Literature on the trophic ecology of small pelagic fish (primarly anchovy Engraulis spp. and sardine Sardinops spp. but including the genera Brevoortia, Clupea, Sardina, Sprattus, and Strangomera) and their interactions with plankton are reviewed using case studies describing research on some economically and ecologically important small pelagic fish from up-welling and temperate non-upwelling ecosystems. Information from morphological studies of the feeding apparatus, field studies on dietary composition and foraging behaviour, and laboratory studies that have provided data for the parameterization of bio-energetic and other models of these small pelagic fish are presented, where available. Two or more small pelagic fish species are described in each case study, and disparities in trophic dynamics between co-occurring anchovy and sardine are consistently seen, supporting the hypothesis that species alternations between the two species could be trophically mediated. Linkages between climate and fish are described for many of the systems, and possible impacts of climate change on some of the species are described.
Small pelagic fish are, in general, microphagous planktivores, and their high abundance levels in upwelling systems, in particular, was attributed to their ability to feed directly on phytoplankton and hence benefit from a short and efficient food chain (Ryther, 1969; Walsh, 1981). This two-step food chain hypothesis, with small pelagic fish being regarded as essentially phytophagus and feeding on large, chain forming diatoms such as Chaetoceros and Fragilaria (Yoneda and Yoshida, 1955; Bensam, 1964; Loukashkin, 1970; King and Macleod, 1976) was initially well supported (Longhurst, 1971; Durbin, 1979; Walsh, 1981).