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Antarctic polynyas are among the most productive areas in the ocean. They are subjected to strong temporal variations, having profound effects on the local ecosystems. We tested the changes occurring in several biogeochemical features [Chlorophyll a (Chl a), phaeopigment, dissolved and particulate organic carbon (DOC and POC) concentrations] as well as in biological dynamics (prokaryotic and nanoplanktonic abundance, heterotrophic carbon production and degradative activities) at the transition between late spring and summer in surface waters (upper 125 m) in the Terra Nova Bay polynya, in the Ross Sea. Samplings were performed from January 18 to 21 and, after an interval of almost 5 days, from January 25 to 27. The first period was characterised by spring conditions still maintained by the presence in the area of two mega-icebergs (B15 and C19), which caused a delay in the ice melting that started during the second survey. Chlorophyll a concentrations were highest during the first period, whereas phaeopigments/Chl a ratio increased during the following sampling time suggesting variations in phytoplankton biomass/physiology and a change in organic matter (OM) quality. No significant differences in DOC and POC concentration were detected between the two periods together with unvaried abundances of prokaryotes and small protists. The changes in OM over time were evidenced also by changing exoenzymatic activity patterns. Notwithstanding the general variations occurring during the surveys, heterotrophic production and prokaryotic growth were not substantially modified, suggesting a rapid (timescales of days) acclimation to changing organic matter quality for the maintenance of prokaryotic metabolic requirements.

Abundance and composition of the planktonic tintinnid ciliates were studied in the Gulf of Trieste (Northern Adriatic Sea, NE Mediterranean Sea) from July 1998 to July 2016. Tintinnids were collected biweekly-monthly from the LTER station C1 (200 m offshore, 17.5 m depth) at four depths (surface, 5 m, 10 m and 15 m). The maximum tintinnid abundance reached 4476 ind. L-1 at surface in February 2016. The tintinnid community comprised a maximum of 35 species and was dominated by the genera Stenosemella, Tintinnopsis, Codonellopsis, Salpingella and Eutintinnus. The most abundant species were Stenosemellanivalis, Tintinnopsisnana, Codonellopsisschabi, Salpingellarotundata and Eutintinnusapertus. We found a species-specific correlation with the abiotic factors considered, i.e., temperature and salinity. Temperature was positively correlated with S.rotundata and E.apertus and negatively with S.nivalis. Salinity was negatively correlated with the majority of the detected species. Agglutinated species presented winter maxima while hyaline species showed higher abundance in summer-autumn. Some key species were present over the whole period studied. Significant differences within the water column were not seen in the species composition, but were seen in the relative abundances of the same species at different depths. Stenosemellanivalis, S.ventricosa and Tintinnopsisberoidea can be considered as keystone species in the area and their possible loss can be seen as a signal of changes in the structure of the entire planktonic system.

The aim of the present study was to investigate the microbial community along the Ligurian coast corresponding to two marine canyons. The study considered pico-, nano- and micro-planktonic fractions, their abundances and composition. Temperature and salinity profiles along the water column showed the same trend at all stations and no significant difference was found among stations of the canyons’ profiles and those of the adjacent slope. A similar trend for abundances and biomasses was observed at all stations: higher values were generally measured at surface and decreased with increasing depth; significant linear regression was highlighted in each of the three transects. Results of the distribution of all microbial heterotrophs from the surface down to 2500 m indicate that prey abundance was generally higher than the feeding threshold of predators; this evidence suggests that the interaction between different size classes is bottom-up regulated in the study area. The slight decrease of the ratio Heterotrophic Bacteria (HB) vs. Heterotrophic NanoFlagellates (HNF) and the weak increase of relative abundance of larger HNF size classes should be the sole evidence of the expected “canyon effect”, and can be ascribed to the major input at the bottom of the canyon of particulate organic matter (POC) that can be used by heterotrophic nanoflagellates directly as a food source. Our results highlighted that the main pattern regulating community composition is depth, and that, in the aphotic layer, the different water masses (WM) present along the column, play a pivotal role in shaping the planktonic assemblage.

Submarine canyons are large geomorphological features that incise continental margins and act as highly dynamic conduits of sediments from shallow to the deep-sea regions. They are often regarded as biodiversity and biomass hotspots, but their role in influencing plankton communities is still poorly known. We studied the ecology of planktonic deep-sea microbes in a submarine canyon system (Polcevera and Bisagno canyons) in the Ligurian Sea (NW Mediterranean Sea), aiming at testing whether these large-scale incisions are peculiar systems, in comparison to the overlying water and the adjacent uncarved slope, in terms of biogeochemical and biological features. We analysed microbial communities’ composition by high-throughput sequencing of 16S and 18S rRNA genes and their functional attributes by measuring heterotrophic carbon production, dissolved inorganic carbon fixation, respiration and the activity of the exoenzymes leucine aminopeptidase, alkaline phosphatase, beta-glucosidase and lipase. We found that both prokaryotic and eukaryotic communities were not significantly different inside the canyons (if compared to the close slope and overlying water), but they were rather shaped by the water masses dynamics in the area. The shallowest Modified Atlantic Waters, Levantine Intermediate Waters and Winter Intermediate Waters hosted higher percentages of Alphaproteobacteria, Bacteroidetes and Dinophyta, while the deepest Western Mediterranean Deep Waters hosted a higher fraction of Gammaproteobacteria, Chloroflexi, Discoba and Fungi. Among the functional measurements, only leucine aminopeptidase activity showed higher rates within the canyons. However, local hotspots within the canyons characterised by high particulate matter loads and high C:N ratio (interpreted as refractory material from sediment local resuspension) displayed pronounced degradation activities.

