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This paper presents the results on simultaneous high time resolution measurements of biogenic aerosol (methane sulfonic acid-MSA, non-sea salt sulfate nssSO42-) with its gaseous precursor dimethylsulfide (DMS) performed at the Italian coastal base Mario Zucchelli Station (MZS) in Terra Nova Bay (MZS) during two summer campaigns (2018–2019 and 2019–2020). The study provides information on marine biological activity in the nearby polynya in the Ross Sea and on the influence of biogenic and atmospheric processes on biogenic aerosol formation. Data on atmospheric DMS concentration are scarce especially in Antarctica. The DMS-maximum at MZS occurs in December, one month earlier than at other Antarctic stations. The maximum of DMS concentration is connected with the phytoplanktonic senescent phase following the bloom of Phaeocystis antarctica that occurs in the polynya when sea ice opens up. The second plankton bloom occurs in January and, despite the high Dimethylsulfopropionate (DMSP) concentration in sea water, atmospheric DMS remains low probably due to its fast biological turnover in sea water in this period. The intensity and timing of the DMS evolution during the two years suggests that only the portion of the polynya close to the sampling site produces a discernible effect on the measured DMS. The closeness to the DMS source area, and the occurrence of air masses containing DMS and freshly formed oxidation products allow to study the kinetic of biogenic aerosol formation and the reliable derivation of the branch ratio between MSA and nssSO42- from DMS oxidation that is estimated to be 0.84 ± 0.06. Conversely, for aged airmasses with low DMS content, an enrichment of nssSO42- with respect to MSA, due to the presence of background concentration of nssSO42- from volcanic origin (Erebus) or from long range transport, takes place. Therefore, the aged air mass presents an MSA / nssSO42- ratio lower than in newly formed biogenic aerosol. By considering the sum of MSA and biogenic nssSO42-, we estimate that the mean contribution of biogenic particulate matter to PM10 is 17 %, with a maximum of 56 %. The high contribution of biogenic aerosol to the total PM10 mass in summer in this area highlights the dominant role of the polynya on biogenic aerosol formation. Finally, due to the regional and year-to year variability of DMS and related biogenic aerosol formation, we stress the need of long-term measurements of atmospheric DMS and biogenic aerosol along the Antarctic coast and in the Southern Ocean.

Ten years of data of biogenic aerosol (methane sulfonic acid, MSA, and non-sea salt sulfate, nssSO42−) collected at Concordia Station in the East Antarctic plateau (75° 06′ S, 123° 20′ E) are interpreted as a function of the Southern Annular Mode (SAM), Chlorophyll-a concentration (Chl-a; a proxy for phytoplankton biomass), sea ice extent and area. It is possible to draw three different scenarios that link these parameters in early, middle, and late summer. In early summer, the biogenic aerosol is significantly correlated to sea ice retreats through the phytoplankton biomass increases. Chl-a shows a significant correlation with nssSO42− in the finest fraction (< 1 μm). In contrast, only Chl-a in West Pacific and Indian Ocean sectors correlates with MSA in the coarse fraction. The transport routes towards the inner Antarctic plateau and aerosol formation processes could explain the different correlation patterns of the two compounds both resulting from the DMS oxidation. In mid-summer, Chl-a concentrations are at the maximum and are not related to sea ice melting. Due to the complexity of transport processes of air masses towards the Antarctic plateau, the MSA concentrations are low and not related to Chl-a concentration. In late summer, MSA and nssSO42− present the highest concentrations in their submicrometric aerosol fraction, and both are significantly correlated with Chl-a but not with the sea ice. In early and mid-summer, the enhanced efficiency of transport processes from all the surrounding oceanic sectors with air masses traveling at low elevation can explain the highest concentrations of nssSO42− and especially MSA. Finally, considering the entire time series, MSA shows significant year-to-year variability. This variability is significantly correlated with SAM but with a different time lag in early (0-month lag) and late summer (4-months lag). This correlation likely occurs through the effect of the SAM on phytoplankton blooms.

Summary Ports are open systems with direct connection to the sea, therefore any potential impact on port waters may have implications for the health of adjacent marine ecosystems. European WFD addressed ports in the category of Heavily Modified Water Bodies (HMWBs) and promoted implementation of protocols to monitor and improve their ecological status. TRIX index, which incorporates the main variables involved in the trophism of marine ecosystems (Nitrogen, Phosphorus, Chlorophyll a, Dissolved Oxygen), is widely utilized in European coastal areas to evaluate trophic status. The relationships between the variables involved in TRIX computation, particularly Chlorophyll a concentration, and water spectral reflectance provides an alternative method to evaluate the quality and ecological status of the port water. Hyperspectral (380–710 nm) water reflectance data were recorded by a portable radiometric system in five ports from the Western and Eastern Mediterranean Basin. The spectral distance between samples was measured by two metrics using both the original and reduced spectra and was implemented within a hierarchical clustering algorithm. The four spectral classes that emerged from this operation were statistically analysed versus standard water quality descriptors and phytoplankton community features to evaluate the ecological significance of the information obtained. The results indicated a substantial coherence of different indicators with more than 60% of the total TRIX variability is accounted for by the proposed classification of reflectance spectra. This classification is therefore proposed as a promising Rapid Assessment Technique of ports water ecological quality, which can serve as an effective monitoring tool for sustainable management of ports.

