Cladocera as indicators of trophic state in Irish lakes |
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| Authors: | Guangjie Chen Catherine Dalton David Taylor |
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| Institution: | (1) Department of Biology, McGill University, Montreal, QC, H3A 1B1, Canada;(2) Department of Geography, Mary Immaculate College, University of Limerick, Limerick, Ireland;(3) School of Natural Sciences, Trinity College Dublin, Dublin, Ireland |
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| Abstract: | We examined the impact of lake trophic state on the taxonomic and functional structure of cladoceran communities and the role
of nutrient loading in structuring both cladoceran and diatom communities. Surface sediment assemblages from 33 Irish lakes
were analysed along a gradient of total phosphorus concentration (TP; 4.0–142.3 μg l−1), using a variety of statistical approaches including ordination, calibration and variance partitioning. Ordination showed
that the taxonomic structure of the cladoceran community displayed the strongest response to changes in lake trophic state,
among 17 measured environmental variables. Trophic state variables chlorophyll-a and TP explained about 20% of the variance in both cladoceran and diatom assemblages from a set of 31 lakes. Procrustes analysis
also showed significant concordance in the structure of cladoceran and diatom communities (P < 0.001). Thus, lake trophic state affects the taxonomic structure of both primary and secondary producers in our study lakes.
We also found a significant decrease in relative abundance of taxa associated with both macrophytes and sediments, or sediments
only, along the TP gradient (r = −0.49, P = 0.006, n = 30), as well as an increase in the proportion of the planktonic group (r = 0.43, P = 0.017, n = 30). This suggests that cladoceran community structure may also be shaped by lake trophic state indirectly, by affecting
habitat properties. We found no relationship between lake trophic state and the relative abundance of each of three cladoceran
groups that display different body size. We compared community structure between bottom and top sediment samples in cores
from six Irish lakes. Results revealed similar trajectories of nutrient enrichment over time, as well as a strong shift in
cladoceran functional structure in most systems. This study confirms that Cladocera remains in lake sediments are reliable
indicators of lake trophic state. This study also highlights the fact that taxonomic and functional structure should both
be considered to account for the multiple factors that shape cladoceran communities. |
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