A high-resolution modeling study on diel and seasonal vertical migrations of high-latitude copepods

Kanchana Bandara,Øystein Varpe,Rubao Ji,Ketil Eiane

doi:10.1016/j.ecolmodel.2017.12.010

Kanchana Bandara, Øystein Varpe + Show 2 more

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https://doi.org/10.1016/j.ecolmodel.2017.12.010

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Abstract

Despite diel and seasonal vertical migrations (DVM and SVM) of high-latitude zooplankton have been studied since the late-19th century, questions still remain about the influence of environmental seasonality on vertical migration, and the combined influence of DVM and SVM on zooplankton fitness. Toward addressing these, we developed a model for simulating DVM and SVM of high-latitude herbivorous copepods in high spatio-temporal resolution. In the model, a unique timing and amplitude of DVM and SVM and its ontogenetic trajectory were defined as a vertical strategy. Growth, survival and reproductive performances of numerous vertical strategies hardwired to copepods spawned in different times of the year were assessed by a fitness estimate, which was heuristically maximized by a Genetic Algorithm to derive the optimal vertical strategy for a given model environment. The modelled food concentration, temperature and visual predation risk had a significant influence on the observed vertical strategies. Under low visual predation risk, DVM was less pronounced, and SVM and reproduction occurred earlier in the season, where capital breeding played a significant role. Reproduction was delayed by higher visual predation risk, and copepods that spawned later in the season used the higher food concentrations and temperatures to attain higher growth, which was efficiently traded off for survival through DVM. Consequently, the timing of SVM did not change much from that predicted under lower visual predation risk, but the body and reserve sizes of overwintering stages and the importance of capital breeding diminished. Altogether, these findings emphasize the significance of DVM in environments with elevated visual predation risk and shows its contrasting influence on the phenology of reproduction and SVM, and moreover highlights the importance of conducting field and modeling work to study these migratory strategies in concert.

Highlights

Vertical migration is a common behavior of many zooplankton taxa
The somatic growth of all developmental stages beyond NV occurred under food limitation (Fig. 6c), and because of reduced growth rates, their predicted development times were higher than those estimated from Belehrádek temperature functions (Fig. 6d)
Diel vertical migration In this model, visual predation risk had the highest influence on the diel vertical migration (DVM), which diminished under low visual predation risk (Figs. 7 and 9, Table 6) and completely ceased when visual predation was removed from the model (K = 0, data not presented)

Summary

Introduction

Vertical migration is a common behavior of many zooplankton taxa. Vertical migrations of high-latitude zooplankton are classified into diel and seasonal components, which have been studied since the late-19th century (reviewed in Russell, 1927; Cushing, 1951; Banse, 1964). The short-term diel vertical migration (DVM) has a periodicity of up to 24 h, and is understood as a strategy that trades off growth potential to reduce the mortality risk imposed by visual predators (Lampert, 1989; Ohman, 1990; Loose and Dawidowicz, 1994).

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