Phytoplankton biomass dynamics with diffuse terrestrial nutrients pollution discharge into bay

Diffuse terrestrial pollution in bay area has important ecological impacts on coastal ecosystems. This study investigated spatiotemporal changes in N, P, and chlorophyll a (Chla) in the Jiaozhou Bay (JZB) and phytoplankton biomass dynamics under terrestrial nutrients loading. The results from SWAT (Soil and Water Assessment Tool) model demonstrated that the annual average total N (TN) and total P (TP) loading from main rivers were 3626.3 t and 335.6 t, respectively, and were affected by land use type, precipitation, and temperature. Chla value interpreted by remote sensing showed a decrease from nearshore to the far shore. Changes in Chla concentration were usually "dual-cycle" in February and September, but explosive growth of Enteromorpha can cause multiple peaks. TN concentration in the bay was more susceptible to the impact of terrestrial input than TP. Phytoplankton biomass had a stronger correlation with P than with N in JZB. Enteromorpha contributing 4.05% of the phytoplankton biomass played a major role in phytoplankton biomass variability and responded most to nutrients loadings reduction. Under setting 5 m filter strip scenario, the Enteromorpha biomass removal efficiency could reach 35.25%. Furthermore, the findings of this study provide insights for sea-land integration and pollution prevention and control in urbanised bays.

Ecology and evolution of competitive trait variation in natural phytoplankton communities under selection

Competition for limited resources is a major force in structuring ecological communities. Species minimum resource requirements (R*s) can predict competitive outcomes and evolve under selection in simple communities under controlled conditions. However, whether R*s predict competitive outcomes or demonstrate adaptive evolution in naturally complex communities is unknown. We subjected natural phytoplankton communities to three types of resource limitation (nitrogen, phosphorus, light) in outdoor mesocosms over 10 weeks. We examined the community composition weekly and isolated 21 phytoplankton strains from seven species to quantify responses to the selection of R* for these resources. We investigated the evolutionary change in R*s in the dominant species, Desmodesmus armatus. R*s were good predictors of species changes in relative abundance, though this was largely driven by the success of D. armatus across several treatments. This species also demonstrated an evolutionary change in R*s under resource limitation, supporting the potential for adaptive trait change to modify competitive outcomes in natural communities.

Photoperiod-driven rhythms reveal multi-decadal stability of phytoplankton communities in a highly fluctuating coastal environment

Phytoplankton play a pivotal role in global biogeochemical and trophic processes and provide essential ecosystem services. However, there is still no broad consensus on how and to what extent their community composition responds to environmental variability. Here, high-frequency oceanographic and biological data collected over more than 25 years in a coastal Mediterranean site are used to shed light on the temporal patterns of phytoplankton species and assemblages in their environmental context. Because of the proximity to the coast and due to large-scale variations, environmental conditions showed variability on the short and long-term scales. Nonetheless, an impressive regularity characterised the annual occurrence of phytoplankton species and their assemblages, which translated into their remarkable stability over decades. Photoperiod was the dominant factor related to community turnover and replacement, which points at a possible endogenous regulation of biological processes associated with species-specific phenological patterns, in analogy with terrestrial plants. These results highlight the considerable stability and resistance of phytoplankton communities in response to different environmental pressures, which contrast the view of these organisms as passively undergoing changes that occur at different temporal scales in their habitat, and show how, under certain conditions, biological processes may prevail over environmental forcing.

Metabolic traits predict the effects of warming on phytoplankton competition

Understanding how changes in temperature affect interspecific competition is critical for predicting changes in ecological communities with global warming. Here, we develop a theoretical model that links interspecific differences in the temperature dependence of resource acquisition and growth to the outcome of pairwise competition in phytoplankton. We parameterised our model with these metabolic traits derived from six species of freshwater phytoplankton and tested its ability to predict the outcome of competition in all pairwise combinations of the species in a factorial experiment, manipulating temperature and nutrient availability. The model correctly predicted the outcome of competition in 72% of the pairwise experiments, with competitive advantage determined by difference in thermal sensitivity of growth rates of the two species. These results demonstrate that metabolic traits play a key role in determining how changes in temperature influence interspecific competition and lay the foundation for mechanistically predicting the effects of warming in complex, multi‐species communities.

The Temperature Dependence of Phytoplankton Stoichiometry: Investigating the Roles of Species Sorting and Local Adaptation

The elemental composition of phytoplankton (C:N:P stoichiometry) is a critical factor regulating nutrient cycling, primary production and energy transfer through planktonic food webs. Our understanding of the multiple direct and indirect mechanisms through which temperature controls phytoplankton stoichiometry is however incomplete, increasing uncertainty in the impacts of global warming on the biogeochemical functioning of aquatic ecosystems. Here, we use a decade-long warming experiment in outdoor freshwater ponds to investigate how temperature-driven turnover in species composition and shifts in stoichiometric traits within species through local thermal adaptation contribute to the effects of warming on seston stoichiometry. We found that experimental warming increased seston C:P and N:P ratios, while the C:N ratio was unaffected by warming. Temperature was also the dominant driver of seasonal variation in seston stoichiometry, correlating positively with both C:P and N:P ratios. The taxonomic composition of the phytoplankton community differed substantially between the warmed and ambient treatments indicating that warming resulted in differential sorting of species from the regional pool. Furthermore, taxonomic composition also changed markedly over the year within each of the warmed and ambient treatments, highlighting substantial temporal turnover in species. To investigate whether local adaptation also played an important role in shaping the effects of warming on seston stoichiometry, we isolated multiple strains of the cosmopolitan alga, Chlamydomonas reinhardtii from across the warmed and ambient mesocosms. We found that warmed isolates had higher C:P and N:P ratios, shifts that were comparable in direction and magnitude to the effects of warming on seston stoichiometry. Our results suggest that both species sorting and local adaptation are likely to play important roles in shaping the effects of warming on bulk phytoplankton stoichiometry and indicate that major shifts in aquatic biogeochemistry should be expected in a warmer world.