Plankton communities are subjected to multiple global change drivers; however, it is unknown how the interplay between them deviates from predictions based on single-driver studies, in particular when trophic interactions are explicitly considered. We investigated how simultaneous manipulation of temperature, pH, nutrient availability and solar radiation quality affects the carbon transfer from phytoplankton to herbivorous protists and their potential consequences for ecosystem functioning. Our results showed that multiple interacting global- change drivers reduced the photosynthetic (gross primary production-to-electron transport rates ratios, from 0.2 to 0.6-0.8) and resource use efficiencies (from 9 to 1 mu g chlorophyll a (Chl a ) mu mol nitrogen-1) and prompted uncoupling between microzooplankton grazing (m) and phytoplankton growth (mu) rates (mu > m ). The altered trophic interaction could be due to enhanced intra-guild predation or to microzooplankton growing at suboptimal temperatures compared to their prey. Because phytoplankton-specific loss rates to consumers grazing are the most significant uncertainty in marine biogeochemical models, we stress the need for experimental approaches quantifying it accurately to avoid bias in predicting the impacts of global change on marine ecosystems.

Climate Change is expected to increase the intensity and frequency of extreme rainfall events in the coastal areas of Patagonia (Southwest Atlantic Ocean, SWAO). These events carry heavy loads of terrestrial materials and nutrients, and minor components such as kaolin and ash, into coastal areas through riverine inputs. The Chubut River estuary was used a reference coastal ecosystem in the SWAO. In its lower course, the river is diverted into irrigation channels that supply water for agricultural activities. These channels are open from spring to early autumn, increasing the runoff of terrestrial material, and are closed during the rest of the year. Furthermore, kaolin mines are located in the upper course of the river and ash deposition coming from volcanos have been registered. A monitoring of terrestrial material of the Chubut River estuary was conducted and the attenuation coefficients of the different components were evaluated, including terrigenous material, kaolin, and ash. The findings show that the terrestrial material, estimated as dissolved organic carbon (DOC), doubles during rainfall conditions and when irrigation channels are open. During extreme rainfall events, DOC concentrations increased by up to fivefold compared to normal conditions, being the main attenuator in the river. This resulted in a PAR attenuation coefficient variable between 1.3 m-1 under baseline conditions (closed channels, no rainfall) to over 8 m-1 following extreme rainfall events in the outer regime (seawater side) of the estuary. Further monitoring of the different under-studied estuarine components in the SWAO and their effects on the attenuation coefficient is crucial for primary productivity studies.

Extreme wind and rainfall events have become more frequent phenomena, impacting coastal ecosystems by inducing increased mixing regimes in the upper mixed layers (UML) and reduced transparency (i.e. browning), hence affecting phytoplankton photosynthesis. In this study, five plankton assemblages from the South Atlantic Ocean, from a gradient of environmental variability and anthropogenic exposure, were subjected to simulated extreme weather events under a global change scenario (GCS) of increased temperature and nutrients and decreased pH, and compared to ambient conditions (Control). Using multiple linear regression (MLR) analysis we determined that evenness and the ratio of diatoms/ (flagellates + dinoflagellates) significantly explained the variations (81-91 %) of the photosynthesis efficiency (i.e. P-chla/ETRchla ratio) for each site under static conditions. Mixing speed and the optical depth (i.e. attenuation coefficient * depth, k(d)z), as single drivers, explained 40-76 % of the variability in the P-chla/ETRchla ratio, while GCS drivers <9 %. Overall, assemblages with high diversity and evenness were less vulnerable to extreme weather events under a GCS. Extreme weather events should be considered in global change studies and conservation/management plans as even at local/regional scales, they can exceed the predicted impacts of mean global climate change on coastal primary productivity.

This article studies the finite-time (FT) convergence of a fast primal-dual gradient dynamics (PDGD), called FT-PDGD, for solving constrained optimization with general constraints and cost functions. Based on the nonsmooth analysis and augmented Lagrangian function, sufficient conditions are established for FT-PDGD to enable the realization of primal-dual optimization in FT. A specific class of nonsmooth sign-preserving functions is defined and analyzed for ensuring FT stability. Particularly, the matrix of linear equations is not required to have a full-row rank and the cost function is not necessary to be strictly convex. By introducing auxiliary variables for general linear inequality constraints, reduced sufficient conditions are further derived for the optimization with linear equality and inequality constraints after transformation. In addition, by the nonsmooth analysis, the switching dynamics evolved in both primal and dual variables are carefully investigated and the upper bound on the convergence time is explicitly provided. Moreover, as applications of FT-PDGD, several FT convergent distributed algorithms are designed to solve distributed optimization with separated and coupled linear equations, respectively. Finally, two case studies are conducted to show the performance of the proposed algorithms.

