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To eat, to be eaten, and a lot of questions: understanding the trophic ecology of small pelagic fish Susana Garrido Portuguese Sea and Atmosphere Institute, Portugal. E-mail: [email protected] Small pelagic fish are typically abundant in the highly productive regions of the world’s oceans where they are thought to control the variability of these ecosystems by exerting top-down control on their plankton prey and bottom-up control on their predators. Whereas some recent studies suggest that at least some of these ecosystems are more stable and diverse than initially thought, the importance of small pelagic fish in mediating energy transfer from plankton to higher trophic levels is indisputable. This talk will describe trophodynamically-mediated processes that influence small pelagic fish dynamics, from the indirect effect of spawner body condition on the quantity and quality of reproductive products, to the direct impact of food availability on larval survival. The plasticity and variability of small pelagic fish diets and feeding behaviours, morphological and behavioural adaptations of populations to prevailing environmental conditions, competition with co-occurring species, cannibalism and intraguild predation, and the simple difficulty of properly quantifying both their prey and their predators in the field make it difficult to assess the impact of environmental changes on the pelagic foodweb. However, studies using stable isotopic composition, laboratory experimentation and modelling are presently being carried out for several (and contrasting) ecosystems, including the Iberia/Canary, Benguela and California eastern boundary upwelling ecosystems and the Mediterranean Sea, which are advancing our knowledge of the relationship between environmental variability and dynamics of small pelagics, and these are briefly described and discussed.