The impact of wader predation on benthic macrofauna in Merja Zerga lagoon, Morocco: an exclosure experiment

To experimentally evaluate the predation effects of migratory waders on macrofauna community structure and organization, an exclosure field experiment was undertaken on the intertidal mudflats of Merja Zerga, Morocco, between September 2014 and March 2015. Three sampling stations on the mudflats most frequently used by waders in winter were selected. Four replicate sampling areas were laid out per station, each replicate consisting of an exclusion plot (a caged area of 2×2 m) and a control plot; five samples were taken in each in September and March. We did not find significant differences in either density or biomass of benthic macrofauna between exclusion and control plots, even though four of the five most abundant prey species in our plots (Peringia ulvae,
Hediste diversicolor, Heteromastus filiformis, and Cyathura carinata) were potentially suitable prey species for the most common wader species present, the small calidrids. The density of the polychaete Hediste diversicolor and the biomass of Heteromastus filiformis significantly increased in both exclusion and control zones, likely because of the seasonal biological cycle of these species. Our results suggest that the density and biomass of the benthic macroinvertebrates assemblages at Merja Zerga lagoon are not impacted by wader predation. However, these conclusions should be treated with caution until more thorough investigations have been undertaken.