Chapter 18: Trophodynamics
Chris Harrod and Christopher D. Stallings
Inhabiting almost all aquatic ecosystems on earth, fish display a striking level of variation in terms of their diet and trophic strategies, occupying all trophic levels beyond that of primary producers (Gerking 1994; Hart 2019). Fish play keystone roles in aquatic systems, acting as both predators and prey, and serve as important vectors of nutrients, energy, contaminants, parasites, and pathogens. Although largely studied by fish ecologists, an understanding of what (also how much, how, where, when, and why) fish eat is key to many different areas of fish biology and associated fields, including fisheries science, aquaculture, environmental science, zoology, and evolutionary biology. Characterizing how energy, nutrients and contaminants move both through and across ecosystems is key to developing an understanding of food webs and community/ecosystem function (Cabana and Rasmussen 1994; Thomas et al. 2016). Ecosystem models such as Ecopath and Atlantis are increasingly used to direct management of ecosystems and fisheries (Pauly and Christensen 2008; Pitcher 2016). Aquaculture production continues to grow and diversify as the sector aims to feed a growing human population (FAO 2018); however, many questions remain regarding the optimal diet for cultured fish, and surprises likely await that may upset perceived certainties regarding fish nutrition (Lazzarotto et al. 2015). There is a large, and growing, toolbox available to fish ecologists to aid their understanding of fish trophic ecology (Majdi et al. 2018; Nielsen et al. 2018; Pethybridge et al. 2018). This chapter aims to provide a topical review of the key methods and their relative uses for fish biologists and allied researchers. Given the need for brevity, we have kept this text as succinct as possible; however, the online supplemental materials for this chapter (OSM18) provide a more detailed discussion of the different subjects covered here, and we refer the interested reader to them throughout the text.