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The temporal evolution of the physical and biogeochemical properties of the Atlantic Jet (AJ) along the first similar to 75 m of the water column during a 4-day journey was analysed by following the trajectory of a drifter dragged by the jet from the Strait of Gibraltar towards the Alboran Sea. Three stages were differentiated based on the evolution of several variables (e.g., velocity, temperature, nutrients, fluorescence). (i) Within the Strait of Gibraltar, the water column was primarily influenced by the tidal cycle, leading to a nutrient-enrichment of surface waters. However, due to the short residence time, the phytoplankton community that was mainly dominated by diatoms, did not demonstrate significant changes. (H) Once outside the Strait, the drifter trajectory was mainly influenced by the frontal dynamics associated with the AJ. The drifter moved forward along the jet but also laterally across it and was continuously attracted to the mainstream (maximum current speed) or detached to its southern edge (minimum current speed). Due to the associated upwelling processes induced by the intensification of the current along the mainstream, the water column was characterized by colder, nutrient-richer water and lower fluorescence values. Conversely, along the southern edge of the jet, the water column was characterized by higher temperature, low nutrient concentration, and higher fluorescence. Along the first stations of this stage, diatom total abundance and biovolume continuously increased, reaching values similar to 12-times higher than the initial concentrations. (Hi) In the last stage, the water parcel was still influenced by the frontal dynamics but with less intensity. Additionally, the colder and denser water of the AJ and the associated phytoplankton community subducted progressively as it moved into the region surrounded by warmer waters. Concomitantly, fluorescence and diatoms total abundance and biovolume decreased and were influenced by the decline of nutrient availability and the increase of mesozooplankton. Our results reveal the coupled processes induced by the entrance of the AJ in the Alboran Sea and highlight the strong control of the physical environment over the ecological processes in this region., The authors gratefully acknowledge the officers, crew and technical staff of the R.V. Sarmiento de Gamboa for their altruistic help during the cruise, all the scientific team that participated in the MEGAN campaign collecting the different datasets, Manuel Arjonilla for nutrient sample measurements, and Reyes Garcia for her collaboration in the treatment of plankton samples. They also thank the Copernicus Marine Environmental Monitoring Service for providing access to satellite data. Neural network analyses were performed in the facilities of the Area de Sistemas de Informacion de la Universidad de Cadiz (https://supercomputacion.uca.es).Finally, the authors acknowledge Sara Soria Piriz (@nautillustrations) for the drawing of the conceptual diagram in Fig. 10. Comments provided by two anonymous reviewers substantially improved subsequent versions of the manuscript. The Spanish National Research Plan through project CTM2013-49048 has supported this work. Iria Sala and Marina Bolado-Penagos were supported by a grant of the FPI fellowship program, Spain. To accomplish this work, Iria Sala carried out a short-term stay with the research group Dinamica del Ecosistema Planctonico at the Instituto Espanol de Oceanografia de Gijon, under the supervision of Dr Angel Lopez-Urrutia, supported by a grant of the FPI fellowship program.

Interactions between autotrophic and heterotrophic bacteria are fundamental for marine biogeochemical cycling. How global warming will affect the dynamics of these essential microbial players is not fully understood. The aims of this study were to identify the major groups of heterotrophic bacteria present in a Synechococcus culture originally isolated from the Red Sea and assess their joint responses to experimental warming within the metabolic ecology framework. A co-culture of Synechococcus sp. RS9907 and their associated heterotrophic bacteria, after determining their taxonomic affiliation by 16S rRNA gene sequencing, was acclimated and maintained in the lab at different temperatures (24–34°C). The abundance and cellular properties of Synechococcus and the three dominant heterotrophic bacterial groups (pertaining to the genera Paracoccus, Marinobacter, and Muricauda) were monitored by flow cytometry. The activation energy of Synechococcus, which grew at 0.94–1.38 d–1, was very similar (0.34 ± 0.02 eV) to the value hypothesized by the metabolic theory of ecology (MTE) for autotrophs (0.32 eV), while the values of the three heterotrophic bacteria ranged from 0.16 to 1.15 eV and were negatively correlated with their corresponding specific growth rates (2.38–24.4 d–1). The corresponding carrying capacities did not always follow the inverse relationship with temperature predicted by MTE, nor did we observe a consistent response of bacterial cell size and temperature. Our results show that the responses to future ocean warming of autotrophic and heterotrophic bacteria in microbial consortia might not be well described by theoretical universal rules.

