Intraspecific variation in growth rates of <i>Rhodomonas marina</i> (Cryptophyceae) under different temperatures and salinities conditions: a comparative study of six Arctic and one temperate strain

Abstract Marine and freshwater cryptophytes are highly valued for their nutritional content and are commonly used as live feed for copepods in aquaculture. Few studies have examined the impact of temperature and salinity on growth rates of several cryptophyte strains isolated from the same water sample. This study presents the first multi-strain autecological analysis of an Arctic marine cryptophyte species, using six strains of Rhodomonas marina and one temperate strain to explore intraspecific variation. Phylogenetic inference based on ITS revealed a close relationship among all R. marina strains (99.6–100 % sequence similarity). The autecological study used batch cultures, examining growth rates at three salinities and five temperatures in one-parameter experiments. One Arctic strain and the temperate strain were also examined at 20.1 and 23.2 °C. All strains grew over a wide range of temperatures and salinities, classifying them as eurythermal and euryhaline. However, the temperate strain exhibited higher phenotypic plasticity concerning temperature, while the Arctic strains showed greater plasticity regarding salinity. Thus, this study identified the presence of intraspecific variation within a confined Arctic marine water mass, highlighting an economic potential when selecting the fastest-growing isolates for biomass production and commercial applications.