nunez-Milland, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA Benjamin S. Twining, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA Ferdi L. Hellweger, Civil and Environmental Engineering Department, Northeastern University, Boston, MA 02115, USA Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Inverse trophic cascades are a well explored and common consequence of the local depletion or extinction of top predators in natural ecosystems. Despite a large body of research, the cascading effects of predator removal on ecosystem functions are not as well understood. Developing microcosm experiments, we explored food web changes in trophic structure and ecosystem functioning following biomass removal of top predators in representative temperate and tropical rock pool communities that contained similar assemblages of zooplankton and benthic invertebrates. We observed changes in species abundances following predator removal in both temperate and tropical communities, in line with expected inverse effects of a trophic cascade, where predation release benefits the predator’s preys and competitors and impacts the preys of the latter. We also observed several changes at the community and ecosystem levels including a decrease in total abundance and mean trophic level of the community, and changes in chlorophyll- a and total dissolved particles. Our results also showed an increase in variability of both community and ecosystem processes following the removal of predators. These results illustrate how predator removal can lead to inverse trophic cascades both in structural and functioning properties, and can increase variability of ecosystem processes. Although observed patterns were consistent between tropical and temperate communities following an inverse cascade pattern, changes were more pronounced in the temperate community. Therefore, aquatic food webs may have inherent traits that condition ecosystem responses to changes in top-down trophic control and render some aquatic ecosystems especially sensitive to the removals of top predators. Content Type Journal Article Pages 1-17 DOI 10.1007/s10452-011-9381-9 Authors Marta Coll, Institute of Marine Science (ICM-CSIC), Passeig maritim de la Barceloneta, 37-49, 08003 Barcelona, Spain Kevin Hargadon, Biology Department, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1, Canada Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Amoebae grazing can be an important loss factor for blooms of the common cyanobacterium Microcystis . Some Microcystis strains seem to be protected against amoebae grazing, but it is unclear whether this is achieved by their colony morphology or biochemically. These factors were investigated in grazing experiments using two Microcystis -grazing amoebae ( Korotnevella sp. and Vannella sp.) and two Microcystis strains with differing colony morphology ( aeruginosa and viridis morphotype) and different sensitivity to amoebae grazing. Amoebae did not increase in density and failed to reduce the growth rate of cultures of the amoebae insensitive viridis strain, irrespective of whether the Microcystis strain was colonial or unicellular. This suggests that the extended mucilage matrix surrounding viridis colonies is not the main defence mechanism against amoebae grazing. At the same time, the growth rate of both unicellular and colonial cultures of the amoebae-sensitive aeruginosa strain was heavily reduced by the growing amoebae. The addition of filtered viridis -conditioned medium to aeruginosa cultures significantly decreased both amoebae growth and its effect on aeruginosa growth rates, which indicates that extracellular compounds constitutively produced by viridis are at least partially responsible for their insensitivity to amoebae grazing. These results demonstrate the potential importance of chemical interactions between lower trophic levels (protists) for Microcystis bloom dynamics. Content Type Journal Article Pages 1-12 DOI 10.1007/s10452-011-9382-8 Authors Jeroen Van Wichelen, Research Group Protistology & Aquatic Ecology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium Ineke van Gremberghe, Research Group Protistology & Aquatic Ecology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium Pieter Vanormelingen, Research Group Protistology & Aquatic Ecology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium Wim Vyverman, Research Group Protistology & Aquatic Ecology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    In Patagonian rocky salt marshes, the presence of the austral cordgrass Spartina densiflora provide habitat for diverse faunal assemblages. Two different mechanisms may influence the distribution and abundance patterns of these associated organisms: those generated by the biological properties of cordgrasses and those caused or mediated by the physical structure supplied by the plants. The aims of this study were: (1) to determine the effect of cordgrasses on macroinvertebrate assemblages dominating a rocky marsh and (2) to determine how much of this effect is caused by the physical structure supply by the plants. In order to achieve these objectives, we conducted two field manipulative experiments. In the first one, we manipulated the presence of defaunated transplants of cordgrass, and in the second one, we did the same with plastic cordgrass mimics simulating the architecture of Spartina densiflora. In both experiments, sessile and mobile assemblages were separately examined to evaluate whether they respond in the same way or not. Abundance and richness of mobile and sessile organisms were higher in transplant and mimic cordgrass plots compared to the controls, indicating that the presence of cordgrasses, either transplanted or artificial, has a positive effect on sessile and mobile assemblages. Furthermore, we found that the composition of mobile and sessile macroinvertebrates assemblages did not differ between transplants and mimics. Therefore, the physical structure of cordgrass was found to be the major factor influencing macroinvertebrates assemblages in the studied Patagonia rocky salt marshes. Within the period of 1 year, mobile and sessile fauna colonized several times more abundantly transplant and artificial cordgrass than the control unvegetated plots, highlighting the key role of cordgrasses in