Life on the farm: are zooplankton communities in natural ponds and constructed dams the same?

Abstract

Constructed waters (e.g. dams and retired quarries) are commonly found to have a different zooplankton composition than are natural waters, and to be more readily invaded by non-indigenous species. Constructed ponds are common on farmland, but zooplankton research in these areas is scarce. Consequently, our aims were to (1) compare zooplankton communities between natural ponds and dams in rural environments and, (2) examine environmental determinants of zooplankton community composition among rural ponds. Thirty-eight ponds on farmland in New Zealand were sampled for zooplankton in winter–spring 2018 and summer 2019. All ponds were eutrophic, and zooplankton taxa typical of such conditions were common in both pond types (e.g. Brachionus, Keratella and Polyarthra species). Zooplankton community composition differed statistically between each type, although we deemed this difference to be ecologically insignificant (one-way ANOSIM, r=0.09, P=0.014). Prevalence of non-indigenous species was low, with 7% of farm dams and 2% of natural ponds being invaded, indicating that farm ponds are not acting as ‘stepping-stones’ for invaders across landscapes. Macrophyte abundance and concentration of humic substances were the dominant environmental variables measured determining zooplankton distribution among ponds.