Sarah P. Lawson

Course Name

Ecology: Populations to Ecosystems

Course Number


Document Type


Original Publication Date

November 20, 2018

Publication Date



Trophic cascades occur when the community structure is influenced by indirect effects of predation on the lower trophic levels. The trophic cascade can be disrupted when an invasive species is introduced. The Asian shore crab, Hemigrapsus sanguineus has invaded ecosystems in New England and we predict this invasion will negatively affect the classic New England trophic cascade. By the predation indirectly affecting lower trophic levels, H. sanguineus can influence the community structure and diversity at the lower levels. To understand the trophic cascade, we manipulated the food source and competitors in four different mini-ecosystems. By introducing H. sanguineus into an environment with L. littorea and two algal species; Fucus distichus and Ulva sp., we confirmed that H. sanguineus disrupts the trophic cascade. Specifically, the Asian shore crab, consumed the snail’s preferred type of algae, which led to the indirect effect on the trophic cascade. The findings of this experiment confirmed that with the presence of the invasive crab, the Asian shore crabs had an indirect effect on the snail. Invasive species can have a negative effect on trophic cascades resulting from competitive exclusion.

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