Stoichiometric microplastics models in natural and laboratory environments.

Microplastics pose a severe threat to marine ecosystems; however, relevant mathematical modeling and analysis are lacking. This paper formulates two stoichiometric producer-grazer models to investigate the interactive effects of microplastics, nutrients, and light on population dynamics under different settings. One model incorporates optimal microplastic uptake and foraging behavior based on nutrient availability for natural settings, while the other model does not include foraging in laboratory settings. We establish the well-posedness of the models and examine their long-term behaviors. Our results reveal that in natural environments, producers and grazers exhibit higher sensitivity to microplastics, and the system may demonstrate bistability or tristability. Moreover, the influences of microplastics, nutrients, and light intensity are highly intertwined. The presence of microplastics amplifies the constraints on grazer growth related to food quality and quantity imposed by extreme light intensities, while elevated phosphorus input enhances the system's resistance to intense light conditions. Furthermore, higher environmental microplastic levels do not always imply elevated microplastic body burdens in organisms, as organisms are also influenced by nutrients and light. We also find that grazers are more vulnerable to microplastics, compared to producers. If producers can utilize microplastics for growth, the system displays significantly greater resilience to microplastics.

Nutrient quotas and carbon content variability of Prorocentrum minimum (Pavillard) Schiller, 1933.

Frequency, severity, and geographic range of harmful blooms caused by a dinoflagellate Prorocentrum minimum have been increasing significantly over the past few decades. The ability to adapt nutrient quotas and carbon content to a wide range of environmental conditions is one of the key factors for the proliferation of P. minimum. Understanding the limits of stoichiometric variability in terms of nutrient quotas and carbon content would help explain the observed trends and assist in P. minimum growth model creation. This manuscript aggregates information from 15 studies to investigate variability in nutrient quotas and carbon content for a broad range of P. minimum isolates and clonal lines. Nitrogen quota, phosphorus quota, and carbon content in the studies varied between 11-107.5pgNcell-1, 1.45-17.58pgPcell-1, and 70-656.36pgCcell-1, respectively. Regression analysis was used to estimate average nitrogen and phosphorus quotas as functions of carbon, and to show that carbon content variability explains 55% of nitrogen and 23% of phosphorus quota variability. Confidence intervals for data (CID) found during the analysis were used to define maximal and minimal nutrient quotas as functions of carbon content. The ratios of the upper and lower CID ranges can, therefore, be used to estimate nutrient storage capacity as a function of carbon content. The new results and comparison with other species show that, at least for P. minimum, carbon-based quotas are more suitable for modelling than cell-based quotas. Finally, results indicate that environmental nutrient availability affects quotas more than light does: while quota variability due to light remains within 80% CID, nutrient variability covers the 95% CID.