This article belongs to the Special Issue Bioactive Compounds Derived from Marine Microalgae 2.0., Polyunsaturated aldehydes (PUAs) are bioactive molecules suggested as chemical defenses and infochemicals. In marine coastal habitats, diatoms reach high PUA production levels during bloom episodes. Two fractions of PUA can usually be analyzed: pPUA obtained via artificial breakage of collected phytoplankton cells and dissolved PUA already released to the environment (dPUA). In nature, resource supply arises as a main environmental controlling factor of PUA production. In this work, we monitored the vertical distribution and daily variation of pPUA associated with large-size phytoplankton and dPUA, at three sites located in the Alborán Sea from mesotrophic to oligotrophic waters. The results corroborate the presence of large-size PUA producers in oligotrophic and mesotrophic waters with a significant (58%–85%) diatom biomass. In addition to diatoms, significant correlations between pPUA production and dinoflagellate and silicoflagellate abundance were observed. 2E,4E/Z-Heptadienal was the most abundant aldehyde at the three sites with higher values (17.1 fg·cell−1) at the most oligotrophic site. 2E,4E/Z-Decadienal was the least abundant aldehyde, decreasing toward the oligotrophic site. For the first time, we describe the daily fluctuation of pPUA attributable to cellular physiological state and not exclusively to taxonomical composition. Our results demonstrate the persistence of threshold levels of dPUA deep in the water column, as well as the different chromatographic profiles of dPUA compared with pPUA. We propose different isomerization processes that alter the chemical structure of the released PUAs with unknown effects on their stability, biological function, and potential bioactivity., This work was supported by the projects MEGAN (CTM2013-49048-C2-1-R) and FICOEXPLORA (RTI2018-101272-B-I00) funded by the Spanish National Research Plan. I.S. and M.B.-P. are supported by a grant of the FPI fellowship program.

In recent decades, the automatic study and analysis of plankton communities using imaging techniques has advanced significantly. The effectiveness of these automated systems appears to have improved, reaching acceptable levels of accuracy. However, plankton ecologists often find that classification systems do not work as well as expected when applied to new samples. This paper proposes a methodology to assess the efficacy of learned models which takes into account the fact that the data distribution (the plankton composition of the sample) can vary between the model building phase and the production phase. As opposed to most validation methods that consider the individual organism as the unit of validation, our approach uses a validation‐by‐sample, which is more appropriate when the objective is to estimate the abundance of different morphological groups. We argue that, in these cases, the base unit to correctly estimate the error is the sample, not the individual. Thus, model assessment processes require groups of samples with sufficient variability in order to provide precise error estimates.

Summary The ‘cytometric diversity’ of phytoplankton communities has been studied based on single-cell properties, but the applicability of this method to characterize bacterioplankton has been unexplored. Here, we analysed seasonal changes in cytometric diversity of marine bacterioplankton along a decadal time-series at three coastal stations in the Southern Bay of Biscay. Shannon–Weaver diversity estimates and Bray–Curtis similarities obtained by cytometric and molecular (16S rRNA tag sequencing) methods were significantly correlated in samples from a 3.5 year monthly time-series. Both methods showed a consistent cyclical pattern in the diversity of surface bacterial communities with maximal values in winter. The analysis of the highly resolved flow cytometry time-series across the vertical profile showed that water column mixing was a key factor explaining the seasonal changes in bacterial composition and the winter increase in bacterial diversity in coastal surface waters. Due to its low cost and short processing time as compared with genetic methods, the cytometric diversity approach represents a useful complementary tool in the macroecology of aquatic microbes.

Studies on the size-scaling of phytoplankton growth rate are usually based on temperature-corrected growth rates or experiments performed at a fixed temperature, but the effects of differing thermal adaptation of small and large species have not been considered. We use an extensive dataset of phytoplankton growth rate responses to temperature and cell size to show that the unimodal size-scaling of phytoplankton growth depends strongly on temperature, and is not significant at high temperatures where the most common picophytoplankton species grow at their optimum. Furthermore, we show that the unimodality results from the different growth rate scaling of picophytoplankton, which differs phylogenetically from larger phytoplankton taxa. Using ribosomal RNA sequences we recalculated the size-scaling allometry with Phylogenetic Generalized Least Squares regression. After phylogenetic correction, the unimodal relationship is not significant at any temperature, suggesting that the observed curvature reflects the evolutionary adaptation of picophytoplankton to the warm conditions usually encountered in oligotrophic environments.

Nutrient availability is one of the major factors regulating marine productivity and phytoplankton community structure. While the response of phytoplankton species to nutrient variation is relatively well known, that of phytoplankton community remains unclear. We question whether phytoplankton community growth rates respond to nutrient concentration in a similar manner to phytoplankton species composing the community, that is, following Monod's model. Data on in situ marine community growth rates in relation to nutrient concentration and the behaviour of a simple multi-species community model suggest that community growth rate does not respond to nutrient concentration according to the Monod equation. Through a simulation study we show this can be explained as a consequence of changes in size structure. Marine biogeochemical models must not parameterize phytoplankton community growth rate response to nutrient concentration using a single Monod equation but rather involve different phytoplankton functional groups each with different equation parameters., SI

This work was funded by project Predicting the metabolic balance of the oceans (METOCA, CTM2009-13882-MAR) and Coastal Ocean Microbial communities and Temperature (COMITE, CTM2010-15840) funded by Spanish National Investigation+Development+Innovation (I+D+I) Plan.

