Abstract
We review the potential for applying traits-based approaches to freshwater testate amoeba, a diverse protist group that are abundant in lakes and are valuable ecological indicators. We investigated the efficacy of geometric morphometric analysis to define Arcellinida test size and shape indices that could summarize freshwater testate amoeba community dynamics along a temporal gradient of eutrophication in Loch Leven, Scotland (United Kingdom). A cluster analysis of test size and shape indices yielded three clusters, each dominated by a single shape: elongate, spherical and ovoid. When plotted stratigraphically, we observed increases in spherical tests, decreases in elongate tests and shrinking of test size coeval with eutrophication in Loch Leven. Decreases in the elongate cluster may reflect benthic conditions with reduced oxygen levels, while increases in the spherical cluster are likely associated with an expanding macrophyte community that promoted pelagic and epibiotic life habits. Shrinking of test size may be a stress response to eutrophication and/or warming temperatures. Tracking community dynamics using test size and shape indices was found to be as effective as using species-based approaches to summarize key palaeolimnological changes, with the added benefits of being free from taxonomic bias and error. The approach thus shows significant potential for future studies of aquatic community change in nutrient impacted lakes.
Highlights
The ever-increasing impact of humans on their environment via urbanization, industrialization and climate change has led to an 80% decline in freshwater biodiversity in the last 50 years (Grooten and Almond, 2018)
The palaeolimnological studies of Salgado et al (2010) and Prentice et al (2018) which utilized plant macrofossils and Arcellinida, respectively, identified three main long-term phases of ecological change in the Loch Leven (LEVE14) core in response to gradual eutrophication: (1) an early phase of oligo-mesotrophic conditions, (2) an intermediate phase of mesotrophic conditions which began after circa 1200 AD, and (3) an upper eutrophic phase
There is no change in the lithology for Zone 4 (3–0 cm) but there is a 15-fold increase in Arcellinida test concentrations compared to Zone 3 and Arcellinida diversity decreased substantially
Summary
The ever-increasing impact of humans on their environment via urbanization, industrialization and climate change has led to an 80% decline in freshwater biodiversity in the last 50 years (Grooten and Almond, 2018). This emphasizes the need to model the trajectory of impacted natural freshwater systems. Testate amoeba are a diverse protist group that enclose their cell body within a test (i.e., a hard shell) that can be used to identify species and preserves well in sediments They are valuable ecological indicators due to their (1) abundance in freshwater, moist soils and wetlands; (2) sensitivity to environmental conditions; (3) high preservation potential; and (4) rapid generation times (Patterson and Kumar, 2002; Mitchell et al, 2008). Lobose testate amoeba dominate (i.e., Arcellinida) and have been used as indicators for: lake acidity (Kumar and Patterson, 2000; Patterson et al, 2013); land-use change (Patterson et al, 2002); industrial impacts (Nasser et al, 2016); water quality (Roe et al, 2010); ecosystem health and seasonal environmental change (Neville et al, 2011); nutrient loading (Patterson et al, 2012; Prentice et al, 2018); and climate change (McCarthy et al, 1995; Boudreau et al, 2005), amongst other variables
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