Screen Mesh Size Affects Estimates of Macro- and Meio-benthos Abundance and Biomass in the Great Lakes

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Abstract
The efficiencies of screens with mesh openings of 595 and 106 μm in retaining, respectively, the macro- and meio-benthos were measured for samples taken in southeastern Lake Michigan. The use of these screens provides adequate estimates of dry weight biomass for both the macro- and meio-benthos, but serious underestimates of the numbers of many taxa, most notably naidids, enchytraeids, chironomids, nematodes, and rotifers, can result. For chironomids, retention on the 595-μm screen varied by species, with overall retention being closely related to both body length and head capsule width. Retention for certain macro-benthic taxa was significantly related to sampling date and water depth, indicating that future studies concerned with these variables should use mesh sizes small enough to retain all (or almost all) of the individuals of the taxa of interest.Key words: mesh size, screen efficiency, percent retention, macrobenthos, meibenthos, Lake Michigan