The seasonal distribution of micro-green algae in two linked but contrasting Welsh lakes

Abstract

Eight species of small green algae and Stigeoclonium sp. were studied over a two-year period in phytoplankton and epipelon of Llyn Peris and Llyn Padarn. Quantitative estimations of algal standing crop were made by culturing samples from water and sediment on nutrient agar plates. Different patterns of distribution and periodicity were exhibited by the algal species studied. Chorella vulgaris var. vulgaris was most widespread and present in large numbers in both algal communities at all four study sites. Chlamydomonas moewusii var. eumetabletos was also common. All micro-green algae exhibited rapid increases in standing crop, but these were irregular. Minimum numbers were recorded during winter. Some species, such as Ankistrodesmus falcatus and Chlorogonium neglectum were of limited distribution. Ordination analyses by Reciprocal Averaging confirmed differences between the growth of micro-green algae within sites and between lakes. In general, the standing crops of micro-green algae were greater in Llyn Padarn the lower lake, and changes in these algae were greater in the plankton at the inflow than the outflow site of the lower lake. In contrast, on the sediments, there was more change in the micro-green algae at the outflow site in Llyn Padarn than at the inflow site in Llyn Peris.