Observations of two nuisance stalk-forming diatoms (Bacillariophyta) from a river in Connecticut, Northeastern U.S.A.: Didymosphenia sp. and Cymbella janischii (A. Schmidt) De Toni

Abstract

The nuisance taxon Didymosphenia geminata was reported in the West Branch of the Farmington River in March, 2011 after a fisherman detected cotton-like tufts attached to rocks. In response, the Connecticut Department of Energy and Environmental Protection (CT DEEP) conducted a comprehensive survey of the river system. After major late summer storms, Didymosphenia geminata was not observed again. Surveys in 2012–2013 tracked the spatial and temporal distribution of stalk-forming diatoms at the confluence of the West Branch of the Farmington and Still Rivers, thereby allowing comparison of data from adjacent rivers with distinct water chemistries. Water chemistry and temperature data were collected to characterize nutrient concentrations associated with these diatoms. Surveys showed no evidence of Didymosphenia geminata but four native stalk-forming diatom species and a taxon previously unreported in Connecticut, Cymbella janischii, were observed throughout the year. Also from November, 2012 through June, 2013, a morphologically distinct diatom in the genus Didymosphenia was observed growing prolifically bank to bank with thick mats of long filamentous stalks. Subsequent examination revealed that the taxon previously reported as Didymosphenia geminata was instead a different taxon, Didymosphenia sp. Furthermore, Didymosphenia sp. continued to flourish in the West Branch of the Farmington River, absent from the neighbouring Still River, suggesting that the physiochemical features and in particular higher nutrients may limit the distribution of this diatom. In contrast, C. janischii was found growing abundantly further downstream in warmer water and higher nutrient levels.