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Nonmetric multidimensional scaling (NMDS) is a powerful statistical tool which enables complex multivariate data sets to be visualized in a reduced number of dimensions. Users typically evaluate the fit of an NMDS ordination via ordination “stress” (i.e., data distortion) against a commonly accepted set of heuristic guidelines. However, these guidelines do not account for the mathematical relationship which links ordination stress to sample size. Consequently, researchers working with large data sets may unnecessarily present ordinations in an intractable number of dimensions, subdivide their data, or forego the use of NMDS entirely and lose the benefits of this highly flexible and useful technique. In order to overcome the limitations of these practices, we advocate for an alternative approach to the evaluation of NMDS ordination fit via the usage of permutation‐based ecological null models. We present the rationale for this approach from a theoretical basis, supported by a brief literature review, and an example usage of the methodology. Our literature review shows that NMDS analyses often far exceed the number of observations under which the original stress guidelines were formulated—with a significant increasing trend in recent decades. Adoption of a permutation‐based approach will consequently provide a more flexible and quantitative evaluation of NMDS fit and allow for the continued application of NMDS in an era of increasingly large datasets.

-1). With respect to biomass ingestion, in every experiment mesozooplankton were found to ingest ciliate carbon at the highest rates (3 to 29 ng C pred.-1 h -1). Our results indicate that while estuarine mesozooplankton are often omnivorous, important species-specific differences exist, and microzooplankton, especially ciliates, are an important component of the upper SFE food web.

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Nonindigenous aquatic species are becoming increasingly common in coastal and inland waters, largely due to the global transport of zooplankton via commercial shipping and recreational boating. The cost of mitigation and lost income due to invasive zooplankton is estimated in the billions of dollars annually, yet we know little about the temporal dynamics of these invaders. Analysis of an 8.5-year (June 2005-December 2013) zooplankton time series from the Columbia River revealed contrasting patterns of invasion dynamics between species, cyclical periods of community invasion, and key environmental variables that constrain populations of invasive zooplankton. We identified four seasonal zooplankton communities (autumn/ invaded, winter/barren, spring/rotifer, and transitional) that are strongly correlated with changes in chlorophyll content and water temperature, with peak abundances of invasive zooplankters occurring during periods of maximum water temperature. Additionally, we observed contrasting patterns of phenology between persistent and ephemeral invasive populations, with successful invaders exhibiting delayed annual peaks in population abundance. Two invasive zooplankters-the copepod Pseudodiaptomus forbesi and larval Asian clam Corbicula fluminea-dominate the zooplankton community in late summer and early autumn. Likewise, our results support conclusions from a growing body of literature that delayed phenology may be a key functional trait for successful invaders.

Research on the ecology and impacts of the zebra mussel (Dreissena polymorpha) has developed in parallel with the long history of their spread across Europe and to North America. There is less scientific knowledge however about the quagga mussel (Dreissena rostriformis bugensis). The recent spread of both zebra and quagga mussels to the Western states of the USA, has spurred on dreissenid research. The 17th International Conference on Aquatic Invasive Species (ICAIS), was held in San Diego, California in September 2010. This special edition of Aquatic Invasions includes topical research presented at ICAIS and also extra subsequent papers on ecology, risk assessment and control of various aquatic invasive species in different parts of the globe.

Abstract. We investigate relationships between environmental governance and water quality in two adjacent growing metropolitan areas in the western US. While the Portland, Oregon and Vancouver, Washington metro areas share many common biophysical characteristics, they have different land development histories and water governance structures, providing a unique opportunity for examining how differences in governance might affect environmental quality. We conceptualize possible linkages in which water quality influences governance directly, using monitoring efforts as a metric, and indirectly by using the change in the sale price of single-family residential properties. Governance may then influence water quality directly through riparian restoration resulting from monitoring results and indirectly through land use policy. We investigate evidence to substantiate these linkages. Our results showed that changes in monitoring regimes and land development patterns differed in response to differences in growth management policy and environmental governance systems. Our results also showed similarities in environmental quality responses to varying governance systems. For example, we found that sales prices responded positively to improved water quality (e.g., increases in DO and reductions in bacteria counts) in both cities. Furthermore, riparian restoration efforts improved over time for both cities, indicating the positive effect of governance on this land-based resource that may result in improved water quality. However, as of yet, there were no substantial differences across study areas in water temperature over time, despite an expansion of these urban areas of more than 20 % over 24 years.The mechanisms by which water quality was maintained was similar in the sense that both cities benefited from riparian restoration, but different in the sense that Portland benefited indirectly from land use policy. A combination of long-term legacy effects of land development, and a relatively short history of riparian restoration in both the Portland and Vancouver regions, may have masked any subtle differences between study areas. An alternative explanation is that both cities exhibited combinations of positive indirect and direct water quality governance that resulted in maintenance of water quality in the face of increased urban growth. These findings suggest that a much longer-term water quality monitoring effort is needed to identify the effectiveness of alternative land development and water governance policies.

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