Decoupling carbon effects and UV protection from terrestrial subsidies on pond zooplankton

Abstract

Studies on spatial subsidies have overwhelmingly addressed their trophic nature. However, certain subsidies might affect recipient communities beyond the feeding pathway. Terrestrial colored dissolved organic matter (DOM) is such a subsidy providing a carbon source for bacteria and heterotrophic nanoflagellates which zooplankton can consume (trophic pathway), but also protecting zooplankton against damaging UV radiation through its color (nontrophic pathway). These mechanisms have been quantified separately, but few studies have attempted to decouple them and evaluate their effects in the context of subsidies. In this study, I experimentally isolated the trophic and non-trophic pathways by which DOM (as maple leaf leachate) affects zooplankton, and also addressed how local food resources (i.e., phytoplankton) could mediate the response of zooplankton to DOM subsidies. Terrestrial subsidies (DOM) effectively shielded zooplankton against damaging UV radiation. Local resources (i.e., phytoplankton), however, did not seem to mediate the fitness response of zooplankton to UV radiation. This study also suggested that the carbon in DOM might be slightly detrimental to zooplankton independent of the UV protection effect. High levels of local resources combined with carbon subsidies from DOM did not translate into higher zooplankton survival, presumably because of the detrimental effects of DOM on zooplankton. This study provides further support for the importance of terrestrial subsidies in affecting communities through non-trophic pathways (UV attenuation) and documents that the trophic pathway might be strongly dependent on subsidy quality. Further studies on the role of subsidies that include the less documented non-trophic pathways are needed to improve our mechanistic understanding of how communities and ecosystems respond to spatial subsidies.

Habitat age influences metacommunity assembly and species richness in successional pond ecosystems

“…Differences in pond ecosystem size over succession also likely drive the observed countergradient in CDOC. The higher concentrations of CDOC in young shallow ponds may have large effects on zooplankton communities by reducing resource availability through lower primary production from light limitation (Geddes ), protecting from UV radiation (Leech and Williamson ), and improving predator avoidance (Wissel et al. ).…”

Direct and indirect effects of additions of chromophoric dissolved organic matter on zooplankton during large‐scale mesocosm experiments in an oligotrophic lake

“…While smaller‐scale enclosure studies have demonstrated an additional role of CDOM in reducing zooplankton exposure to UV (e.g. Cooke et al ., ; Geddes, ), our larger‐scale experiments indicate that UV attenuation is less important than trophic stimulation in driving Daphnia responses.…”

“…First, controlled UV‐exposure assays as well as in situ mesocosm experiments have suggested that Daphnia spp. are generally more UV‐sensitive than calanoids (Williamson et al ., ; Leech, Padeletti & Williamson, ), although other studies have found that both taxa may exhibit some UV sensitivity (Rautio & Korhola, ) and benefit from UV attenuation by CDOM (Geddes, ). Second, Daphnia spp.…”

A Source of Terrestrial Organic Carbon to Investigate the Browning of Aquatic Ecosystems

“…But larger experimental units (and more DOC) are required if one is interested in elucidating the interactive effects that terrestrial DOC has on food webs, physical processes, and ecosystem functioning. Terrestrial DOC has been manipulated in aquatic mesocosms (∼10–1,000 L) through the addition of leachates from soils [19], deciduous leaves [20], or peat moss [21]. The downside of this approach, however, is that leaching sometimes involves artificial processing of the organic material [22], [23].…”