Plankton growth dynamic driven by plankton body size in deterministic and stochastic environments

In this paper, we establish a new phytoplankton-zooplankton model by considering the effects of plankton body size and stochastic environmental fluctuations. Mathematical theory work mainly gives the existence of boundary and positive equilibria, and shows their local as well as global stability in the deterministic model. Additionally, we explore the dynamics of V-geometric ergodicity, stochastic ultimate boundedness, stochastic permanence, persistence in the mean, stochastic extinction and the existence of a unique ergodic stationary distribution in the corresponding stochastic version. Numerical simulation work mainly reveals that plankton body size can generate great influences on the interactions between phytoplankton and zooplankton, which in turn proves the effectiveness of mathematical theory analysis. It is worth emphasizing that for the small value of phytoplankton cell size, the increase of zooplankton body size can not change the phytoplankton density or zooplankton density; for the middle value of phytoplankton cell size, the increase of zooplankton body size can decrease zooplankton density or phytoplankton density; for the large value of phytoplankton body size, the increase of zooplankton body size can increase zooplankton density but decrease phytoplankton density. Besides, it should be noted that the increase of zooplankton body size can not affect the effect of random environmental disturbance, while the increase of phytoplankton cell size can weaken its effect. There results may enrich the dynamics of phytoplankton-zooplankton models.

Grazing Induced Shifts in Phytoplankton Cell Size Explain the Community Response to Nutrient Supply

Phytoplankton cell size is important for a multitude of functional traits such as growth rates, storage capabilities, and resistance to grazing. Because these response traits are correlated, selective effects on mean community cell size of one environmental factor should impact the ability of phytoplankton to cope with other factors. Here, we experimentally apply expectations on the functional importance of phytoplankton cell size to the community level. We used a natural marine plankton community, and first altered the community’s cell size structure by exposing it to six different grazer densities. The size-shifted communities were then treated with a saturated nutrient pulse to test how the changes in community size structure influenced the mean community growth rate in the short-term (day 1–3) and nutrient storage capacity in the postbloom phase. Copepod grazing reduced the medium-sized phytoplankton and increased the share of the smallest (<10 µm3) and the largest (>100,000 µm3). Communities composed of on average small cells grew faster in response to the nutrient pulse, and thus confirmed the previously suggested growth advantage of small cells for the community level. In contrast, larger phytoplankton showed better storage capabilities, reflected in a slower post-bloom decline of communities that were on average composed of larger cells. Our findings underline that the easily measurable mean cell size of a taxonomically complex phytoplankton community can be used as an indicator trait to predict phytoplankton responses to sequential environmental changes.

Detection of marine microalgae (phytoplankton) quality to support seafood health: A case study on the west coast of South Sulawesi, Indonesia

Tambaru R, Burhanuddin AI, Massinai A, Amran MA. 2021. Detection of marine microalgae (phytoplankton) quality to support seafood health: a case study on the west coast of South Sulawesi, Indonesia. Biodiversitas 22: 5179- 5186. The research aimed to detect marine microalgae quality to support seafood health was carried out from January to November 2020 along the west coast of South Sulawesi, Indonesia. Samples were collected from the coastal waters of Pangkep District, Maros District, and the northern part of Makassar City. Phytoplankton cell counts were obtained using the deposition method developed by Uthermol. Phytoplankton cell abundances were calculated through sweeping (census) using a Sedgwick Rafter Cell (SRC). Two-way analysis of variance (ANOVA) was used to compare the distribution of marine microalgae community abundance between observation stations and periods. Based on the types and relative abundance of phytoplankton present, i.e., harmful algal bloom (HAB) forming or not (non-HAB), the results showed the quality of marine microalgae, specifically, phytoplankton was relatively good. Many more non-HAB (94-98%) than HAB (2-6%) marine microalgae were detected. Thus, the phytoplankton flourishing in these waters is mostly suitable as food for other organisms, including fish and shellfish. This also means that if fishers harvest these fish and shellfish, they should be fit and safe for human consumption.

Microrheology reveals microscale viscosity gradients in planktonic systems

Microbial activity in planktonic systems creates a dynamic and heterogeneous microscale seascape that harbors a diverse community of microorganisms and ecological interactions of global significance. In recent decades great effort has been put into understanding this complex system, particularly focusing on the role of chemical patchiness, while overlooking a physical parameter that governs microbial life and is affected by biological activity: viscosity. Here we reveal spatial heterogeneity of viscosity in planktonic systems by using microrheological techniques that allow measurement of viscosity at length scales relevant to microorganisms. We show the viscous nature and the spatial extent of the phycosphere, the region surrounding phytoplankton. In ∼45% of the phytoplankton cells analyzed we detected increases in viscosity that extended up to 30 µm away from the cell with up to 40 times the viscosity of seawater. We also show how these gradients of viscosity can be amplified around a lysing phytoplankton cell as its viscous contents leak away. Finally, we report conservative estimates of viscosity inside marine aggregates, hotspots of microbial activity, more than an order of magnitude higher than in seawater. Since the diffusivities of dissolved molecules, particles, and microorganisms are inversely related to viscosity, microheterogeneity in viscosity alters the microscale distribution of microorganisms and their resources, with pervasive implications for the functioning of the planktonic ecosystem. Increasing viscosities impacts ecological interactions and processes, such as nutrient uptake, chemotaxis, and particle encounter, that occur at the microscale but influence carbon and nutrient cycles at a global scale.

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