title: Positive feedback between chironomids and algae creates net mutualism between benthic primary consumers and producers.
abstract: The chironomids of Lake Mývatn show extreme population fluctuations that affect most aspects of the lake ecosystem. During periods of high chironomid densities, chironomid larvae comprise over 90% of aquatic secondary production. Here, we show that chironomid larvae substantially stimulate benthic gross primary production (GPP) and net primary production (NPP), despite consuming benthic algae. Benthic GPP in experimental mesocosms with 140,000 larvae/m2was 71% higher than in mesocosms with no larvae. Similarly, chlorophyll a concentrations in mesocosms increased significantly over the range of larval densities. Furthermore, larvae showed increased growth rates at higher densities, possibly due to greater benthic algal availability in these treatments. We investigated the hypothesis that larvae promote benthic algal growth by alleviating nutrient limitation, and found that (1) larvae have the potential to cycle the entire yearly external loadings of nitrogen and phosphorus during the growing season, and (2) chlorophyll a concentrations were significantly greater in close proximity to larvae (on larval tubes). The positive feedback between chironomid larvae and benthic algae generated a net mutualism between the primary consumer and primary producer trophic levels in the benthic ecosystem. Thus, our results give an example in which unexpected positive feedbacks can lead to both high primary and high secondary production.
authors.affiliation: Freshwater and Marine Science Program, University of Wisconsin - Madison, Madison, Wisconsin, USA.|Department of Zoology, University of Wisconsin - Madison, Madison, Wisconsin, USA.
authors.forename: Cristina M
authors.initials: CM
authors.lastname: Herren
authors.affiliation: Department of Zoology, University of Wisconsin - Madison, Madison, Wisconsin, USA.
authors.forename: Kyle C
authors.initials: KC
authors.lastname: Webert
authors.affiliation: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Drake
authors.affiliation: Center for Limnology, University of Wisconsin - Madison, Madison, Wisconsin, USA.
authors.forename: M
authors.initials: M
authors.lastname: Jake Vander Zanden
authors.affiliation: Faculty of Life and Environmental Sciences, Mývatn Research Station, Iceland and University of Iceland, Reykjavík, Iceland.
authors.forename: Árni
authors.initials: Á
authors.lastname: Einarsson
authors.affiliation: Department of Zoology, University of Wisconsin - Madison, Madison, Wisconsin, USA.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Ives
authors.affiliation: Department of Entomology, University of Wisconsin - Madison, Madison, Wisconsin, USA.
authors.forename: Claudio
authors.initials: C
authors.lastname: Gratton
mesh_terms: D000818:Animals; D002683:Chironomidae / Q000502:physiology*; D002734:Chlorophyll; D000077194:Chlorophyll A; D017753:Ecosystem; D060106:Lakes; D058086:Microalgae / Q000502:physiology*; D013559:Symbiosis
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: benthic primary production; consumer-resource dynamics; facilitation; nutrient cycling; positive feedback