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Seasonal variation in size structure and production of autotrophic plankton community in eutrophied, low-light environment: A focus on Mesodinium rubrum

Labucis Atis, Labuce Astra, Jurgensone Iveta, Barda Ieva, Andersone Ingrida, Ikauniece Anda

Oceanologia

2023

Vol. 65 (2)

398--409

Temporal variations in the primary production of the size-fractionated autotrophic plankton community were studied in coastal-estuarine waters of the eutrophic Gulf of Riga, Baltic Sea. The community was net-autotrophic during spring and summer and net-heterotrophic during autumn. The results of the present study clearly demonstrate strong covariation between net primary production (NPP) and <56 µm fractionated community biomass, particularly small-sized (16–33 µm) Mesodinium rubrum, implying that the majority of NPP stems from the lower end of the size spectrum. A pronounced size distribution shift was observed within the M. rubrum population. Large-sized (length ≥34 µm) M. rubrum was the most abundant in the first half of the productive season (until week 24), whereas small-sized M. rubrum dominated during the stratified period.

Growth rates of common pelagic ciliates in a highly eutrophic lake measured with a modified dilution method

Rychert K.

Oceanological and Hydrobiological Studies

2016

Vol. 45, No. 2

216--229

The growth rates of ciliates estimated under natural conditions with the widely used size fractionation method are much lower than those observed in cultures. However, recent studies performed with a modified dilution method demonstrated that the size fractionation method underestimates the ciliate growth, because it does not remove predators of the same size as the organisms studied. Thus, it is still unresolved whether ciliates are food-limited in different systems and whether their growth rates are indeed lower than those in cultures. This study was conducted in highly eutrophic Lake Gardno using a modified dilution method. Each time, two dilution experiments were performed (around noon and around midnight). Four small, common ciliates from the genera Rimostrombidium, Tintinnidium, Cyclidium, and Urotricha were studied. The first three ciliates demonstrated very high mean diel growth rates exceeding 0.1 h-1, which corresponded well to the highest values reported in the literature for the ciliate growth in cultures at similar temperatures. Tintinnidium sp. demonstrated a diel growth rhythm. Urotricha sp. was sensitive to the experimental procedure, and measurements of its growth were unsuccessful. Concentrations of food particles were analyzed to check whether organisms studied were food satiated.