Phytoplankton community structure changes in Thi Nai lagoon (South - Central Vietnam) from 2004 to 2020

Phytoplankton species composition, abundance, biodiversity indices and their influence by environmental conditions were examined in Thi Nai lagoon using data from four surveys in 2004, 2008, 2009 and 2020. A total of 367 taxa of phytoplankton belonging to ten groups was recorded, of which diatoms were dominant with over 60% of the total species. In Thi Nai lagoon, the number of phytoplankton species decreased from the upper lagoon (283 taxa) to the lagoon mouth area (224) and was lowest in river stations (139). The species number was much lower in the rainy season (<95 species) and increased from 2004 to 2020. Among the biodiversity indices, Shannon, ∆, s∆+, Λ+ and sФ+ were lower in the rainy season, whereas ∆*, ∆+ and Ф+ had lower values in the dry season. For long-term analysis, the differences were especially significant at upper and lower lagoon for ∆, ∆*, ∆+, s∆+ and sФ+. In the dry season, the mean density of phytoplankton was lower at the river stations and upper lagoon, but higher at the lower lagoon and the lagoon mouth area. There was a clear difference of species assemblages between the two seasons with average dissimilarities in each area ranging from 94.16% to 95.57%. During 2004–2020, the difference in ratios between the main phytoplankton groups were small over years but there was a complete change in dominance of particular species, assemblage dissimilarities were from 73.4 to 77.9, greatest between 2009 and 2020. The lagoon was low in biodiversity for the whole investigated time indicated by taxonomic index ∆+. Among biodiversity indices, species richness (S), taxonomic indices (∆*, s∆+), and phylogenetic indices (Ф+, sФ+) were more sensitive to the changes of the aquatic environment than other traditional indices.

The Combined Effects of Increased pCO2 and Warming on a Coastal Phytoplankton Assemblage: From Species Composition to Sinking Rate

In addition to ocean acidification, a significant recent warming trend in Chinese coastal waters has received much attention. However, studies of the combined effects of warming and acidification on natural coastal phytoplankton assemblages here are scarce. We conducted a continuous incubation experiment with a natural spring phytoplankton assemblage collected from the Bohai Sea near Tianjin. Experimental treatments used a full factorial combination of temperature (7 and 11°C) and pCO2 (400 and 800 ppm) treatments. Results suggest that changes in pCO2 and temperature had both individual and interactive effects on phytoplankton species composition and elemental stoichiometry. Warming mainly favored the accumulation of picoplankton and dinoflagellate biomass. Increased pCO2 significantly increased particulate organic carbon to particulate organic phosphorus (C:P) and particulate organic carbon to biogenic silica (C:BSi) ratios, and decreased total diatom abundance; in the meanwhile, higher pCO2 significantly increased the ratio of centric to pennate diatom abundance. Warming and increased pCO2 both greatly decreased the proportion of diatoms to dinoflagellates. The highest chlorophyll a biomass was observed in the high pCO2, high temperature phytoplankton assemblage, which also had the slowest sinking rate of all treatments. Overall, there were significant interactive effects of increased pCO2 and warming on dinoflagellate abundance, pennate diatom abundance, diatom vs. dinoflagellates ratio and the centric vs. pennate ratio. These findings suggest that future ocean acidification and warming trends may individually and cumulatively affect coastal biogeochemistry and carbon fluxes through shifts in phytoplankton species composition and sinking rates.

