The model of the phytoplankton population functioning in the arctic regional seas in the summer period

Fursova, P.V.; Riznichenko, G.Y.; Konyukhov, I.V.; Pogosyan, S.I.

Авторы: Fursova P.V., Riznichenko G.Yu, Konyukhov I.V., Pogosyan S.I.
Журнал: Biophysical Reviews
Том: 15
Год издания: 2023
Издательство: Springer Verlag
Местоположение издательства: Germany
Первая страница: 1733
Последняя страница: 1734
DOI: 10.1007/s12551-023-01150-w
Аннотация: Sunlight and the availability of mineral nutrition are the main factors that ensure the existence of phytoplankton communities. Their impact primarily affects photosynthetic activity, which can be assessed using fluorescent methods. By measuring the parameters of algal chlorophyll fluorescence, one can determine the potential efficiency of photosynthesis, find out its dependence on different light intensities, detect a deficiency of mineral nutrients, establish the degree of algae adaptation to light intensity in the phytoplankton habitat. According to the expeditions data in the basins of the Kara Sea and the Laptev Sea, in situ measurements of the chlorophyll content by the fluorimetric method demonstrate extremely diverse depth distributions [1]. The maximum can be near the surface and at depths below the jump in water density, or in the upper and lower layers simultaneously. At the same time, some cells from samples of the upper horizon demonstrate adaptation to dark conditions, and from samples of the lower horizon, to high illumination. It should be noted that diatoms make up a significant part of the phytoplankton biomass in the Arctic seas in summer, they are not capable of active movement. The water column consists of two practically non-mixing layers of water - the upper desalinated, deficient in nutrients, and the lower, more saline and enriched in nutrients. The upper layer of water is sufficiently well lit, while in the lower layer the light intensity is too low for photosynthesis. A natural question arises: how are diatom populations maintained in a stationary state in such a system? In mathematical models, the vertical movement of phytoplankton in the absence of directional transport can be described, for example, by turbulent diffusion [2, 3]. However, under conditions of stratification of the aquatic environment, this process cannot explain the observed distributions. In the present work, the following hypothesis is suggested [4]. In the illuminated layer of water, the cell accumulates biomass due to photosynthesis and increases its density by maintaining the volume due to the presence of solid silicon valves. As density increases, the cell gradually sinks until its density equals that of more saline and denser water. In this layer, rich in minerals, the cell replenishes its intracellular reserves. Once in the absence of light, the cell begins to spend the accumulated carbohydrates on various metabolic processes, including respiration. The released carbon dioxide is retained around the cell in the resulting mucus sac. At the same time, the specific gravity of this “formation” (cell + “bag”) gradually decreases. Upon reaching the critical density value, the cell floats to the surface, and the gas bubble collapses.Based on the proposed hypothesis, an agent-based model of the phytoplankton population dynamics was built in the NetLogo environment (http://ccl.northwestern.edu/netlogo/). Cells-agents are divided into two groups - upper and lower. For each cell increase/decrease of its density; storage/expense minerals; division; death; transition from one group to another; moving are available. Cells of the upper group photosynthesize increasing density, while consuming intracellular minerals. The cells of the lower group replenish the intracellular content of minerals and carry out the main metabolism, their density decreases. The medium is divided into 2 layers: in the upper layer, the nutrient content is assumed to be zero, the light intensity decreases with depth in accordance with the exponential law. In the lower layer, there is no illumination, nutrients are evenly distributed. It is assumed that all "resources" are in abundance, their content does not change when consumed by agent cells.The behavior of model solutions was analyzed. The key parameters were the level of near-surface illumination and the distance by which cells are displaced in a random direction at each moment of time. By changing these parameters, one can obtain different distributions of cells—numbers in the upper and lower layers—typical for expeditionary observations. With small displacements of cells, the population demonstrates a periodic change in abundance. The constant predominance of cells in one of the layers or the successive change in dominance is determined by the given illumination. Moving cells over long distances smooth out population fluctuations. The model experiment demonstrates a decrease in the total number of cells compared to a similar experiment in the absence of significant cell movements, since the "availability" of sunlight is reduced. Under conditions of higher surface illumination, the total number of cells moving over long distances becomes higher, since they are less susceptible to photodegradation. The dynamics of the numbers in each of the layers also changes: at a normal level of illumination, the maxima of the numbers of the upper and lower cells replace each other, which is typical for cells that move weakly in low light conditions. Further studies will be aimed at refining the parameters of the model and a more detailed comparison of the results with experimental data.The study was carried out within the framework of the scientific project of the state task of Lomonosov Moscow State University No. 121032500060-0.1. Ekosistemy Karskogo morya i morya Laptevykh. Ekspeditsionnye issledovaniya 2016 i 2018 gg./ IO RAN. – M.: Izdatel' Erkhova I.M., 2021. – 368 p.2. Abakumov A.I., Izrailsky Yu.G. Environment Influence on the Phytoplankton Distribution in a Basin // Math. Biol. Bioinf. 2012;7(1), 274-283.3. Belyaev V.I. Modelling the influence of turbulence on phytoplankton photosynthesis // Ecol.Modelling, 1992, V.60, 11-29.4. Fursova P.V., Riznichenko G.Yu., Konyukhov I.V., Pogosyan S.I. Agent-based model of diatom population dynamics in marginal arctic seas in summer (hypothesis) // Oceanology, 2023 (in print).
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