An experimental test of artifacts from repeated sampling in soft-sediments

Abstract Experimental and monitoring studies done in soft-sediments are made difficult by the need to disrupt physically the structure of the habitat in order to sample the biota, which often lives buried beneath the surface. Collection of a sample causes some disturbance as sediment moves to fill the hole left by the removed core or grab, possibly exposing animals in the surrounding sediment to predators. Physical disturbance from sampling may also disrupt microbial assemblages in the sediments or breakdown biotic structures which help bind the sediments (eg. animals tubes, roots and rhizomes or microbial mats). An experiment was done specifically to test the hypothesis that disturbance from repeated sampling in soft-sediments leads to artifacts which affect subsequent estimates of the structure of populations and assemblages. Repeated sampling of the same patches is often necessary due to the logistical constraints of establishing experiments in soft-sediments. The results of the experiment demonstrate the potential for disturbance from previous sampling to affect the abundance and species richness of molluscan assemblages in soft-sediments. After two weeks, there were still detectable differences between patches of sediment which had been initially disturbed to simulate the collection of samples, and control (undisturbed) patches. The results were not consistent between the two sites used for the experiment, nor between the two levels of initial disturbance applied, suggesting that artifacts from repeated sampling cannot be considered as being `equal' across all treatments. Where repeated sampling of the same patches is required, the potential for artifacts should be addressed to determine how these may affect interpretation of the results from experiments or sampling programmes.