In unicellular phytoplankton, the size scaling exponent of chlorophyll content per cell decreases with increasing light limitation. Empirical studies have explored this allometry by combining data from several species, using average values of pigment content and cell size for each species. The resulting allometry thus includes phylogenetic and size scaling effects. The possibility of measuring single-cell fluorescence with imaging-in-flow cytometry devices allows the study of the size scaling of chlorophyll content at both the inter- and intraspecific levels. In this work, the changing allometry of chlorophyll content was estimated for the first time for single phytoplankton populations by using data from a series of incubations with monocultures exposed to different light levels. Interspecifically, our experiments confirm previous modeling and experimental results of increasing size scaling exponents with increasing irradiance. A similar pattern was observed intraspecifically but with a larger variability in size scaling exponents. Our results show that size-based processes and geometrical approaches explain variations in chlorophyll content. We also show that the single-cell fluorescence measurements provided by imaging-in-flow devices can be applied to field samples to understand the changes in the size dependence of chlorophyll content in response to environmental variables affecting primary production. IMPORTANCE The chlorophyll concentrations in phytoplankton register physiological adjustments in cellular pigmentation arising mainly from changes in light conditions. The extent of these adjustments is constrained by the size of the phytoplankton cells, even within single populations. Hence, variations in community chlorophyll derived from photoacclimation are also dependent on the phytoplankton size distribution.

Prokaryotic planktonic organisms are small in size but largely relevant in marine biogeochemical cycles. Due to their reduced size range (0.2 to 1 mu m in diameter), the effects of cell size on their metabolism have been hardly considered and are usually not examined in field studies. Here, we show the results of size-fractionated experiments of marine microbial respiration rate along a latitudinal transect in the Atlantic Ocean. The scaling exponents obtained from the power relationship between respiration rate and size were significantly higher than one. This superlinearity was ubiquitous across the latitudinal transect but its value was not universal revealing a strong albeit heterogeneous effect of cell size on microbial metabolism. Our results suggest that the latitudinal differences observed are the combined result of changes in cell size and composition between functional groups within prokaryotes. Communities where the largest size fraction was dominated by prokaryotic cyanobacteria, especially Prochlorococcus, have lower allometric exponents. We hypothesize that these larger, more complex prokaryotes fall close to the evolutionary transition between prokaryotes and protists, in a range where surface area starts to constrain metabolism and, hence, are expected to follow a scaling closer to linearity., SI

Any technique developed to enumerate plankton must take into account the size structure of the plankton community. Automatic sampling devices must be capable of analysing a minimum number of cells of the largest size to cover the whole size range intended to be sampled effectively. The Flow Cytometer And Microscope (FLowCAM ® ) has been used in the last decade to estimate the size structure of the plankton community Few attempts, however, have been made to compare FlowCAM measurements with the results provided by traditional microscopy methods for size-structure estimations. FlowCAM can operate in three working modes: autoimage, fluorescence triggered and side-scatter triggered. Autoimage and fluorescence triggered cannot only count accurately a mono-specific suspension of cells, but they are also useful to estimate the size structure of natural samples. The side-scatter-triggered mode is not effective to estimate the size structure of natural samples, although it can count a sparse mono-specific solution accurately. The analysis of natural samples with FlowCAM requires a planned pre-processing of the samples to adjust the density of triggering particles (concentrating or diluting the sample) and to pre-filtrate the sample to avoid cell clumping or obstruction of the flow chamber. The size structure obtained with FlowCAM and with microscopy counts on preserved samples are comparable. Sample preservation, however, alters the size structure of the sample, which suggests that results based on preserved samples must be taken with caution. Automatic sampling devices like FlowCAM could provide a more precise analysis of plankton communities, increasing the resolution of surveys and avoiding the effects of preservation and sample storage.

Spatial and temporal changes of the copepod community have been investigated and related to the environmental variability of the Balearic Sea (Western Mediterranean). The period studied spans from 1994 to 1999 during which we analyzed the abundance and structure copepod variability over a cross-shore transect. Results showed a close link between hydrological changes and the variations of copepod abundance. The synchronous variability of copepods and hydrography indicated the rapid response of this zooplankton group to the inflow of cold and warm water masses coming through the study area. Cluster analysis revealed four main copepod assemblages that distinguished the coastal from the oceanic species and those species with different water masses preference. The copepod assemblage composed of Calanus helgolandicus, Clausocalanus arcuicornis, C. pergens, C. paululus, Calocalanus tenuis and Pleuromamma gracilis was associated with cool salty waters, whereas the assemblage formed by Temora stylifera, C. pavo, C. styliremis, Centropages bradyi and Acartia danae was related to warmer less saline Mediterranean waters. Moreover, it is suggested that changes in sea water temperature and salinity are linked to large-scale changes likely occurring at a basin scale, which is reflected in the Western Mediterranean mesoscale hydrographic changes. Therefore, it is stressed that changes in the Balearic copepod community can be used as potential tracers of the western Mediterranean water masses.

Heterotrophic bacteria play a major role in organic matter cycling in the ocean. Although the high abundances and relatively fast growth rates of coastal surface bacterioplankton make them suitable sentinels of global change, past analyses have largely overlooked this functional group. Here, time series analysis of a decade of monthly observations in temperate Atlantic coastal waters revealed strong seasonal patterns in the abundance, size and biomass of the ubiquitous flow-cytometric groups of low (LNA) and high nucleic acid (HNA) content bacteria. Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size. Although decadal cell shrinking was observed for both groups, it was only LNA cells that were strongly coherent, with ecological theories linking temperature, abundance and individual size on both the seasonal and interannual scale. We explain this finding because, relative to their HNA counterparts, marine LNA bacteria are less diverse, dominated by members of the SAR11 clade. Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size. Concurrent with rising temperatures in spring, significant decadal trends of increasing standing stocks (3% per year) accompanied by decreasing mean cell size (-1% per year) suggest a major shift in community structure, with a larger contribution of LNA bacteria to total biomass. The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump., SI

