Picturing plankton: Complementing net-based plankton community assessments with optical imaging across diverse marine environments

Abstract

In recent years, optical imaging has emerged as a promising tool for in situ observations of plankton. In this study, we aimed to compare the plankton community estimates obtained from a Video Plankton Recorder (VPR) imaging device with net-based approaches. By collecting VPR and net samples in clear waters with large-sized plankton and eutrophic waters with small-sized plankton, spatial and temporal patterns in plankton densities and community composition were compared. Furthermore, it allowed the evaluation of the performance of imaging methods under diverse hydrographic conditions. We observed pronounced spatial differences in density estimates. In the eutrophic site, the WP2 net densities consistently surpassed those from a VPR, while in the clear water site the observed densities of the VPR and a MultiNet were more similar. Variations in water column turbidity, plankton body size, plankton nets and their mesh size, and the total sampled water volume were found to likely play a role in the observed inconsistencies between the sampling sites. The results suggested that a VPR is particularly well-suited for use in clear waters inhabited by large-sized plankton. The VPR demonstrated potential in enhancing density estimates of fragile (Phaeocystis) and gelatinous taxa (Cnidaria and Ctenophora) in specific environments being non-invasive. Overall, the VPR and other optical imaging devices show valuable insights into zooplankton ecology and distribution, complementing density estimates of traditional net sampling methods, and enhancing our understanding of the role of zooplankton in marine ecosystems.