Biological indicators reveal mesozooplankton foray behaviour in dynamic physical environments: Reply to Kaartvedt et al. (2024)

Abstract

Kaartvedt et al. (2024; Mar Ecol Prog Ser 734:173-175) comment on the role internal waves played in the findings of Dewar-Fowler et al. (2023; Mar Ecol Prog Ser 715:27-39) that foray behaviour was present across a number of zooplankton species in the Polar Frontal Zone of the Southern Ocean. Kaartvedt et al. (2024) contend that foray behaviour may not be responsible for the capture of zooplankton by fixed-depth bi-directional net-traps because the influence of internal waves on transporting these organisms into the traps was not accounted for. In Figs. 4 & 5 of Dewar-Fowler et al. (2023), directional biases were apparent in the abundance and taxon-ratios captured by the upward and downward looking nets, which can only be explained by the active swimming and avoidance behaviours of zooplankton. This refutes the contention that physical processes such as internal waves dominated capture rates by the net-trap. Even within this physically dynamic oceanic frontal zone, biological indicators such as these biases support the assertion of Dewar-Fowler et al. (2023) that foray behaviour is detectable and prevalent within zooplankton communities.