Size spectra exhibit common patterns of variation and predictable responses to pressures across ecosystem types, functional guilds and taxonomic groups. Here, we extend the size spectra approach to phytoplankton ecological status assessment in transitional waters by developing, testing and validating a multi-metric index of size spectra sensitivity (ISS-phyto), which integrates size structure metrics with others such as phytoplankton diversity, biomass and sensitivity of size classes to anthropogenic disturbance. The ability of various theoretical models of size spectra sensitivity to discriminate between disturbed and undisturbed ecosystems and levels of anthropogenic stress was evaluated. We used data on phytoplankton samples collected in 14 Mediterranean and Black sea transitional water ecosystems (coastal lagoons) from Italy, Albania, Greece, Bulgaria and Romania, and compared the models’ efficiency by looking at their pressure–impact response along salinity and enrichment gradients, the latter quantified as variations in dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP). Data from a fifteenth Mediterranean lagoon was used for external validation purposes. Right asymmetric models of size class sensitivity, implying higher sensitivity of smaller cell size classes, were found to contribute to the ISS-phyto multimetric tool more effectively than symmetric and left asymmetric models, distinguishing disturbed from undisturbed lagoons and disturbed from undisturbed stations within the same lagoon. When based on right asymmetric sensitivity models, i.e., those that were most efficient in identifying anthropogenic impacts, ISS-phyto also showed the best fit of pressure–response relationships along the salinity and enrichment gradients; at low to high levels of impact ISS response was driven by size class sensitivity and at very high impacts by phytoplankton biomass. A scheme for the classification of Ecological Quality Status based on ISS-phyto is proposed and validated. The validation procedure found that ISS-phyto is an effective and sensitive monitoring tool, robust, easy to apply and to inter-calibrate among laboratories.

Sympagic microzooplankton were studied during late winter in the northern Weddell Sea for diversity, abundance and carbon biomass. Ice cores were collected on an ice floe along three dive transects and seawater was taken from under the ice through the central dive hole from which all transects were connected. The areal and vertical microzooplankton distributions in the ice and water were compared. Abundance (max. 1300 ind. l-1) and biomass (max. 28.2 µg C l-1) were high in the ice cores and low in the water below the sea ice (max. 19 ind. l-1, 0.15 µg C l-1, respectively). The highest abundances were observed in the bottom 10 cm of the ice cores. The microzooplankton community within the sea ice comprised mainly aloricate ciliates, foraminifers and micrometazoans. In winter, microzooplankton represent an important fraction of the sympagic community in the Antarctic sea ice. They can potentially control microalgal production and contribute to particulate organic carbon concentrations when released into the water column during the ice melt in spring. Continued reduction of the sea ice may undermine the roles of microzooplankton, leading to a reduction or complete loss of diversity, abundance and biomass of these sympagic protists.

Ostreopsis ovata Fukuyo is a benthic dinoflagellate widespread from tropical to subtropical and warm temperate coastal areas world-wide. Since the species produces palytoxin-like substances that can accumulate in seafood, the apparent expansion of its range in recent years represents an increasing risk for human health. This leads to the necessity of monitoring protocols that enable the rapid detection of the presence of this microalga in environmental samples and sea-food. We developed an identification protocol based on real-time PCR (qPCR) to detect O. cf. ovata presence in different matrices. The protocol was proved to be able to reveal microalgal traces in both soft tissues and intervalvar liquid of mussels exposed to O. cf. ovata in natural and experimental conditions as well as in seawater samples. O. cf. ovata could also be detected in mussel tissues after the end of the bloom, when it was no longer detectable in sea water. We were able to detect O. cf. ovata in copepods fed on unialgal cultures as well. Cell density estimates based on standard curves resulted to be comparable to direct microscopical counts. The method is therefore suitable to ascertain the origin of palytoxin-like substances in toxic seafood. In addition, our results confirm that mussels and other predators can actually ingest O. cf. ovata cells and act as a vector for toxin transfer through both benthic and planktonic food webs.

Abundance and composition of microzooplankton were studied over a 15 years period (from March 1986 to December 1990 and from July 1998 to December 2010) in the Gulf of Trieste (Adriatic Sea, NE Mediterranean Sea). Sampling was conducted biweekly-monthly at the surface at the historical station C1, 200 m offshore (bottom depth 17.5 m). Aloricate ciliates dominated in both periods (median 117 and 243 ind. L −1 in the first and second period respectively) while tintinnids were more abundant in the first period (median 55 ind. L −1 vs 16 ind. L −1 ). For heterotrophic dinoflagellates there are no data during the first period and in the second one they represented the second major group. Micrometazoans remained almost constant over time. In the first period all microzooplankton groups showed a maximum in April, while in the last period the peak has shifted to September. This is particularly evident for both aloricate ciliates and micrometazoans. Tintinnids, that in the past had the absolute maximum in spring, in the second period maintained the only, lower peak in October. Tintinnids in the first period were constituted by 27 species and dominated by the genera Tintinnopsis , Stenosemella and Salpingella . In the last 10 years we registered a dramatic decrease in abundance, paralleling an increase in species (40) with some “new entries” as well as the almost complete disappearance of genera Helicostomella , Favella , Coxiella and Steenstrupiella . The observed changes of the seasonal dynamics of microzooplankton abundance, as well as of the tintinnids composition over the long period considered in our study, might suggest a climatic forcing together with the known anthropogenic oligotrophication of the entire North Adriatic.

High spatial and temporal variabilities of biogeochemical properties are prominent features of regions under freshwater influence as a result of multiple factors. Understanding the ecological functioning of these ecosystems, which provide important services for humans, is challenging since it requires adequate observational strategies and efforts. Multi-years (1999–2006) continuous observations in the northernmost part of the Adriatic Sea (Gulf of Trieste) allowed us to compute a climatological description of seasonal dynamics of biogeochemical properties for three relevant sites: a coastal area directly influenced by a river, an off-shore area located in the centre of the Gulf and a coastal area located far from potential source of external nutrients. The analysis of the climatologies provides a quantitative corroboration of the conceptual scheme for biogeochemical and ecological seasonal dynamics of temperate coastal areas under freshwater influence already proposed in literature, highlighting the role of river input, lateral transport, stratification regime and interaction with bottom environment as driving factors. While all areas follow a common pattern of succession of ecological processes, spatial variability accounts for a significant decrease of the absolute trophic state, and for a phase delay in biogeochemical dynamics. Results show that spatial heterogeneity is an inherent structural feature of coastal ecosystems, suggesting that the evaluation of the quality status of coastal ecosystems should be made by using different reference terms for different sub-areas.

