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Harmful algal blooms (HABs) are globally increasing in number and spatial extent. However, their propagation dynamics along environmental gradients and the associated interplay of abiotic factors and biotic interactions are still poorly understood. In this study, a nutrient gradient was established in a linear meta‐ecosystem setup of five interconnected flasks containing an artificially assembled phytoplankton community. The harmful dinoflagellate Alexandrium catenella was introduced into different positions along the nutrient gradient to investigate dispersal and spatial community dynamics. Overall, total algal biovolume increased, while community evenness decreased with increasing nutrient concentrations along the gradient. Alexandrium was able to disperse through all flasks. On the regional scale, diatoms dominated the community, whereas on the local scale the dinoflagellate showed higher contributions at low nutrient concentrations and dominated the community at the lowest nutrient concentration, but only when initiated into this flask. A control treatment without dispersal revealed an even stronger dominance of Alexandrium at the lowest nutrient concentration, indicating that dispersal and the associated nutrient exchange may weaken dinoflagellate dominance under low nutrient conditions. This study presents a first approach to experimentally investigate spatial dynamics and ecological interactions of a harmful dinoflagellate along an environmental gradient in a meta‐ecosystem setup, which has the potential to substantially enhance our understanding of the relevance of dispersal for HAB formation and propagation in combination with local environmental factors., Volkswagen Foundation http://dx.doi.org/10.13039/501100001663

Pronounced atmospheric and oceanic warming along the West Antarctic Peninsula (WAP) has resulted in abundance shifts in populations of Antarctic krill and Salpa thompsoni determined by changes in the timing of sea-ice advance, the duration of sea-ice cover and food availability. Krill and salps represent the most important macrozooplankton grazers at the WAP, but differ profoundly in their feeding biology, population dynamics and stoichiometry of excretion products with potential consequences for the relative availability of dissolved nitrogen and phosphorus. Alternation of the dissolved nutrient pool due to shifts in krill and salp densities have been hypothesized but never explicitly tested by using observational data. We therefore used the Palmer LTER dataset in order to investigate whether the dominance of either grazer is related with the observed dissolved nitrogen:phosphorus (N:P) ratios at the WAP. Across the whole sampling grid, the dominance of salps over krill was significantly correlated to higher concentrations of both N and P as well as a higher N:P ratios. Using actual long-term data, our study shows for the first time that changes in key grazer dominance may have consequences for the dynamics of dissolved nitrogen and phosphorus at the WAP.

Climatic warming is a primary driver of change in ecosystems worldwide. Here, we synthesize responses of species richness and evenness from 187 experimental warming studies in a quantitative meta-analysis. We asked 1) whether effects of warming on diversity were detectable and consistent across terrestrial, freshwater and marine ecosystems, 2) if effects on diversity correlated with intensity, duration, and experimental unit size of temperature change manipulations, and 3) whether these experimental effects on diversity interacted with ecosystem types. Using multilevel mixed linear models and model averaging, we also tested the relative importance of variables that described uncontrolled environmental variation and attributes of experimental units. Overall, experimental warming reduced richness across ecosystems (mean log-response ratio = -0.091, 95% bootstrapped CI: -0.13, -0.05) representing an 8.9% decline relative to ambient temperature treatments. Richness did not change in response to warming in freshwater systems, but was more strongly negative in terrestrial (-11.8%) and marine (-10.5%) experiments. In contrast, warming impacts on evenness were neutral overall and in aquatic systems, but weakly negative on land (7.6%). Intensity and duration of experimental warming did not explain variation in diversity responses, but negative effects on richness were stronger in smaller experimental units, particularly in marine systems. Model-averaged parameter estimation confirmed these main effects while accounting for variation in latitude, ambient temperature at the sites of manipulations, venue (field versus lab), community trophic type, and whether experiments were open or closed to colonization. These analyses synthesize extensive experimental evidence showing declines in local richness with increased temperature, particularly in terrestrial and marine communities. However, the more variable effects of warming on evenness were better explained by the random effect of site identity, suggesting that effects on species' relative abundances were contingent on local species composition.

