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34946049 14 Titocci J., Bon M., Fink P. Morpho-Functional Traits Reveal Differences in Size Fractionated Phytoplankton Communities but Do Not Significantly Affect Zooplankton Grazing. Paul et al. [[10]] explored the combined effects of elevated temperatures and CO SB 2 sb on a natural phytoplankton community from the Baltic Sea, dividing phytoplankton into edible and inedible cell size classes for mesozooplankton grazers. Their findings highlighted that the mean cell size of a taxonomically complex phytoplankton community can be used as an indicator trait to predict phytoplankton responses to sequential environmental changes. [Extracted from the article]

In this work, we grouped phytoplankton species according to their cell geometric shape for the first time in lake ecosystems. Field multiannual data were analyzed in order to understand the phytoplankton cell geometric shape distribution along the seasonal environmental variability in two Mediterranean lakes, a shallow natural lake and a deeper artificial lake. We characterized seasonally each lake on the basis of dominant phytoplankton cell geometric shapes, detecting the following common highlights comparing the two ecosystems: a complex and globular geometric shape (Cone + Half Sphere) with high mean volume and low mean surface-to-volume ratio in winter (at the deepest mixing layer); a variety of geometric shapes in spring (at the lowest nutrient concentrations), with a relevant contribution of simple and compact geometric shapes (Sphere and Cube) with low mean volume and high mean surface-to-volume ratio; a simple and elongated geometric shape (Cylinder) in summer (at thermal stratification conditions); a variety of geometric shapes in autumn (at intermediate environmental conditions), when the geometric shapes detected were at similar size. We provide new insights on how phytoplankton cell geometric shapes with similar and different sizes relate to the seasonal environmental variations in lake ecosystems, a topic relatively neglected in literature. [ABSTRACT FROM AUTHOR]

Data from five sites of the International Long Term Ecological Research (ILTER) network in the North- Eastern Pacific, Western Arctic Ocean, Northern Baltic Sea, South-Eastern North Sea and in the Western Mediterranean Sea were analyzed by dynamic factor analysis (DFA) to trace common multi-year trends in abundance and composition of phytoplankton, benthic fauna and temperate reef fish. Multiannual trends were related to climate and environmental variables to study interactions. Two common trends in biological responses were detected, with temperature and climate indices as explanatory variables in four of the five LTER sites considered. Only one trend was observed at the fifth site, the Northern Baltic Sea, where no explanatory variables were identified. Our findings revealed quasi-synchronous biological shifts in the different marine ecosystems coincident with the 2000 climatic regime shift and provided evidence on a possible further biological shift around 2010. The observed biological modifications were coupled with abrupt or continuous increase in sea water and air temperature confirming the key-role of temperature in structuring marine communities. [ABSTRACT FROM AUTHOR]

Reservoirs are primary water resources for many uses in the Mediterreanean region and need dedicated studies for understanding the complexity of their dynamics particularly vulnerable to local and global stressors. This study focused on phytoplankton variations in relation to seasonal environmental changes on a multiannual time scale (2006-2015) at a Mediterranean eutrophic reservoir (Bidighinzu Lake, Italy) belonging to the Italian, European and International Long Term Ecological Research networks. Phytoplankton cell density, volume and biomass and chlorophyll a concentrations were analysed together with meteo-climatic, hydrological, physical and chemical variables to detect trends and correlations. The period under study was also compared with previous years to assess the presence of significant differences in the environmental and planktonic compartments. Multiannual changes were more pronounced in summer than in the other seasons during the decade under study. The most conspicuous environmental changes were a significant decrease in summer nutrient concentrations in the reservoir and a simultaneous anthropic pressure reduction in the watershed. In addition, the mixing zone and euphotic zone ratio also increased. Multiannual changes in summer phytoplankton composition consisted of an increased density of smaller Bacillariophyceae and Cyanophyceae, which replaced larger species of the same phytoplankton classes. This resulted in opposite trends of total phytoplankton cell density (increasing) and mean phytoplankton cell volume (decreasing) over the study years. The nutrient decrement was statistically the strongest environmental driver of the phytoplankton changes observed in the reservoir. However, the Nature Conservation 34: 163-191 (2019) doi: 10.3897/natureconservation.34.30116 http://natureconservation.pensoft.net Copyright Silvia mixing zone and the euphotic zone ratio and water temperature also significantly affected the multiannual phytoplankton variations. Therefore, we conclude that the success of small cell-sized phytoplankton in Bidighinzu Lake was most probably due to the synergic interactions of more environmental forces related to changing anthropic pressures and climate variability. Our results highlight the importance of long-term monitoring of reservoirs in the Mediterranean basin, especially in semi-arid regions where the need and scarcity of high quality water will be further exacerbated due to the global climate change. [ABSTRACT FROM AUTHOR]

