Contrasting patterns of allochthony among three major groups of crustacean zooplankton in boreal and temperate lakes

Abstract

The importance of terrestrial-derived organic matter for lake zooplankton communities remains debated, partly because little is known about the basic pathways by which allochthonous carbon is transferred to zooplankton, and whether these vary among the major taxonomic and functional groups. We quantified allochthony of three zooplankton groups (Cladocera, Calanoida, and Cyclopoida) across 18 lakes in Quebec, spanning broad gradients of dissolved organic matter (DOM) and lake trophy, using a multi-isotope (delta2H + delta13C), multi-source (terrestrial, phytoplanktonic, benthic) approach. All three zooplankton groups had significant levels of allochthony, but differed greatly in their respective patterns across lakes. Allochthony in Calanoida and Cyclopoida was linked to detrital food chains based on particulate organic matter (POM) and on DOM, respectively, whereas in Cladocera it appeared related to both pathways; not surprisingly this latter group had the highest mean allochthony (0.31; compared to 0.18 in Cyclopoida and 0.16 in Calanoida). This study highlights the complexity of the pathways of delivery and transfer of terrestrial organic matter in freshwaters, and underscores the role that microbial food webs play in this transfer.

Selective consumption and metabolic allocation of terrestrial and algal carbon determine allochthony in lake bacteria

“…Interestingly, our results suggest a lower limit in bacterial biomass allochthony in the order of~70% even in more productive systems where terrestrial DOC becomes more diluted by algal C (Figure 1). These patterns are coherent with previous studies which noted similar high levels of allochthony of bacterial biomass (79% ± 16) across a wide range in lake productivity or color in Québec on the basis of the isotopic composition of bacterial fatty acids (Berggren et al, 2014), as well as in a lake in northern Sweden (480%) (Karlsson et al, 2012) and Selective carbon consumption and allocation F Guillemette et al in two Wisconsin lakes (Kritzberg et al, 2004), although lower estimates have also been reported in the latter (range of 35-70%). Our results are also consistent with a recent hypothesis, suggesting that the rapid transfer and efficient incorporation of compounds exported from soils and leaf litter, or produced via photochemical degradation, may account for a large share of total bacterial production in boreal streams and lakes (up to 80%) (Berggren et al, 2010a, b).…”

“…Here we used previously published values for these parameters, and also a well-established isotopic model (IsoError; Phillips and Gregg, 2001) to account for their variability, but we cannot discard that some methodological biases, isotopic artifacts or secondary C incorporation pathways such as anaplerotic C fixation may have influenced our estimates of allochthony (See Supplementary Note 1 for a discussion of these issues). It should be emphasized that our estimates of bacterial biomass allochthony fall well within the range recently reported in other regions (Kritzberg et al, 2004;Karlsson et al, 2012;Berggren et al, 2014), and that the patterns in BR of terrestrial C also agree with previous reports, that is, that BR in unproductive lakes is dominated by terrestrial C (Karlsson et al, 2007;Karlsson et al, 2008). In addition, it is unlikely that the link that we found between the patterns of allocation of terrestrial versus algal C in the experimental incubations with ambient lake Chl a and phosphorous concentration (both of which being completely unconnected to the actual isotopic or metabolic mass balance), would emerge from chance or methodological bias, providing further evidence that these patterns in bacterial DOC utilization and allocation across lakes that we describe here are real.…”

“…We further used the range of zooplankton allochthony 9-23% (±1 s.d.) reported by Mohamed and Taylor, 2009, which also covers the range found in the boreal region of Northern Québec (Berggren et al, 2014), as a measure of uncertainty of the algal endmember. Finally, we used a similar approach to that of Karlsson et al (2007) and Attermeyer et al (2014), and corrected the isotopic signature of respiratory CO 2 for a +0.5‰ fractionation during respiration according to Hullar et al, 1996.…”

“…The increase in terrestrial C incorporation efficiency into biomass with increasing system productivity implies that even in eutrophic systems, where bacteria overwhelmingly consume algal-derived C, the isotopic signature of bacterial biomass may still be largely terrestrial. There is now irrefutable evidence of widespread allochthony in freshwater zooplankton and fish (Cole et al, 2011;Karlsson et al, 2012;Berggren et al, 2014), but these metazoans have a low capacity to consume and grow on detrital terrestrial C (Brett et al, 2009), so this transfer must necessarily involve an efficient repackaging of terrestrial C in the form of aquatic bacterial biomass (Berggren et al, 2010b) that can then circulate within aquatic food webs. Given the large losses that occur during the transfer of C in food webs, the systematically high terrestrial signature of bacterial biomass may be one of the keys to sustaining the widespread presence of terrestrial C measured in zooplankton even in more productive or nutrient enriched systems (Cole et al, 2002).…”

Spatial distribution of crustacean zooplankton in a large river-connected lake related to trophic status and fish

“…Crustacean zooplankton which comprise cladocerans and copepods are one of the most important organisms, because they occupy an intermediate position between microorganisms (microalgae, rotifers, protozoa, and bacteria) and larger organisms (e.g., fish) (Berggren et al, 2014;Sarma et al, 2006). Meanwhile, because crustacean zooplankton often have wide geographical distributions, sensitive to individual stressors, and their morphology are easy to identify (Cairns et al, 1993), factors affecting community structure of crustacean zooplankton have been studied intensively in the last few years.…”