Animal-plant interactions constitute a ubiquitous element of ecological communities and herbivory represents a major, direct influence of animals upon plants’ survival and abundance. Animals can also have indirect effects on plants by changing their environments, i.e. animals as ecological engineers. The extent and magnitude of these effects are thought to vary with the behaviour and abundances of animal species in question.

Hermit crabs are common omnivores in intertidal habitats of Amakusa, western Kyushu. They were observed to ‘clip’ the fronds of a calcareous algal species, Corallina pilulifera (Rhodophyta), thereby exerting negative effects on the latter. However, our observation revealed that hermit crabs did not actually consume the algae and seemed to remove the fronds in order to obtain food items in or under the algal tuft. This behaviour has therefore been termed ‘pseudo-herbivory’ to distinguish it from the conventional form of herbivory. We have conducted an experimental and observational study on this ‘pseudo-herbivory’ and part of this work will be presented in this presentation.