Support of benthic invertebrates by detrital resources and current autochthonous primary production: results from a whole‐lake ¹³C addition

Abstract

1. Secondary production of benthic invertebrates in lakes is supported by current autochthonous primary production, and by detritus derived from a combination of terrestrial inputs and old autochthonous production from prior seasons. We quantified the importance of these two resources for the dominant benthic insects in Crampton Lake, a 26 ha, clear-water system. 2. Daily additions of NaH 13 CO 3 to the lake caused an increase in the stable carbon isotope ratios (d 13 C) of the current primary production of phytoplankton and periphyton. We measured the response of four insect groups (taxon-depth combinations) to this manipulation, quantifying their current autochthony (% reliance on current autochthonous primary production) by fitting dynamic mixing models to time series of insect d 13 C. 3. The d 13 C of all four groups increased in response to the manipulation, although the magnitude of response differed by taxon and by depth, indicating differences in current autochthony. Odonate larvae (Libellulidae and Corduliidae) collected at 1.5 m depth derived 75% of their C from current autochthonous primary production. Chironomid larvae collected at 1.5, 3.5 and 10 m depths derived, respectively, 43%, 39% and 17% of their C from current autochthonous primary production. 4. Both taxon-specific diet preferences and depth-specific differences in resource availability may contribute to differences in current autochthony. Our results demonstrate significant but incomplete support of insect production by current autochthony, and indicate that allochthonous inputs and old autochthonous detritus support a substantial fraction (25-83%) of insect production.

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

“…31 and Table S1). The 13 C addition experiments have two potential biases that could result in overestimates of allochthony: deep feeding by vertically migrating zooplankton and consumption of detritus of algal origin that was produced before the addition of the label (15,21). However, the ambient isotope approach used here did not give substantially lower estimates of ϕT than the 13 C additions, indicating that neither of these potential biases were of major importance for zooplankton in these lakes.…”

“…Second, autochthonous primary production that occurred before the 13 C addition would not have been labeled, and the resulting autochthonous detritus again could be counted as allochthonous by the analysis. Although these issues were partially addressed (15,20,29), Brett et al (21) recently argued that these 13 C addition experiments greatly overestimated allochthony to zooplankton. Here, we estimate allochthony to zooplankton with an independent and unique approach.…”

“…Using multiple approaches (litter exclusion, gut contents, biomarkers, and stable isotopes), a number of authors have reported that some fishes and benthic invertebrates in streams and the littoral zones of rivers and lakes are indeed supported in part by terrestrial organic matter (e.g., refs. [9][10][11][12][13][14][15][16]. Demonstrating a terrestrial influence on pelagic food webs in lakes had been both more difficult and more controversial.…”

Periphyton support for littoral secondary production in a highly humic boreal lake

“…Since older unlabeled autochthonous detrital periphyton can significantly support invertebrate production (Solomon et al 2008), the SIAR mixing model is likely to have overestimated the proportion of allochthonous OM in the diets of certain taxa. Also, some taxa like Trichoptera and Ephemeroptera were hard to find in the spring and appeared later in the summer, when most of the periphyton was already labeled.…”

Shoreline urbanization interrupts allochthonous subsidies to a benthic consumer over a gradient of lake size

“…These studies have prioritized the pelagic (open water) zone, while de-emphasizing the benthic (lake bottom) zone despite repeated calls to dedicate more research to benthic processes and organisms [6,7]. Investigations of allochthonous and autochthonous dynamics in benthic consumers of lakes are scarce and often limited to single-site case studies [8,9], failing to generalize trends over the large gradients of lake size and productivity that have enlightened pelagic food web work [10,11].…”