Morphological variation within the diatom taxon Cyclotella comensis and its importance for quantitative temperature reconstructions

Abstract

1. The morphologically complex taxon Cyclotella comensis Grunow had no clear relationship with environmental parameters in a study using sediment surface samples from the Swiss Alps. The morphological heterogeneity of the taxon was investigated by applying a principal component analysis (PCA) to 9000 presence/absence descriptions of valves from surface samples of six lakes from different altitudes (15 characteristics, 100 valves each lake). The PCA allowed the classification of six morphs, which differed mainly in size and length of striae. Photographs of the morphs are shown in this paper. 2. Sixty‐eight sediment surface samples were analysed using these newly defined six morphs. Summer temperature explained a major part of the variance between the morphs as assessed by a redundancy analysis (RDA). Summer temperature optima and tolerances were estimated using weighted averaging. 3. The influence of the revised C. comensis taxonomy on the diatom inferred summer temperature of a high alpine lake is discussed in a multiproxy context for the past 800 years.

Water colour, phosphorus and alkalinity are the major determinants of the dominant phytoplankton species in European lakes

“…Cyclotella comensis showed a particularly strong relationship with surface area. This species is common in alpine lakes (Zabelina et al, 1951;Hausmann & Lotter, 2001;Scheffler & Morabito, 2003). Our analyses supported this, showing that it was dominant in higher altitude locations of ES, IT, NO and SE (with average altitude 397.6 m).…”

Holocene and Lateglacial summer temperature reconstruction in the Swiss Alps based on fossil assemblages of aquatic organisms: a review

“…These transfer functions have been applied to down-core records to produce a number of summer temperature reconstructions on Holocene and Lateglacial time scales (e.g. Hausmann & Lotter 2001;Heiri et al 2003a;Heiri & Lotter 2003;Heiri & Millet 2005). Records from three localities, Gerzensee, Hinterburgsee and Sägistalsee (Fig.…”

“…As a consequence, diatom records from the Holocene and Lateglacial sediments discussed in this article are not available, even though diatom analysis was originally planned for these sites. At present, a single quantitative diatombased summer temperature reconstruction is available from the Swiss Alps, covering only the youngest part of the Holocene (the past c. 800 years) (Hausmann & Lotter 2001). This reconstruction from Bachsee, a small lake situated at 2265 m a.s.l.…”

Conventional and geometric morphometric studies of valve ultrastructural variation in two closely relatedCyclotellaspecies (Bacillariophyta)

“…Conventional morphometric techniques have proven effective for clarifying species limits, especially in the centric genus Stephanodiscus (Theriot & Stoermer, 1984a, b), as well as other diatom genera, and to investigate intraspecific morphological variation (Theriot, 1987;Hausmann & Lotter, 2001;Droop, 1995;Teubner, 1995). Whereas the data used for such analyses can include a diverse collection of measurements, counts and angles, geometric morphometrics place greater emphasis on a more complete use of two-or three-dimensional geometric information .…”