Abstract

Benthic grazers can affect the nutrient stoichiometry of periphyton through different pathways: 1) grazers can reduce periphyton biomass, thereby increasing the relative amount of nutrients for the remaining periphyton; 2) grazers can change benthic algal community composition toward grazer-resistant taxa that might differ in their C:N:P stoichiometry from less resistant benthic algae; 3) grazers can differentially recycle or incorporate nutrients, thereby changing periphyton nutrient content; and 4) mechanical removal of high-C detritus by grazers can decrease C:nutrient ratios. Nutrient-mediated grazer effects on periphyton nutrient stoichiometry depend on the relative availability of nutrients in the system in relation to the nutrients made available through grazing. We tested the relative importance of the different pathways under differing nutrient conditions in a 3-wk laboratory experiment in which grazer presence and dissolved N and P concentrations were manipulated. The effects of the gastropod grazer Viviparus viviparus (L.) on periphyton nutrient stoichiometry, algal taxonomy and biomass, and dissolved nutrients were determined with a 2 3 4 factorial design. Factors were grazers (þ/–) and nutrient addition (ambient, þN,þP, andþNP). Grazers decreased periphyton C:P and N:P in theþN andþP treatments. Grazers mainly affected periphyton nutrient stoichiometry by changing benthic algal taxonomic composition because the percentage of mucilage-producing algae Chaetophora spp. was much higher in grazed than in ungrazed treatments. Mucilage has high C and N content, but low P content. Grazer stoichiometry indicated that grazers might have retained more P in the þN and þP treatment than in the other nutrient treatments. We conclude that nutrient addition interacted with grazer effects on periphyton nutrient stoichiometry and that grazer effects on periphyton nutrient stoichiometry can be explained only by considering the combined effects of nutrient availability, differential nutrient recycling by grazers, and grazer-induced changes in algal taxonomy

Keywords

ecological stoichiometry; grazer; Viviparus viviparus; benthic algae; mucilage; indirect grazer effects

Published in

Journal of the North American Benthological Society
2009, Volume: 28, number: 2, pages: 283-293

SLU Authors

• Kahlert, Maria

  • Department of Environmental Assessment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use
Fish and Aquacultural Science


Publication identifier

DOI: https://doi.org/10.1899/08-115.1

Permanent link to this page (URI)

https://res.slu.se/id/publ/27641