Accounting for Spatial Variability in the Design of Sampling Programmes for Chaoborus Larvae

Abstract

We developed a model to estimate the number of net hauls (n) needed to quantify the mean abundance (m) of vertically migrating species of Chaoborus larvae (C. flavicans, C. punctipennis andC. trivittatus) in the entire pelagic zone of lakes at a specified level of precision (D = SE/m, where SE is the standard error). The model was n = 1.94m–0.30D–2. It was derived by combining Taylor's power law with a model that estimated sample size (i.e. number of net hauls) for a specified level of precision. The model indicates that for a typical temperate lake Chaoborus population of 50 larvae m–3, 15 net hauls are required to obtain a precision of 0.2. As the precision of a single pelagic, vertical haul is only 0.77 at such typical Chaoborus densities, caution should be exercised in assessing the role of Chaoborus in food webs using data based on the traditional approach to plankton sampling, i.e. one mid-lake station.