The EU Marine Strategy Framework Directive 2008/56/EC (MSFD) defines a framework for Community actions in the field of marine environmental policy in order to achieve and/or maintain the Good Environmental Status (GES) of the European seas by 2020. Microbial assemblages (from viruses to microbial-sized metazoa) provide a major contribution to global biodiversity and play a crucial role in the functioning of marine ecosystems, but are largely ignored by the MSFD. Prokaryotes are only seen as "microbial pathogens", without defining their role in GES indicators. However, structural or functional prokaryotic variables (abundance, biodiversity and metabolism) can be easily incorporated into several MSFD Descriptors (i.e. D1. Biodiversity, D4. Food webs, D5. Eutrophication, D8. Contaminants and D9. Contaminants in seafood) with beneficial effects. The present review provides a critical analysis of the current MSFD descriptors and illustrates the reliability and advantages of the potential incorporation of some prokaryotic variables within the set of indicators of marine environmental quality. Following a cost/benefit analysis against scientific and economic criteria, we conclude that marine microbial components, and particularly prokaryotes, are highly effective for detecting the effects of anthropogenic pressures on marine environments and for assessing changes in the environmental health status. We thus recommend the inclusion of these components in future implementations of the MSFD.

Deep-sea environments host the largest pool of microbes and represent the last largely unexplored and poorly known ecosystems on Earth. The Ross Sea is characterized by unique oceanographic dynamics and harbors several water masses deeply involved in cooling and ventilation of deep oceans. In this study the V9 region of the 18S rDNA was targeted and sequenced with the Ion Torrent high-throughput sequencing technology to unveil differences in protist communities (>2 μm) correlated with biogeochemical properties of the water masses. The analyzed samples were significantly different in terms of environmental parameters and community composition outlining significant structuring effects of temperature and salinity. Overall, Alveolata (especially Dinophyta), Stramenopiles and Excavata groups dominated mesopelagic and bathypelagic layers, and protist communities were shaped according to the biogeochemistry of the water masses (advection effect and mixing events). Newly-formed High Salinity Shelf Water (HSSW) was characterized by high relative abundance of phototrophic organisms that bloom at the surface during the austral summer. Oxygen-depleted Circumpolar Deep Water (CDW) showed higher abundance of Excavata, common bacterivores in deep water masses. At the shelf-break, Antarctic Bottom Water (AABW), formed by the entrainment of shelf waters in CDW, maintained the eukaryotic genetic signature typical of both parental water masses.

The aim of this study was to describe the microzooplankton composition under the sea ice in the Ross Sea (Antarctica) and its possible role as seed for the open-water community. We compared the under-sea-ice data to the communities present in the ice-free waters and at the retreating ice edge in order to test the hypothesis that the microzooplankton composition and abundance depend on the temporal development of the ecosystem. In December 2011, microzooplankton were sampled through two boreholes in sea ice, and 1 month later, in nearby stations that had been free from ice for a short time. The data from these samples were compared with a previous campaign (January 2011) when all of the area had been free of ice for a longer period. Our data indicate that under the sea ice the communities were very different from those of the ice-free waters, both in terms of abundance and diversity, with the prevalence of heterotrophic dinoflagellates and aloricate ciliates. Tintinnids were almost absent below the sea ice, and their abundance increased during the sampling at the intermediate depths. The present study provides evidence for the effect of the environment on the microzooplankton distributions, and indicates that the microzooplankton presence mainly depends on the sampling period. The community under the sea ice appears not to seed the open water community once the ice has retreated. The presence of the ice appears to influence the whole water-column production, which might thus not feed the deeper communities. The most important constraint appears to be the time that has lapsed from the presence of ice cover to the ice-free period.

Over the last two decades, increasing attention has been paid to the impact of jellyfish blooms on marine communities. Aurelia aurita is one of the most studied of the Scyphozoans, and several studies have been carried out to describe its role as a top-down controller within the classical food web. However, little data are available to define the effects of these jellyfish on microbial communities. The aims of this study were to describe the predation impact of A. aurita ephyrae on a natural microplanktonic assemblage, and to determine any reshaping effects on the prokaryote community composition and functioning. Surface coastal water was used to set up a 24-h grazing experiment in microcosms. Samples were collected to determine the variations in prey biomass, heterotrophic carbon production, extracellular leucine aminopeptidase activity, and grazing pressure. A next-generation sequencing technique was used to investigate biodiversity shifts within the prokaryote and protist communities through the small subunit rRNA tag approach. This study shows that A. aurita ephyrae were responsible for large decreases in the abundances of the more motile microplankton groups, such as tintinnids, Dinophyceae, and aloricate ciliates. Bacillariophyceae and Mediophyceae showed smaller reductions. No evidence of selective predation emerged in the analysis of the community diversity down to the family level. The heterotrophic prokaryote biomass increased significantly (by up to 45%), in parallel with increases in heterotrophic carbon production and leucine aminopeptidase activity (40%). Significant modifications were detected in prokaryotic community composition. Some classes of Gammaproteobacteria and Flavobacteriia showed higher relative abundances when exposed to A. aurita ephyrae, while there was a net decrease for Alphaproteobacteria. Overall, this study provides new insight into the effects of A. aurita on microbial communities, underlining their selective predation toward the more motile groups of microplankton and their impact on prokaryotic assemblages, by favoring blooms of copiotrophic taxa.

