Abstract
The ubiquitous oceanic copepod Calanus finmarchicus is the major link between primary producers and important fish stocks in the North Atlantic Ocean and adjacent seas. Despite over a century of research on growth and development of this key species, the effect of predation risk on these processes remains elusive. We tested how food level and chemical cues from a fish predator influence growth and development of C. finmarchicus, using a predator naïve laboratory population. Copepods reached adult stage earlier both in response to high food and to predator cues in our experiment. High food also increased growth and lipid accumulation. In contrast, perceived predation risk triggered reduced size and lipid fullness, indicating a decoupling of growth and development rates. Our results demonstrate that chemical predator cues can influence life history strategies in C. finmarchicus, and suggest that present and future patterns in oceanic zooplankton size and population dynamics may also reflect differences in predation risk.
Highlights
Nonlethal effects of predator presence shape the behavior, morphology, and life history of prey, with potentially stronger effects on prey populations than direct consumption (Lima 1998, Preisser et al 2005)
Prosome area increased from C4 to C6F, with C6M being between C5 and C6F; lipid fullness and C:N was higher in C5 and C6M compared to C4 and C6F; and RNA : DNA was highest in C6F and lowest in C6M (Fig. 3a–d)
The effect estimates of food level and predator cue, calculated using data standardized per stage, underscore that the largest differences between treatments occurred in C6F with and without predator cues; and the presence of predator cues had strongest effect on prosome area, thereafter lipid fullness and C:N, and a relatively weaker effect on RNA : DNA
Summary
Nonlethal effects of predator presence shape the behavior, morphology, and life history of prey, with potentially stronger effects on prey populations than direct consumption (Lima 1998, Preisser et al 2005). Auditory, and tactile/hydrodynamic cues, prey perceive risk via chemical cues emitted by predators. Effects of chemical predator cues have been widely studied in lakes and in benthic marine invertebrates (Kats and Dill 1998). Chemical cues, and even predation risk, were traditionally considered irrelevant in the pelagic ocean (Verity and Smetacek 1996), but it is well established that the interplay between pelagic organisms depends on chemical signals (Pohnert et al 2007, Heuschele and Selander 2014). Pelagic copepods are omnipresent and likely the most abundant animal group on the planet, playing critical roles in marine ecosystems and biogeochemical cycles (Schminke 2007). In contrast to in air, diffusion of small molecules, such as chemical predator cues, is typically slow in water (on the order of 10−5cm2Ás−1; Kiørboe 2008). Chemical cues are arguably less useful for assessing immediate predation risk in the ocean, as the predator may be long gone
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