Ptacnik, Robert ... et al.-- 10 pages, 4 figures, 1 table, supplementary information https://dx.doi.org/10.1038/srep29286, Mixotrophs combine photosynthesis with phagotrophy to cover their demands in energy and essential nutrients. This gives them a competitive advantage under oligotropihc conditions, where nutrients and bacteria concentrations are low. As the advantage for the mixotroph depends on light, the competition between mixo- and heterotrophic bacterivores should be regulated by light. To test this hypothesis, we incubated natural plankton from the ultra-oligotrophic Eastern Mediterranean in a set of mesocosms maintained at 4 light levels spanning a 10-fold light gradient. Picoplankton (heterotrophic bacteria (HB), pico-sized cyanobacteria, and small-sized flagellates) showed the fastest and most marked response to light, with pronounced predator-prey cycles, in the high-light treatments. Albeit cell specific activity of heterotrophic bacteria was constant across the light gradient, bacterial abundances exhibited an inverse relationship with light. This pattern was explained by light-induced top-down control of HB by bacterivorous phototrophic eukaryotes (PE), which was evidenced by a significant inverse relationship between HB net growth rate and PE abundances. Our results show that light mediates the impact of mixotrophic bacterivores. As mixo- and heterotrophs differ in the way they remineralize nutrients, these results have far-reaching implications for how nutrient cycling is affected by light, The experiment was financed by the European Union Seventh Framework Program MESOAQUA (FP7/2009-2013) coordinated by JCN under grant agreement no. 228224. R.P. further acknowledges financial support by the German Research Council (DFG Pt 5/3-1), JMG by Spanish project REMEI (CTM2015-70340) and AC by project PROTOS (CTM2009-08783) from the Spanish Ministry of Economy and Competitiveness

Ecosystem functioning is affected by horizontal (within trophic groups) and vertical (across trophic levels) biodiversity. Theory predicts that the effects of vertical biodiversity depend on consumer specialization. In a microcosm experiment, we investigated ciliate consumer diversity and specialization effects on algal prey biovolume, evenness and composition, and on ciliate biovolume production. The experimental data was complemented by a process-based model further analyzing the ecological mechanisms behind the observed diversity effects. Overall, increasing consumer diversity had no significant effect on prey biovolume or evenness. However, consumer specialization affected the prey community. Specialist consumers showed a stronger negative impact on prey biovolume and evenness than generalists. The model confirmed that this pattern was mainly driven by a single specialist with a high per capita grazing rate, consuming the two most productive prey species. When these were suppressed, the prey assemblage became dominated by a less productive species, consequently decreasing prey biovolume and evenness. Consumer diversity increased consumer biovolume, which was stronger for generalists than for specialists and highest in mixed combinations, indicating that consumer functional diversity, i.e. more diverse feeding strategies, increased resource use efficiency. Overall, our results indicate that consumer diversity effects on prey and consumers strongly depend on species-specific growth and grazing rates, which may be at least equally important as consumer specialization in driving consumer diversity effects across trophic levels. Synthesis In a microcosm experiment, we investigated multitrophic consumer diversity and specialization effects using ciliate consumers and microalgal prey. Consumer diversity increased consumer biovolume, which was highest in combinations containing both generalists and specialists. Specialist consumers showed a stronger negative effect on prey biovolume and evenness than generalists. These experimental data were supported by a process-based model, indicating that the large effect of the specialists was based on high per capita grazing rate on the two most productive prey species. Species-specific traits such as growth and grazing rates were equally important for multitrophic diversity effects than consumer specialization.

