Fereidoun Rassoulzadegan (1943–2026)

In early January of 2026, we lost a pioneer contributor to the field of microbial ecology, Fereidoun Rassolzadegan (Fig. 1). He arrived in France, from his native Iran in the 1970s, to pursue studies in biology. At the Station Zoologique in Villefranche-sur-Mer, Fereidoun turned his attention to the ciliates of the microzooplankton. At the time, the ciliates of the marine plankton, previously neglected, were receiving increasing attention as a potentially important group in food web dynamics due to the studies of Jack Beers, Larry Pomeroy, and others (e.g., Beers and Stewart 1969; Pomeroy 1974). Fereidoun soon made his mark as an expert on the two main groups of ciliates, oligotrich and tintinnids, through a series of field studies (Rassoulzadegan 1977a; Rassoulzadegan 1979; Rassoulzadegan and Gostan 1976) as well laboratory experiments (Rassoulzadegan 1977b, 1978, 1980, 1982; Rassoulzadegan and Etienne 1981). Shortly after the appearance of his series of studies on ciliates of the marine plankton, Fereidoun participated in the organization of a key event in the development of microbial ecology, the 1981 workshop “Marine Pelagic Protozoa and Microzooplankton Ecology” in Villefranche-sur-Mer. Among the approximately 30 participants were many established authorities of the time, such as Ramon Margalef, Tom Fenchel, Michael Droop, Max Taylor, as well as young researchers, including the likes of Diane Stoecker and Gerard Capriulo, who later marked the field. The 1982 volume of papers from the workshop was reviewed in Limnology and Oceanography (Banse 1984), and the papers have been cited hundreds of times. Fereidoun was also involved in the organization of a larger, in some ways a follow-up workshop in 1988, “Protozoa and Their Role in Marine Processes” held in Plymouth (UK). Many papers from this later workshop were published in a special issue of the journal Fereidoun had founded in 1985, Marine Microbial Food Webs. Marine Microbial Food Webs was, admittedly, with its limited scope, a “boutique journal”. Nonetheless, the small journal published articles authored by relatively big names in microbial ecology such as Larry Pomeroy, Barry and Evelyn Sherr, Akira Taniguchi, and Peter le B. Williams. In 1994, the publisher, the Institut Océanographique, abruptly closed its journal division (i.e., without any advance notice!). Marine Microbial Food Webs was taken over by Inter Research in 1995 as Aquatic Microbial Ecology, the sister journal of Marine Ecology Progress Series. Fereidoun was an Editor-in-Chief of Aquatic Microbial Ecology until his recent untimely demise. Throughout his years in Villefranche, right up until his retirement in 2008, Fereidoun hosted many researchers, of diverse interests. Often, they could be found in deep conversation with Fereidoun, as guests usually occupied the spare desk in his office, directly facing his own. Among others, hosted researchers included Louis Legendre, Ray Sheldon, Frede Thingstad, and Paul Wassmann. Often, they hatched small research projects such as experimental investigations of the predator–prey dynamics of bacteriovores and bacteria (e.g., Rassoulzadegan and Sheldon 1986), or a large projects such as the European program Cyclops that investigated phosphorus cycling in the Mediterranean (e.g., Thingstad et al. 2005). Many of us in marine microbial ecology have been touched, directly or indirectly, by Fereidoun. Moreover, he also had an impact on many members of ASLO, a society he first joined in 1986. Fereidoun was a regular of the Ocean Sciences meetings where he co-chaired special sessions. He was the epitome of an “ideas man,” playing an important role in the development of now familiar concepts such as the role of hydrodynamics in determining food web structures (Legendre and Rassoulzadegan 1996), and the role of viruses in diversity dynamics of bacterioplankton (i.e., Weinbauer and Rassoulzadegan 2004). His imaginative and open spirit will be sorely missed.