Quantification of marine metazooplankton: Do we need to include juveniles?

Abstract

In 1966, Working Party 2 of the Scientific Committee on Ocean Research (SCOR) chose the mesh size of 200 µm to collect zooplankton of a width of >200 µm. In the proceeding decades, research has described various zooplankton taxa with widths narrower than 200 µm. For example, we have become more aware of the existence of juvenile stages and small zooplankton species. Yet, utilizing nets with 200 µm mesh has continued to some extent, although it is recognized that juvenile stages and smaller species are not quantitatively collected. We suggest that zooplankton sampling be reconsidered by using meshes or methods which quantitatively collect small species and juvenile stages (nauplii and copepodids). These new methods should take into account the narrowest dimensions of the taxon to be studied, thus allowing quantitative sampling of the forms under investigation. To maintain previous time-series, we suggest to continue sampling with cylinder-cone nets of 200 µm mesh for mesozooplankton and add sampling with 30 l Go/Flo bottles at various depths sieved through 20 µm mesh to retain all nauplii and small copepodid stages.