Using a global data set on egg hatch times in zooplanktonic and nektonic ectotherms from marine waters, the combined effects of body size, temperature and life-history attributes on development times were examined. After correcting for mass and temperature the mean egg hatch times (from laying to hatching) were 20 times faster in some taxa than in others. Some of the divergence in hatch times can be accounted for by the disposition strategy of the eggs. Eggs that are protected after laying (e.g. carried by the female, or attached to a substrate or floating in clumped masses) take 3.3 times longer on average to develop to hatching than those spawned individually and freely into the pelagic environment (i.e. ‘unprotected’), and this difference is independent of egg size. Given that unprotected eggs typically have higher mortality rates, it is proposed that evolution has acted to shorten this vulnerable period. Not only do hatch times appear to diverge on the basis of egg protection strategy, but also a similar degree of separation was apparent in cell cycle duration (i.e. time from 2 to 4 cell stage). These results reinforce the importance of egg disposition on development rate processes and their evolution.

Oceanic communities are sources or sinks of CO 2 , depending on the balance between primary production and community respiration. The prediction of how global climate change will modify this metabolic balance of the oceans is limited by the lack of a comprehensive underlying theory. Here, we show that the balance between production and respiration is profoundly affected by environmental temperature. We extend the general metabolic theory of ecology to the production and respiration of oceanic communities and show that ecosystem rates can be reliably scaled from theoretical knowledge of organism physiology and measurement of population abundance. Our theory predicts that the differential temperature-dependence of respiration and photosynthesis at the organism level determines the response of the metabolic balance of the epipelagic ocean to changes in ambient temperature, a prediction that we support with empirical data over the global ocean. Furthermore, our model predicts that there will be a negative feedback of ocean communities to climate warming because they will capture less CO 2 with a future increase in ocean temperature. This feedback of marine biota will further aggravate the anthropogenic effects on global warming.

Appendicularians have some of the highest growth rates among metazoans but they are usually outnumbered by the slower growing copepods in mesozooplankton communities. We present experimental evidence that the eggs and juveniles of the appendicularian Oikopleura dioica are actively consumed by various copepod species. Clearance rates of Calanus helgolandicus, Candacia armata, Centropages typicus, Eucalanus crassus, and Temora longicornis on eggs of O. dioica were usually above 300 ml copepod-1 d-1. The ingestion rates of C. helgolandicus on O. dioica eggs did not reach saturation even at the highest egg concentrations (4,560 eggs L-1). Although C. helgolandicus, C. typicus, and C. armata preyed actively on 1-mm-long O. dioica (approximately 0.2 mm in trunk length), predatory pressure decreased with increasing appendicularian size. We suggest that the association of dense appendicularian populations with phytoplankton blooms could be explained by their opportunistic response to beneficial conditions before copepod densities become high enough to cause a decline in appendicularian populations due to predation. Our results indicate that, in addition to the direct shunt of biomass from picoplankton to fish, appendicularians can occupy a similar role to that of microzooplankton in the ocean. They represent an intermediate step in the less efficient, picoplankton–appendicularia–copepod-fish food chain.

We used suspensions of 0.2, 0.5, 0.75, 1, 2, 3 and 6 µm fluorescent beads in combination with analytical flow cytometry to determine the efficiency of retention by small (165 µm trunk length), medium (347 µm) and large (689 and 734 µm) Oikopleura dioica, and by large (585 µm) Frit- illaria borealis. Large O. dioica and F. borealis were the most efficient at retaining the 2 µm beads, and small and medium O. dioica were most efficient for 1 µm beads. Large O. dioica and F. borealis showed efficiencies of ca. 15% for 0.2 µm, 33% for 0.5 µm, 58% for 0.75 µm beads, 66% for 1 µm beads and 88% for 2 µm beads. However, small O. dioica showed higher efficiencies, measuring ca. 10% for 0.2 µm, 43% for 0.5 µm, 72% for 0.75 µm beads, 87% for 1 µm beads and 93% for 2 µm beads. The combination of our measured appendicularian particle-retention efficiency spectra with typical particle size-distribution spectra in the ocean indicates that large and small appendicularians obtain 80% of their diet from particles smaller than 15 and 7 µm respectively, and that the smallest particles represent a significant part of their diet only when they strongly dominate the biomass size spectra. Comparison with data from the literature indicates that although the appendicularian:prey length ratio is extremely high, the appendicularian:prey body-carbon ratio (14 538:1) is within the reported range for mesozooplankton (1:1 to ca. 3 × 10 6 :1), and statistically undistinguishable from that of copepods (1603:1).