This review of studies on long term series on river discharges, oceanographic features, plankton, fish and benthic compartments, collected since the 1970s revealed significant changes of mechanisms and trophic structures in the northern Adriatic ecosystems. A gradual increase of eutrophication pressure occurred during the 1970s until the mid 1980s, followed by a reversal of the trend, particularly marked in the 2000s. This trend was ascribed to the combination of a reduction of the anthropogenic impact, mainly due to a substantial decrease of the phosphorus loads, and of climatic modifications, resulting in a decline of atmospheric precipitations and, consequently, of the runoff in the northern Adriatic Sea. Significant decreases of the phytoplankton abundances were observed after the mid 1980s, concurrently with changes in the species composition of the communities, with an evident shift toward smaller cells or organism sizes. Moreover, changes in the zooplankton community were also observed. A decrease of demersal fishes, top predators and small pelagic fishes was ascribed to both overfishing and a demise of eutrophication. Macrozoobenthic communities slowly recovered in the last two decades after the anoxia events of the 1970s and 1980s. An increasing number of non-autochthonous species has been recorded in the last decades moreover the increasing seawater temperature facilitated the spreading of thermophilic species.

The growth, activity and structure of a marine plankton assemblage from the Gulf of Trieste (NE Adriatic Sea) were monitored in a short-term mesocosm experiment (25 L) in order to investigate the influence of phosphorous availability on the production and utilization of organic matter. The coastal community, dimensionally selected (b200 μm), was grown under different P-concentrations. The results obtained from the nutrient enriched enclosures highlighted the microbial food web potential in high productivity systems: the phytoplankton community grew to a bloom-like state and resulted particularly productive enhancing the development of the prokaryotic population (especially of its active fraction). Glucidic exoenzymes operated at high hydrolysis rates in order to recycle extracellular carbohydrate/exudates produced by the abundant phytoplankton community. Intense prokaryotic production, directed prevalently to replication rather than to biomass production, increased the density of prokaryotic cells on levels that particularly favoured virus proliferation, acting thus as feedback control on the bacterial population. Different P concentrations also strongly influenced the structure of the bacterial community (either directly or indirectly) analyzed through denaturing gradient gel electrophoresis (DGGE), by selecting two diverse assemblages at the end of the experiment. Conversely to high N:P ratios observed throughout the year in the Northern Adriatic Sea, our study simulated a phosphorous-balanced condition and pointed out how nutrient limitation affects the entire microbial plankton community, reducing the trophic status of the environment through the control of phytoplankton production.

During the summer 2005/06, an oceanographic cruise was carried out in the Ross Sea, from Cape Adare, through the Terra Nova Bay polynya to the eastern edge of the Ross Ice Shelf. We analysed microbial activities (prokaryotic carbon production, protease, phosphatase, beta-glucosidase and lipase activity) and bacterial community structure (using Denaturing Gradient Gel Electrophoresis - DGGE) in order to establish if differences in bacterioplankton assemblages and their metabolic requirements occur within the five Ross Sea water masses: Antarctic Surface Waters (AASW), High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW), Antarctic Bottom Water (AABW), Circumpolar Deep Water (CDW). Differences in activities were found between the highly active AASW and all the other water bodies. A Principal Component Analysis highlighted two main gradients: in the Cape Adare area (AASWn, CDW and AABW) higher phosphatase, lipase and glycolytic activities, increasing towards the surface, were identified, whereas in the southern sector of the basin [AASWs and (m)HSSW] higher leucine uptake and polypeptide degradation characterized the second gradient. DGGE fingerprinting showed for the first time that different water masses harboured diverse bacterial communities, highlighting the high specificity of deep water assemblages.Alpha- andGammaproteobacteriarepresented the main phylogenetic groupings in all samples and no substantial difference in the phylogenetic composition of assemblages was found between different water masses.

The identification of bacterial community structure has led, since the beginning of the 1990s, to the idea that bacterioplankton populations are stratified in the water column and that diverse lineages with mostly unknown phenotypes dominate marine microbial communities. The diversity of depth-related assemblages is also reflected in their patterns of activities, as bacteria affiliated to different groups can express different activities in a given ecosystem. We analysed bacterial assemblages (DGGE fingerprinting) and their activities (prokaryotic carbon production, protease, phosphatase, chitinase, beta-glucosidase and lipase activities) in two areas in the Ross Sea, differing mainly in their productivity regime: two stations are located in the Terra Nova Bay polynya area (highly productive during summer) and two close to Cape Adare (low phytoplankton biomass and activity). At every station a pronounced stratification of bacterial assemblages was identified, highlighting epipelagic communities differing substantially from the mesopelagic and the bathypelagic communities. Multivariate analysis suggested that pressure and indirectly light-affected variables (i.e. oxygen and fluorescence) had a great effect on the bacterial communities outcompeting the possible influences of temperature and dissolved organic carbon concentration. Generally activities decreased with depth even though a signal of the Circumpolar Deep Water (CDW) at one of the northern stations corresponded to an increase in some of the degradative activities, generating some ‘hot spots’ in the profile. We also found that similar assemblages express similar metabolic requirements reflected in analogous patterns of activity (similar degradative potential and leucine uptake rate). Furthermore, the presence of eukaryotic chloroplasts’ 16S rDNA in deep samples highlighted how in some cases the dense surface-water formation (in this case High Salinity Shelf Water—HSSW) and downwelling can affect, at least for some phylotypes, the bacterial (16S rDNA based) community structure of the dark ocean.

