The transition from nauplii to copepodites: susceptibility of developing copepods to fish predators

Abstract

Escape success of copepod nauplii (N5–6) of the copepod Acartia tonsa was signifi-cantly lower than that of copepodites (C1–2) when exposed to a coral reef fishAcanthemblemaria paula, but no difference was observed when exposed to the sea-horse Hippocampus zosterae. The addition of low level turbulence inhibited feedingby the seahorse but did not affect overall capture success in A. paula, although ashift in predator behavior occurred. This study highlights the importance of con-sidering predatory mode and behavior in the context of planktonic predator–preydynamics.KEYWORDS: copepod; Acartia tonsa; development; escape; fish predationCopepods are subject to high predation rates and theserates are often greatest for the younger, developingstages (Sell et al., 2001).Earlier developmental stages arepresumably less capable of detecting a potential preda-tor, and when a predator is detected, the escaperesponse of a young copepod is less effective comparedwith that of later stages (Sell et al., 2001; Titelman2001). However, the ability to produce an escape jumpis present in even the earliest naupliar stage (N1)(Buskey, 1994). However, the escape is produced by adifferent set of appendages than in the adult and manyof the mechanoreceptors for the hydrodynamic sensingof an approaching predator are missing in the youngeststages (Mauchline, 1998). During an escape, copepodsare propelled forward by metachronal strokes of thethoracic pereiopods (Strickler, 1985) and can achievespeeds over 500 body lengths per second (Buskey et al.,2002; Lenz et al., 2004). However, the mechanism forescape differs for naupliar stages. Nauplii lack pereio-pods, so instead they must use the first and secondantennae to generate escapes (Gauld, 1958). The devel-opment of pereiopods in copepodites results in anescape that is faster (Bradley, 2009). With each sub-sequent molt from C1 to C5, a new pair of pereiopodsemerge and older ones become larger (Dahms, 1990)and presumably more powerful.The molt from the N6 naupliar stage to the C1 cope-podite stage is arguably the most significant. Duringthis molt, the copepod’s change in mass proportional toother molts is small (Leandro et. al., 2006), yet there is a