, Volume 139, Issue 3, pp 427–432 | Cite as

Trophic cascades in rocky shore tide pools: distinguishing lethal and nonlethal effects

  • Geoffrey C. TrussellEmail author
  • Patrick J. Ewanchuk
  • Mark D. Bertness
  • Brian R. Silliman
Community Ecology


The effects of predators on the density of their prey can have positive indirect effects on the abundance of the prey’s resource via a trophic cascade. This concept has strongly influenced contemporary views of how communities are structured. However, predators also can transmit indirect effects by inducing changes in prey traits. We show that the mere presence of predator risk cues can initiate a trophic cascade in rocky shore tide pools. In large (mean surface area =9 m2), natural tide pools, we manipulated crab density and their foraging ability to examine the relative importance of lethal (density-mediated) and non-lethal (trait-mediated) predator effects to algal community development. We found that perceived predation risk reduced snail density as much as the direct predation treatment, showing that green crab predation was not an important factor regulating local snail density. Instead, snail emigration away from resident crabs appears to be the most important factor regulating local snail density. As a result, the abundance of ephemeral green algae was similar in the predation risk and direct predation treatments, suggesting that the consumption of snails by crabs plays a minimal role in mediating the trophic cascade. Increased attention to trait-mediated effects that are transmitted by predator-induced changes in prey behavior may change our view of how predators exert their strong influence on community structure.


Trophic cascade Green crab Green alga Snails 



We thank the Andrew Mellow Foundation and the National Science Foundation (OCE-0240265) for support. A. Bortolus, G. Bernatchez, S. Lee and C. Mullan provided much needed help in the field and we thank R. Bertin and J. Witman for comments. O. Schmitz and two anonymous reviews provided comments that improved this paper considerably.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Geoffrey C. Trussell
    • 1
    • 2
    Email author
  • Patrick J. Ewanchuk
    • 1
    • 2
  • Mark D. Bertness
    • 1
    • 2
  • Brian R. Silliman
    • 1
    • 2
  1. 1.Marine Science CenterNortheastern UniversityNahantUSA
  2. 2.Department of Ecology and Evolutionary BiologyBrown UniversityProvidenceUSA

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