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Multiple Tube Sampler for Benthic and
Pelagic Invertebrates in Shallow Wetlands

Introduction


Quantitative ecological investigations of aquatic invertebrates in wetlands are increasing in response to studies stressing the importance of aquatic invertebrates to waterfowl. Prior to the late 1960's, waterfowl were thought to feed mostly on plant foods (Cottam 1939, Martin and Uhler 1939). Improved food habit techniques (Swanson and Bartonek 1970) stimulated investigations that demonstrated the dietary value of aquatic invertebrates to waterfowl throughout the year (Swanson et al. 1979, Reinecke and Owen 1980, Euliss and Harris 1987). Interest in aquatic invertebrates also resulted from investigations that demonstrated their role in the epizootiology of avian botulism (Bell et al. 1955, Jensen and Allen 1960, Duncan and Jensen 1976), and their value as biological indicators of pesticide residues in wetlands (Grue et al. 1989).

Ecologists need sampling devices and techniques that will function in aquatic habitats utilized by waterfowl. Sampling devices used for estimating standing crops of invertebrates (Swanson 1978a,b, 1983, and several devices described by Merritt and Cummins 1984) have been designed to sample water column or benthic invertebrates in lentic habitats. To adequately quantify wetland invertebrates, information is needed on both water column and benthic invertebrates. However, there are no devices that simultaneously sample from both habitats. Pooling data from different sampling devices that estimate water column and benthic invertebrates separately can create bias because of the double sampling of organisms that are associated with the benthic-pelagic interface.

Spatial distribution of invertebrates compounds sampling problems because most taxa are contagiously distributed into aggregations of individuals (Elliott 1977, Resh 1979, Downing 1979). Data sets frequently contain a high proportion of zero observations and have large variances associated with a negative binomial sampling distribution (Elliott 1977). Because of large variance, the number of samples required to estimate means with nominal confidence is limited by available manpower. Sorting of invertebrates is also time consuming and often limits the level of precision attainable in specific investigations.

Sampling devices that minimize bias and provide precise estimates of invertebrate populations are needed. Herein, we describe a device that eliminates the bias related to oversampling because water column and benthic organisms are sampled simultaneously; has the statistical advantage of partitioning samples into 4 subsamples; and can be used to estimate within-sample variance of invertebrates in shallow wetlands.

We thank P. L. Hudson, C. E. Korschgen, and J. H. Selgeby for critical review of this manuscript. D. M. Mushet prepared the figure.


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