Cocconeis cascadensis, a new monoraphid diatom from mountain streams in Northern California, USA

Abstract

A new diatom species, Cocconeis cascadensis, is reported from streams in the Southern Cascade Mountain Range in California (USA). Light and scanning electron microscopy reveals morphological novelties related to the structure of the areolae on the sternum valve, which are surrounded externally by crater-like depressions, as well as apically elongated bumps in the submarginal hyaline area of the raphe valve. The valve morphology of the coarsely striated taxa, Cocconeis placentula var. lineata, C. pseudolineata and C. neodiminuta from the studied streams, and C. disculus from freshwaters in Europe, is presented for comparison. The newly described species possesses a unique combination of morphological features, representing an intermediary between the more complex valve ultrastructure of marine Cocconeis taxa and the freshwater members of the C. placentula species complex, with simple slit-like areolae. Cocconeis cascadensis inhabits cold-water mountain streams with low conductivity, low nutrients and low dissolved organic carbon concentrations.

Keywords:

• diatoms
• Cocconeis
• new species
• streams
• Southern Cascade Mountain Range
• California

Acknowledgements

Sierra Pacific Industries and the California Natural Resources Agency provided data for the present and a previous study on diatoms from streams in Northern California (Stancheva et al. 2016). The Department of Biological Sciences, California State University San Marcos and Professor Robert Sheath provided laboratory facility for this study. The author acknowledges the assistance by Ryan Anderson and Paul Warren in scanning electron microscopy at the Nano3 Facility at the University of California, San Diego, and by Marco Sigala and Dr Cajun James who provided site characterization data. The author is thankful to Lena Eggers at the Friedrich-Hustedt-Zentrum für Diatomeenforschung Institute for Polar and Marine Research, Germany for providing C. disculus material. The comments and suggestions provided by the associate editor, Dr Jonathan Taylor, and two anonymous reviewers improved the presentation of this paper.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

Sierra Pacific Industries and the California Natural Resources Agency funded the present and a previous study on diatoms from streams in Northern California. The California State Water Resources Control Board Surface Water Ambient Monitoring Program provided funding.