Jellyfishes have functionally replaced several overexploited commercial stocks of planktivorous fishes. This is paradoxical, because they use a primitive prey capture mechanism requiring direct contact with the prey, whereas fishes use more efficient visual detection. We have compiled published data to show that, in spite of their primitive life-style, jellyfishes exhibit similar instantaneous prey clearance and respiration rates as their fish competitors and similar potential for growth and reproduction. To achieve this production, they have evolved large, water-laden bodies that increase prey contact rates. Although larger bodies are less efficient for swimming, optimization analysis reveals that large collectors are advantageous if they move through the water sufficiently slowly., Sí

The 'cytometric diversity' of phytoplankton communities has been studied based on single-cell properties, but the applicability of this method to characterize bacterioplankton has been unexplored. Here, we analysed seasonal changes in cytometric diversity of marine bacterioplankton along a decadal time-series at three coastal stations in the Southern Bay of Biscay. Shannon-Weaver diversity estimates and Bray-Curtis similarities obtained by cytometric and molecular (16S rRNA tag sequencing) methods were significantly correlated in samples from a 3.5 year monthly time-series. Both methods showed a consistent cyclical pattern in the diversity of surface bacterial communities with maximal values in winter. The analysis of the highly resolved flow cytometry time-series across the vertical profile showed that water column mixing was a key factor explaining the seasonal changes in bacterial composition and the winter increase in bacterial diversity in coastal surface waters. Due to its low cost and short processing time as compared with genetic methods, the cytometric diversity approach represents a useful complementary tool in the macroecology of aquatic microbes.

Photoacclimation of picophytoplankton was studied in the mixed layer of 3 stations in the central Cantabrian Sea (southern Bay of Biscay). Picophytoplankton chl a:carbon ratios (θ) presented minimum values during summer, when irradiance, temperature, and biomass of prokaryotes reached maximum values and inorganic nutrient concentrations were low. Conversely, the maximum θ were reached during winter, coincident with lowest annual irradiance but maximum concentration of inorganic nutrients and higher relative biomass of eukaryotes. Changes in θ were modeled using irradiance as an independent variable. Exponentially decreasing functions of θ with irradiance were significant only when the mean temperatures in the mixed layer were above 14°C. These functions presented light-saturated minimum ratios (θmin) that decreased linearly with temperature and low-light maximum ratios (θmax) that increased exponentially with temperature. Such relationships were used to establish an empirical model that reproduced the seasonality of picophytoplankton θ in the mixed layer, with minima in summer and maxima in winter. A maximum potential θ, θN,T-max, was determined to estimate picophytoplankton growth rates in the central Cantabrian Sea. Combinations of picophytoplankton growth rates and biomass in the mixed layer were used to estimate areal picophytoplankton primary production rates in the euphotic zone that presented a bimodal seasonal cycle, with maxima in late winter (ca. 100 mg C m-2 d-1) and in late autumn (>200 mg C m-2 d-1) and mean annual values around 120 mg C m-2 d-1. En prensa

Oikopleura dioica is an excellent model for studying food flow through the digestive system because of its transparency, non-motility and because fecal pellets move along the digestive system in an orderly sequence which can be easily timed. By observing fecal pellet circulation within the gut of healthy individuals, we have concluded that the average number of fecal pellets inside the gut of O. dioica is 2.878 ± 0.015 (mean±SE, n = 43). Thus, gut passage time (GPT, min) can be estimated from the time interval between successive fecal pellets (DI, min fecal pellet -1 ) as GPT = 2.878 DI. This establishes the basis for estimating GPT from simple fecal pellet production rate incubations, and is one way of determinating GPT without manipulating food concentration or quality, a major shortcoming of current techniques. In laboratory experiments, GPT of O. dioica was independent of body size. At 15°C, GPT (min) decreased with increasing food concentration (FC, μg C l -1 ) when the prymnesophyte Isochrysis galbana (4.5 μm in size), the prasinophyte Tetraselmis suecica (10 μm) or the chlorophyte Chlorella sp. (3 μm) were used as food, according to the power function GPT = 29.4 FC -0.245 . There were no significant differences in GPT between algal types. The GPT of O. dioica exhibited a Q 10 of 0.687 over a temperature range of 10 to 20°C, independent of food concentration. Since the interaction between food concentration and temperature was not significant, GPT can be estimated as GPT = 51.67e -0.03761 FC -0.245 .

Flow cytometry has become a standard method to analyze bacterioplankton. Analysis of samples by flow cytometry is automatic, but it is followed by manual classification of the bacterioplankton groups in flow cytometry standard (FCS) files. This classification is a time consuming and subjective task performed by manually drawing the limits of the groups present in cytograms, a process referred to as gating. The automation of flow cytometry data processing based on pattern recognition techniques could provide an efficient tool to overcome some of these disadvantages. Here, we propose the use of model-based clustering techniques for the automatic detection of low (LNA) and high (HNA) nucleic acid bacterioplankton groups in FCS files. To validate our method, we compared the automatic classification with a flow cytometry database from a 9 yr time series collected in the central Cantabrian Sea that had been manually analyzed. The correlation between automatic and manual gating methods was >0.9 for cell counts and 0.7 to 0.95 for side scatter values, a proxy of cell size. In addition, no significant differences were found in the mean annual cycle of LNA and HNA cell abundance depicted by both methods. We also quantified the subjectivity of manual gating. The coefficient of variation for heterotrophic bacteria counts obtained by different analysts was around 10 to 20%. Our results suggest that the combination of flow cytometry and automatic gating provides a valuable tool to analyze microbial communities objectively and accurately, allowing us to safely compare bacterioplankton samples from different environments., SI

