Differences in zooplankton feeding rates and isotopic signatures from three temperate lakes |
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| Authors: | Anurani D Persaud Peter J Dillon |
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| Institution: | (1) Department of Chemical Sciences, Trent University, Peterborough, ON, K9J 7B8, Canada |
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| Abstract: | Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence,
we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding
experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance
and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion
rates are correlated with their δ15N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly
among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids.
For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion
rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes
for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton
ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among
zooplankton. Zooplankton δ15NDOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations
were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass.
Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher
δ15NDOMC are likely exploiting food sources from higher trophic levels. |
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