Foray foraging behavior: seasonally variable, food-driven migratory behavior in two calanoid copepod species

Abstract

We tested a hypothesis we termed 'foray foraging', which states that zooplankton make repeated short-term and short-distance migrations between food-rich surface layers and deeper layers throughout the night. Ultimately, the reason for the behavior is to balance the necessity of feeding with the predation risk in surface waters. We tested the hypothesis on 2 species of marine copepods, Calanus pacificus and Metridia pacifica, in Dabob Bay, Washington, USA. Zooplankton nets and traps were used to collect females of both species from specific layers and while migrating up into and down out of the surface mixed layer to determine turnover rates in the surface layer. Gut contents of individuals were measured to determine if feeding history varied between individuals caught migrating upward and downward or in different layers. Turnover rates of the surface layer were highly variable, ranging from near zero to over 1000%, and were higher in summer and autumn than in spring for both species. Gut contents were consistently higher in animals migrating downward than in those migrating upward, but overall gut contents were higher in spring than in summer or autumn. These results suggest that foray behavior varies in magnitude seasonally and occurs throughout the year for both species but is most pronounced for M. pacifica. These findings suggest that vertical migration behaviors occurring in periods shorter than diel scales may affect zooplankton population dynamics through feeding and predation and likely impact the flux of energy and material into and out of the surface mixed layer.

Recommendations for the formulation of grazing in marine biogeochemical and ecosystem models

“…In the vertical, this assumption is well supported by observations of zooplankton aggregating in foodrich layers (Herman and Platt, 1983;Lampert, 2005;Giske et al, 1997). While it is difficult to observe individual lateral migration in the open ocean (Pearre, 2003), it is plausible that zooplankton, known to forage vertically between different depths based on the balance between predation risk and hunger (Pearre, 2003;Pierson et al, 2013), may drift with currents for longer at depth between unsuccessful forays to the surface, before vertically migrating less and staying closer to the surface once they find food (Bandara et al, 2021). This would lead to a similar consolidation of zooplankton around horizontally distributed T. Rohr et al high-density prey patches.…”

Changes in Selection Regime Cause Loss of Phenotypic Plasticity in Planktonic Freshwater Copepods

“…4A , Table 2 ). Consequently, LP females emerge probably only for nocturnal feeding (a similar behaviour is discussed for marine copepods; [51] , [52] ). Additionally, the minimization of surface time would decrease fish predation pressure to which females are more vulnerable than males due to their larger sizes [53] .…”

Recommendations for the Formulation of Grazing in Marine Biogeochemical and Ecosystem Models

“…In the vertical, this assumption is well supported by observations of zooplankton aggregating in food-rich layers (Giske et al, 1997;Herman & Platt, 1983;Lampert, 2005). While it is difficult to observe individual lateral migration in the open ocean (Pearre, 2003), it is plausible that zooplankton, known to forage vertically between different depths based on the balance between predation risk and hunger (Pearre, 2003;Pierson, Frost, & Leising, 2013), may drift with currents for longer at depth between unsuccessful forays to the surface, before vertically migrating less and staying closer to the surface once they find food (Bandara, Varpe, Wijewardene, Tverberg, & Eiane, 2021). This would lead to a similar consolidation of zooplankton around horizontally distributed high-density prey patches.…”