Risk effects of the predatory crab (Carcinus maenas) on behavioral trait changes of Littorina littorea
Tina, F.W. (2011). Risk effects of the predatory crab (Carcinus maenas) on behavioral trait changes of Littorina littorea. MSc Thesis. Alfred Wegener Institute for Polar and Marine Research, Biologische Anstalt Helgoland: Helgoland. 48, V pp.
Prey can detect their predators through different forms of chemical information and avoid them to reduce the predation risk. Risk of predation affects many aspects of prey´s life such as morphology, behavior, life history and prey need to develop defenses or modify behavioral traits to reduce that predation risk. Risk effects of predatory Carcinus maenas (L.) on trait changes of periwinkle, Littorina littorea (L.) due to 24 hrs permanent exposure to risk cues have been observed in this study. Not only the effect of constant 24 hrs crab exposure but also the effect of temporal variation in risk on Littorina littorea was tested. It was examined whether the 24 hrs constant presence of predatory crabs changed the shell mass of periwinkle within three months. The shell mass accumulation of snails was determined by calculating their shell mess increment (%) and found that there was no significance difference of shell mass increment (%) between snails with and without crabs. Therefore we cannot make an assumption that L. littorea may change their shell morphology in presence of predatory crabs within three months. Prey can change their behavioral traits to reduce the predation risk by avoiding their predators or by reducing their feeding, mating frequency and reproduction activities that has an impact on food consumption and reproduction. Animals have to trade-off the predation risk with different ways such as less foraging activity in high risk but more activity in low risk situation to get the required energy. Two different experiments were conducted to observe the (1) avoidance behavior and (2) egg production, feeding and mating behavior of snails due to 24 hrs constant exposure to crabs. Snails with crabs showed significantly more (on average 60%) avoidance behavior (crawling out of water) but less feeding (on average 23%) and mating (on average 23%) frequency (except egg production) than the snails without crabs. This study also investigated the effects of temporal variation of risk on egg production, feeding and mating behavior of snails due to different exposure duration and frequency to risk cues and tested the two basic predictions of risk allocation hypothesis. The result of this study showed that snails significantly reduced their egg production, food consumption and mating frequency with the increasing of exposure duration to crabs. In case of very frequent high risk situation they increased their foraging activity and reduced anti-predator activities that supports the two predictions of risk allocation hypothesis. The results of these experiments suggest that risk effects of Carcinus maenas have an important influence on behavioral trait changes of Littorina littorea. Further studies should investigate the effects of temporal risk variation under natural field conditions and compare the results with the laboratory experiment results.
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