In situ automated imaging, using the Plankton Imager, captures temporal variations in mesozooplankton using the Celtic Sea as a case study

The Plankton Imager (PI) is an underway semi-automated, high-speed imaging instrument, which takes images of all passing particles and classifies the mesozooplankton present. We used data (temperature, salinity and mesozooplankton abundance) collected in the Celtic Sea in spring and autumn from 2016 to 2019 to assess the ability of the PI to describe temporal changes in the mesozooplankton community and to capture the seasonality of individual taxa. The description obtained using the PI identified both seasonal and interannual changes in the mesozooplankton community. Variation was higher between years than seasons due to the large variation in the community between years in autumn, attributed to the breaking down of summer stratification. The spring community was consistent between years. The seasonality of taxa broadly adhered to those presented in the literature. This demonstrates the PI as a robust method to describe the mesozooplankton community. Finally, the potential future applications and how to make best use of the PI are discussed.