Comparative zooplankton sampling efficiency of a ring net and bongo net with comments on pooling of subsamples

We analyzed the comparative sampling efficiency of CalCOFI 1 m diameter ring nets and bongo nets in a series of paired comparisons from the California Current. Seventeen major taxa of holozooplankton were enumerated and species-specific analyses were carried out for hyperiid amphipods. The only consistent difference detected between these two nets was a significant increase in abundance of salps in the bongo net. In contrast with comparisons of abundance, the species diversity of hyperiid amphipods was higher when estimated from ring net than from bongo net collections, at higher numbers of individuals enumerated. Analysis of a sample pooling procedure revealed that the average abundance of the more numerous taxa was generally similar, whether determined by enumerating plankton samples individually or from a pooled sample comprising quantitative splits of individual samples. The average abundance of rare taxa was not well represented in the pooled sample. Sample pooling is particularly inappropriate for studies of pelagic species diversity