I encountered a diatom in a sample yesterday that I had not seen before and, after checking some books, am fairly confident that this is Navicula supergregaria Rumrich & Lange-Bertalot 2000 and that this is the first record of the species from the U.K. I found this in a sample collected from the River Alver, close to Kingfisher Caravan Park in Gosport, Hampshire from April 2014. It was a gritty sample that did not make for easy counting and contained several taxa that suggested that the river at this point is brackish.
As the name suggests, Navicula supergregaria is similar to Navicula gregaria, albeit larger (> 6.5 mm breadth) and the pores in the striae are just about visible with the light microscope (24-28/10 mm). My previous post mentioned three distinct forms of Navicula gregaria recognised by Eileen Cox; N. supergregaria is an additional form, previously recorded in similar habitats in the Netherlands and Germany as well as in the USA. In this sample, it mingled with “true” Navicula gregaria and a distinctive population of Navicula salinarum too.
Navicula supergregaria from the River Alver, Gosport, Hampshire, April 2014. Scale bar: 10 micrometres (1/100th of a millimetre).
Navicula salinarum from the River Alver, Gosport, Hampshire, April 2014. Scale bar: 10 micrometres (1/100th of a millimetre).