Recent research has demonstrated that the TRophic IndeX (TRIX) is informative on the ecological quality of Mediterranean port waters and can be estimated by the processing of multispectral observations collected in situ. The current study investigates the alternative use of multispectral data acquired by medium-high spatial resolution optical satellite sensors, i.e. the Landsat-8 (L8) Operational Land Imager (OLI) and the Sentinel-2 (S2) MultiSpectral Instrument (MSI). The study analyzes the impact of the main factors influencing TRIX estimation using datasets collected in several Mediterranean ports and particularly in those of Civitavecchia and Viareggio (Central Italy). The experimental results indicate that the spectral configurations of OLI and MSI have a marginal impact on TRIX estimation, while major effects are caused by the different spatial and temporal features of the two sensors. The enhanced spatial properties of MSI are important particularly in the smaller port of Viareggio; the higher acquisition frequency of this sensor brings significant advantages for operational monitoring applications. Overall, the accuracy of TRIX estimation based on in situ spectral measurements is reduced significantly by the use of OLI images and only marginally by that of MSI images. Both image types represent an advancement for the operational monitoring of port waters.

Marine phytoplankton production (PP) represents an influential force on the carbon cycle and the climatic processes on a global scale, being responsible for up to 40% of the biological fixation of atmospheric CO2. Understanding and predicting the effects of climate change on marine phytoplankton is crucial within the analysis of climate change scenarios as it affects the ecological responses of the higher trophic levels. In this context, the development of predictive models for the estimation of PP provides useful scientific responses to address the issues of sustainability in a climatically changing world. The need to estimate PP more accurately allows to face the impacts of global change on highly vulnerable areas such as such as regional seas and polar regions. In this work we present the Phyto-VFP (Variable Fluorescence Phytoplankton Production), a new bio-optical model which enables to compute PP by integrating the effects of the photo-acclimation processes of phytoplankton with the dynamic conditions of the water column. To parametrise the photo-physiological behavour of phytoplankton cells a series of laboratory experiments based on in vivo variable fluorescence measures were conducted on culture species selected according to the ecological features of the investigated areas. The performance of Phyto-VFP was evaluated with concurrent estimates of radiocarbon (14C) uptakes and the results obtained with the use of the Morel bio-optical model, under different dynamic and optical conditions, during two oceanographic cruises in the Mediterranean Sea. Here we present the results of the model validation as well as the application of Phyto-VFP model to different highly vulnerable regions to climate change.

The Biogenic Aerosol and Primary Production in the Ross Sea - BioAPRoS project, funded by funded by the Ministry for the Education, University and Scientific Research (MIUR) through the National Antarctic Research Programme (PNRA) aims to improve the understanding of the ocean-atmosphere interactions with particular attention to the interconnections between oceanic primary production and atmospheric gaseous and particulate compounds. These processes have a strong climatic relevance due to the aerosol interaction with solar radiation, its possible interaction with cloud formation and properties, in a region where other aerosol sources are very limited. To achieve the objectives of the project, measurements and sampling in the atmosphere (dimethylsulfide, in the gas phase, and methanesulfonic acid, sugars, amino acids and methoxyphenols in the aerosols) and in sea water (nutrients, chlorophyll, phytoplankton composition and physiological state, DMSP as a precursor of atmospheric DMS) were carried out simultaneously for the first time at the Italian "Mario Zucchelli" Station (MZS; 74.7°S, 164.1°E). We report here the data obtained in two Antarctic field campaigns carried out in summers of 2018-19 and 2019-20. The DMS atmospheric concentration was measured directly in situ by Gas Chromatography. It showed concentrations up to 921 pptv (the highest value obtained in both campaigns); the timing of maximum concentration was strongly related to the timing of sea ice melting in the surrounding oceanic areas. Within the project, the low-cost ACHAB (Antartic low-Cost Hydro Arduino Bio-optic profiler) probe has been developed for the acquisition of physical and bio-optical data along the water column, during the 2019-20 campaign. Furthermore, the Phyto-VFP (Phytoplankton Variable Fluorescence Production) bio-optical model was refined to be applied to the Southern Ocean for the estimation of primary production in Terranova Bay and Ross Sea at micro and mesoscale resolutions, respectively. Phyto-VFP was specifically set-up using as input chl a satellite data (merged products based on MODIS-A, MERIS, SeaWIFS, VIIRS-N for low resolution images and Sentinel-2 for high resolution ones) as well as the photosynthetic parameters obtained from a series of laboratory experiments conducted on polar species, enabling to take into account the effect of a nutrient limitation on their photosynthetic performance. The evolution of concentration of the atmospheric compounds arising from phytoplankton activity was investigated with respect to oceanic parameters (chlorophyll and primary productivity, in turn related to the phytoplankton taxonomic composition and physiological state), to the variations of solar and photosynthetically active radiation, and to the dynamics of sea ice in the Ross Sea. Understanding and quantifying the correlation between atmospheric compounds and oceanic primary productivity (affecting the oceanic and atmospheric CO2 budget) has a relevant importance in studies on global change because this interaction is influenced by, and in its turn influences, climatic variations.

