Continuous plankton recorder underestimates zooplankton abundance

A comparison between monthly mean Continuous Plankton Recorder (CPR) data and zooplankton data caught during winter and early spring with different sampling devices in the North Sea is presented to estimate the relative error in abundance of CPR measurements. CPR underestimates the abundance of zooplankton by a factor 25 during winter and early spring and by a factor 18 if Oithona spp. is not considered. This has serious implications for estimation of biomass as well as for modelling ecosystem dynamics.

► Direct comparison of conventional net catches indicates that CPR underestimates zooplankton abundance by a factor 25.
► If Oithona spp. is not considered the underestimation is by a factor 18.
► These findings have implications for estimation of biomass and consequences for ecosystem modelling.