Summary Browning and nutrient inputs from extreme rainfall, together with increased vertical mixing due to strong winds, are more frequent in coastal ecosystems; however, their interactive effects on phytoplankton are poorly understood. We conducted experiments to quantify how browning, together with different mixing speeds (fluctuating radiation), and a nutrient pulse alter primary productivity and photosynthetic efficiency in estuarine phytoplankton communities. Phytoplankton communities (grazers excluded) were exposed simultaneously to these drivers, and key photosynthetic targets were quantified: oxygen production, electron transport rates (ETRs), and carbon fixation immediately following collection and after a 2‐d acclimation/adaptation period. Increasing mixing speeds in a turbid water column (e.g. browning) significantly decreased ETRs and carbon fixation in the short term. Acclimation/adaptation to this condition for 2 d resulted in an increase in nanoplanktonic diatoms and a community that was photosynthetically more efficient; however, this did not revert the decreasing trend in carbon fixation with increased mixing speed. The observed interactive effects (resulting from extreme rainfall and strong winds) may have profound implications in the trophodynamics of highly productive system such as the Southwest Atlantic Ocean due to changes in the size structure of the community and reduced productivity.

The coastal Atlantic area of Patagonia has a marked variability in physicochemical and biological properties. It is already affected by global change, as evidenced in historical patterns of environmental drivers and in direct anthropogenic influences. Here we focus on the effects of global change on plankton, mostly on phytoplankton, which constitute the base of this highly productive ecosystem. The short-term impacts range from an inhibition of primary productivity, with solar ultraviolet radiation (UVR) as the dominant driver, to an enhancement mainly caused by increased inputs of nutrients. Most studies evaluated the individual responses of bacterio-, phyto-, and meroplankton to solar UVR, while a few others have assessed the spatial distribution of zooplankton in relation to anthropogenic influence. Long-term effects of global change drivers (e.g., antagonistic or synergistic) include taxonomic changes of the communities toward those dominated by potential mixo−/heterotrophic nanoflagellates, which may alter the atmosphere-sea exchange and the sequestration of CO2. The interaction of phytoplankton – heterotrophs – can affect the overall response to the global change of plankton food webs mainly by cascading effects, and very few studies have considered trophic interactions. Multi-trophic experiments are needed to improve our understanding of the impact of global change on the coastal plankton of Patagonia.

Rainfall events bring both, terrigenous materials (including DOM) and nutrients to the aquatic system (e.g., via riverine runoff) having potential effects on the structure and metabolism of the phytoplankton communities. As extreme rainfall events in Patagonia occurred more frequently in the last decade (2010-2019) as compared to the previous ones (1972-2009), we exposed winter and summer phytoplankton communities (using microcosms) to solar radiation, simulating two rainfall conditions a single extreme vs. intermittent i.e., with gradual inputs, and we assessed their photosynthetic and growth rates responses and taxonomic changes. Rainfall scenarios significantly increased growth of both communities, mainly of small nanoplanktonic species, as compared to the control. Small nanoplanktonic centric diatoms increased and dominated in both rainfall scenarios, as compared to the control, during winter and summer, with significantly smaller cells during summer as compared to winter. Photosynthetic efficiency increased in both rainfall scenarios at the end of the experiment as compared to the control. Overall, the change towards small cells (associated to rainfall events) that can use more effectively solar radiation and nutrients (as compared to large cells) may have a significant impact on the trophic webs of the South West Atlantic Ocean by favoring grazing pressure by microzooplankton, especially during summer.

Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters (Isla Escondida, IE). We exposed samples to two contrasting scenarios: Present (nutrients at in situ levels) vs. Future (with lowered pH and higher nutrients inputs), and determined growth and photosynthetic responses after 2 days of acclimation. Under the Future condition phytoplankton growth was higher in the estuarine site compared to those in PM and IE. This effect was the most pronounced on large diatoms. While the increase of photosynthetic activity was not always observed in the Future scenario, the lower photosynthetic electron requirement for carbon fixation ( Φ e,C = ETR/P m B ) in this scenario compared to the Present, suggests a more effective energy utilization. Long-term experiments were also conducted to assess the responses along a 4 days acclimation period in PU. Diatoms benefited from the Future conditions and had significantly higher growth rates than in the Present. In addition, Φ e,C was lower after the acclimation period in the Future scenario, compared to the Present. Our results suggest that the availability, frequency and amount of nutrients play a key role when evaluating the effects of global change on natural phytoplankton communities. The observed changes in diatom growth under the Future scenario in PU and IE and photosynthesis may have implications in the local trophodynamics by bottom up control.

