Motile behavior and predation risk in planktonic copepods

Abstract

Predation is an important source of mortality in zooplankton but factors governing predation risk in marine food webs are still not well understood. Here, we examine the role of zooplankton behavior in determining predation risk. We first quantified motility of copepods with different feeding behaviors (ambush feeding, cruising, and feeding-current feeding). Second, we estimated remote predator detection and escape characteristics of the studied copepods. Third, we proposed a simple behavior-dependent encounter model to predict copepod predation risk from rheotactic predators. Finally, we compared our predictions with predation risk previously determined experimentally. For similar sized copepods, predicted predation risks were similar between feeding-current feeders and cruising feeders, whereas predation was up to 8.5 times lower (range: 1.5-8.5) for ambush feeders. Predicted predation risks further differed between males and females depending on feeding behavior: in ambush feeders males actively search for non-motile females and their predation risk was up to 6 times higher (range 1.2-6) than for females. In contrast, feeding current-and cruising feeders showed small differences in predation risk between genders. In all cases, predicted relative predation risks between particular behaviors were confirmed by empirical data from previous predation experiments. Our results demonstrate that prey behavior of zooplankton may lead to a predictable variation in predation risk from rheotactic predators of up to an order of magnitude, and therefore that individual behavior is an important factor in structuring zooplankton communities.

Prey perception mechanism determines maximum clearance rates of planktonic copepods

“…Since the first video observations of planktonic copepods in the 1980s (Alcaraz et al ; Koehl and Strickler ; Paffenhöfer et al ), several studies have emphasized the importance of investigating small‐scale individual behaviors to attain a better mechanistic understanding of planktonic organisms’ interactions and marine food webs dynamics (Henriksen et al ; Kiørboe , ; Kiørboe et al ). Our previous research and others studies on behavioral observations and feeding mechanisms of planktonic copepods (e.g., Price et al ; Kiørboe et al ; Kiørboe ; Bruno et al ; Cheng et al ; Gonçalves et al ; van Someren Gréve et al ) allow us to interpret the results obtained here from bottle incubations.…”

Foraging response and acclimation of ambush feeding and feeding‐current feeding copepods to toxic dinoflagellates

“…Female adults were transferred to filtered seawater and starved overnight in the experiment room before each 5‐d experiment to remove or minimize any effects of the different feeding regimes of the animals in the cultures. T. longicornis is a feeding current feeder that produces a continuous feeding current (van Someren Gréve et al ), while A. tonsa can switch between feeding current and ambush feeding depending on the prey type. When offered large motile prey, like in the present experiments, A. tonsa is ambush feeding (Kiørboe et al ).…”

“…We analyzed two‐dimensional projections of copepod swimming tracks using Labtrack software (DiMedia), and subsequently ran the swimming tracks through a custom made R‐script that classified the behavior of each individual over time (sinking, swimming, jumping) and quantified jump length, speeds, and event durations, all as described by van Someren Gréve et al (). The density of A. tonsa in this filming experiment was high, up to 1 copepod mL −1 , which exceeds typical densities in nature although such high densities have been reported (Berasategui et al ).…”

“…We described the feeding behavior of the copepods during the 5-d incubation period by video-recording T. longicornis and A. tonsa following the procedures of Xu et al (2017) and van Someren Gr eve et al (2017), respectively. We made video recording continuously during the first 4 h after introducing the phytoplankton and then 1 h every day during the subsequent 5 d. The data of T. longicornis for the first 4 h were taken from Xu et al (2017).…”

“…Thus, the PSP that we measure may not be the compounds that cause behavioral changes or toxic effects in the copepods. PSP can cause serious human illness (Hille 1968;Halstead and Schantz 1984) and paralytic shellfish poisoning and consequently Alexandrium spp.-the main PSP producers-have been widely studied, including their effects on zooplankton grazers (Turner and Tester 1997;Bricelj et al 2005;Wiese et al 2010;Turner 2014). However, in many cases, the interactions between Alexandrium spp.…”