The release of chemicals following herbivore grazing on primary producers may provide
feeding cues to carnivorous predators, thereby promoting multitrophic interactions. In
particular, chemicals released following grazing on phytoplankton by microzooplankton
herbivores have been shown to elicit a behavioural foraging response in carnivorous
copepods, which may use this chemical information as a mechanism to locate and remain
within biologically productive patches of the ocean. In this paper, we use a 1D spatial
reaction-diffusion model to simulate a tri-trophic planktonic system in the water column,
where predation at the top trophic level (copepods) is affected by infochemicals released
by the primary producers forming the bottom trophic level. The effect of the
infochemical-mediated predation is investigated by comparing the case where copepods
forage randomly to the case where copepods adjust their vertical position to follow the
distribution of grazing-induced chemicals. Results indicate that utilization of
infochemicals for foraging provides fitness benefits to copepods and stabilizes the system
at high nutrient load, whilst also forming a possible mechanism for phytoplankton bloom
formation. We also investigate how the copepod efficiency to respond to infochemicals
affects the results, and show that small increases (2%) in the ability of copepods to
sense infochemicals can promote their persistence in the system. Finally we argue that
effectively employing infochemicals for foraging can be an evolutionarily stable strategy
for copepods.