, Volume 137, Issue 1, pp 97–103 | Cite as

Negative effects overpower the positive of kelp to exclude invertebrates from the understorey community

  • Sean D. ConnellEmail author
Community Ecology


Marine macroalgal forests are one of the most widespread and studied habitats on subtidal coasts, but there remain challenges in understanding why many sessile invertebrates are anomalously absent from understorey communities. In a series of experiments on recruitment of invertebrates, I partitioned the habitat-modifying effects of kelp into their positive and negative effects. Experiments revealed that a reduction of light intensity and removal of sediment by canopies acted to facilitate recruitment, but physical abrasion by the canopy acted as a negative force to overpower these positive effects. Understorey assemblages, therefore, represent biased subsets of taxa from a local pool capable of colonization. On balance, negative effects acted to exclude invertebrates from the understorey community. The asymmetric strength of negative effects not only explains the enigma of exclusion but also indicates that, when it exists, understorey coexistence with canopy plants must reflect a more even match between positive and negative effects.


Canopy Disturbance Facilitation Sedimentation Subtidal 



This manuscript was improved by the comments of Bronwyn Gillanders, Tim Glasby, Jason Tanner and two anonymous referees. Many hours of capable diving assistance were provided by B. Gillanders, M. Fowler-Walker, A. Irving and A. Melville. This research was financed by an Australian Research Council grant.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Southern Seas Ecology Laboratories, School of Earth and Environmental SciencesThe University of AdelaideAustralia

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