The results of the updated and quality-checked data base of field observations on chlorophyll a (Chl a) collected in the period 1970-2007 in the Northern Adriatic Sea are presented. From the last decade, SeaWiFS satellite information was also considered. Results demonstrate a global tendency towards Chl a reduction in the period of investigation, which is more marked in the eutrophic area under the influence of the Po River. In the rest of the basin, which presents meso- or oligotrophic characteristics, long-term changes are more difficult to detect. The long-term field dataset can be divided into two periods: the last decade characterized by the strong decrease observed in the whole northern Adriatic and the earlier period with no or slight increase. The recent substantial reduction of Chl a concentrations is confirmed all over the basin (-0.11 mg m-3 year-1) from satellite-derived information. Results are consistent with recently evidenced decrease in concentrations of phosphate and ammonia and point to the existence of oligotrophication in the Northern Adriatic. Results indicate forcefully that the still common perception of the Adriatic Sea as a very eutrophic basin is no longer appropriate, at least for its northern part and in recent years.

Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica) during austral summer 2003 was phenotypically characterized and its capability of degrading organic matter was tested. We evaluated specific bacterial growth rates (mu) to understand at which temperatures bacterial growth shows a linear and direct relationship with the available substrate (4-22 degrees C) and afterwards we tested H. glaciei growth curves and degradative potential at 0, 10 and 37 degrees C using two different media (one enriched and one depleted in PO(4)). The strain grew exponentially only at 10 degrees C. The fastest hydrolysis rates were expressed by enzymes aimed at polysaccharide degradation (alpha-D-glucosidase, beta-D-glucosidase and beta-D-galactosidase) while alkaline phosphatase and aminopeptidase activities were rather low. Our data suggest a preferential demand for carbon derived from carbohydrates rather than from proteins: ectoenzyme activities transformed into carbon mobilization from organic polymers, showed that the total carbon potentially released from polysaccharides can be almost one order of magnitude higher than the protein carbon mobilization. Principal component analysis of the enzyme affinity separated the six experimental conditions, highlighting how different physical (temperature) and chemical (PO(4) enrichment or depletion) features actively lead to a differentiation in the efficiency of the ectoenzymes produced, resulting in preferential degradation of diverse kinds of organic substrates.

The variability of dissolved organic carbon (DOC) over days to a multi-year time span has been investigated in the Gulf of Trieste (northern Adriatic Sea) over a period of 5 years (January 1999 to December 2003). Samples were collected in a grid of 9 to 12 stations on monthly frequency and in one station on weekly (2003) and daily (1-month) frequency. DOC samples were analyzed by the HTCO method. DOC concentration varied over the five years in the range of 50 to 194 μM with annual median values ranging from 88 to 98 μM. Over the years 1999–2002, DOC showed a clear annual periodicity with winter minima and late summer maxima, higher in 1999 and 2000. During 2003 no seasonality was detected. The absence of DOC seasonality and the lower DOC concentrations during 2003 are most likely related to the drought that characterized the whole year. Accumulation was calculated as the difference between averaged winter minima (59 ± 7 μM) and the monthly averaged integrated value. DOC that had accumulated from spring to summer totally disappeared from the water column in winter when DOC concentrations reached the background value. The Gulf of Trieste, as with the rest of the Northern Adriatic each year, seems to be able to bring back DOC concentrations at low levels despite the significant external (mainly Isonzo River inputs) and internal organic matter loads. DOC concentration exhibited quite wide fluctuations weekly and daily, suggesting there might be DOC of different turnover time through production, consumption, migration and accumulation.

A preliminary study was carried out on a picocyanobacterial mixed culture harvested from the Gulf of Trieste (Northern Adriatic) and identified as Synechococcus spp. both by transmission electron microscopy observations, biliprotein composition and molecular analyses. Absorption and fluorescence spectra revealed phycourobilin and phycoerythrobilin chromophores, suggesting the presence of both CU- and C-phycoerythrin, besides phycocyanobilin chromophores typical for phycocyanins and allophycocyanins. Both biliprotein analyses and molecular identification indicated the presence of at least two Synechococcus subgroups presumably differing either in phycoerythrin type or in physiological traits. Among the exoenzymatic activities acting on different substrates, only aminopeptidase showed high hydrolysis rates and the uptake of organic molecules was positive for leucine but not for thymidine. The protein carbon mobilized was high compared with the leucine incorporation rates, resulting in low percentages of newly mobilized carbon utilized by cultures. The organic carbon incorporated as leucine was compared with the photosynthetically produced one, and the balance between the phototrophic- and heterotrophic-like processes was c. 3 : 1. Our findings suggest that the Synechococcus heterotrophy plays an important role in cell's metabolism, and that the photoheterotrophic behavior, together with their chromatic adaptation capability, might represent the key for the absolute dominance of this genus in the Adriatic Sea.

From January 2003 to December 2004 microphytobenthic primary production was estimated both from in situ (MPPs) and in the laboratory (MPPp) 14 C-incubation of slurries collected in a coastal site of the Gulf of Trieste (northern Adriatic Sea). MPPs values varied from −7.54 ± 3.12 to 34.59 ± 7.66 mg C m −2 h −1 over the whole period. The lowest MPPs were observed in November 2003 and August 2004, while the highest MPPs in July 2003 and May 2004, in correspondence with high PAR at the bottom. Significant correlations between MPPs and the microphytobenthic biomass (BIOM) ( r = 0.75, p r = 0.54, p r = 0.50, p

In the marine realm picoplanktonic cyanobacteria (PC) show a broad distribution from the surface ocean to the offshore and coastal waters of semi-enclosed seas and, because of their photoheterotrophy, they are responsible for a substantial fraction of both primary production and organic matter degradation/utilization. In the present study, we investigated PC distribution related to some physical–chemical parameters (temperature, salinity and dissolved oxygen), in the most productive periods of the year, spring and fall, at 37 stations located in seven transitional systems all along the Italian coast of the Adriatic Sea: Grado and Marano, Venezia, Pialassa Baiona, Margherita di Savoia, Torre Guaceto, Cesine and Alimini. The aim of the study was to determine if PC are common elements of these transitional systems (lagoons, marshes and solar salterns) or whether they are only occasionally important during stochastic bloom events. PC mean abundances were all over the seven habitats more than one order of magnitude higher (>5 × 107 cells L−1) than those found in coastal and offshore waters of the Adriatic Sea. Their range of variability was also broader (105–109 cells L−1 vs. 106–108 cells L−1). PC populations appeared well adapted to ample variations in salinity (5–87). The highest abundances (close to 109 cells L−1) were found at extremely high/low salinity values. Even oxygen concentrations close to hypoxia did not seem to negatively affect PC abundances. Because of their ability in adapting to extreme conditions, PC may become the prevailing fraction of the phototrophic plankton in these sites and their role in such ecosystems should not be underestimated.