Effect of a Once in 100-Year Flood on a Subtropical Coastal Phytoplankton Community

Subtropical systems experience occasional severe floods, dramatically altering the phytoplankton community structure, in response to changes in salinity, nutrients, and light. This study examined the effects of a 1:100 year summer flood on the phytoplankton community in an Australian subtropical bay – Moreton Bay – over 48 weeks, from January to December 2011. Immediately after maximum flood levels were reached on the rivers flowing into the bay, the lowest salinity, and highest turbidity values, in more than a decade, were measured in the Bay and the areal extent of the flood-related parameters was also far greater than previous flood events. Changes in these parameters together with changes in Colored Dissolved Organic Matter (CDOM) and sediment concentrations significantly reduced the light availability within the water column. Despite the reduced light availability, the phytoplankton community responded rapidly (1–2 weeks) to the nutrients from flood inputs, as measured using pigment concentrations and cell counts and observed in ocean color satellite imagery. Initially, the phytoplankton community was totally dominated by micro-phytoplankton, particularly diatoms; however, in the subsequent weeks (up to 48-weeks post flood) the community changed to one of nano- and pico-plankton in all areas of the Bay not usually affected by river flow. This trend is consistent with many other studies that show the ability of micro-phytoplankton to respond rapidly to increased nutrient availability, stimulating their growth rates. The results of this study suggest that one-off extreme floods have immediate, but short-lived effects, on phytoplankton species composition and biomass as a result of the interacting and dynamic effects of changes in nutrient and light availability.

ICE AND PLANKTON FLORA IN KISLO-SLADKOE LAKE PARTIALLY SEPARATED FROM THE WHITE SEA IN MARCH AND APRIL 2019

Paper examines ice algae and phytoplankton species composition and abundance in a stratified salt lake separated from the White Sea, in spring after a complete winter washing.

Phytoplankton as a bioindicator of the water quality of Lake Malenets (Pskov Region)

This paper shows the use of planktonic algae in determining the ecological state of the reservoir. Phytoplankton is an important link in the aquatic ecosystem, which is the first to react to the slightest fluctuations in environmental conditions by changing its structure and quantitative characteristics, and therefore is very convenient in bioindication studies. In the summer of 2017, the planktonic algaflora of Lake Malenets, located on the territory of the Mikhailovskoye Museum-Reserve in the Pushkinogorsk District of the Pskov Region, was studied for the first time. In total, 87 species and intraspecific taxa of phytoplankton were identified from 8 phylums, 12 classes, 20 orders, 35 families, and 58 genera. The dominant algaflora complex is characterized as diatom-chlorophytic with the presence of golden algae. Using the Sierensen-Chekanovsky index, the degree of similarity of the phytoplankton species composition of Lake Malenets with the nearby Lake Kuchane was estimated. The calculation of quantitative indicators of phytoplankton abundance and biomass was carried out, the ecological and geographical characteristics of microalgae were presented, and the water quality class of Lake Malenets was established. The obtained results are of practical importance, since they allow to establish the ecological state of the water body as well as to develop methodological recommendations for its improvement and stabilization.

Phytoplankton species composition and abundance in a freshwater ecotone, Akwa Ibom State, South-Eastern Nigeria

Phytoplankton composition and abundance could be used to evaluate the health of any aquatic ecosystem. Phytoplankton species were quantitatively sampled for twelve calendar months from Abak River, Nigeria using standard methods. Data generated were pooled and subjected to appropriate statistical analysis including descriptive and inferential statistics. The results showed that 3,901 cells/l, 45 species, 36 genera and 4 phytoplankton taxonomic groups were identified. The dominant species in terms of number of cells/l was Phormidium valderiae (1,770 cells/l; 45.37%) while the least (1 cell/l; 0.02%) were Closteriopsis longissima and Netrium digitus. Order of significance in terms of number of species was: Chlorophyta (20 species; 44.45 %) > Bacillariophyta (15 species; 33.33%) > Cyanophyta (9 species; 20.00%) > Xanthophyta (1 species; 2.22%). Dominance of the phytoplankton cell counts were observed in the following trend: Cyanophyta (65.27%) > Bacillariophyta (20.06%) > Chlorophyta (13.30%) > Xanthophyta (1.38%). Low abundance of this flora accompanied by the high occurrence of Cyanophyta cells and species are indications of pollution of this important aquatic ecosystem. Hence, wastes generation and dumping without pretreatments into the river especially, organic and inorganic fertilizers should be discouraged. Keywords: Phytoplankton group, abundance, species composition, cell counts