Aquatic ecosystems cover over two thirds of our planet and play a pivotal role in stabilizing the global climate as well as providing a large array of services for a fast-growing human population. However, anthropogenic activities increasingly provoke deleterious impacts in aquatic ecosystems. In this paper we discuss five sources of anthropogenic pollution that affect marine and freshwater ecosystems: sewage, nutrients and terrigenous materials, crude oil, heavy metals and plastics. Using specific locations as examples, we show that land-based anthropogenic activities have repercussions in freshwater and marine environments, and we detail the direct and indirect effects that these pollutants have on a range of aquatic organisms, even when the pollutant source is distant from the sink. While the issues covered here do focus on specific locations, they exemplify emerging problems that are increasingly common around the world. All these issues are in dire need of stricter environmental policies and legislations particularly for pollution at industrial levels, as well as solutions to mitigate the effects of anthropogenic pollutants and restore the important services provided by aquatic ecosystems for future generations.

Estuaries represent the interface between riverine and marine ecosystems and they are among the most productive areas on Earth; thus it is of utmost importance to understand their functioning in a global change scenario. So far, it is virtually unknown how the interaction between nutrient inputs, acidification and fluctuating light regimes could alter photosynthesis, growth, and phytoplankton structure in the end members (i.e., river and sea) of estuaries. Using the Chubut river estuary (Argentina) as a model ecosystem, we conducted experimentation during the austral summer (i.e., the windy season, February of 2016) with both, river and seawater phytoplankton communities to assess these topics. We evaluated the impact of fluctuating irradiance (static vs. mixed conditions) using short- (<one day) and mid-term acclimation (five days) and mimicking scenarios of higher acidification and nutrients (Future) as compared with an unmodified Present. The growth of both communities increased significantly under the Future as compared to the Present scenario, but mixing decreased growth only in seawater phytoplankton. Small centric diatoms (mainly Thalassiosira spp.) co-dominated with unidentified flagellates in the seawater, but the relative abundance of diatoms was higher in the Future as compared with the Present scenario. Diatoms and cryptophytes co-dominated in the river at the end of the experiments for both static and mixed conditions. Net primary productivity (NPP) decreased in the Future scenario and this was coupled with higher inhibition (k) of photosystem II (PSII), in both communities. Our results indicate that fluctuating irradiance, under a future global change scenario, as simulated here, has a significant impact on the structure and growth of seawater phytoplankton, together with increases in photochemical inhibition and decreases in NPP. However, these changes are much smaller in the river phytoplankton. Thus, the overall effects of mixing on the trophodynamics of the area will be more important at the sea than in the river end of the estuary.

Increases in rainfall, continental runoff, and atmospheric dust deposition are reducing water transparency in lakes worldwide (i.e. higher attenuation Kd). Also, ongoing alterations in multiple environmental drivers due to global change are unpredictably impacting phytoplankton responses and lakes functioning. Although both issues demand urgent research, it remains untested how the interplay between Kd and multiple interacting drivers affect primary productivity (Pc). We manipulated four environmental drivers in an in situ experiment—quality of solar ultraviolet radiation (UVR), nutrient concentration (Nut), CO2 partial pressure (CO2), and light regime (Mix)—to determine how the Pc of nine freshwater phytoplankton communities, found along a Kd gradient in Mediterranean ecosystems, changed as the number of interacting drivers increased. Our findings indicated that UVR was the dominant driver, its effect being between 3–60 times stronger, on average, than that of any other driver tested. Also, UVR had the largest difference in driver magnitude of all the treatments tested. A future UVR × CO2 × Mix × Nut scenario exerted a more inhibitory effect on Pc as the water column became darker. However, the magnitude of this synergistic effect was 40–60% lower than that exerted by double and triple interactions and by UVR acting independently. These results illustrate that although future global-change conditions could reduce Pc in Mediterranean lakes, multiple interacting drivers can temper the impact of a severely detrimental driver (i.e. UVR), particularly as the water column darkens.