Abstract Seasonal dynamic of Utermöhl fraction of phytoplankton (UFP, cell size > 3 μm) and picophytoplankton (Pico, cell size < 3 μm) were compared in three eutrophic coastal lagoons located in the same geographical area (Western Mediterranean Sea). Considering data on density, biomass, volume and composition of each size class, we focused on three aspects: i) the contribution of UFP and Pico to total phytoplankton; ii) the responses of UFP and Pico to seasonal variations of selected environmental variables; iii) the identification of the main environmental drivers of UFP and Pico seasonal dynamics. Pico contribution to total phytoplankton density was from 20% to 90%, highlighting the potential importance of Pico also in eutrophic ecosystems. Pico contribution to total phytoplankton biomass was lower, from 9% to 16%. Statistically, temperature resulted the strongest environmental factor controlling both the UFP and Pico seasonal variations in all the studied lagoons. In addition, the role of salinity, water transparency and nutrient concentrations was important in relation to the study site and the size class considered. In this work, the effects of temperature, salinity, transparency and nutrient availability on two different phytoplankton size classes have been described in Mediterranean shallow coastal lagoons for the first time, providing new insight for this ecosystem typology worldwide. Graphical abstract Image 1 Highlights • Potential importance of picophytoplankton in eutrophic ecosystems was established. • Temperature was the strongest driver of seasonal cell size structure. • Role of salinity, transparency and nutrients was size- and site-specific. • Synergic interaction of several drivers affected seasonal cell size structure. [ABSTRACT FROM AUTHOR]

Picophytoplankton (Pico) seasonal dynamics and ecology were investigated in three eutrophic coastal lagoons (Calich, Santa Giusta, and Corru S'Ittiri) located in the same geographic region (Sardinia, Mediterranean Sea). Pico dynamics were examined to determine a relationship with variability in environmental conditions characterizing the three sites, and identify which parameters affected observed Pico dynamics. Results showed Pico density reached 10 cells L and biomass values did not exceed 72.8 μg C L. Statistical analyses detected significant differences in hydrographic and nutrient conditions among lagoons, which were also characterized by variable Pico seasonal dynamics and composition. Calich and Santa Giusta were dominated all year around by picocyanobacteria. Maximum picocyanobacteria abundance was observed during summer in both lagoons, associated with the highest temperatures recorded. Picocyanobacteria abundance and nutrient concentrations showed a significant negative and positive correlation in Calich and Santa Giusta, respectively. In contrast, picoeukaryotes dominated Pico assemblages in Corru S'Ittiri, where the highest transparency and salinity and the lowest seasonal variation in salinity were recorded. In Corru S'Ittiri, the maximum Pico abundance was observed in autumn, when lower temperature and the highest nutrient concentrations were observed. Our study provides information on Pico assemblage ecology, which remains scarce in coastal and transitional environments, particularly in Mediterranean climate regimes. [ABSTRACT FROM AUTHOR]

Intraspecific diversity is a substantial part of biodiversity, yet little is known about its maintenance. Understanding mechanisms of intraspecific diversity shifts provides realistic detail about how phytoplankton communities evolve to new environmental conditions, a process especially important in times of climate change. Here, we aimed to identify factors that maintain genotype diversity and link the observed diversity change to measured phytoplankton morpho-functional traits Vmax and cell size of the species and genotypes. In an experimental setup, the two phytoplankton species Emiliania huxleyi and Chaetoceros affinis, each consisting of nine genotypes, were cultivated separately and together under different fluctuation and nutrient regimes. Their genotype composition was assessed after 49 and 91 days, and Shannon's diversity index was calculated on the genotype level. We found that a higher intraspecific diversity can be maintained in the presence of a competitor, provided it has a substantial proportion to total biovolume. Both fluctuation and nutrient regime showed species-specific effects and especially structured genotype sorting of C. affinis. While we could relate species sorting with the measured traits, genotype diversity shifts could only be partly explained. The observed context dependency of genotype maintenance suggests that the evolutionary potential could be better understood, if studied in more natural settings including fluctuations and competition. [ABSTRACT FROM AUTHOR]