Contrasting effects of Daphnia on ratios of nitrogen to phosphorus in a eutrophic, hard‐water lake

Sarnelle, Orlando

doi:10.4319/lo.1992.37.7.1527

Cited by 35 publications

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“…Field observations indicate that Daphnia spp. tissues play an important role in the sedimentation of P in lakes (Sarnelle 1992). It should be noted that the effects of ambient Ca on the relative importance of different routes of P loss may be affected by the P content of the diets.…”

Section: Discussionmentioning

confidence: 99%

Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling

Tan¹,

Wang

2009

Aquat. Biol.

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We examined the influence of environmental calcium on phosphorus biokinetics and regulation in Daphnia magna. When the Ca concentration in culturing media increased from 0.5 to 200 mg l -1 , the specific P content of D. magna feeding on P-sufficient algae decreased significantly from 1.43 to 1.05% of dry weight. There was a significant negative relationship between the specific Ca and P contents (% dry wt) of daphnids. However, measured biokinetic parameters, including the assimilation efficiency (AE) of dietary P, the weight-specific ingestion rate (IR), the uptake of inorganic P from water, and the efflux rate constant (k e ) of P, were similar over the wide range of Ca concentrations, with some exceptions at the lowest Ca level (0.5 mg l -1 ). Diet was the dominant source of P for daphnids, and only 1 to 2% of P was incorporated from water, based on the biokinetic calculation. With the elevation of the Ca level from 0.5 to 200 mg l -1 , the proportion of P lost through molting by D. magna feeding on P-sufficient diets increased 2.5-fold, whereas the dissolved release decreased 1.9-fold. P released into the dissolved phase is readily re-utilized by primary producers, while P contained within the shed molts sinks out of the epilimnion and becomes at least temporarily unavailable to primary producers; thus, the effects of Ca on molting and dissolved release have significant implications for P cycling in freshwater lakes. Our results suggest that the availability of P to primary producers can be reduced by sedimentation of P-rich daphnid molts in high-Ca lakes, and Ca concentration in the water needs to be considered in studying the stoichiometric regulation of P in freshwater cladocerans. KEY WORDS: Phosphorus regulation · Phosphorus cycling · Phosphorus biokinetics · Effects of calcium · Daphnia magna Resale or republication not permitted without written consent of the publisherThe relative importance of different routes of phosphorus loss from Daphnia magna (via excretion, reproduction and molting) is affected by the calcium level in the water. Photo: Ke Pan OPEN PEN ACCESS CCESSAquat Biol 5: [1][2][3][4][5][6][7][8][9][10][11] 2009 of P is distributed within the carapace, possibly bound with Ca. Sterner et al. (1993) found that D. obtusa on a P-deficient diet has problems in molting. Shedding molts accounts for ~70 and ~50% of P loss from juvenile and adult D. magna over a 3 to 4 d period, respectively (He & Wang 2007). The link between Ca and P in D. magna is also indicated by the crystalline calcium phosphate composition of the shell of its ephippia (Kawasaki et al. 2004). Ca levels in the water considerably affect the calcification of the carapace of daphnids (Alstad et al. 1999) and, thus, their total Ca content (Jeziorski & Yan 2006, Tan & Wang 2008. It is therefore tempting to ask whether the content and distribution of P in daphnids is also affected by the aqueous Ca level, considering the close association of these 2 elements in these organisms. Among the various freshwater zooplankton s...

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Section: Discussionmentioning

confidence: 99%

Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling

Tan¹,

Wang

2009

Aquat. Biol.

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“…The lake resides in a steep-sided basin and consequently has a small littoral zone (75% of the lake bottom is .5 m deep, maximum depth 5 13 m). Total phosphorus (TP) concentrations in the mixed layer average about 300 mg P L 21 during winter mixing periods and range from 50 mg P L 21 to 250 mg P L 21 during thermally stratified periods (Sarnelle 1992). Previous enclosure experiments in Zaca Lake revealed large negative effects of Daphnia on total phytoplankton biomass and cyanobacterial dominance (Sarnelle 1993;Sarnelle 2003), but these experiments were initiated before cyanobacteria were a significant fraction of total phytoplankton biomass.…”

