MEPS 349:171-181 (2007)  -  DOI: https://doi.org/10.3354/meps07123

ABSTRACT: The heterogeneous distribution of water flow over structurally complex environments, such as coral reefs, may play an important role in the interactions between copepods and planktivorous fish by interfering with the copepods’ ability to detect and evade predators. The escape response and capture rates of the copepod Acartia tonsa were examined in laboratory flumes that created both unidirectional and oscillatory flow conditions similar to those found near coral reefs. Two turbulent regimes were produced in each flume: ‘smooth’ flow was formed using a grid collimator and ‘rough’ flow was generated by placing a branched coral skeleton upstream of the flume’s working section. A predator was simulated by a fixed siphon to generate a stimulatory flow field. Copepod detection of the siphon was measured as the distance from the siphon tip to where an escape response was initiated. This reactive distance remained the same in low-flow conditions as in still water, but was reduced by 25% at higher flow speeds, indicating a decline in the copepods’ ability to detect velocity gradients formed by the siphon. Rough turbulence regimes intensified the effect of current speeds, resulting in an even shorter copepod reactive distance. Capture rates of copepods by the siphon increased with current speed, wave motion, and in rough flow, while the capture rates of non-evasive prey, Artemia nauplii, did not vary with flume conditions. The differences in capture rates between evasive and non-evasive prey suggest that behavioral shifts in copepod escape thresholds may account for increases in predation by reef-dwelling fishes observed in hydrodynamically complex coral environments.

KEY WORDS: Turbulence · Copepods · Escape behavior · Planktivores · Coral reefs