congresos y reuniones científicas
Glacier melting and stoichiometric implications in lake community structure: zooplankton species distribution in a light gradient
CECILIA LASPOUMADERES; BEATRIZ MODENUTTI; MARÍA SOL SOUZA; MARCELA BASTIDAS NAVARRO; FLORENCIA CUASSOLO; ESTEBAN BALSEIRO
Encuentro; World Lake Student Meeting; 2012
World Water and Climate Network
Glacier melting and stoichiometric implications in lake community structure: zooplankton species distributions in a natural light-gradient. Cecilia Laspoumaderes Global warming will have serious consequences for all kinds of ecosystems. With increasing temperatures glaciers around the world are now melting rapidly, threatening the world fresh water reservoirs with significant changes in the receiving environments. The meltwater, carried by rivers, contains high amounts of suspended sediment particles producing longitudinal gradients in the receiving lakes, from very turbid water close to the discharge to clear water far away from the river inflow. Primary production changes due to the turbidity-induced attenuation of photosynthetic active radiation (PAR), affecting the upper trophic levels via changes in their food resources. Usually one can expect changes in food quantity for herbivores due to decreases in light intensities, but what about food nutritional quality? The light:nutrient hypothesis (LNH) and stoichiometric theory predict, under high PAR intensities and low levels of inorganic phosphorus (P), a disproportionate accumulation of carbon (C) relative to P in producer biomass, and that the impact of the change in elemental food quality should vary for different zooplankton species according to their P requirement. Therefore glacier melting would impact the receiving environments via changes in the optical properties of the lakes, that would in turn affect the nutritional state by changes in the C:P ratio of producers, generating the dominance of P rich species in a formerly P-poor dominated environment. In this work, we aim to take advantage of a natural gradient of light intensity in Lake Mascardi (Argentina) due to glacial flour inputs in one end of the lake. We analyzed if zooplankton distribution is associated with the light gradient via stoichiometric mechanisms of food quality. For this propose we sampled for two years across a six-station transect to quantify variations in light:nutrient ratio, in stoichiometric food quality of the seston, and in zooplankton distributions. We found differences in optical properties, nutrients, and zooplankton species distribution across the lake. Consistent with the light:nutrient hypothesis, increases in light intensity in lake regions distant from the glacial flour input were accompanied by decreases in sestonic quality (increased seston C:P ratio). Accompanying these changes, there was a switch from dominance of P-rich Daphnia commutata in low-light regions to dominance of low-P calanoid copepod Boeckella gracilipes in clearer waters. Thus, the overall patterns are consistent with predictions of the stoichiometric light:nutrient hypothesis and indicate that shifts in environmental light:nutrient ratio as a result of glacial melting may contribute to shifts in the relative abundance of stoichiometrically contrasting taxa in consumer guilds altering the original community structure.