Parasites of small pelagics reflect their role in marine ecosystems

Abstract

Small pelagics occupy an intermediate trophic level in marine ecosystems, serving as prey for a variety of predators and thus playing a very important role in these ecosystems. This review collates information gleaned from parasitological studies of small pelagics (fish, squid and euphausiids) and describes the valuable biological information they can provide. We describe why parasitology studies are important and how they have contributed to our understanding of the role of small pelagics in marine ecosystems. Pertinent general patterns in marine parasite ecology relevant to trophic interactions in small pelagics, including variations in parasite faunas with features such as host size, depth distribution and feeding behaviour are synthesized. With their relatively long life spans relative to stomach contents and stable isotopes, trophically transmitted parasites can provide a unique dietary history for the host. Therefore, we summarize the trophically transmitted parasites found most frequently in small pelagics and assess the potential of different parasite taxa as indicators of host diet. The use of multiple techniques, including stomach contents and stable isotopes, along with parasites, are evaluated to better reveal fish diets. Parasites provide complementary, and additional, information compared to other techniques. Furthermore, we discuss how the presence of certain parasites in small pelagics can be used to infer their main predators and emphasize the neglected but important role of parasites in elucidating a host’s role in marine food webs. Lastly, we identify important gaps in our knowledge of the parasites of small pelagics and what can be done to fill these gaps.