Strong evidence for terrestrial support of zooplankton in small lakes based on stable isotopes of carbon, nitrogen, and hydrogen

Abstract

Cross-ecosystem subsidies to food webs can alter metabolic balances in the receiving (subsidized) system and free the food web, or particular consumers, from the energetic constraints of local primary production. Although cross-ecosystem subsidies between terrestrial and aquatic systems have been well recognized for benthic organisms in streams, rivers, and the littoral zones of lakes, terrestrial subsidies to pelagic consumers are more difficult to demonstrate and remain controversial. Here, we adopt a unique approach by using stable isotopes of H, C, and N to estimate terrestrial support to zooplankton in two contrasting lakes. Zooplankton (Holopedium, Daphnia, and Leptodiaptomus) are comprised of ≈20-40% of organic material of terrestrial origin. These estimates are as high as, or higher than, prior measures obtained by experimentally manipulating the inorganic 13 C content of these lakes to augment the small, natural contrast in 13 C between terrestrial and algal photosynthesis. Our study gives credence to a growing literature, which we review here, suggesting that significant terrestrial support of pelagic crustaceans (zooplankton) is widespread.allochthony | terrestrial subsidy

Adaptive genetic variation mediates bottom-up and top-down control in an aquatic ecosystem

“…In this study, we found that intraspecific variation stemming from local adaptation is sufficient to drive similar patterns. For example, pelagic crustaceans, such as calanoid copepods, have been shown to rely heavily on terrestrial material in oligotrophic lakes [40] and are also a common prey for sticklebacks [28]. We observed that mesocosms containing litter from the most productive cottonwood genotypes fostered a greater abundance of calanoid copepods, which ultimately led to a larger decrease in calanoid abundance when fish were present ( figure 3).…”

Estuarine consumers utilize marine, estuarine and terrestrial organic matter and provide connectivity among these food webs

“…The OM sources sampled were selected based on the feeding modes of the primary consumers selected (zooplankton and Corbicula fluminea): phytoplankton (freshwater, estuarine and marine), macroalgae, microphytobenthos (MPB), sediment organic matter (SOM), particulate organic matter (POM), and vascular plants (terrestrial and aquatic; Cole et al 2011, Dias et al 2014.…”

Allochthonous dissolved organic carbon in river, lake and coastal systems: transport, function and ecological role

“…Alternatively, other theories such as the Flood Pulse Concept (FPC) of Junk et al (1989) suggest that the movement of terrestrial resources from the floodplain and catchments during flooding and rainfall events may be a significant source of energy to aquatic systems. More recently, paradigms about autochthonous carbon dominating lakes are being questioned (Cole et al 2011). The significance of allochthonous DOC to aquatic ecosystems is being further recognised with the understanding that terrestrial subsidies are playing a much greater role in some systems than previously thought (Tanentzap et al 2014).…”