Heterosigma akashiwo shows remarkable ultrastructural changes during the recovery from a late stationary phase (“aged” culture) induced by nutrient depletion. H. akashiwo cells showed different morphological types in “aged” cultures, with an increase in irregular cells and cell fragments. The irregular cells mostly corresponded to an amoeboid shape of the cell. Many of these cells showed chloroplasts with a homogeneous matrix of medium electron density lacking most thylakoids and condensed nucleus, probably as a result of cyst/resting cells germination. In other cells, we observed nuclear blebbing without chromatin condensation and changes in mitochondrion ultrastructure. Some vegetative cells in active phase (“young” culture) were connected to each other, apparently phagocytizing cytoplasmic fragments and intact chloroplasts in the medium. An explanation for the phenomenon may reside in the need of acquiring organic material after nutrient reduction for a faster recovery. On the basis of our obse...

This study examines the relationships linking methanesulfonic acid (MSA, arising from the atmospheric oxidation of the biogenic dimethylsulfide, DMS) in atmospheric aerosol, satellite-derived chlorophyll a (Chl-a), and oceanic primary production (PP), also as a function of sea ice melting (SIM) and extension of the ice free area in the marginal ice zone (IF-MIZ) in the Arctic. MSA was determined in PM10 samples collected over the period 2010-2012 at two Arctic sites, Ny Ålesund (78.9°N, 11.9°E), Svalbard islands, and Thule Air Base (76.5°N, 68.8°W), Greenland. PP is calculated by means of a bio-optical, physiologically based, semi-analytical model in the potential source areas located in the surrounding oceanic regions (Barents and Greenland Seas for Ny Ålesund, and Baffin Bay for Thule). Chl-a peaks in May in the Barents sea and in the Baffin Bay, and has maxima in June in the Greenland sea; PP follows the same seasonal pattern of Chl-a, although the differences in absolute values of PP in the three seas during the blooms are less marked than for Chl-a. MSA shows a better correlation with PP than with Chl-a, besides, the source intensity (expressed by PP) is able to explain more than 30% of the MSA variability at the two sites; the other factors explaining the MSA variability are taxonomic differences in the phytoplanktonic assemblages, and transport processes from the DMS source areas to the sampling sites. The taxonomic differences are also evident from the slopes of the correlation plots between MSA and PP: similar slopes (in the range 34.2-36.2 ng m-3of MSA/(gC m-2 d-1)) are found for the correlation between MSA at Ny Ålesund and PP in Barents Sea, and between MSA at Thule and PP in the Baffin Bay; conversely, the slope of the correlation between MSA at Ny Ålesund and PP in the Greenland Sea in summer is smaller (16.7 ng m-3of MSA/(gC m-2 d-1)). This is due to the fact that DMS emission from the Barents Sea and Baffin Bay is mainly related to the MIZ diatoms, which are prolific DMS producers, whereas in the Greenland Sea the DMS peak is related to an offshore pelagic bloom where low-DMS producer species are present. The sea ice dynamic plays a key role in determining MSA concentration in the Arctic, and a good correlation between MSA and SIM (slope = 39 ng m-3 of MSA/106 km2 SIM) and between MSA and IF-MIZ (slope = 56 ng m-3 of MSA/106 km2 IF-MIZ) is found for the cases attributable to bloomings of diatoms in the MIZ. Such relationships are calculated by combining the data sets from the two sites and suggest that PP is related to sea ice melting and to the extension of marginal sea ice areas, and that these factors are the main drivers for MSA concentrations at the considered Arctic sites. © 2016 The Authors.

Marine primary production (PP) is a key factor in the regulation of the global carbon cycle, with important potential feedback on climate. Seventy percent of marine PP is generated by phytoplankton photosynthesis. However, the phytoplankton productivity rate is dependent on the photo-physiological state of phytoplankton cells, as well as other environmental conditions. To consider these variables appropriately, refine the current estimates of PP, and reduce the laboursome and lengthy methodologies of radiocarbon estimates, we have created “Phyto-VFP” (Variable Fluorescence Phytoplankton Production), a new bio-optical model classified as a Wavelength and Depth-resolved (WDR) model. The model integrates the effect of the photo-acclimation processes on the “active” fraction of the phytoplankton population with the dynamic of the water column, parametrised through a series of laboratory experiments based on in vivo variable fluorescence measures on the marine diatom Skeletonema costatum (Greville) Cleve. The performance of Phyto-VFP was compared with concurrent estimates of radiocarbon (14C) uptakes, under different dynamic and optical conditions, during two oceanographic cruises (SAMCA3 and SAMCA4) in the Mediterranean Sea. The low Root Mean Square Differences (RMSDs) show that Phyto-VFP performs well when estimating phytoplankton PP. When compared to other bio-optical models, Phyto-VFP estimates of PP in coastal waters were closer to radiocarbon measurements than other models could predict [e.g., the Morel model (MM)]. The application of Phyto-VFP to the SAMCA dataset and its comparison to MM allowed the assessment of model performance under three different physical and biological conditions, in which it was possible to analyse how photo-physiological responses of phytoplankton influence PP.