optimizing the colonization rate of macroinvertebrate communities in this rocky bottom environment. Since Spartina densiflora is invading different regions worldwide, our study may help to predict its potential effect on the invaded communities. Content Type Journal Article Pages 1-12 DOI 10.1007/s10452-011-9379-3 Authors María Cruz Sueiro, Grupo de Ecología en Ambientes Costeros, CENPAT-CONICET, Blvd. Brown 2915 (U9120ACD), Puerto Madryn, Chubut, Argentina Alejandro Bortolus, Grupo de Ecología en Ambientes Costeros, CENPAT-CONICET, Blvd. Brown 2915 (U9120ACD), Puerto Madryn, Chubut, Argentina Evangelina Schwindt, Grupo de Ecología en Ambientes Costeros, CENPAT-CONICET, Blvd. Brown 2915 (U9120ACD), Puerto Madryn, Chubut, Argentina Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Various species of Daphnia usually play a key role in the food web of temperate freshwater systems. There is much evidence to show that climate change may influence Daphnia population dynamics, consequently altering both predator–prey interactions and the efficiency of algal biomass control in these ecosystems. This review will analyse and discuss the current knowledge on Daphnia responses to climate warming based on an analysis of selected papers. The presented results indicate that warming may have important direct and indirect effects on Daphnia biology and ecology via its influence on their life-history processes (metabolism, growth, reproduction) and the properties of their habitats. The plasticity of daphnids in terms of adaptive responses is generally high and includes phenotypic adaptations and changes in genotypes, although it also depends upon the strength of selection and the available genetic variation. The seasonal timing and magnitude of temperature increases are important for seasonal biomass fluctuations of Daphnia and similarly influence the potential synchrony of daphnids and phytoplankton succession (the timing hypothesis). In light of the most recent studies on this topic, even a minor warming during short but critical seasonal periods can cause factors that disturb Daphnia population dynamics to coincide, which may destabilize lake food webs by decoupling trophic interactions. Both winter and spring are important critical periods for determining future seasonal fluxes of Daphnia spp. and, consequently, the time of the clear-water phase and the occurrence and duration of Daphnia midsummer decline. Winter conditions may also affect the impact of fish predation on daphnids during summer months. However, the effects of global warming on Daphnia population dynamics and on ecosystem functioning are often difficult to predict due to their complexity and the presence of both antagonistic and synergistic drivers. Thus, the diverse responses of daphnids to climate anomalies depend on both biotic (predator abundance and seasonal phytoplankton succession) and abiotic factors (e.g. hydrodynamics, intensity and duration of thermal stratification, trophic state or geomorphology) of lakes, which are directly influenced by weather changes. The analysis and quantification of such complex interactions require the involvement of different kinds of specialists and the development of accurate research approaches, such as molecular genetic methods or mathematical modelling. Content Type Journal Article Pages 1-17 DOI 10.1007/s10452-011-9380-x Authors Adrianna Wojtal-Frankiewicz, Department of Applied Ecology, University of Lodz, Banacha 12/16 Str, 90-237 Lodz, Poland Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Although community structure may be largely determined by local abiotic and biotic conditions under moderate levels of dispersal, anthropogenic activities can enhance dispersal rates far beyond what would otherwise occur in natural systems. We investigated the potential impact of recreational canoeing on crustacean zooplankton community structure in Killarney Provincial Park, Canada, where canoes that are transported between lakes via portage routes may enhance zooplankton community connectivity by providing a dispersal “short-cut.” We conducted a study to (1) quantify zooplankton attachment to canoe hulls after paddling through a lake and assess the importance of canoes to overall seasonal dispersal within a lake relative to other means of dispersal, (2) test the prediction that zooplankton survivorship is negatively correlated with portage duration using a mesocosm experiment, and (3) test whether variation in lake community composition was better explained by models based on reduced portage-corrected distances or true edge-to-edge distances between lakes along popular canoe routes. Here, we report the findings that canoes have the potential to act as frequent dispersal vectors, but appear to have little impact on community structure in portage-connected lakes. Substantial numbers of adult zooplankton became attached to canoe hulls and were able to establish viable populations even after exposure to portage conditions for 30 min. However, canoe-mediated dispersal only accounted for a very small proportion (〈1% in this case) of overall seasonal dispersal. Moreover, environmental variables explained the greatest amount of variation in community composition among park lakes. Nevertheless, this study indicates that canoe dispersal could be more effective for specific species such as Sida crystallina than is evident by analysis of entire communities and could facilitate the spread of invasive species amenable to attaching to boat hulls. Thus, the debate about whether community composition is more strongly influenced by local environmental conditions or regional dispersal may vary depending on the scale of consideration (i.e., individual species vs. whole community). Content Type Journal Article Pages 1-16 DOI 10.1007/s10452-011-9378-4 Authors Ashley D. Stasko, Department of Biology, Queen’s University, 116 Barrie St., Kingston, ON K7L 3J9, Canada Theresa Patenaude, Department of Biology, Queen’s University, 116 Barrie St., Kingston, ON K7L 3J9, Canada Angela L. Strecker, Department of Environmental Science and Management, Portland State University, PO Box 751, Portland, OR 97207, USA Shelley E. Arnott, Department of Biology, Queen’s University, 116 Barrie St., Kingston, ON K7L 3J9, Canada Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588