As part of our research, we have designed and developed sensor-actuated network for marine monitoring. The network consists of ten static buoy nodes and one mobile robotic boat for real-time in-situ measurements and analysis of chemical, physical and biologically pertinent phenomena governing the abundance of micro-organisms at relevant spatio-temporal scales. The goal of the network is to obtain high-resolution information on the spatial and temporal distribution of plankton assemblages in aquatic environments using the in situ presence afforded by the network, and to make possible network-enabled robotic sampling of hydrographic features of interest. This work constitutes advances in (1) real-time observing in aquatic ecosystems and (2) sensor-actuated sampling for biological analysis.

Lingulodinium polyedrum is a marine, bioluminescent dinoflagellate that is a common red tide species and potential toxin producer (yessotoxin) along a large expanse of the coast of Southern California. Little is known about the factors leading to bloom formation, or its impact on planktonic food webs. Bloom abundances can reach over 1000 cells/ml, events in which the interplay of physical forces (wind and surface currents) and of algal behavior (vertical migration) presumably play an important role. Using the CENS laboratory test bed, we have examined the pattern and timing of vertical migration by the dinoflagellate in a 2m water column on an 11h:13h light:dark photoperiod.

Lingulodinium polyedrum is a marine, bioluminescent dinoflagellate that is a common red tide species and potential toxin producer (yessotoxin) along a large expanse of the coast of Southern California. Little is known about the factors leading to bloom formation, or its impact on planktonic food webs. Bloom abundances can reach over 1000 cells/ml, events in which the interplay of physical forces (wind and surface currents) and of algal behavior (vertical migration) presumably play an important role. Using the CENS laboratory test bed, we have examined the pattern and timing of vertical migration by the dinoflagellate in a 2m water column on an 11h:13h light:dark photoperiod. Species-specific detection and enumeration of this organism was accomplished using an 18S rDNA-based quantitative real-time PCR (qPCR) approach developed in our lab. Positive phototaxis of L. polyedrum resulted in dense aggregations of the dinoflagellate within the top few centimetres of the water column during the light period, while cells were evenly distributed during the night.

The Networked Aquatic Microbial Observing System (NAMOS) is an array of embedded networked sensors that has been developed to study plankton populations in marine and aquatic environments. The application of NAMOS in Lake Fulmor, adjacent to the James Mountain Reserve, California, has begun to yield valuable insights into plankton community structure and dynamics, including phytoplankton spatial and temporal distributions throughout the lake. Data collected during deployments of the system in May, July, and October, 2005 revealed decreases in water column temperature stratification, accompanied by overall increases in chlorophyll in the lake throughout the three deployments. Chlorophyll concentrations (indicative of phytoplankton biomass) exhibited strong diel variations at a depth of one meter, with highest concentrations during the evening and early morning (18:00-06:00) and much lower values during the day. These findings presumably indicate a strong vertical migratory behavior of the phytoplankton assemblage.

As part of our research, we have designed and developed a sensor-actuated network for marine monitoring. The network consists of ten static buoy nodes and one mobile robotic boat for real-time in-situ measurements and analysis of chemical, physical and biologically pertinent phenomena governing the abundance of micro-organisms at relevant spatio-temporal scales. The goal of the network is to obtain high-resolution information on the spatial and temporal distribution of plankton assemblages in aquatic environments using the in situ presence afforded by the network, and to make possible network-enabled robotic sampling of hydrographic features of interest.

With an increase in blooms of harmful algae on both national and global levels, it is becoming ever more important to be able to detect these organisms at high spatial and temporal resolutions. It is also imperative that methods of detection are able to identify target cells at low concentrations. To this end we present a number of immunologically-based techniques for detecting cells of Aureococcus anophagefferens, the cause of ’¡ÈBrown Tides’¡É off the Mid-Atlantic coast. These techniques include flow cytometry, atomic force microscopy, and nanowire- and nanotube-based sensing. We also detail experiments carried out in a laboratory testbed demonstrating ecologically significant behavior patterns in two harmful algal species responsible for ’¡ÆBrown’¡Ç and ’¡ÆRed’¡Ç tides on the east and west coast, respectively.