Elemental stoichiometry of lower food web components in arctic and temperate lakes

Lakes were surveyed to assess the potential patterns of latitudinalvariation in carbon:nitrogen:phosphorus (C:N:P) stoichiometryof lower food web components. Thirty-four lakes were surveyedat an arctic latitude (68°38'N, 149°38'W) and 10 lakesat a temperate latitude (46°13'N, 89°32'W) during 1997.The temperate data set was augmented with earlier survey resultsemploying similar methods. It was hypothesized that differencesin environmental variables across latitude would cause differencesin community C:N:P ratios, leading to differences in trophicinteractions. Physical measurements (light, temperature), sestonand zooplankton were collected from each lake. Seston and zooplanktonwere analyzed for C, N and P content, and zooplankton were countedand measured for biomass estimates. The degree of trophic interactionbetween seston and zooplankton was assessed by (i) measuringelemental imbalances between seston and zooplankton and (ii)calculating the potential recycling ratio by the zooplanktoncommunity available for seston. Seston C:nutrient, but not N:P,ratios were higher in temperate than arctic lakes. Conversely,arctic zooplankton had higher C:nutrient, but not N:P, ratiosthan zooplankton in temperate lakes. Elemental imbalances weregreater in temperate than in arctic lakes, but N:P stoichiometryof potential zooplankton recycling was nearly identical betweenthe two latitudes. Zooplankton community C:N:P ratios were notrelated to either latitude or seston C:N:P. In accordance withstoichiometric theory, relative abundances of calanoid copepodswere positively correlated with seston C:N in temperate lakes.Additionally, relative abundances of Daphnia were negativelycorrelated with seston C:N ratios in temperate and arctic lakes,and positively correlated with N:P ratios in the arctic. Ingeneral, these results suggest that seston and zooplankton communitystoichiometry differ across latitude, and these differenceshave the potential to affect trophic interactions.