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Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplankton communities largely consisting of the diatom Aulacoseira islandica (O. Muller) Simonsen. To assess the activity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O 2 ) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the activity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O 2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie.

The limnology of offshore Lake Erie during periods of extensive (> 70%) ice cover was examined from ship borne sampling efforts in 2007 to 2010, inclusive. Dense and discrete accumulations of the centric filamentous diatom Aulacoseria islandica (> 10 μg Chl- a /L) were located in the isothermal (

Using light and electron microscopy, the diatom species Aulacoseira islandica (O. Mull.) Sim. was examined with special emphasis on the following characteristics: structure of the valve areolae, heterovalvy, and distribution of the rimoportulae. The mantle and valve face areolae were pores containing volate occlusions. However, observations only using transmission electron microscopy may result in an incomplete interpretation because of the fragility of the dissected system of volae. Relief valves with a stepped mantle and intaglio valves with a plain mantle occurred. Another form of heterovalvy resulted from the formation of separation valves. Linking valves had spatulate spines while separation valves bore tapering spines. In Aulacoseira, the rimoportulae usually occurred near the “Ringleiste.” The presence of several rimoportulae on the mantle was one of the most striking features in Aulacoseira islandica.

Reliable identification of the diatoms is of crucial importance to understand the changing environmental signals stored in the sediments of Lake Baikal. Light and scanning electron microscopy combined with mathematical methods, including principal components analysis, were used to estimate morphological diversity in the structure of mantles of the two dominant species of Lake Baikal, Aulacoseira baicalensis (K. Meyer) Simonsen and Aulacoseira islandica (O. Muller) Simonsen. Species-specific features, such as areolar density, ultrastructure and form of linking spines, were found to be widely variable within cells of the same filaments of A. baicalensis. This finding suggests that the diagnosis of this species will have to be broadened. Besides the thin-walled frustules and the ability to form spores, the population of A. islandica in Lake Baikal is characterized by a higher density of areolae on the mantle compared to the published diagnoses, including the diagnosis of the subspecies helvetica. Mo...

The winter phytoplankton of the Russian part of the hyper-trophic Curonian Lagoon (Baltic Sea) was studied in 2010. Diatoms, cyanobacteria and cryptomonads prevailed in phytoplankton. Diatom Aulacoseira islandica was dominant and especially prevailing in the southern area of the lagoon, i. e. the area influenced by the Deyma River. Cyanobacteria Planktothrix agardhii was also a dominant species. The composition of the complex of dominant species and vertical distribution of phytoplankton differed compared to the results obtained 30 years ago in the same area. The study revealed the increase of the abundance of winter phytoplankton compared to the formerly recorded data.