Previous work showed in tomato plants harbouring the Agrobacterium rhizogenes rolB gene overexpression of genes involved in chloroplast function and stress response, significant increase in non-photochemical quenching and chlorophyll a and b content, and reduced chlorophyll a/b ratio. The latter condition being typical of plant shade where far-red is dominant, suggested a role for rolB in improving photosynthesis in such condition. To gain a better insight into these results, the photosynthetic performance of transgenic and control plants was compared by means of variable fluorescence kinetics with a WATER-PAM chlorophyll fluorometer, after 6 days-exposure to white light and to a far-red-enriched light source. Photosynthetic parameters analysed were quantum yield of photosystem II photochemistry Y(II); qL, corresponding to the fraction of open PSII reaction centers in a "lake" model of photosystem II; non-photochemical quenching and Y(NO), describing, respectively, regulated and non-regulated pathways for dissipation of excess energy. Chlorophyll a and b content was also analysed by HPLC. Finally, real-time PCR was performed to quantify the expression level of some of the chloroplast-related genes already shown to be overexpressed in transgenic plants. Quantum yield of photosystem II photochemistry decreased with increasing light intensity, showing no significant differences in both plant genotypes and light regimen. qL, on the other hand, was significantly higher at low PAR intensities, in particular in FR-treated transgenic plants. Fate of remaining light energy, channelled into regulated or non-regulated dissipation pathways, was different in transgenic and control plants, indicating a higher capability for protection from photodamage in rolB plants, particularly after exposure to far-red-enriched light. Chlorophyll a/b ratio was also decreased in transgenic plants under far-red-enriched light with respect to white light. Finally, qPCR showed that the expression of genes encoding small heat shock protein, chlorophyll a/b binding protein and carbonic anhydrase was significantly induced by far-red-enriched condition. Taken together, these data suggest the involvement of rolB in photosynthesis modulation under far-red-rich light in tomato.

Three algorithms based on MODIS imagery were evaluated for the estimation of Chlorophyll-a concentration ([CHL]) in the Western Mediterranean Sea. The first algorithm (OC3M) is usually applied at global scale, while the second (MedOC3), has been used in the Mediterranean basin. The third algorithm (SAM_LT), specifically developed for the Ligurian and North Tyrrhenian Seas, is here described and applied, in its updated version. The three algorithms were assessed through comparison with 240 sea [CHL] samples collected during the 2002-2011 decade. The results obtained show that OC3M is the most accurate algorithm when used for the entire Western Mediterranean, but is outperformed by SAM_LT in the area where this was originally developed. The impact of different MODIS quality flags on the three algorithms has been finally evaluated, providing guidelines for their operational application in the study area.

We investigated the composition of diatom communities in annual fast ice and their variations over time during the 1999 austral spring in Terra Nova Bay (Ross Sea, Antarctica). Diatoms varied along the ice core in both cell abundance and species composition, with a minimum in the lower layer and a peak in the platelet ice. Planktonic species constituted in total about 98% of the diatom assemblage in the surface layers of the ice core down to the thickness of 220 cm. In the bottom ice and the underlying platelet-ice layer, the contribution of planktonic diatoms was lower (60% and 65%, respectively) at the beginning of the sampling period, and then decreased further to reach 30% in the bottom ice, where a remarkable biomass increase over time was caused by in situ growth and accumulation of benthic species. By contrast in the platelet-ice layer only small changes were recorded in the composition of the diatom assemblage, which was mainly constituted by the bloom of Fragilariopsis nana. The benthic species are generally not found in the water column, while species in the platelet-ice layer presumably constitute the seed for the initial plankton bloom during the ice-free periods in Terra Nova Bay.

According to recommendations of the international community of phytoplankton functional type algorithm developers, a set of experiments on marine algal cultures was conducted to (1) investigate uncertainties and limits in phytoplankton group discrimination from hyperspectral light absorption properties of assemblages with mixed taxonomic composition, and (2) evaluate the extent to which modifications of the absorption spectral features due to variable light conditions affect the optical discrimination of phytoplankton. Results showed that spectral absorption signatures of multiple species can be extracted from mixed assemblages, even at low relative contributions. Errors in retrieved pigment abundances are, however, influenced by the co-occurrence of species with similar spectral features. Plasticity of absorption spectra due to changes in light conditions weakly affects interspecific differences, with errors

In remote marine areas, biogenic productivity and atmospheric particulate are coupled through dimethylsulfide (DMS) emission by phytoplankton. Once in the atmosphere, the gaseous DMS is oxidized to produce H2SO4 and methanesulfonic acid (MSA), both species can affect the formation of cloud condensation nuclei. This study analyses eight years of biogenic aerosol evolution and variability at two Arctic sites: Thule (76.5&deg, N, 68.8&deg, W) and Ny &Aring, lesund (78.9&deg, N, 11.9&deg, E). Sea ice plays a key role in determining the MSA concentration in polar regions. At the beginning of the melting season, in April, up to June, the biogenic aerosol concentration appears inversely correlated with sea ice extent and area, and positively correlated with the extent of the ice-free area in the marginal ice zone (IF-MIZ). The upper ocean stratification induced by sea ice melting might have a role in these correlations, since the springtime formation of this surface layer regulates the accumulation of phytoplankton and nutrients, allowing the DMS to escape from the sea to the atmosphere. The multiyear analysis reveals a progressive decrease in MSA concentration in May at Thule and an increase in July August at Ny &Aring, lesund. Therefore, while the MSA seasonal evolution is mainly related with the sea ice retreat in April, May, and June, the IF-MIZ extent appears as the main factor affecting the longer-term behavior of MSA.

