COS 118-3 - Fish community size structure and foraging behavior drive ecosystem-level primary production through differing mechanisms in seagrass ecosystems

Abstract: Consumers are important sources of nutrients for primary production in many ecosystems. The extent to which consumers influence production may be affected by consumer behavior. For example, the amount of time consumers spend either foraging or sheltering may result in nutrients being distributed to different parts of the ecosystem, with ecosystem-level consequences for primary production. Assessing where production occurs within the primary producer (i.e., allocation to aboveground AG and belowground BG production) helps to further understand the mechanisms of production. We used an individual-based model of a patch reef system in a seagrass bed to test how different foraging strategies of two reef fish species of different body sizes affected seagrass production. Specifically, we asked how interspecific and intraspecific behavior affect primary production relative to the well-documented effects of consumer body size and biomass. In all cases, we found populations dominated by small fish that spend a large proportion of time foraging off reef increased ecosystem-level primary production. Interestingly, while BG production increased with foraging, AG production decreased with foraging as fewer fish sheltering decreased the concentration of nutrients needed to allocate BG to AG production. Variation in foraging behavior among individuals also affected production both at the ecosystem-scale as well as BG and AG production. Specifically, we found that populations dominated by bold individuals who forage more increased BG production, while populations dominated by shy individuals who shelter more increased AG production. These findings suggest that the role of consumer size structure and foraging behavior affects both ecosystem-scale primary production as well as the differing mechanisms of production.