Effects of removal of seagrass canopy on assemblages of small motile invertebrates

Abstract

To test the importance of seagrass canopy to epifaunal invertebrates in a southern Australian estuary, patches of the short, fine-leaved seagrass Zostera muelleri Irmisch ex Aschers. were cleared of canopy. All other factors were known to be consistent with seagrass presence, and a procedural control was used to measure any effects of the method used to remove seagrass. Effects on epifauna were measured as changes in abundance and biomass of key taxa and in total production, and as differences amongst assemblages, tested using an analysis of similarity (ANOSIM) randomisation routine. Removal of seagrass canopy had a weak but detectable effect on epifauna over and above the slight effect caused by the disturbance concomitant with seagrass removal. Epifauna associated with habitat from which seagrass had been removed did not, however, match that from areas unvegetated prior to the experiment. The epifauna from these previously unvegetated areas were characterised by low abundance and biomass of several key taxa, apart from 1 group, cumaceans, which were far more common in this habitat. The results suggest that the overriding importance of Z. muelleri to epifauna is not simply the presence of seagrass canopy, and explanations of the higher abundance of epifaunal invertebrates in vegetated compared to unvegetated habitats based merely on the presence of seagrass canopy are not supported.