Contributions to Zoology, 70 (2) (2001)Henry C. Merchant; Ritindra N. Khan; Robert E. Knowlton: The effect of macrophytic cover on survival of Palaemonetes pugio and P. vulgaris (grass shrimp) in the presence of predatory Fundulus heteroclitus (killifish)
Results

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Behavior of prey and predator

Although the focus of the present work was not to describe the behavior of the participants during exposure of the prey to the predator, certain behaviors and features of the predator-prey interaction were repeatedly observed and noted in all of the experiments. These behaviors are reported here because they may provide additional insight into understanding the role of macrophytic cover in the predator-prey interaction between FundulusandPalaemonetes.

In the absence of the predator,Palaemoneteswas found within the cover and on the substrate around the cover. At any given time, a small number ofanimals(<10%)swam in the water column above the cover.

Outside and within macrophytic cover, individuals of both species of Palaemonetesspent the majority of time resting (rest = time spent in no overall body movement; antennae, mouth parts, and appendages may or may not be in motion during rest). Typically Palaemonetes moved from one resting place to another by a short burst of swimming activity that was accomplished by typical metachronal waving of the pleopods. This movement of the appendages lifted the individual up (from its resting place), carried it through the water, and settled it at another resting place. An approach or attack by a predator (attack = a short thrust by the predator toward a prey individual) stimulated the shrimp’s caridoid escape reflex (characteristic backward movement of carideans, brought about by sudden flexure of the abdomen) and ended when the predator caught the prey or the prey individual swam rapidly away from the predator (usually towards cover). As reported elsewhere (Khan et al., 1997), both the predator and the prey were observed entering and moving within all three types of macrophytic cover, but Fundulus, which tended to rest around the edges of the cover or swim in the water column above the cover, entered the cover rarely and then usually when in pursuit of a prey individual that had entered the cover. In general, predators attacked prey when prey were swimming, and predators would pass by closer, inactive prey to attack more distant moving prey. Chases (chase = a longer episode of Palaemonetes swimming while being pursued by an attacking Fundulus) were uncommon and occurred when the shrimp was swimming above the cover near the water surface. With and without a predator present, P. pugio appeared to be a more active swimmer than P. vulgaris, spending consistently more time swimming above or outside the cover. In response, attacks upon and chases of prey more often involved P. pugio than P. vulgaris. From five to forty attacks (not necessarily directed against the same individual) were required for Fundulus to successfully grab an individual shrimp. Capture usually involved Fundulus grabbing the head of the shrimp with its mouth. Typically, 5 minutes elapsed from time of capture to complete consumption of a prey individual.