Phytoplankton adaptation strategies under the influence of climatic changes and anthropogenic pressure on the Black Sea coastal ecosystems on the example Sevastopol Bay

Some ways of the Black Sea coastal waters phytoplankton community adaptation to changes in water temperature, nutrients concentration and anthropogenic pollution have been identified on the example of the Sevastopol Bay. The increase in water temperature and decrease in nutrient content in the studied waters during 2000 – 2014 caused a gradual decrease in the chlorophyll a concentrations, total phytoplankton biomass and its re-composition, predominantly in the summer and autumn periods. The phytoplankton restructuring was predominantly reflected by a decrease in relative diatoms contribution in the total phytoplankton biomass and an increase in dinoflagellates contribution. Among the dominant diatoms species, the share of resistant species to high temperatures, pollution, low nitrate content in the water and microzooplankton grazing was increasing. An increase in nitrate concentration in the studied waters in 2020 led to increase in total phytoplankton biomass and a predominance of diatoms species, which under the stated conditions did not lead to bloom emergence as were regularly observed earlier in the Sevastopol region.

Influence of the phytoplankton community on the hydrochemical structure of the Caspian Sea

The hydrochemical structure of the Caspian Sea, which is formed and changed under the influence of the dynamics of water and the intensity of production and destruction processes, has been studied. The formation of the biogenic base and hydrochemical structure of the waters of the Caspian Sea is greatly influenced by the phytoplankton community. The dominant species of Pseudosolenia calcar-avis and Prorocentrum cordatum, which constitute 60–95% of the population and more than 80% of the total phytoplankton biomass, are mainly responsible for the redistribution of chemical components in the sea.

The Mediterranean subsurface phytoplankton dynamics and their impact on Mediterranean bioregions

Ocean bioregions are generally defined using remotely-sensed sea surface chlorophyll fields, based on the assumption that surface chlorophyll is representative of euphotic layer phytoplankton biomass. Here we investigate the impact of subsurface phytoplankton dynamics on the characterisation of ocean bioregions. The Mediterranean Sea is known for its contrasting bioregimes despite its limited area, and represents an appropriate case for this study. We modelled this area using a high resolution regional dynamical model, NEMO-MED12, coupled to a biogeochemical model, PISCES, and focused our analysis on the bioregions derived from lower trophic levels. Validated by satellite and Biogeochemical-Argo float observations, our model shows that chlorophyll phenology can be significantly different when estimated from surface concentrations or integrated over the first 300 m deep layer. This was found in both low chlorophyll, oligotrophic bioregions as well as in high chlorophyll, bloom bioregions. The underlying reason for this difference is the importance of subsurface phytoplankton dynamics, in particular those associated with the Deep Chlorophyll Maximum (DCM) at the base of the upper mixed layer. Subsurface phytoplankton are found to significantly impact the bloom bioregions, while in oligotrophic regions, surface and subsurface chlorophyll are of similar importance. Consequently, our results show that surface chlorophyll is not representative of total phytoplankton biomass. Analysis of the DCM finds that its dynamics are extremely homogeneous throughout the Mediterranean Sea, and that it follows the annual cycle of solar radiation. In the most oligotrophic bioregion, the total phytoplankton biomass is almost constant along the year, implying that the summertime DCM biomass increase is not due to DCM photoacclimation, nor an increase of DCM production, but instead of the migration – with photoacclimation – of surface phytoplankton into the DCM.

Effects of zooplankton and nutrients on phytoplankton: an experimental analysis in a eutrophic tropical reservoir

Experiments were conducted to evaluate the N:P ratio, as well as the effects of the interaction between this ratio and zooplankton, on phytoplankton in a tropical reservoir. Three experiments were performed in the presence (+Z) or absence (–Z) of zooplankton and the addition of N and P in different ratios (N:P molar ratio of 5, 16 and 60).In Experiment I, the total phytoplankton biomass and biomass by taxonomic class and species of the N:P 16–Z treatment did not differ significantly from that of the control, whereas for N:P 16+Z, there was a reduction in total phytoplankton. In Experiment II, there was a significant increase in Bacillariophyceae and the biomass of two species in the N:P 60–Z treatment. For the N:P 60+Z treatment, a significant reduction was observed in the total phytoplankton biomass and the biomass of three phytoplankton classes and three species. In Experiment III, there was an increase in the biomass of Dinophyceae with the N:P 5–Z treatment. In the N:P 5+Z treatment, there was a significant reduction in total phytoplankton biomass and the biomass of the phytoplankton class and five species. The findings of the present study reveal that zooplankton species native to a tropical reservoir can change the structure of the phytoplankton community and the response of these organisms to variations in nutrients.

Qualitative and quantitative studies on phytoplankton and chlorophyll content in the pelagic water of Lake Żarnowieckie in 1974

Species composition of phytoplankton, its biomass, share of nannoplankton, and concentration of chlorophyll and pheophytin in phytoplankton and nannoplankton were assessed basing on the materials collected from two pelagic stations of Lakę Żarnowieckie during the period 30 March - 6 December 1974. Average and maximal values of phytoplankton biomass (4-5 and 10-11 mg/1 respectively), as well as the concentration of chlorophyll (1.7 -10.0 μg/l together with pheophytin) point to slightly advanced eutrophication of the lake. Share of nannoplankton in total phytoplankton biomass was very low (as a rule below 3%) with an increase to 15% only in spring. Relatively slight taxonomic differentiation of phytoplankton (164 taxons), its qualitative composition with the predominance of <i>Cyanophyceae</i> in summer, and of <i>Bacillariophyceae</i> in spring and autumn, as also seasonal succession of algae, point to eutrophic character of the lake.

Sigmoid Relationships between Phosphorus, Algal Biomass, and Algal Community Structure

It has long been recognized that there is a positive relationship between total phytoplankton biomass and eutrophication. Recent independent studies demonstrated that algal biomass (chlorophyll) actually responds in a nonlinear, sigmoidal fashion with increasing phosphorus levels among lakes. Chlorophyll has been considered (by some authors) as an inconsistent estimate of algal biomass. Using a wide range of published data, we first demonstrate that the sigmoidal nature of the phosphorus–biomass relationship is quite robust, and not simply generated by a systematic variation in the relationship between algal chlorophyll to cell volume ratio and nutrient levels. We show that the sigmoid relationship with total phosphorus persists whether algal biomass is measured by chlorophyll or biovolume. We hypothesize that this nonlinearity actually reflects an underlying systematic variation in one or more of the components of total phytoplankton biomass. In this paper, we examine two functional size groups and show that the large inedible fraction exhibits a strong, nonlinear response to increasing nutrient levels, while the small edible algae do not vary systematically with phosphorus. We hypothesize that this discontinuous shift in the ratio of edible to inedible phytoplankton should be accompanied by concomitant shifts in the structure of the herbivore community.

Response of a Phytoplankton Community to Controlled Partial Recovery from Experimental Acidification

Lake 223 was experimentally acidified with H2SO4 from 1976 to 1989. The pH was reduced from 6.7 (1974) to 5.0 (1981) and held there for 3 yr (1981–83). Beginning in 1984 the pH was allowed to increase at a controlled rate by reduction of acid additions, resulting in a two-step recovery of 4 yr at pH ~5.5 and 2 yr at pH ~5.8. During the first 6 yr of early recovery, species diversity of the phytoplankton community increased linearly with pH and the number of common species increased. Total phytoplankton biomass remained elevated above preacidification estimates or increased. Dinoflagellates and cyanophytes remained codominant with little evidence of other taxonomic groups increasing.