We evaluated the dual role of DOM (i.e., as a source of inorganic nutrients and as an absorber of solar radiation) on a phytoplankton community of the western South Atlantic Ocean. Using a combination of microcosms and a cluster approach, we simulated the future conditions of some variables that are highly influenced by global change in the region. We increased nutrients (i.e., anthropogenic input) and dissolved organic matter (DOM), and we decreased the pH, to assess their combined impact on growth rates (μ), species composition/abundance and size structure, and photosynthesis (considering in this later also the effects of light quality i.e., with and without ultraviolet radiation). We simulated two Future conditions (Fut) where nutrients and pH were similarly manipulated, but in one the physical role of DOM (Futout) was assessed whereas in the other (Futin) the physico-chemical role was evaluated; these conditions were compared with a control (Present condition, Pres). The μ significantly increased in both Fut conditions as compared to the Pres, probably due to the nutrient addition and acidification in the former. The highest μ were observed in the Futout, due to the growth of nanoplanktonic flagellates and diatoms. Cells in the Futin were photosynthetically less efficient as compared to those of the Futout and Pres, but these physiological differences, also between samples with or without solar UVR observed at the beginning of the experiment, decreased with time hinting for an acclimation process. The knowledge of the relative importance of both roles of DOM is especially important for coastal areas that are expected to receive higher inputs and will be more acidified in the future.

The short- and mid-term effects of a simulated global change scenario (i.e., Future) of increased nutrients, acidification, and solar radiation, in the presence or absence of grazers, were evaluated on a freshwater plankton community of Patagonia, Argentina. We used a cluster experimental design with microcosms incubated outdoors simulating the in situ (i.e., Present) and the Future conditions. Short-term changes in net productivity and respiration, together with mid-term changes in the community (abundance, biomass, and phytoplankton cell size) were measured. Phytoplankton had lower net productivity and higher respiration and zooplankton had, in general, higher respiration under the Future than that under the Present condition when organisms were exposed to UVR. The mid-term impacts of the Future condition were neither significant on zooplankton abundances, nor in phytoplankton abundances, biomass, and cell size. Nevertheless, the zooplankton–phytoplankton interaction strength was greater under the Future condition. Zooplankton exerted a strong top-down pressure, regardless of the experimental scenarios, grazing preferentially on small phytoplankton cells, thus decreasing their abundances and biomass. Overall, there were significant short-term impact of our Future global change scenario; however, its effects on mid-term time scales were not significant, and indeed, the zooplankton top-down pressure was the main driver that shaped the phytoplankton community.

Experiments to determine the long-term (i.e., 12-14 days) combined effects of solar radiation and nutrient addition were conducted with natural phytoplankton assemblages collected at three sites off the Patagonian coast, Argentina – 42 44°S (i.e., Bahía Engaño, Bahía Camarones and Bahía Nueva) during January – March 2003. Samples from each site were put in UVR transparent containers and incubated under three (ambient) radiation treatments: a) Samples exposed to UVR + PAR (280-400 nm) PAB treatment; b) Samples exposed to UV-A + PAR (320-400 nm) – PA treatment, and, c) Samples exposed to PAR only (400-700 nm) – P treatment. Nutrients (i.e., f/2 concentration) were added to the samples either at the beginning (i.e., N0 cultures) or after 6-7 days of exposure to solar radiation (i.e., Nx cultures). Growth (i.e., estimated from chl a measurements) and floristic composition were monitored every 1-2 days; in addition, primary productivity rates were determined at the beginning and during the exponential phase of N0 cultures. At the three sites we determined significantly higher growth rates in the Nx than in the N0 cultures. In addition, we found that photosynthetic inhibition due to UV-A was higher than that produced by UV-B, and that overall inhibition decreased with time suggesting acclimation of cells to the new (i.e., experimental) radiation conditions. At all sites the communities were dominated by small flagellates but differences in the diatom composition were found between experiments, as well as within radiation / nutrient treatments. N0 cultures of Bahía Engaño were characterized by Guinardia delicatula, whereas in the Nx cultures this diatom co-dominated with other species. In Bahía Camarones, and except for N0_P cultures, where Asterionellopsis glacialis was dominant, Nitzschia longissima always accounted for an important fraction of the diatom community. In Bahía Nueva Skeletonema costatum generally dominated the diatom community, but co-dominated with Leptocyilindrus sp. in the treatments N0 _ PAB and N0 _ PA cultures. Overall, our results indicate that no generalizations can be made in regard to the responses of different phytoplankton assemblages to the combination of solar radiation exposure and nutrient addition. The responses seem to be related to the initial composition of the assemblages, the previous light history and the nutrient status of cells. However, UVR exposure and nutrient addition do seem to account, at least in part, for an important part of the observed phytoplankton biodiversity from Patagonian waters.