Insertion of Agrobacterium rhizogenes rolB gene into plant genome affects plant development, hormone balance and defence. However, beside the current research, the overall transcriptional response and gene expression of rolB as a modulator in plant is unknown. Transformed rolB tomato plant (Solanum lycopersicum L.) cultivar Tondino has been used to investigate the differential expression profile. Tomato is a well-known model organism both at the genetic and molecular level, and one of the most important commercial food crops in the world.\ud \ud Through the construction and characterization of a cDNA subtracted library, we have investigated the differential gene expression between transgenic clones of rolB and control tomato and have evaluated genes specifically transcribed in transgenic rolB plants. Among the selected genes, five genes encoding for chlorophyll a/b binding protein, carbonic anhydrase, cytochrome b6/f complex Fe-S subunit, potassium efflux antiporter 3, and chloroplast small heat-shock protein, all involved in chloroplast function, were identified. Measurement of photosynthesis efficiency by the level of three different photosynthetic parameters (Fv/Fm, rETR, NPQ) showed rolB significant increase in non-photochemical quenching and a, b chlorophyll content. Our results point to highlight the role of rolB on plant fitness by improving photosynthesis.

The annual cycle of pelagic primary production (PP) from ocean colour is analysed in a transition area between Ligurian and Tyrrhenian waters, where a general oligo-mesotrophic status is seasonally modified by anthropic impact near the Tuscany coast. Based on the common ecological features six different zones were delimited. Remote sensing data from different satellites (Meteosat, Aqua) were used as input in a primary production model. The daily production of the entire area was computed on pixel by pixel basis (4x4 km) using a modified GIS software. Overwhelming importance of oceanic bloom and high spatial variance of PP (90 ±54 gC m -2 y r -1 ) show that remote sensed data can allow a better

We investigated the physical conditions of the Spring pack ice environment at Terra Nova Bay to understand their influence on the structure and physiology of sympagic microalgae. Bio-optical methods were used to study the availability and spectral quality of solar radiation, both inside and underneath the ice cover. Pack ice thickness was around 2.5 m, with a temperature between −2 and −7°C. On average, only 1.4% of surface PAR penetrated to the bottom ice and less than 0.6% below platelet ice level. Surface UV-B radiation under the bottom ice was 0.2–0.4%. Biomass concentrations up to 2400 mg Chl a m−3, dominated by two species of diatoms (Entomoneis kjellmannii and Nitschia cf. stellata), showed marked spatial and temporal patterns. Maximum values were in the platelet ice during the first half of November, and in the bottom ice two weeks later. Strong shade adaptation characteristics emerged clearly and explained the relevant abundance of microalgae within the sea ice, with specific absorption coefficients (a*) as low as 0.005 m2 (mg Chl a)−1 and the photo-acclimation index (Ek) in the range of in situ irradiance. The biomass specific production values were low, around 0.12–0.13 mg C mg Chl a−1 h−1. The hypothesis suggesting bottom ice colonization by platelet ice microalgae is supported here.

The sand-bubbler crab, Dotilla fenestrata (Hilgendorf, 1869), has evolved a surface deposit feeding habit and exhibits stereotyped and flexible behaviours that allow this species to respond to both the predictable and unpredictable elements of intertidal environments. In a mangrove swamp of Kenya, field studies revealed that, at the emergence from burrows with the receding tide, a portion of this crab's population abandoned the residential zone and wandered in droves. The rest fed and engaged in other surface activities exclusively around their burrow (either a feeding-trench burrow or an igloo). Laboratory analyses were carried out to assess the functional significance of the choice of D. fenestrata between these opposing spatial strategies. If crabs are small individuals or ovigerous females, the only option is to engage in burrow-orientated activities. For the other population categories, the choice will depend on the richness in edible organic content of the substrate in the residential area and on the balance between the risk of being preyed upon and the benefits of foraging over richer substrata.

Studies on the chemical and biological properties of annual pack ice at a coastal station in Terra Nova Bay (74°41.72′S, 164°11.63′E) were carried out during austral spring at 3-day intervals from 5 November to 1 December 1997. Temporal changes of nutrient concentrations, algal biomasses, taxonomic composition, photosynthetic pigment spectra and P–E relationships were studied. Quantity, composition and degradation rates of organic matter in the intact sea ice were also investigated. In addition, microcosm experiments were carried out to evaluate photosynthetic and photo-acclimation processes of the sympagic flora in relation to different light regimes. High concentrations of ammonia were measured in four ice-cores (weighted mean values of the cores ranged from 4.3 ± 1.9 μM to 7.2 ± 3.4 μM), whereas nitrate and phosphate displayed high concentrations (up to 35.9 μM and 7.6 μM, respectively) only in the bottom layer (135–145 cm depth). Particulate carbohydrate and protein concentrations in the intact sea ice ranged from 0.5 to 2.3 mg l−1 and 0.2 to 2.0 mg l−1, respectively, displaying a notable accumulation of organic matter in the bottom colored layer, where bacterial enzymatic activities also reached the highest values. Aminopeptidase activity was extremely high (up to 19.7 μM l−1 h−1 ± 0.05 in the bottom layer), suggesting a rapid turnover rate of nitrogen–enriched organic compounds (e.g. proteins). By contrast, bacterial secondary production was low, suggesting that only a very small fraction of mobilized organic matter was converted into bacterial biomass (

Planktonic communities hold a relevant role in the framework of the EU Marine Strategy Framework Directive. This paper summarizes the current state of art in the use of plankton as indicator for the assessment of the environmental status of marine environments, contributing to the discussion of new perspectives in its application for the implementation of the Directive.

