Preface

Recent studies on food quality for zooplankton have developed two new hypotheses, the importance of the dietary carbon to phosphorus (C : P) ratio and of certain ‘essential’ fatty acids. These new hypotheses, the controversies they have provoked and the general lack of field studies prompted us to organize a workshop. Thus, the first international Plankton Ecology Group (PEG) workshop on The Role of Food Quality for Zooplankton was held from 17 to 21 March 1996 at the Centre of Limnology in Nieuwersluis, the Netherlands. The main objectives were to take stock of the state‐of‐the‐art in food quality research, to address the factors that determine food quality, and to integrate the available information into a coherent and consistent view of food quality for the zooplankton. In contrast to most PEG meetings, we restricted the meeting to about 35 participants. However, international participation was broader than usual and included colleagues from North America and Asia, as well as Europe. The workshop’s organizers, Ramesh Gulati, a senior scientist, and Paul M. M. Weers, a post‐doc at the Centre Of Limnology, approached potential speakers, in some cases suggesting topics for presentation. Each of five sessions was introduced with a review paper or a modelling paper.This special volume of Freshwater Biology contains twenty‐six papers, including a summary by R. Gulati & B. DeMott. This paper briefly describes the findings of the workshop, and discusses them in light of the literature, discussions at the workshop and written comments from participants. Each of the workshop papers was peer reviewed, usually by two but in some cases by three referees. We learned that fatty acids and phosphorus are not mutually exclusive alternatives; the content of polyunsaturated acids of certain algae, especially eicosapentaenoic acid (EPA), is markedly affected by the algal P content. Thus, elemental limitation and fatty acid limitation may have additive or interacting effects. Although further research might modify this view, the accumulating evidence for P limitation seems stronger than for fatty acids limitation. However, despite laboratory studies that have clarified the potential mechanisms of food quality, the paucity of field studies prevents a consensus on the importance of specific mechanisms in nature. We also learned much from aquaculture studies, which have developed techniques for enriching zooplankton food with fatty acids and essential nutrients. We believe that the workshop proceedings will both contribute to our understanding and stimulate further research on food quality for zooplankton. Lastly, we take cognizance that cyanobacterial toxins are an important area of food quality research, which for practical reasons, did not receive our attention. Several presentations, however, revealed that cyanobacteria are also potentially poor food due to both higher C:P ratios and lower fatty acid content than many other algal species.Paul Weers’ efforts in organizing the workshop were very helpful. We acknowledge the facilities, funds and encouragement provided by staff and administration of the Centre of Limnology. We are also grateful to the participants for their cooperation and to the reviewers, many of whom were workshop participants.RAMESH D. GULATIBILL DEMOTT