Linking lower and higher trophic levels requires special focus on the essential role played by mid-trophic levels, i.e., the zooplankton. One of the most relevant pieces of information regarding zooplankton in terms of flux of energy lies in its size structure. In this study, an extensive data set of size measurements is presented, covering parts of the western European continental shelf and slope, from the Galician coast to the Ushant front, during the springs from 2005 to 2012. Zooplankton size spectra were estimated using measurements carried out in situ with the Laser Optical Plankton Counter (LOPC) and with an image analysis of WP2 net samples (200 μm mesh size) performed following the ZooScan methodology. The LOPC counts and sizes particles within 100–2000 μm of spherical equivalent diameter (ESD), whereas the WP2/ZooScan allows for counting, sizing and identification of zooplankton from ~ 400 μm ESD. The difference between the LOPC (all particles) and the WP2/ZooScan (zooplankton only) was assumed to provide the size distribution of non-living particles, whose descriptors were related to a set of explanatory variables (including physical, biological and geographic descriptors). A statistical correction based on these explanatory variables was further applied to the LOPC size distribution in order to remove the non-living particles part, and therefore estimate the size distribution of zooplankton. This extensive data set provides relevant information about the zooplankton size distribution variability, productivity and trophic transfer efficiency in the pelagic ecosystem of the Bay of Biscay at a regional and interannual scale.

Three types of primary productivity (PP) models were evaluated in a mesoscale area around the South Shetland Islands (Antarctica). Input variables were: phytoplankton carbon biomass, Chlorophyll a, sea water temperature, daily irradiance, among others, collected in situ during an oceanographic cruise (COUPLING, January 2010). Models of the first type were based on Chl a measurements: the widely used model VGPM (Behrenfeld and Falkowski, 1997) and a derived version developed for the Western Antarctic Peninsula (Dierssen et al., 2000). The second type included two models based on phytoplankton carbon biomass: one developed for the whole Southern Ocean (Arrigo et al., 2008) and one based on the Metabolic Theory of Ecology developed by López-Urrutia et al. (2006), being the first time that a model with these features is used for Antarctic waters. The third type was an updated version of the carbon-based model CbPM (first described by Behrenfeld et al. (2005)) based on the Chl a/carbon biomass ratio modulation. The degree of agreement among the results between the different types of models turned out to be low (>. 30% of difference), but high within models of the same type (, This work was supported by the CTM2008-06343-C02-02/ANT project from the Spanish Ministry of Science and Education. C.G-M.'s work was supported by a predoctoral fellowship from the Spanish Council for Research (CSIC), JAE-Predoc 2009. The work of A.L-U was supported by the CTM2009-13882/MAR project from the Spanish Ministry of Science and Education.

The metabolic theory of ecology (MTE) states that metabolic rate, ruled mainly by individual mass and temperature, determines many other biological rates. This view of ecology as ruled by the laws of physics and thermodynamics contrasts with life-history-optimization (LHO) theories, where traits are shaped by evolutionary processes. Integrating the MTE and LHO can lead, however, to a synthetic theory of ecology. In this work, we link the two theories to show that offspring development time is the result of both maternal investment in offspring and the metabolic constraints on offspring growth. We formulate a model that captures how offspring development time is the consequence of both offspring growth rate, determined by temperature and allometric scaling in accordance with the MTE, and the size reached by offspring at the end of the developmental period, determined mainly by LHO and reproductive strategies. We first extend the trade-off between offspring size and offspring number to ectotherms, showing that increased body temperatures result in increased resources available for reproduction. We then combine this trade-off with the general ontogenetic growth model to show that there is a trade-off between the number of offspring produced and offspring development time. The model predicts a shorter developmental time in organisms producing larger numbers of offspring.

Four time-series of copepod species biomass in the north of Spain were contrasted to demonstrate spatial autocorrelation of local communities and their responses to short-term local and regional variability in oceanographic conditions. The series represented coastal and oceanic environments along a marked gradient of influence of seasonal upwelling from Galicia to the Mar Cantábrico (S Bay of Biscay), and each one included at least 10 years of continuous data collected at monthly frequency. Community composition (i.e. species number and diversity) was very consistent through the region, but local variations in the presence of new species and the relative proportions of common species allowed for the characterisation of the response to the environment at each site. Small-sized species were more frequent near the coast. A few species, however, captured the main patterns of variability in all series. Calanus helgolandicus and Acartia (mainly Acartia clausi) were generally the main contributors to total biomass, while other species as Paracalanus parvus and Clausocalanus spp. were important only at some locations. Most copepod indices were positively correlated with upwelling, either considering the whole community (biomass, species richness and diversity) or individual species, but only in the coastal series analysed since 1991. Copepods in the nearby ocean, however, showed negative correlations with upwelling in the period 1960–1986. The effects of upwelling may have been modulated by local factors, as showed by the increases in biomass, number of species and diversity in associations with increases in sea surface temperature in Galicia, while in the Mar Cantábrico only the warming-tolerant species increased and those typical of upwelling decreased. Density stratification of the water column was associated with decreases in total copepod biomass in Galicia, while it favoured the increase in species richness in the Mar Cantábrico. Nearly all significant responses of copepods to environmental variability were delayed by up to 5 months, showing the importance of considering time-lags in the analysis of temporal responses of zooplankton.

