Experimental evidence that subsidy quality affects the temporal variability of recipient zooplankton communities

Theory suggests spatial subsidies affect the stability of recipient food webs. Furthermore, context dependencies such as subsidy quality might influence how stabilizing/destabilizing a subsidy may be. Previous studies have shown that high-quality resources destabilize consumers, yet this prediction has rarely been tested empirically within a subsidy framework. I compared the effects of a low-quality, terrestrial carbon subsidy (cDOM derived from maple leaves) and a high-quality one (sucrose) on zooplankton communities. Subsidy quality strongly affected temporal variability of zooplankton taxa, while their mean abundance was less affected. Variability of several taxa was higher in the sucrose than in control and cDOM treatments. In addition, multivariate analyses of zooplankton assemblages indicated that community-level response to subsidy quality was consistent with responses of individual taxa. Zooplankton communities in the sucrose treatment exhibited higher temporal dispersion (greater community variability) relative to controls and cDOM additions. Although the higher biomass of edible phytoplankton in the sucrose treatment could induce zooplankton destabilization, this mechanism failed to explain the observed patterns. Instead, indirect evidence suggested that the increased temporal variability in zooplankton was likely mediated by the effect of subsidy quality on microbial communities, an alternative food source for several zooplankton species. This study thus provides experimental evidence indicating that the more labile carbon subsidy destabilized zooplankton consumers, and implies that subsidy quality may mediate the concordance between theoretical predictions and observations regarding how consumers respond to subsidies.