Silica-scaled chrysophytes (Stramenopiles, Ochrophyta) along a salinity gradient: a case study from the Gulf of Bothnia western shore (northern Europe)
Abstract
Silica-scaled chrysophytes (Stramenopiles, Ochrophyta) are represented predominantly by freshwater flagellates. Diverse-scaled chrysophyte communities were previously reported from brackish waters of the Baltic Sea.
However, it was clear that part of the community was delivered by freshwater river inputs. To investigate the effect of salinity on species diversity and community structure, we sampled the lakes in the close proximity to the shoreline (up to 5 km) and in almost separated deep bays (salinity values of 0.01-3.08 practical salinity units) of the Gulf of Bothnia, Baltic Sea.
We excluded exposed seashore sites to minimalize river flow impact. Species determination was based on scale morphology, which was investigated with a transmission electron microscope.
Salinity was the important predictor of diversity; the Simpson index significantly declined with increasing salinity. Community structure of silica-scaled chrysophytes was influenced most strongly by pH.
The effect of salinity was also important; however, the net effect of salinity was overridden by pH which was highly correlated to salinity. The occurrence of twelve recorded silica-scaled chrysophytes (out of 83 taxa) was significantly negatively correlated to salinity.
Conversely, six species incl. Mallomonas tonsurata and M. alpina favored more saline habitats.