MEPS - Vol. 339 - Feature article

When algal canopies of Hormosira banksii (top left) are removed, this leads to nearly total loss of associated species (right); intermediate canopy losses (bottom left) result in species-specific density changes. Photos: S. Lilley

Schiel DR, Lilley SA

 

Gradients of disturbance to an algal canopy and the modification of an intertidal community

 

Disturbances to marine communities occur over varying intensities. In beds of dominant algae, disturbance may produce a gradient of canopy loss. How does this affect local diversity and its variation across benthic seascapes? Schiel & Lilley experimentally reduced canopies of the intertidal fucoid alga Hormosira banksii in a 5-step gradient from 0 to 100%. After 13 months, 75% of the variation in species richness of invertebrates and algae was due to the canopy gradient. Local diversity was greatest beneath intact canopies, reduced by around 60% where canopies were completely removed, and intermediate across the intermediate disturbances. The abundance of individual associated species changed gradually in some cases and abruptly in others. The results demonstrate that environmental impacts on key species such as H. banksii set off a cascade of effects in benthic assemblages.

 

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