In the summers of 2000, 2001 and 2002, large amounts of sticky mucilaginous material aggregated to form masses of impressive dimensions over large areas of the Adriatic Sea, particularly in its northern part. Aggregates differing in size were sampled by SCUBA divers and submitted to chemical (nutrient and organic matter concentrations) and biological analysis (virus, bacteria and phytoplankton abundances and bacterial metabolism). Suspended and sinking mucilaginous aggregates were biota-rich environments where the abundance of planktonic organisms and the concentration of nutrients were orders of magnitude higher than in the surrounding seawater. The embedded phytoplankton was mostly composed of diatoms, but the dinoflagellate Gonyaulax fragilis, previously reported in association with the aggregates, was also present. A variety of processes occurred within the mucilaginous aggregates which resulted in the transformation of the organic matter composition and lability and contributed to a partial degradation of mucilage. For an efficient degradation of mucilage, several conditions are necessary: high bacterial abundance and activity and an efficient recycling of nutrients within the aggregates. Most of these conditions, appear to change depending on the type and age of the aggregate. During the first phase of aggregation (cobwebs and ribbons), bacterial activities addressed the degradation of organic matter, particularly that of the nitrogen fraction. The degradation products were rapidly taken up by bacteria, supporting an increase in their abundance and production. In aged mucilage (clouds), the degradation processes decreased and the bacterial metabolism suggested the presence of new organic labile compounds probably due to phytoplankton production. On the basis of our results, stringers, generally considered the first step of the aggregation process, seemed to be the result of a mechanical disruption of other types of aggregates.

Spatial and temporal changes in phytoplankton production and bacterial C demand were investigated at four stations in the Northern Adriatic Sea over 3 years. The effect of the Po River plume was observed at the western stations; in particular, the northernmost one (B06) showed the highest values of primary production, both as hourly peaks (up to 14 mg C m− 3 h− 1) and daily water column integrated values (up to 740 mg C m− 2 day− 1), the southern station (C04) was only sporadically influenced and did not differ significantly from the easternmost ones (C12 and B13), where the lowest TPP values were recorded (around 1 mg C m− 3 h− 1). In this study the first in situ data are reported on short-term phytoplankton C extra cellular release in the Northern Adriatic Sea. At every station a considerable percentage of primary production (PER > 20% as an average, with peaks of up to 70%) was released as dissolved organic carbon. In particular, an association of fairly high PER (> 10%) and specific production (Pb > 10 mg C mg chl− 1 h− 1) was observed from spring to summer, when the mucilage phenomenon usually starts. This result might suggest the presence of an uncoupling between photosynthesis and growth, probably related with nutrient availability, which would be responsible for a high production of extra cellular organic carbon. Phytoplankton primary production and bacterial carbon production were closely related and bacterial C production accounted, on average, for a higher percentage of primary production than the values typically reported in the literature on aquatic environments. The flow of organic matter from phytoplankton to bacteria seems to satisfy the bacterial carbon demand during most of the spring and summer, at least in the upper water layers. However, during the summer, there is evidence that BCD sometimes exceeds the amount of C produced by phytoplankton. Neither phytoplankton nor bacterial production showed significant differences over the relevant years, and their absolute values did not change when comparing periods with or without mucilage. However, there were indications of an uncoupling between phytoplankton photosynthesis and growth and of a shift from an autotrophic to a heterotrophic metabolism, especially during the spring and summer period when mucilage might occur.

Primary production of the microphytobenthic community and carbohydrates concentrations were studied in the lagoonal system of Grado and Marano, located in the Northern Adriatic coast. Sediment samples were collected along a salinity gradient. Abundance and species composition of the microphytobenthic communities were analysed and the benthic microalgal biomass was estimated as Chlorophyll a (Chl a). Primary production of benthic diatoms was estimated using 14C-tracer. Extracellular carbohydrates were extracted from the sediment and separated in two operationally defined fractions (colloidal and EDTA-extractable). Salinity was higher in the Grado lagoon, where the benthic microalgal community was mainly composed of marine diatoms. In the Marano lagoon, which has a lower salinity, freshwater species were also found. In both lagoons, photosynthetic efficiency showed an inverse relationship with salinity and a direct relationship with the main biological variables. Photosynthetic activity was directly related to Chl a and abundance of benthic microalgae, suggesting that in the benthic system microalgal community is responsible for primary production. Overall, salinity was also influent on the microphytobenthic primary production, which was greater in the more saline Grado lagoon.

