Features of the seasonal succession of phytoplankton in the Crimean coastal area (Black Sea) in years with different climatic conditions (2009–2014)

Under conditions of climatic changes, it is of great interest to study the dynamics of various functional complexes of phytoplankton species. The long-term influence of previous cold winters on the course of the seasonal succession of phytoplankton, as well as the intensity of blooms in the open waters of the Black Sea, were shown earlier. In the coastal zone, this relationship has not yet been sufficiently studied. Based on regular monitoring studies in the coastal area of Sevastopol from 2009–2014, features of the course of seasonal succession of phytoplankton in years with different climatic conditions were revealed: the “cold” years differed from the “warm” ones by a longer dominance of diatom complexes in terms of cell abundance, especially of small-celled species, which characterize the initial stage of seasonal succession of phytoplankton. The level of development of both diatoms and dinoflagellates was minimal compared to other years, with a shift in the periods of maxima to later months. In contrast, the "warm" years were characterized by the predominance of dinoflagellates for most of the study period, with a shift in timing of the maxima to earlier months. Both diatoms and dinoflagellates reached their maximal development in “warm” years in spring and autumn. In the “moderate” years, phytoplankton development proceeded either by analogy with the “cold” (2009) or “warm” (2011) years. The seasonal succession described above is typical for the northwestern Black Sea, in particular, the Sevastopol coastal area, and differs from the average pattern for the northwestern part described earlier for 1992–1993. The difference consisted of an increase in the proportion of stages I and III due to a decrease in stage II compared to 1992–1993.

Traveling waves and spreading properties for a reaction-diffusion competition model with seasonal succession*

In this paper, we investigate the propagation dynamics of a reaction–diffusion competition model with seasonal succession in the whole space. Under the weak competition condition, the corresponding kinetic system admits a globally stable positive periodic solution ( u ^ ( t ) , v ^ ( t ) ) . By the method of upper and lower solutions and the Schauder fixed point theorem, we first obtain the existence and nonexistence of traveling wave solutions connecting (0, 0) to ( u ^ ( t ) , v ^ ( t ) ) . Then we use the comparison arguments to establish the spreading properties for a large class of solutions.

Seasonal Variations in the Biodiversity, Ecological Strategy, and Specialization of Diatoms and Copepods in a Coastal System With Phaeocystis Blooms: The Key Role of Trait Trade-Offs

Although eutrophication induced by anthropogenic nutrient enrichment is a driver of shifts in community composition and eventually a threat to marine biodiversity, the causes and consequences on ecosystem functioning remain greatly unknown. In this study, by applying a trait-based approach and measuring niche breadth of diatoms and copepods, the drivers and underlying mechanisms of the seasonal species succession of these ecological communities in a coastal system dominated in spring by Phaeocystis blooms were explored. It is suggested that the seasonal succession of diatoms and copepods is the result of several trade-offs among functional traits that are controlled by the seasonal abiotic and biotic pressure encountered by the plankton communities. The results of this study highlight that a trade-off between competition and predator, i.e., weak competitors are better protected against predation, plays an important role in promoting plankton species richness and triggers the Phaeocystis bloom. As often observed in eutrophicated ecosystems, only the biotic homogenization of the copepod community and the shift in the diet of copepods toward Phaeocystis detrital materials have been detected during the Phaeocystis bloom. The diatom and copepod communities respond synchronously to fluctuating resources and biotic conditions by successively selecting species with specific traits. This study confirms the key role of competition and predation in controlling annual plankton succession.

Physiological and nutritional constraints on zooplankton productivity due to eutrophication and climate change predicted using a resource-based modeling approach

Emerging evidence suggests that zooplankton production is affected by physiological and nutritional constraints due to climate change and eutrophication, which in turn could have broad implications for food-web dynamics and fisheries production. In this study, we developed a resource-based zooplankton production dynamics model that causally links freshwater cladoceran and copepod daily production-to-biomass (P/B) ratios with water temperature, phytoplankton biomass and community composition, and zooplankton feeding selectivity. This model was used to evaluate constraints on zooplankton growth under four hypothetical scenarios: involving natural plankton community seasonal succession; lake fertilization to enhance fisheries production; eutrophication; and climatic warming. Our novel modeling approach predicts zooplankton production is strongly dependent on seasonal variation in resource availability and quality, which results in more complex zooplankton dynamics than predicted by simpler temperature dependent models. For mesotrophic and hypereutrophic lakes, our study suggests that the ultimate control over zooplankton P/B ratios shifts from physiological control during colder periods to strong resource control during warmer periods. Our resource-based model provided important insights into the nature of biophysical control of zooplankton under a changing climate that has crucial implications for food web energy transfer and fisheries production.