The most commonly used biomass estimate for microalgae is obtained from cell biovolume, usually calculated from microscopically measured linear dimensions. Although reliable, this is a highly time-consuming and specialized technique. Automated sampling devices that acquire images of cells and use pattern recognition techniques to identify the images have been developed as an alternative to microscopy-based methods. There are some aspects of automatic sampling and classification methods, however, which can be improved for the analysis of field samples including living and non-living particles. In this work, we demonstrate how the accuracy of a state-of the-art technique for plankton classification (Support Vector Machine) can be improved up to 86% if a previous automated step designed to remove non-living images is included. There is a tendency with the currently applied automatic methods to misestimate cell biovolume due to the two-dimensionality of the images. Here, we present a data set of more than 500 samples to show that the greatest effect is caused by the incorrect estimation of biovolume of the chain-forming diatoms. This results in an overestimate of biomass of between 20 and 100% where chain-forming diatoms represent more than the 20% of the biomass of the sample. We show how the classification method can be adapted to provide not only taxonomic but also the morphological classification of cells in order to obtain a more reliable estimate of biovolume according to the predicted cell shape, in a way comparable with microscopy-based estimates., Sí

Chen and Liu (2010) investigated the effects of cell size on phytoplankton-mass-specific growth rate using a compilation of field measurements from surface waters around the world. After correcting for the effects of temperature, their analysis indicates that there is a modal size around 2.8-5.8 mm where mass-specific growth is maximal. As Chen and Liu (2010) acknowledge, their analysis contrasts with allometric scaling theories that predict a continuous decrease of mass-specific growth rate with increasing size (Brown et al. 2004; Lopez-Urrutia et al. 2006). In contrast, Chen and Liu's (2010) analysis shows that bellow the modal size, that is in the pico- to nanophytoplankton size range, growth rate increases with cell size. They argue that the unimodal pattern stems from picoplankton having evolved to have inherently low growth rates, independently of nutrient availability. Here we argue that the unimodal pattern they obtain might be due to an incorrect temperature correction and to an internal inconsistency in their database because a large portion of their picoplankton data contain a correction for photo- acclimation effects, while the rest of their data do not. To carry out their study, Chen and Liu (2010) used two data sets, one from 14 C incorporation and a second from dilution experiments. In both data sets, a unimodal pattern between mass-specific growth rate and cell size emerges. In these two data sets, however, cell size is correlated with nutrient availability, so it could be argued that, rather than a direct effect of cell size, the lower growth rates of smaller

The macroecological relationships among marine phytoplankton total cell density, community size structure and temperature have lacked a theoretical explanation. The tiniest members of this planktonic group comprise cyanobacteria and eukaryotic algae smaller than 2 μm in diameter, collectively known as picophytoplankton. We combine here two ecological rules, the temperature-size relationship with the allometric size-scaling of population abundance to explain a remarkably consistent pattern of increasing picophytoplankton biomass with temperature over the ―0.6 to 22 °C range in a merged dataset obtained in the eastern and western temperate North Atlantic Ocean across a diverse range of environmental conditions. Our results show that temperature alone was able to explain 73% of the variance in the relative contribution of small cells to total phytoplankton biomass regardless of differences in trophic status or inorganic nutrient loading. Our analysis predicts a gradual shift toward smaller primary producers in a warmer ocean. Because the fate of photosynthesized organic carbon largely depends on phytoplankton size, we anticipate future alterations in the functioning of oceanic ecosystems.

Our view of the effects of temperature on bacterial carbon fluxes in the ocean has been confounded by the interplay of resource availability. Using an extensive compilation of cell-specific bacterial respiration (BRi) and production (BPi), we show that both physiological rates respond to changing temperature in a similar manner and follow the predictions of the metabolic theory of ecology. Their apparently different temperature dependence under warm, oligotrophic conditions is due to strong resource limitation of BP, but not of BRi. Thus, and despite previous preconception, bacterial growth efficiency (BGE = BPi/[BPi + BRi]) is not directly regulated by temperature, but by the availability of substrates for growth. We develop simple equations that can be used for the estimation of bacterial community metabolism from temperature, chlorophyll concentration, and bacterial abundance. Since bacteria are the greatest living planktonic biomass, our results challenge current understanding of how warming and shifts in ecosystem trophic state will modify oceanic carbon cycle feedbacks to climate change.

Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 2 (2007): 172-187.

We review current knowledge and understanding of the biology and ecology of Centropages typicus in the European shelf-seas (e.g. North Sea, English Channel and Bay of Biscay). Our study is based on observations at seven coastal time-series stations as well as on the Continuous Plankton Recorder dataset. This paper focuses on the influence of the environmental parameters (e.g. temperature and Chla) on the life cycle and distribution of C. typicus and provides a comparison with its congeneric species C. hamatus and C. chierchiae in the study area. Data on abundance, seasonality and egg production have been used to define the temperature and chlorophyll optima for occurrence and reproduction of Centropages spp. within this region of the European shelf-seas., 3

