Defining Seasonal Functional Traits of a Freshwater Zooplankton Community Using δ13C and δ15N Stable Isotope Analysis

Ruth Rawcliffe,Roberta Piscia,Amedeo Fadda,Rossana Caroni,Anna Visconti,Marina Manca

doi:10.3390/w10020108

Ruth Rawcliffe, Roberta Piscia + Show 4 more

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https://doi.org/10.3390/w10020108

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Abstract

Functional-based approaches are increasingly being used to define the functional diversity of aquatic ecosystems. In this study, we proposed the use of δ13C and δ15N stable isotopes as a proxy of zooplankton functional traits in Lake Maggiore, a large, deep subalpine Italian lake. We analyzed the seasonal pattern of δ13C and δ15N signatures of different crustacean zooplankton taxa to determine food sources, preferred habitats, and trophic positions of species throughout one year. The cladocerans Daphnia longispina galeata gr., Diaphanosoma brachyurum, and Eubosmina longispina were grouped into a primary consumer functional group from their δ13C and δ15N isotopic signatures, but while the former two species shared the same food sources, the latter exhibited a more selective feeding strategy. Cyclopoid copepods occupied a distinct functional group from the other secondary consumers, being the most 15N enriched group in the lake. The δ15N signature of calanoid copepods showed trophic enrichment in comparison to Daphnia and Eubosmina and linear mixing model results confirmed a predator-prey relationship. In our study, we have demonstrated that the use of δ13C and δ15N stable isotopes represented an effective tool to define ecological roles of freshwater zooplankton species and to determine functional diversity in a lake.

Highlights

Functional-based approaches are increasingly being used to study aquatic ecosystems as an alternative to traditional taxonomy-based approaches
We propose the use of δ13 C and δ15 N stable isotope analysis to quantify some of the “qualitative functional traits” [2] for pelagic crustacean zooplankton taxa in Lake Maggiore, a large, deep subalpine lake in Italy
The variation of δ13 C in Daphnia was most depleted in spring, with a value of −36.3h ± 0.6 (SD), and became most enriched during the summer in August, with a value of −26.0h ± 0.1 (SD)

Summary

Introduction

Functional-based approaches are increasingly being used to study aquatic ecosystems as an alternative to traditional taxonomy-based approaches. Functional diversity is a biodiversity measure based on the ecological role of the species present in a community. Many recent ecological studies [2,4,5] suggest the importance of species ecological roles, and not just the number of taxonomic species, in the relationship between biodiversity and ecosystem functioning. This is a central concept if we are to understand and predict the resilience of a community to perturbations. The loss of functional diversity in the ecosystem is mitigated, as the species lost does not possess unique functional traits. The sum of organism functional traits within an ecosystem can be said to represent an indirect measure of its functional diversity [1,8]

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