Primary production (PP) and, nitrate (QNO(3)) and ammonium (QNH(4)) uptakes were measured together with other environmental parameters from October 1999 to February 2001 in the Gulf of Trieste (N Adriatic Sea). Their trends showed a high variability because of the combined effects of meteorological conditions, water circulation and river discharges. PP ranged from 0.2 to 1.5.9 mumol C dm(-3) d(-1), whereas QNO(3) varied from 0.8 to 442 nmol N dm(-3) d(-1), showing a trend similar to that of carbon basically ascribable to the autotrophic activity. QNH(4) ranged from 20 to 1308 nmol N dm-3 d-' and it reached the highest values during the declining phases of phytoplankton blooms, indicating that bacterial community can also be involved in its uptake. Regenerated PP generally prevailed over the new production (depth-integrated f-ratios from 0.05 to 0.50). C/N uptake ratios by planktonic community (annual average of 16 +/- 11) showed the repetitive carbon overconsumption (23-33) during periods of high production, and lower values (2-13) during: the post-bloom phases and in the months of scarce autotrophic activity. Residence time of freshwater in the area (1 d in November and January, up to 23 d in July) indicated the fast export of low salinity waters in winter and their longer permanence in summer. These values were closer to the ammonium turnover times (1-34 d) than to the nitrate ones (2-831 d). Riverine nitrate load (3-67 t N d-') generally exceed the biological demand of this nutrient (uptakes from 0.2 to 8 t N d-'), whereas the ammonium load (0.1-33 t N d(-1)) was almost always insufficient (uptakes, from 2.6 to 33 t N d(-1)). These results evidenced the major role of physical transport and recycling processes to regulate, respectively, nitrate and ammonium availability in this shallow ecosystem., La production primaire et l’assimilation de nitrates et d’ammonium ont été mesurées en même temps que les facteurs du milieu entre octobre 1999 et février 2001 dans le golfe de Trieste. La variabilité est élevée en raison de l’action combinée des conditions météorologiques, de la circulation et des apports des rivières. La production primaire varie entre 0,2 et 15,9 μmol C dm–3 j–1 alors que l’assimilation de nitrates va de 0,8 à 442 nmol N dm–3 j–1, montrant une tendance identique au carbone lié à la production autotrophe. L’assimilation d’ammonium varie entre 20 et 1308 nmol N dm–3 j–1 et elle atteint ses valeurs maximales durant le déclin de la floraison planctonique, indiquant que la communauté bactérienne est impliquée dans cette assimilation. La production primaire régénérée surpasse la production nouvelle (le facteur f intégré en fonction de la profondeur varie entre 0,05 et 0,5). Les taux C/N d’assimilation de la communauté planctonique (moyenne annuelle de 16 ± 11) soulignent la surconsommation répétitive de carbone (23–33) durant les phases de production actives ; les valeurs minimales (2–13) caractérisent les phases postérieures à la floraison et les mois de faible activité autotrophe. Le temps de résidence d’eau douce dans la zone (d’un jour en novembre et janvier à 23 jours en juillet) indiquent l’exportation rapide d’eau de basse salinité en hiver et leur permanence en été. Ces valeurs sont plus proches des temps de renouvellement de l’ammonium (1 à 34 jours) que des nitrates (2 à 831 jours). L’apport de nitrates par les fleuves (3–67 t N j–1) surpasse les besoins (0,2 à 8 t N j–) alors que l’apport d’ammonium (0,1–3,3 t N j–1) est presque toujours insuffisant (assimilation de 2,6 à 33 t N j–). Ces résultats mettent en lumière le rôle majeur du transport et du recyclage dans la régulation de la disponibilité en nitrate et ammonium dans des écosystèmes de faible profondeur.

In the frame of PRISMA II Project samples for plankton analyses were carried out during four cruises (June, 1996; February and June, 1997; February, 1998) in order to assess the relative importance in term of biomasses of the three main size fractions (pico- 20 r µm). Spatial and temporal distribution of the three plankton fractions were described as abundance and contribution to the total carbon content in an area between Po River mouth and Rimini. The relative contribution of picoplankton resulted higher in the offshore zone, while that of nanoplankton in the inshore waters. In February 1998 microphytoplankton, mainly constituted by diatoms, was very abundant in the inshore waters. Micro-zooplankton was always very scarce. Cluster analyses performed on these data grouped the stations on the basis of their community structure, and agreed with the hydrological features. Small size classes contributed more significantly to the total plankton carbon content in mo...

1. The relevance of biodiversity to ecosystem processes is a major topic in ecology. Here, we analyse the relationship between biodiversity and productivity of the nano- and micro-phytoplankton guilds in coastal marine ecosystems. 2. The patterns of variation of species richness, diversity and primary productivity (as 14C assimilation) were studied in two marine areas: a eutrophic–mesotrophic area beside the River Po delta (northern Adriatic) and an oligotrophic area around the Salento peninsula (southern Adriatic–Ionian). The study was carried out at 23 sites in the northern area and at 45 sites in the southern area. Sites were arranged on expected spatial and temporal gradients of primary productivity variation, according to distance from the coast, optical depths and seasonal period. 3. 167 taxa were identified in the northern area and 153 taxa in the southern area. In both areas, the taxonomic composition of the nano- and micro-phytoplankton guilds exhibited greater temporal than spatial variation. The latter was much higher in the southern area than in the northern area (average dissimilarity between stations being 70.7±0.8% and 44.7±4.2% respectively). 4. Primary productivity varied in space and time on the gradients considered. Phytoplankton species richness and diversity exhibited significant patterns of variation in space and time; overall, these were inversely related to the primary productivity patterns in the northern area, whereas they were directly related in the southern area. 5. The small individual size and the high turnover rate of phytoplankton are likely to underlie the observed relationships, which emphasized a threshold response to nutrient enrichment in agreement with the ‘paradox of enrichment’. Under resource enrichment conditions, the high turnover of producers leads to hierarchical partitioning of the available resources with an increasing dominance of a few species. Therefore, the relationship observed here seems likely to be explained by the complementarity hypothesis. Copyright © 2003 John Wiley & Sons, Ltd.

Viruses and prokaryotes represent the smallest and the most abundant biological entities in marine environments. The interest for viruses and their interactions with marine organisms is continuously rising but the studies are generally limited to short-time investigations. This study conducted in the Gulf of Trieste on monthly resolution investigates for the very first time relationships between viruses and prokaryotes (both heterotrophs-HP and autotrophs-AP) over ten years (2000–2010). From our results emerged that no clear relationship between the abundances of viruses and prokaryotes is observed unless for rather restricted time intervals. Some of the sporadic peaks of viral abundances can be attributable to infections occurred during the autumn phytoplankton blooms, thus probably contributing to the end of the bloom. We infer that the general uncoupling between viruses and prokaryotes in the Gulf of Trieste is due to the variety of factors that regulate viral infection, proliferation and persistence such as the diversity of viral life cycles that are determined by environmental factors, the abundance and the physiological status of their hosts.

