Trade-Offs Between Supportive and Provisioning Ecosystem Services of Forage Species in Marine Food Webs

In marine fisheries, there are trade-offs between the supporting role of small pelagic fish and cephalopods in food webs, and the provisioning service they play as a major target of fisheries.  Because these species play central roles in food webs by providing a conduit of energy from small prey to upper trophic level predators, we hypothesized that trade-offs between these two ecosystem services could be predicted based on energetic properties of predator-prey linkages and food web structure.  We compiled information from 27 marine food web models, and developed a novel analytical framework to estimate how changes in yields of forage species would propagate through food webs and other fisheries. The estimated trade-offs between yields of forage fish and predator species were highly variable, and roughly one-third of this variance was related to an interactive effect of fishing and predation intensity; strong trade-offs were predicted when fishing intensity on forage species is high and when predators account for a high proportion of total forage mortality.  Contrary to our expectations, trade-offs were not easily predicted from energetic properties, because predators of forage species exhibited a high degree of intra-guild predation and also consumed many of the same prey as forage species.