To understand the relationship between the density of an introduced crayfish species (P. clarkii) and the abundance and composition of pelagic and surface microalgae (hereafter referred to as phytoplankton and phytoneuston, respectively) we ran an in situ experiment in a Mediterranean wetland. In May 2004, we delimited six 10 x 7m areas along a channel in the "Padule di Fucecchio" (Italy). Each area was randomly chosen to host crayfish populations at either low (1 crayfish/m 2 ) or high densities (14 crayfish/m 2 ). Phytoplankton and phytoneuston samplings were conducted in August and in September 2004, corresponding to the periods in which the highest and the lowest numbers of free-moving crayfish were found, respectively, during the lentic phase of the water regime. Results showed that (1) phytoneuston biomass, composed of cyanobacteria and, to a lesser extent, of euglenoids, was strongly affected by the presence of dense populations of P. clarkii in August; (2) crayfish seemed to modify the composition of microalgal communities; (3) these effects were not accompanied by significant differences between experimental areas in water chemistry and temperature; (4) physico-chemical measures highly varied with sampling periods along with a change in phytoplankton and phytoneuston abundance; and (5) high crayfish densities did not to exert any measurable effect on phytoplankton abundance. The decrease of phytoneuston may be the result of top-down effects of crayfish removing invertebrate grazers or, most likely, of direct grazing of crayfish. Indeed, crayfish were often observed climbing on macrophytes and feeding on the floating film.

During the fifteenth Italian Antarctic expedition, in the framework of the Pack Ice Ecosystem Dynamics programme, we investigated structure and functioning of the sympagic communities in the annual pack ice at Terra Nova Bay (74 °41.72' S, 164 °11.63' E). From November 1 to November 30 1999, we collected intact sea ice cores and platelet ice samples at an interval of 3 days. Ice samples were analysed for inorganic nutrients concentrations, algal biomass and productivity, pigment spectra, extracellular enzymatic activities and bacterial carbon production, micro-algal and metazoan community structure. Autotrophic biomass in the bottom ice increased more than two orders of magnitude from the beginning to the end of November 1999 (i.e. from c. 1-400 mg chlorophyll a m-3). In the same temporal interval, inorganic nutrients concentrations as well as dissolved organic matter sharply increased. Pigment spectra and microscopic analyses revealed that bottom ice communities were different from those of the platelet ice. The bottom-ice sympagic flora was represented almost exclusively by cryobenthic species, whereas platelet ice was characterised by the presence of both cryopelagic and cryobenthic species. Metazoan community in the bottom sea ice was largely dominated by copepods. In particular, the calanoiod Stephos longipes and the harpacticoid Harpacticus furcifer accounted for more than 90% of the sympagic fauna. In the bottom sea ice concentrations of phaeophorbides and other degraded phytopigments were low indicating that most of the sympagic flora was active. These findings suggest that grazing pressure might be only a minor factor controlling or regulating inorganic nutrient concentrations. Conversely, potential degradation rates of organic carbon mediated by extracellular enzymatic activity were very high and largely exceeded organic matter production by photosynthesis.

The cryptophyte Cryptomonas sp. was cultured in nitrogen- and light-limited conditions to investigate relationships between inherent optical properties (absorption and fluorescence), pig- ment contents, N/C ratio and somatic growth rate. The 2 limitations induced large variations in phy- coerythrin (PE) and chlorophyll a (chl a) contents, with a significantly higher variation in PE than chl a under nitrogen stress. Under N limitation, there is a significant relationship between the PE/chl a ratio and the growth rate. In the case of light perturbation, the ratio PE/chl a was slightly modified during photoacclimation. Emission and excitation spectra of PE and chl a showed that the coupling efficiency between these pigments is less affected by nitrogen than by light changes. It is suggested that transfer of energy between PE and chl a is regulated differently when growth is limited by light or nitrogen. Under nitrogen deprivation, the pool of PE is preferentially degraded to reduce the energy transmitted to chl a, and to support the N demand. Under a light change, the energy har- vested by PE and transferred to chl a is regulated by the coupling efficiency between the 2 pigments, and secondarily by synthesis or degradation of the PE quota. For each limitation, different relation- ships are shown between optical characteristics based on fluorescence ratios and growth rate.

The temporal evolution and spatial distribution of phytoplankton assemblages were investigated, in coastal and open waters of the western Ross Sea, during three austral summers. Terra Nova Bay shows a first massive bloom (up to 107 cell |-1) of Fragilariopsis cf. curta between December and January in the receding ice-edge zone and another increase in February also with the contribution of different species. Phytoplankton shows a patchy distribution, with areas of bloom dominated by diatoms (Fragilariopsis, Nitzschia) and Phaeocystis sp., and less rich zones, mainly dominated by dinoflagellates and other flagellates. The different phytoplankton assemblages show characteristics corresponding to different stages that alternate during the summer season in the different areas, but which are related to the temporal development of environmental conditions after the melting of the ice.

Three years of investigation in the western Ross Sea reveal that despite the general abundance of phytoplankton biomass, the ratios between biomass and nutrient availability are low due to high nutrient concentrations. The N/P ratio is practically identical to that of Redfield; however, during blooms the ratio can be severely altered due to very low phosphate concentrations. Phytoplankton biomass during summer shows a bimodal cyclic pattern with two blooms in early and late summer. The spatial and temporal distribution of these blooms follows the latitudinal distribution of daily irradiance, which determines the advance of sea-ice melting from south to north forming an upper mixed layer rich in nutrients. This mixed layer is well illuminated and warmer than the deeper layer, thereby favouring the development of the early bloom. Afterwards, in the mixed water column, biomass decreases and reaches the summer minimum. A new stabilization of the water column is followed by a second bloom, less extensive than the first. In all 3 years, similar cycles have been recorded, giving corroborative evidence for the existence of a second bloom.