Section: Methodsmentioning

confidence: 99%

“…Water samples for phytoplankton enumeration were preserved in Lugol's solution. Macrozooplankton (crustaceans) were sampled with vertical hauls of a 13-cmdiameter, 102-mm-mesh net, which was assumed to have an efficiency of 60% based on previous empirical experience (Sarnelle 1992). Four net hauls from each enclosure were pooled into a single sample, and samples were preserved in sucrose-formalin (Haney and Hall 1973).…”

Section: Methodsmentioning

confidence: 99%

Initial conditions mediate the interaction between Daphnia and bloom‐forming cyanobacteria

Sarnelle

2007

Limnology & Oceanography

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To assess whether Daphnia populations in eutrophic lakes can increase when bloom-forming cyanobacteria dominate the phytoplankton assemblage and whether such an increase can result in strong suppression of phytoplankton biomass, I created contrasting initial conditions (high Daphnia pulicaria, low cyanobacteria vs. low D. pulicaria, high cyanobacteria) via fish manipulation in large enclosures, then removed fish from some enclosures and subsequently monitored zooplankton and phytoplankton abundance for 48 days. After being released from fish predation, D. pulicaria was apparently able to reduce cyanobacteria and total phytoplankton biomass to very low levels despite the fact that the phytoplankton assemblage was initially composed of about 90% Microcystis aeruginosa, a species that has inhibited Daphnia growth and reproduction in many laboratory studies. Thus, it appears possible for Daphnia to graze down an established bloom of cyanobacteria. In contrast, in enclosures where fish were never present, M. aeruginosa was eventually able to increase from low levels despite initially high D. pulicaria biomass. As a result, the apparent effect of D. pulicaria on M. aeruginosa at the end of the experiment was very different across enclosures with different initial conditions.

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“…Further, the general models currently available are not testable in a strict sense because some of the parameters cannot be (or at least have never been) independently estimated. Experimental studies are potentially the most powerful approach to determining zooplankton effects, but they are limited to lakes and to simple designs (ϩ/Ϫ macrozooplankton; Uehlinger and Bloesch 1987;Bloesch and Bürgi 1989;Sarnelle 1992). In several studies, zooplankton have been manipulated indirectly by establishing treatments with and without zooplanktivorous fish (Langeland et al 1987;Carpenter et al 1988;Mazumder et al 1989;Reinertsen et al 1990;Vanni et al 1997), an approach that may confound mechanistic interpretation because fish can affect phytoplankton abundance and species composition independently of their effects on zooplankton (Vanni and Layne 1997).…”

Section: Acknowledgmentsmentioning

confidence: 99%

Zooplankton effects on vertical particulate flux: Testable models and experimental results

Sarnelle

1999

Limnology & Oceanography

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The effects of herbivorous zooplankton on the sedimentation of particles out of the euphotic zone are examined with mathematical models, a large-scale field experiment, and descriptive data from a eutrophic lake. The theory is rooted in the population dynamics of phytoplankton and zooplankton and so explicitly accounts for the potential effect of zooplankton grazing on primary production and the connection between the rate at which phytoplankton cells sink and sustainable zooplankton biomass. The models predict positive, negative, or unimodal zooplankton effects, depending on the values of four parameters: rate of direct phytoplankton sinking, fraction of zooplankton fecal material exiting the euphotic zone, zooplankton assimilation efficiency, and system productivity. Models were parameterized with data from a eutrophic lake to make a priori predictions about the shape and direction of zooplankton effects. Predictions were tested against the results of an independent experiment in which a gradient of Daphnia biomass was established in large enclosures. Daphnia negatively affected sedimentation rates of carbon, nitrogen, and phosphorus in the enclosure experiment, which confirmed model predictions. Daphnia had a strong negative effect on phytoplankton biomass, and phytoplankton biomass was positively correlated with sedimentation in the enclosures. Experimental results were congruent with relationships between Daphnia biomass and sedimentation rate in the lake. Successful application of the theory suggests that these models may be of utility for assessing the direction of zooplankton effects on vertical flux in other systems. More generally, the models help to identify parameters that should be measured in studies of zooplankton effects on downward particle flux.

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Contrasting effects of Daphnia on ratios of nitrogen to phosphorus in a eutrophic, hard‐water lake

Cited by 35 publications

References 29 publications

Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling

Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling

Initial conditions mediate the interaction between Daphnia and bloom‐forming cyanobacteria

Zooplankton effects on vertical particulate flux: Testable models and experimental results

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