The third MedSeA training activity focused on the standardization of the experimental design of acidification perturbation experiments on planktonic organisms, and it was held at the Hellenic Centre for Marine Research (HCMR) premises at Anavyssos (Greece), on 21^st-23^rd September 2011.

In the morning the training activity included theoretical and review lectures and in the afternoon hands-on laboratory experiences on chemical and biological techniques and protocols related to OA experimental design on selected planktonic organisms. The local organizing team was led by Eva Krasakopoulou, with the help of Ioanna Varkitzi and the contribution of specialists within the MedSeA consortium and collaborators from BIOACID, EPOCA and UK OA projects. The lectures and laboratory techniques presented by Kai Schulz (IFM-GEOMAR – Leibniz Institute of Marine Sciences), Alex Poulton (National Oceanography Centre Southampton), Frederic Gazeau (UPMC – Laboratoire d’Oceanographie de Villefranche), Patrizia Ziveri (UAB-ICTA), Marcello Vichi (CMCC) and Popi Pagou (HCMR), gave the opportunity to the participants to gather key knowledge and useful insights for setting up and performing OA experiments.

A total of 23 PhD students, postdoctoral researchers and PIs from Egypt, France, Italy, Morocco, UK, Spain, Greece involved in the MedSeA project and 1 from Sweden involved in the EPOCA project attended the workshop.

During the training, in parallel to the theoretical presentations, instructors also provided demonstrations of software packages used to calculate CO₂ system parameters (CO2SYS, seacarb) and showed the use of the TRIS seawater buffer to get accurate pH measurements in seawater. The short perturbation experiments were conducted on cultures of one calcifying (Emiliania huxleyi) and one non-calcifying phytoplanktonic organism (Dunaliella tertiolecta) with the purpose of showing the basics of how the carbonate chemistry manipulation is performed and how cell growth affects the CO₂ system. The carbonate system was monitored through pH measurements and A_T titration. The experimental planning included the study of growth rates, primary production via O₂ dynamics and ¹⁴C incorporation of the two species and calcification rate of Ehux by A_T consumption and following the ¹⁴C-based ‘Micro-Diffusion Technique’, in the different pH levels.

The aim of the workshop was to provide an opportunity for training on appropriate techniques and protocols related to ocean acidification research using a combination of lectures and laboratory work build upon the recommendations of the ‘Guide to best practices for ocean acidification research and data reporting’.

A major impact of the workshop was to provide to the new generation of European OA experimentalists the fundamentals of ocean acidification experimental design, such as manipulation of seawater chemistry, biological perturbation approaches, and lab- and field-based methods for measuring organism calcification and other physiological responses to seawater chemistry changes.