The primary production characteristics of phytoplankton coenoses were investigated during three summer periods (1987–88, 1989–90 and 1994–95), in Terra Nova Bay. The basic photosynthetic parameters of the P vs. E curves were analyzed, as well as the in vivo spectral absorption and fluorescence properties, which allow the maximum quantum yield for carbon uptake and for PSII fluorescence to be appreciated and compared, in order to evaluate the physiological conditions and the photoacclimation performance of this phytoplankton. Low light acclimation features (elevated values of αB, PB max and φm, with Ek between 11 and 102µE m-2 s-1) are clearly present in these natural populations. High daily productions of the water column have been estimated through a biooptical model (0.1–3.1 g C m-2 day-1), and a seasonal integrated value of 125g C m-2 has been appreciated at Terra Nova Bay, for the period from December through February.

Seawaters detailed spectroscopic analyses were carried out in the ENEA mobile fluorosensor laboratory participating to the oceanographic campaign within the XIII Italian Antarctic Mission (R/V Italica, Nov. '97 - Jan '98). A complete set of in-vivo emission and excitation spectra was measured during cruises in the Ross Sea and along Southern Ocean transects up- to New Zealand. Measurements allowed for distinguishing among natural seawater components (tyrosine and tryptophan protein- like substances) and for identifying phytoplankton pigments (Chl-a, b, c, carotenoids, phycoerithrin, and phaeopigments). Georeferenced data have been collected at fixed time intervals and released on thematic maps.

Upper ocean dynamics is characterized by a strong variability, at different scales, both in direction and structure of the flow. Mesoscale variability, which is ubiquitous in the world ocean, is often the dominant component in the variance spectrum of velocity with relevant implications on water mass mixing and transformation and on the carbon transfer in the marine food web. Mesoscale activity is manifested through the formation of instabilities, meanders and eddies. Eddies generate either a doming of isopycnals (cyclones) or a central depression (anticyclones). This in turn modifies, among the others, nutrient and organism distributions in the photic zone eventually enhancing or depressing photosynthetic activity and other connected biological responses. The mechanism is similar to what has been thoroughly studied for the warm and cold core rings but at different spatial and temporal scales. The enhancement of phytoplankton growth and the modification of photosynthetic parameters has been shown to occur in situ by means of a modulated fluorescence probe. More recently, an attempt to estimate the magnitude of this specific forcing on nutrient fluxes and primary production has also been conducted at different scales by modeling exercises, though with contrasting estimates the relative importance concerns. Because phytoplankton growth takes place when light, nutrients and cells are found at the same place, the increase in primary production favored by mesoscale eddies cannot be easily predicted. The incident light, the seasonality, the life-time of the structure, its intensity etc. can all influence the final yield. In addition, it has still to be determined which component of the community reacts faster and takes advantage of the new nutrients and how efficiently the new carbon is channeled in the food web. For what remote sensing is concerned, the detectability form the space of such structures is certainly dependent on the depth at which the upward distortion of isopycnals takes places. It can be supposed that a change in bio-optical signature of the whole structure could occur because of the 3-D dynamics of the eddy. If this holds true, then color remote sensing coupled with sea level topography and sea surface temperature should be a powerful tool to track such transient structures. The ALT-SYMPLEX program has been designed to better understand the relationship between short living eddies and carbon transfer in the food web. This is based on several experiments aimed to integrate remote sensing data (ocean color and surface topography) and in situ data in order to evaluate the relationship between surface and sub-surface physical dynamics and its relations on chemical and biological aspects in presence of mesoscale features.

Photoacclimation in prokaryotic phytoplankton species commonly found in the ocean is not as well documented as for eukaryotes. Variations in the pigment cellular content and composition were observed in Synechococcus1 and Prochlorococcus2 in response to changes in light conditions. These variations lead to changes in the magnitude and spectral shape of light absorption capabilities3•4• Partensky et al. 2 reported a significantly higher photosynthetic capacity in Prochlorococcus grown under high light. Besides these signs of the capability of prokaryotic phytoplankton to photoacclimate, it is known that they possess no flagellae and do not operate a xanthophyll cycle5. So, keeping in mind the specific character of prokaryotes, it could be thought that the number of photoacclimation strategies is smaller compared with eukaryotes. Nevertheless, prokaryotic phytoplankton dominate large parts of the ocean, especially oligotrophic systems where it grows at high rates6. In the present study, we aim at understanding why prokaryotic phytoplankton have such an ecological success in the ocean. Specifically, our objectives are ( 1) to clearly identify the photoacclimation strategies deployed by these organisms, significant in terms or carbon fixation, and (2) to quantify the timescales on which they are deployed. Finally, we discuss how these strategies are effective in the ocean. To reach our objectives, we studied the photoacclimation kinetics of Prochlorococcus sp. We chose this species firstly because it often dominates the prokaryotic phytoplankton communities of oligotrophic systems7 . Secondly, there is a need for a better documentation on this recently discovered species, which was shown to account for up to 50 % of net primary production6 in oligotrophic systems.

