MEPS 477:161-176 (2013)  -  DOI: https://doi.org/10.3354/meps10141

ABSTRACT: Laboratory experiments were conducted to determine whether turbulence could be an environmental cue associated with the behavior of pink shrimp Farfantepenaeus duorarum postlarvae during their flood-tide migration to the nursery grounds. Postlarvae were exposed to variations of turbulent kinetic energy (TKE) generated by the flow speed of a water pump and variations of combined flow speed and vertical motions of an actuator-driven cylinder array. The position and swimming activity of the postlarvae were recorded using a video camera. Images of postlarvae were analyzed at 3 depths of the water column (upper half, bottom half, and floor of the experimental chamber). During trials varying flow speed alone, both TKE levels (<0.009 cm² s^-2) and the number of postlarvae in the upper half of the water column were low, suggesting that the TKE levels were below their stimulation threshold. In contrast, swimming activity increased substantially during trials incorporating additional TKE generated by the actuator. TKE levels varied between 1.1 and 3.5 cm² s^-2, and postlarvae vertical position reflected increases and decreases in TKE. A statistically significant (p <0.05) higher percentage of postlarvae in the upper half of the water column coincided with high TKE values. Increases in postlarval response relative to increases in TKE diminished after reaching TKE values of 2.5 cm² s^-2, suggesting a dose-limited behavioral response. This trend was supported by a significant horizontally asymptotic regression of change in postlarval response against percent change in TKE relative to the previous time step. The results suggest turbulence involvement during flood-tidal migration behavior of this species. During most of the flood tide, TKE levels would be sufficiently high to stimulate postlarvae to swim in the water column and remain there while moving in the direction of settlement habitats. At the end of the flood tide, as the TKE decreases, postlarvae would descend to near the bottom.

KEY WORDS: Turbulence · Turbulent kinetic energiy · TKE · Selective tidal transport · Pink shrimp · Postlarval behavior · Environmental cue · Farfantepenaeus duorarum