Abstract
The invasive and nuisance microalga Gonyostomum semen has recently expanded its geographical distribution and increased its biomass in Sweden and Finland. Temperatures, total organic carbon (TOC), water colour and phosphorous are main factors suggested as drivers for its success. Already in the 1980s there were indications of the same patterns also in Norway, and in this study we further examine these observations based on the hypotheses that (1) G. semen has continued its increase in abundance in Norway since then, (2) after settling in a lake, G. semen may increase its biomass, provided a simultaneous change in climatic factors. We use existing data from Norwegian monitoring databases for the study and additional water samples to investigate distribution. G. semen was detected by microscopy and quantitative PCR, while trends over time in G. semen biomass and possible explanatory variables were analysed by simple regression. We show that G. semen has increased its distribution in Norway since the 1980s, geographically and to new lakes. In eight of the nine lakes studied, the proportion of G. semen biomass in lake phytoplankton has increased with time. These changes seem to be explained only to some degree by temperature, TOC, water colour and phosphorous.
Highlights
The Raphidophyte Gonyostomum semen (Ehr.) Diesing is a flagellated microalga currently inhabiting freshwaters in Europe, Africa, Asia and North- and South-America (Eloranta & Raike, 1995)
G. semen exists in low amounts, and is never found in high abundances or known to cause blooms, while in other lakes it might be the dominant alga over the majority of the growth season, causing frequent blooms from July to September (Pithart & Pechar, 1997; Brettum & Andersen, 2005; Haande et al, 2012; Lebret et al, 2012b)
total organic carbon (TOC) and colour values for Gjølsjøen and Lundebyvannet were on the border of being too scarce for a valid regression, the results show significant increases for both parameters, and since this is in line with previous studies reporting dissolved organic carbon (DOC) and water colour increases in Scandinavia (Monteith et al, 2007) and in Norwegian lakes (Hongve et al, 2004) during the past decades, we conclude that our regressions are plausible
Summary
The Raphidophyte Gonyostomum semen (Ehr.) Diesing is a flagellated microalga currently inhabiting freshwaters in Europe, Africa, Asia and North- and South-America (Eloranta & Raike, 1995). G. semen exists in low amounts, and is never found in high abundances or known to cause blooms, while in other lakes it might be the dominant alga over the majority of the growth season, causing frequent blooms from July to September (Pithart & Pechar, 1997; Brettum & Andersen, 2005; Haande et al, 2012; Lebret et al, 2012b) Due to these blooms and their potential consequences, G. semen is considered to be a problematic and nuisance alga with potential of considerable negative impact for the public and local governments (Rengefors et al, 2012). The problems have continued in Norway since (Bjørndalen, 1982; Bjørndalen & Løvstad, 1984) and have caused several bathing sites to lose attractiveness (Hertzberg et al, 1989) or to need investments to prevent discomfort and skin reactions, such as lakeside showers (personal comment Kjell Olausen, Eidsberg commune, Norway)
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