The Effect of Mesh Size on the Interpretation of the Life History of Two Mayflies from South Australia
Using a Surber-type benthic sampler with a double net collecting system, the efficiency of nets having aperture sizes of 480 μm and 110 μm was assessed over a twelve month period in two streams in South Australia. Efficiency was defined as the percentage increase in yield (numbers) of animals obtained by use of 110 μm mesh instead of 480 μm mesh. The average annual increase in sampling efficiency of the fine net as compared with the coarse for mayfly nymphs was 412% and 235% for Spring Creek and Deep Creek respectively. The life cycles of two species of mayfly Tasmanocoenis tillyardi (Lestage) and Baetis soror Ulmer from Deep Creek are presented and the effect of the two mesh sizes on the interpretation of the life histories is discussed. Interpreted from the coarse mesh only, the life cycle of both species is bivoltine, each having one winter generation and one summer generation. Combining both fine and coarse net collections, the life cycle interpretation is distinctly different, illustrating the difficulties in drawing conclusions from coarse mesh samples. Not only is the number of generations misinterpreted in B. soror, but conclusions on the duration of the egg stage and length of each generation are also inaccurate for both species.
KeywordsBiomass Ethyl Depression Polyethylene Gravel
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