We review current knowledge and understanding of the biology and ecology of the calanoid copepod Calanus helgolandicus in European waters, as well as provide a collaborative synthesis of data from 18 laboratories and 26 sampling stations in areas distributed from the northern North Sea to the Aegean and Levantine Seas. This network of zooplankton time-series stations has enabled us to collect and synthesise seasonal and multi-annual data on abundance, body size, fecundity, hatching success and vertical distribution of C. helgolandicus. An aim was to enable comparison with its congener Calanus finmarchicus, which has been studied intensively as a key component of European and north east Atlantic marine ecosystems. C. finmarchicus is known to over-winter at depth, whereas the life-cycle of C. helgolandicus is less well understood. Overwintering populations of C. helgolandicus have been observed off the Atlantic coast between 400 and 800 m, while in the Mediterranean there is evidence of significant deep-water populations at depths as great as 4200 m. The biogeographical distribution of C. helgolandicus in European coastal waters covers a wide range of habitats, from open ocean to coastal environments, and its contribution to mesozooplankton biomass ranges from 6% to 93%. Highest abundances were recorded in the Adriatic and off the west coast of Spain. C. helgolandicus is generally found in 9–20 C water, with maximum abundances from 13–17 C. In contrast, C. finmarchicus is found in cooler water between 0 and 15 C, with peak abundances from 0 to 9 C. As water has warmed in the North Atlantic over recent decades, the range of C. helgolandicus and its abundance on the fringes of its expanding range have increased. This review will facilitate development of population models of C. helgolandicus. This will not only help answer remaining questions but will improve our ability to forecast future changes, in response to a warming climate, in the abundance and distribution of this important species. Versión del editor

[Figure][1] CREDIT: LUC VIATOUR/WIKIMEDIA COMMONS Kutschera questions our use of the word “primitive” when referring to jellyfishes as compared with zooplanktivorous fishes. We did not intend to invoke the idea of a “lower rank” in the “ladder-of -life,” an old, yet popular, prejudice ([ 1 ][2]). We limited our use of the word to the context of prey encounter mechanisms. We argued that the jellyfish mechanism—stirring water to increase the chance that prey will collide with their collection surfaces—is less complex than the visual predation by the zooplanktivorous fishes. However, we then showed how the simple mechanism of contact predation is bioenergetically as efficient (i.e., as evolved) as the seemingly more complex visual mechanism. In other words, the main point of our Report could well be used in support of Kutschera's contention. 1. [↵][3] , The Origin of Species (John Murray, London, ed. 6, 1872). [1]: pending:yes [2]: #ref-1 [3]: #xref-ref-1-1 "View reference 1 in text"

Many macroecological theories have been developed to study the diversity on our planet. All these theories require the existence of consistent databases to test their predictions. In this work, we compiled a data set of marine microplankton species abundances at 788 stations with an extensive geographical coverage. Data were collected on different oceanographic cruises between 1992 and 2002. This database consists of abundances (cells/mL) for each species at each station and depth, together with estimates of the biomass and biovolume for each species. One of the key strengths in this database is that species identifications were made by the same taxonomist, which provides greater strength to the collection and ensures that estimates of species diversity are reliable. Environmental information has also been compiled at each station (chlorophyll, temperature, photosynthetically active radiation [PAR], nutrients) in order to have a characterization of the study area and to be used in studies on the environmental and biological controls of marine biodiversity.

The physical and biological factors affecting the abundance and ingestion rates of dif- ferent appendicularian species were investigated from April 1999 to May 2000 at a coastal station in the English Channel and on a transect of 3 stations across the shelf in the central Cantabrian Sea. Individual gut chlorophyll and gut food volume contents were used to determine the ingestion rates on autotrophic prey and on total particulate material. Body size was the variable explaining most of the variability in gut contents. For most species, over 60% of the ingested material came from non- chlorophyll-containing prey. Appendicularian community grazing impact was higher at the oceanic stations during early spring and autumn, with maximum values close to 10% of the total phytoplank- ton biomass removed daily. Oikopleura longicauda and O. fusiformis were the species with the high- est grazing impact. During the study period, appendicularians removed an average of 8% of the pri- mary production (PP) measured at the only station for which we have concurrent measurements. Our results suggest that the bulk of appendicularian populations resides in the surface mixed layer and that their grazing rates increase with increasing PP. However, the percentage of the PP removed by the appendicularian community decreases with increasing productivity, indicating that their grazing impact is relatively more important under oligotrophic conditions. Appendicularians could account for close to 40% of the total mesozooplankton grazing.

Through an extensive review of reports on appendicularian ecology, we have developed a set of equations on the feeding, metabolic and growth rates of temperate epipelagic appendicularian species. We have used these equations to study the conditions in which these species are likely to ex- perience food-limited growth. As Oikopleura dioica is the most-studied appendicularian species, we have used equations developed for this one species to construct a metabolic budgetary model. Our re- sults suggest that large O. dioica are less likely to experience food-limited growth than other meso- zooplankton, and that growth during early development could be more limited by food concentration in the environment. The degree of food limitation strongly depends on the assimilation efficiency of non-autotrophic material, which comprises a great proportion of the appendicularian diet. However, examination of direct measurements of growth rate over a wide range of food concentrations showed no significant relationship between food concentration and weight-specific growth rates. Temperature alone explained more than 60% of the variance in appendicularian weight-specific growth rates. Since there were no clear differences in the growth rates of different appendicularian species, we have com- bined the available data to develop a temperature-dependent equation to predict their weight-specific growth rates. We have also modified the growth rate equation to take into consideration the expendi- ture in house secretion. Combination of this growth rate equation with biomass estimations allows us to evaluate their contribution to secondary production. In contrast with the traditional view of appen- dicularians as important members of oligotrophic ecosystems, our results show that in the study area their contribution to secondary production was higher during more productive conditions.