Difficult to answer precisely. About 115 scientist and engineers are registered as participants, and these work part or full-time on the project. But most receive their salaries from home institutions.
In addition, the Secratariat in Arendal, Norway includes Tone Falkenhaug and me who work about 80% of the time on MAR-ECO. Other management people are also involved (please see the website).
Unfortunately, the project cannot offer jobs unless we receive extra funding from e.g. Research Councils or other sources. We are continuously trying to win grants in order to hire students and other staff, and we've had some success.