Using geometric morphometrics to disentangle Didymosphenia hullii and D. geminata (Bacillariophyceae) from Connecticut, USA, and two congeneric relatives

ABSTRACT

Two morphologically similar populations of Didymosphenia were reported from the West Branch of the Farmington River, Connecticut, USA in 2014 and 2016. We described one of them as a new species, D. hullii. The other was observed subsequently in late 2016 and resembled D. geminata, but given the worldwide nuisance characteristic of this species, the identification required confirmation. In this work we used geometric morphometrics analysis to test for quantitative distinctions between the two Connecticut populations, along with two morphologically similar taxa from the literature, D. laticollis and D. pumila. We successfully separated the four entities and confirmed the identity of the second blooming diatom in the Farmington River, Connecticut, as D. geminata, which is the first confirmed report of this species for the state. We conclude that geometric morphometrics, in combination with features viewed with scanning electron microscopy and light microscopy, enhances the ability to distinguish among these morphologically similar species of Didymosphenia. We summarize these findings and pinpoint morphological distinctions that can be used to separate the taxa during routine light microscopy analyses.

HIGHLIGHTS

• Geometric morphometrics was used to differentiate four Didymosphenia taxa.

• Morphological comparisons of D. hullii and D. geminata are shown.

• Didymosphenia geminata was recently reported in Connecticut, USA.

KEYWORDS:

• Benthic diatoms
• brown algae
• diatom
• Didymosphenia
• fine structure
• invasive species
• morphometrics
• nuisance species
• stalk-forming diatoms

Acknowledgements

We are grateful for the late D. Metzeltin’s expert opinion and his support of our research. We wish to dedicate this manuscript to him in his remembrance. We thank Three Rivers Community College’s S. Goetchius, K. Barfield, S. Cohen, D. Jewett, retired President G.S. Jones and President M.E. Jukoski for providing support for this continued research. We are grateful for the expert assistance of emeritus M. Cantino, X. Sun, of the EM lab at UCONN, NSF 1126100 supporting the purchase of the Nova Nano SEM, J. Morrison, East Hartford, USGS. E.A. Morales was funded in part by the European Union through the European Regional Development Fund, framed in COMPETE 2020 (Operational Programme Competitiveness and Internationalization), through the ICT project (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and the Agência Portuguesa do Ambiente, APA-00004DFIN.AALP/2017 integrated within the Operational Program for Sustainability and Efficiency in the Use of Resources 2014-20, POSEUR-03-2013-FC000001. We thank the reviewers for their helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2022.2068075

Supplementary fig. 1: The map of the West Branch Farmington and Still Rivers. The blue square shows where Didymosphenia geminata bloomed in late 2016. The dark blue circle indicates where D. hullii was found further downstream mixing in some cases with Cymbella janischii.

Author contributions

D. A. Khan-Bureau: original concept, fieldwork, produced LM and SEM images, analysed data, drafted and edited the manuscript; S. Blanco: geometric morphometrics analyses, reviewed LM and SEM images, drafted and edited the manuscript; E. A. Morales: reviewed and interpreted LM and SEM images, drafted and edited the manuscript; L. Ector: reviewed LM and SEM images and edited the manuscript; M.S. Beauchene: provided historical information and edited the manuscript; L.A. Lewis: reviewed LM and SEM images and edited the manuscript.

Additional information

Funding

We thank Trout Unlimited Connecticut and The Eightmile River Committee for funding this project and Rivers Alliance of Connecticut for support of this project. EAM was co-funded by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 – ICT (Institute of Earth Sciences), and the Agência Portuguesa do Ambiente, APA-000004DFIN.AALP/2017 integrated within the Operational Program for Sustainability and Efficiency in the Use of Resources 2014-20, POSEUR-03-2013-FC-000001. LE was also partly funded in the framework of the DIATOMS project (LIST-Luxembourg Institute of Science and Technology).