Numerical analysis of small Arctic diatoms (Bacillariophyceae) representing the Staurosira and Staurosirella species complexes

Abstract

T.M. Paull, P.B. Hamilton, K. Gajewski and M. LeBlanc. 2008. Numerical analysis of small Arctic diatoms (Bacillariophyceae) representing the Staurosira and Staurosirella species complexes. Phycologia 47: 213–224. DOI:10.2216/07-17.1

Small benthic fragilarioid diatoms (Bacillariophyceae) are dominant taxa in circumpolar Arctic lakes and ponds. These small forms are difficult to identify under light microscope (LM) because of valve size, the limited number of visible characters, and considerable morphological variability within populations. For this reason, ultrastructural characters visible only under a scanning electron microscope (SEM) such as areolae and spine structure are usually recommended for species- and even genus-level identification. This is, however, often impractical. In this study we show that selected characters of Staurosirella pinnata (Ehrenberg) Williams & Round and Staurosira venter (Ehrenberg) Cleve & Möller measurable under LM correlate with diagnostic characters that can only be evaluated under SEM. We measured 32 morphological characters from SEM observations of 510 valves representing Staurosirella pinnata sensu Hustedt, Staurosira venter sensu Hustedt, and two morphologically distinct forms of S. venter sensu lato from lakes in Canada, Fennoscandia, and Siberia. Specimens from the circumpolar Arctic region identified as Staurosirella pinnata can be distinguished from Staurosira venter sensu lato using valve width and areola length (at margin), both visible under LM. Specimens with areolae lengths (at margin) larger than 0.4 µm are Staurosirella pinnata. For specimens with areolae lengths (at margin) smaller than 0.4 µm, those with valves wider than 2.9 µm are Staurosira venter sensu lato, whereas those with valves smaller than 2.9 µm are Staurosirella pinnata. Application of these numerical criteria allows for correct identification of 94% of specimens to either Staurosira venter (including morphotypes) or Staurosirella pinnata.

Key Words::

• Arctic
• Classification tree
• Diatoms
• Discriminant analysis
• Fragilaria
• morphology
• Staurosira venter
• Staurosirella pinnata

ACKNOWLEDGMENTS

This study was supported by grants from the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Museum of Nature (RAC). We thank J. Weckström and J.P. Smol for providing sediment from Fennoscandia and Siberia, respectively. We also thank M. Potapova and E.A. Morales for their helpful comments that improved the manuscript.