International audience; Measurements of in vivo spectral absorption, a(lambda), and fluorescence excitation, F-m(lambda), of phytoplankton were performed in two contrasted situations (oligotrophic and mesotrophic) of the tropical North Atlantic, during October 1991. The vertical and inter-site variability of these properties, and the relative fluorescence yield (F-m/a)(lambda) were investigated, in relation to light conditions and to the pigment and taxonomic composition of the natural populations. The large vertical variations in the chi-specific absorption coefficients (a*) at the oligotrophic site appear to be related to both the decrease of the non-photosynthetic pigment concentration, and the increase of the package effect with depth. At the mesotrophic site, lower a* coefficients are observed, likely originating from the larger average size of the phytoplanktonic organisms, which induces a larger package effect. Both vertical and intersite variation of the chi-specific fluorescence (F-m*) shows opposite trends compared to a*. The variable presence of non-photosynthetic carotenoids (mainly zeaxanthin) is revealed to be the most clearly identifiable source of variation for the relative fluorescence yield, with a drop in the blue-green region. Prochlorococcus, Synechococcus and picoeukaryotes show a strong photoacclimation capacity to low irradiances. In addition there is evidence in the phytoplankton communities for a complementary chromatic adaptation process to the prevailing spectral irradiance conditions at both sites. Copyright (C) 1996 Elsevier Science Ltd

Absorption spectra of laboratory cultures of eight species of phytoplankton were studied. These spectra, normalized per unit of chlorophyll a concentration (specific absorption) show variability in magnitude and spectral form. Specific absorption at 440 nm varied over a factor of three. Spectra of phytoplankton belonging to the same taxonomic group tended to have similar forms. Over 95% of the variability in specific absorption could be explained in terms of changes in cell size, intracellular pigment concentration, and the relative importance of auxiliary pigments. Shape was not an important factor for this sample set. The spectral characteristics of absorption by intact cells of phytoplankton have been the subject of various studies because of their importance in primary production, radiative transfer in seawater, and in passive remote-sensing of phytoplankton. At sufficiently low concentrations, the total absorption coefficient a of a given substance at a given wavelength X can be expressed as a product of a specific absorption coefficient a*c and the concentration of the substance C. That is

Annual cycle of phytoplankton in the coastal waters of the « Parco Naturale della Maremma ». I. Quantitative variations.—Principal hydrological variables and phytoplankton cell densities have been measured monthly at seven stations in the nearshore sea waters of the Parco Naturale della Maremma. This area is influenced by the Ombrone river discharge. Hydrographic variations caused by freshwater are remarkable, especially in the stations north of the river mouth. On the contrary, numeric differences of phytoplanktonic populations are not so evident, among the stations, even in cases of differences in salinity and temperature, except in occasion of spring bloom, which is delayed in the fresh water influenced stations. The annual cycle does not differ from the characteristic shapes of those generally reported for the north temperate seas, with two maxima, the main in February and the second in November, and two minima, the first in Summer and the other in Winter. Possible causes of this cyclic behav...

Annual cycle of phytoplankton in the coastal waters of the « Parco Naturale della Maremma ». II. Flora and communities variations.—The hydrology of the marine coastal area of the Parco Naturale della Maremma and the annual cycle of phytoplankton standing crop have been examined in a preceding paper (Lenzi Grillini e Lazzara, 1978). In the present paper the species list and the main features of marine phytoplankton communities of the same area are reported as a result of an annual cycle of monthly collections effected in seven stations. The most conspicuous seasonal bloomings are due to Skeletonema costatum (Grev.) Cleve in February and to some species of the Chaetoceros gen. in November; the dinoflagellates play a minor role throughout the year, except for Gonyaulax minima Matz. with a light blooming episode in summer. The annual cycle of bottom living diatoms found in the samples appears to be very similar in its shape to the cycle of the pelagic species, as for the standing crop and for the spe...

The growth rate of a diatom (Chaetoceros protubcram) was followed during transfers from moderate to higher or lower irradianccs (PAR) with differing spectral compositions (“white,” “blue,” and “green” light). Chlorophyll-specific and carbon-specific absorption coefficients of the algae were monitored, allowing changes in the quantum yield for growth (@),) to be assessed. All the parameters appear to be practically unaffected by chromatic conditions, provided that the photosynthetically usable radiation (PUR) is made equal. Diatoms respond to the energy level whatever the color. Nevertheless, due to opposite influences of the modifications in the “package” eflt thereafter it remains low and steady. Conversely the enhanced value observed just after transfer to low irradiance is not maintained beyond 2 or 3 d; after that, a’, is restored practically to its initial value.

The Raphidophycean Fibrocapsa japonica Toriumi & Takano was detected for the first time offshore in the Eastern Alboran Sea (Western Mediterranean) in October 2006. Its distribution appeared very localised and atypical, as it was abundant only in the open waters of a cyclonic eddy. Microscope counts of the natural phytoplankton assemblages revealed that F. japonica was dominant in the microplankton, together with Dinophyceae, within and below the cyclonic nutrient-rich dome (25 - 30 m). Bacillariophyceae were the primary microplanktonic fraction in only a few samples. Moderately high abundances of F. japonica (maximum of 60 cells ml-1), with preliminary cysts and many cells aggregated in mucous nets, indicated a senescent phase. We also suggest a Mediterranean origin for this species. This was confirmed by molecular identification and by a water temperature of 15 °C, which could have favoured pre-cyst formation. Finally, we hypothesise that F. japonica, which is generally a coastal species, could have a coastal origin. Since F. japonica was confined to the cyclonic waters, which typically derive from coastal waters, it was collected at a depth of 40-60 m at the coastal sites and it is generally a coastal species, we hypothesise that it could have a coastal origin and it was entrapped by the cyclonic eddy, which could have carried offshore this harmful species.