Predation vulnerability of planktonic copepods:consequences of predator foraging strategies and prey sensory abilities

Abstract

We investigated the vulnerability of 2 copepod species (Eurytemora affinis and Temora longicornis) to predation by predators with different foraging modes, three-spined stickleback Gasterosteus aculeatus juveniles and mysid shrimps Neomysis integer. Copepods were videofilmed escaping from predators and from an artificial flow field, and the results were used in a model of hydrodynamic disturbance generated by a predator The copepods detected mysids from a significantly larger distance than they detected sticklebacks (0 45 and 0.24 cm, respectively). Consequently, the capture success of the sticklebacks was higher than that of mysids. In the case of sticklebacks foraging on E. affim-S, copepod reaction distance was significantly correlated with stickleback approaching speed; sticklebacks captured a copepod only if they were able to slowly approach to within a strike distance of <0.1 cm from the prey. Also, there was a major difference between the vulnerabilities of the 2 prey species: the capture success of sticklebacks was 92 % with T. longicornis and 53 % with E. affinis. This corresponded with experiments with artificial flow, where the threshold fluid velocity gradient eliciting an escape response in copepods was 4 times higher in T, lonqicornis than in E, affjnis (8.2 and 2.1 S-', respectively). The hydrodynamic model accurately predicted the positive relationship between stickleback approaching speed and copepod reaction distance, as well as the difference between the 2 copepod species. This suggests that, by using simple artificial flow experiments, we can rank various zooplankton species according to their escape capabilities, and thus predict their vulnerability to predation by small fish with different motility patterns. In contrast, the model did not conform with observations on mysids. Apparently, the hydrodynamic disturbance created by a mysid is not related to its swimming speed, but to some other factor, such as the beat rate of swimming appendages.

Feeding mechanism and capture success of european whitefish (Coregonus lavaretusL.) larvae

“…Hydromechanical perception of predators in copepods has been widely documented (Yen and Strickler, 1996;Hwang and Strickler, 2001;Wagget and Buskey, 2007). It is also known that copepods can sense faster predators at a longer distance (Viitasalo et al, 1998), and can adjust their escape response to the intensity of the mechanical stimuli (Heuch et al, 2007). The positive correlation between strike speed and prey escape speed for reared whitefish larvae in this study supports these hypotheses and shows that the faster the larva is, the faster the escape response is.…”

“…As a result, the attack success of whitefish larva seems to be determined by events occurring upstream of the strike. Viitasalo et al (1998) and MacKenzie and Kiørboe (2000) attributed the capture success of fish larva to the ability of the predator to get within a strike distance close enough to the prey without triggering an escape response. This empirical observation was tested and confirmed by a mechanistic modelling approach (Caparroy et al, 2000).…”

Escape behavior of planktonic copepods in response to hydrodynamic disturbances: high speed video analysis

“…Variability in reactivity was quite large in these experiments, as it has proven to be in other experiments on Acartia spp. and other copepods using siphon tube stimuli (Fields & Yen 1996, 1997b, Viitasalo et al 1998. Even stimuli >10 times threshold elicited escape in only 60% of our individuals.…”

The lethal and sublethal effects of the aquatic macrophyte Myriophyllum spicatum on Baltic littoral planktivores

“…We adjusted the zooplankton density in the experimental aquarium to a level above natural density (Ͼ20 copepods L Ϫ1 , cf. Viitasalo et al 1995) to prevent prey depletion and, hence, ensure continuous feeding of the larvae.…”

“…An attack was determined as a rush forward to capture a prey (cf. Viitasalo et al 1998). We did not measure the actual prey consumption because we could not determine the escape success of the zooplankton prey from the tapes.…”