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Lessons from a Disturbance Experiment in the Intertidal Zone of an Exposed Sandy Beach
Journal article   Peer reviewed

Lessons from a Disturbance Experiment in the Intertidal Zone of an Exposed Sandy Beach

David S Schoeman, A McLachlan and J E Dugan
Estuarine, Coastal and Shelf Science, Vol.50(6), pp.869-884
2000
DOI: https://doi.org/10.1006/ecss.2000.0612
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https://doi.org/10.1006/ecss.2000.0612View
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Abstract

Earth Sciences Environmental Sciences Biological Sciences exposed sandy beach intertidal macrofauna disturbance Donax fishery South Africa
Exposed sandy beaches are important, sensitive and widespread coastal habitats. Although they have been studied for more than 50 years, investigators have been reluctant to attempt manipulative experiments due to the dynamic nature of these environments. Consequently, the ecology of exposed sandy beaches remains relatively poorly understood. We conducted a community-level, manipulative experiment involving a simulated anthropogenic disturbance on an exposed microtidal sandy beach in the Eastern Cape, South Africa; the first of its kind and scale. This study comprised pre- and post-impact sampling at an experimental site and two control sites. The impact involved excavating and removing a 200 m2quadrat of sand from the mid-intertidal of the experimental site to a depth of 0·3 m. The intention was to address the prediction that anthropogenic disturbances would be detectable if appropriate spatial and temporal scales were investigated. The following variables were monitored: transect gradient; species richness; macrofaunal abundance; and both the abundance and biomass of the dominant infaunal species, the beach clam Donax serra Röding. Analyses revealed significant differences in temporal patterns of all response variables amongst sites. Some evidence linked these changes to the experimental disturbance, although impacts appear temporary, being ameliorated within, at most, one semi-lunar cycle. This confirms that it is possible to successfully conduct manipulative experiments on exposed sandy beaches. However, the uncontrollable, natural dynamics of the beach face, as expressed by intertidal gradient, contributed significantly to the description of spatio-temporal variation in biotic response variables. It is concluded that to isolate treatment effects from those of natural variation, two advances are necessary on the current research approach. First, experimental designs must take cognizance of the fact that exposed, microtidal sandy beaches have little in common with other intertidal habitats; and second, large-scale treatments must be replicated in space.

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