Copepod feeding and reproduction in relation to phytoplankton development during the PeECE III mesocosm experiment

Abstract

Within the frame of the Pelagic Ecosystem CO2 Enrichment (PeECE III) experiment, re- production and feeding of the copepod Calanus finmarchicus was monitored in relation to phytoplankton development in two mesocosms, at present 1 (350 atm) and ca 3 5 present (1050 atm) CO2 concentrations, respectively. Both mesocosms showed rapid phytoplankton growth after the initial nutrient additions and reached maximum chloro- phyll (Chl) concentrations around day 10. Flow-cytometry and specific pigment analy- sis (HPLC-CHEMTAX), showed that diatoms and prymnesiophyceae (Emiliania huxleyi (Ehux) and other nanoplankton) dominated the biomass. Feeding and egg production 10 rates of C. finmarchicus developed similarly in both mesocosms, and were positively correlated with Chl, Ehux, diatom and prymnesiophyceae concentrations. Although the total number of copepod nauplii recruited during the experiment was similar in 1 and 3, significantly less nauplii were recruited in 3 during the peak of the bloom compared to in 1. We conclude that the algae responsible for the higher biomass in 15 3 during the peak of the bloom (diatoms and Ehux), may have been relatively inferior food for C. finmarchicus naupliar recruitment, possibly due to a high C:N ratio (8). Nevertheless, the 3 fold increase in CO2 concentration did not show any clear overall eðect on bulk phytoplankton or zooplankton development over the whole experiment, suggesting a more complex coupling between increased CO2 and the nutritional status 20 of the system.