Search

Negative relationships between dissolved organic carbon (DOC) concentration and fish productivity have been reported from correlative studies across lakes, but to date there have not been experimental tests of these relationships. We increased the DOC concentration in a lake by 3.4 mg x [L.sup.-1], using a before-after control-impact design, to quantify the effects on the productivity and population structure of largemouth bass (Micropterus salmoides). Greater DOC reduced the volume of the epilimnion, the preferred habitat of largemouth bass, resulting in increased bass density. The likelihood that adult bass had empty diets decreased despite this increase in bass density; diet composition also changed. There was no apparent change in bass growth or condition. Overall, there was no net change in largemouth bass productivity. However, changes in young of year and juvenile recruitment and feeding success suggest the possibility that future effects could occur. Our results are the first to examine the effects of an increase in DOC on fish productivity through a 5-year temporal lens, which demonstrates that the relationship between DOC and fish productivity is multidimensional and complex. Des etudes correlatives sur des lacs multiples ont fait etat de relations negatives entre la concentration de carbone organique dissous (COD) et la productivite de poissons, mais aucun test experimental permettant de valider ces relations n'a ete propose a ce jour. Nous avons accru la concentration de COD dans un lac de 3,4 mg x [L.sup.-1] et employe un schema avant-apres temoin-intervention pour quantifier les effets sur la productivite et la structure de la population d'achigans a grande bouche (Micropterus salmoides). Une plus grande concentration de COD s'est traduite par une reduction du volume de l'epilimnion, l'habitat privilegie des achigans a grande bouche, entrainant une augmentation de la densite d'achigans. La probabilite que des achigans adultes aient des regimes alimentaires vides a diminue malgre la densite accrue d'achigans; la composition des regimes alimentaires a egalement change. La croissance et l'embonpoint des achigans ne presentent pas de changement apparent. Globalement, il n'y a pas eu de changement net de la productivite des achigans a grande bouche. Cependant, des modifications du recrutement de jeunes de l'annee et de juveniles et du succes d'alimentation indiqueraient que des effets futurs sont possibles. Nos resultats sont les premiers a examiner les effets d'une augmentation du COD sur la productivite de poissons dans une optique quinquennale, qui demontre que la relation entre le COD et la productivite de poissons est complexe et multidimensionnelle. [Traduit par la Redaction], Introduction Dissolved organic carbon (DOC) concentrations vary widely across lake-rich landscapes, and many lakes in the Northern Hemisphere are increasing in DOC (Hanson et al. 2007; Monteith et al. 2007). [...]

Globally, lakes are warming and browning with ongoing climate change. These changes significantly impact a lake's biogeochemical properties and all organisms, including invertebrate consumers. The effects of these changes are essential to understand, especially during critical periods after and before the growing season, that is, autumn and spring, which can determine the composition of the invertebrate consumer community.In this study, we used a large‐scale experimental pond system to test the combined effect of warming (+3°C) and increased input of terrestrial and coloured dissolved organic carbon (gradient of 1.6–8.8 mg/L in the ambient and 1.6–9.3 mg/L in the warm)—which causes browning—on zooplankton and benthic macroinvertebrate biomass and composition during the autumn and the following spring.Total zooplankton biomass decreased with warming and increased with browning, while total zoobenthos did not respond to either treatment. Warming and browning throughout the autumn had no overall interactive effects on zooplankton or zoobenthos. Autumnal warming decreased total pelagic consumer biomass, caused by a decrease in both Rotifera and Copepoda. In contrast, there was no effect on overall benthic consumer biomass, with only Asellus sp. biomass showing a negative response to warming. An autumnal increase in dissolved organic carbon led to increased total pelagic consumer biomass, which was related to increases in Daphnia sp. biomass but did not affect zoobenthos biomass. While we expected zooplankton and zoobenthos biomass to follow responses in primary and bacterial production to treatments, we did not find any relationship between consumer groups and these estimates of resource production.Our results suggest that consumer responses to warming and browning during autumn may lead to less overarching general changes in consumer biomass, and responses are mostly taxon‐specific.This study gives novel insights into the effects of warming and browning on consumer biomass during autumn and spring and increases the understanding of the effects of climate change on invertebrate community biomass in the different habitats. [ABSTRACT FROM AUTHOR]