Most of the ambient dissolved organic carbon (DOC) is refractory to microbial degradation; bacteria can consume a minor but variable part of the DOC pool over periods of hours and days. It is important to increase our knowledge of the dynamics of the biodegradable fraction of DOC (BDOC) to understand the global carbon budget. Several methods for determining BDOC have been developed; however, the problem of most of them is the time (days/weeks) required for the colonization and/or determination. In this paper, we describe the application to seawater of a plug-flow bioreactor to measure BDOC within 3-4 h. The bioreactor was built following Søndergaard and Worm [Søndergaard, M., Worm, J., 2001. Measurement of biodegradable dissolved organic carbon (BDOC) in lake water with a bioreactor. Water Res. 35, 2505-2513.] protocols for the measurement of BDOC in lake water. We analyzed BDOC on samples collected in the Gulf of Trieste during autumn-winter and summer 2003-2004. BDOC concentrations varied from 8 to 24 microM and represented from 10.3% to 25.5% of the total DOC. To evaluate the effectiveness of this method, we compared bioreactor BDOC measurement with data obtained from batch cultures. The results indicate that BDOC in coastal seawater can be measured rapidly and reliably with this bioreactor.

During the 2006 Italian Antarctic expedition a diel sampling was performed close to Cape Hallett (Ross Sea) during the Austral summer. Under-ice seawater samples (∼4 m) were collected every 2 h for 28 h in order to estimate prokaryotic processes' variability and community structure dynamics. Prokaryotic and viral abundances, exoenzymatic activities (β-glucosidase, chitinase, lipase, alkaline phosphatase and leucine aminopeptidase), prokaryotic carbon production ( 3 H -leucine incorporation) and community structure (Denaturing Gradient Gel Electrophoresis – DGGE fingerprints) were analysed. Results showed that the diel variability of the prokaryotic activity followed a variation in salinity, probably as a consequence of the periodical thawing of sea ice (driven by solar radiation and air temperature cycles), while negligible variation in viral and prokaryotic abundances occurred. The Bacterial and Archaeal community structures underwent an Operational Taxonomic Units (OTUs) temporal shift from the beginning to the end of the sampling, while Flavobacteria -specific primers highlighted high variations in this group possibly related to sea ice melting and substrate release.

A preliminary study was carried out on a picocyanobacterial mixed culture harvested from the Gulf of Trieste (Northern Adriatic) and identified as Synechococcus spp. both by transmission electron microscopy observations, biliprotein composition and molecular analyses. Absorption and fluorescence spectra revealed phycourobilin and phycoerythrobilin chromophores, suggesting the presence of both CU- and C-phycoerythrin, besides phycocyanobilin chromophores typical for phycocyanins and allophycocyanins. Both biliprotein analyses and molecular identification indicated the presence of at least two Synechococcus subgroups presumably differing either in phycoerythrin type or in physiological traits. Among the exoenzymatic activities acting on different substrates, only aminopeptidase showed high hydrolysis rates and the uptake of organic molecules was positive for leucine but not for thymidine. The protein carbon mobilized was high compared with the leucine incorporation rates, resulting in low percentages of newly mobilized carbon utilized by cultures. The organic carbon incorporated as leucine was compared with the photosynthetically produced one, and the balance between the phototrophic- and heterotrophic-like processes was c. 3 : 1. Our findings suggest that the Synechococcus heterotrophy plays an important role in cell's metabolism, and that the photoheterotrophic behavior, together with their chromatic adaptation capability, might represent the key for the absolute dominance of this genus in the Adriatic Sea.

The feeding ecology of the transparent goby Aphia minuta was examined in spring (May 2003) in the coastal waters off Comacchio, in the northwestern Adriatic Sea. Stomach content analysis indicated A. minuta to be a planktivorous species, feeding exclusively on pelagic invertebrates. The diet composition was dominated by the calanoid copepods Acartia clausi and Temora longicornis, followed in decreasing order of importance by other copepods (especially calanoids and Oncaea spp.) and larvae of decapods, polychaetes and bivalves. A. minuta exhibited a generalistic feeding strategy with a relatively broad niche width. Abundant taxa in the environment, such as A. clausi and T. longicornis, were seldom selected, whereas rare taxa, such as larvae of polychaetes and decapods, were highly selected. According to the observed ontogenetic shift in diet, small-size individuals relied preferentially on juvenile T. longicornis and Oncaea spp., whereas large-sized specimens consumed preferably A. clausi and calanoids. The positive relationship found between prey and fish size may help to mitigate the intraspecific competition for food resources.

The applicability of the delayed fluorescence (DF) for the purpose of distinguishing the cells growing in different nutrient conditions was researched on the marine unicellular algae Dunaliella tertiolecta Butcher (Chlorophyta). The DF intensity (DFI), as a measure of living algal biomass, was compared with other biomass measures – the cell concentration, chlorophyll a and fluorescence. The photosynthetic activity index (PhAI), a non-dimensional physiological index of photosynthesis calculated from a combination of DFI and F 0 was introduced. The nitrogen deprivation was indicated by more than 50% drop of PhAI. DF decay kinetics was measured with two different illuminations ( 650 nm). The measured curves were divided and the resulting peak utilized for the differentiation among nutrient conditions. DF decay kinetics of D. tertiolecta differed among the cells growing in various nutrient conditions, indicating changes in the photosynthesis physiology.

Mesozooplankton community composition at the species/taxa level was investigated from January to December 2001, at eight stations in the northern Adriatic Sea. Annual dynamics, taxonomic composition and spatial diversity in relation to different trophic conditions are discussed as related to previous studies and to different conditions, such as the presence of mucilage events. Zooplankton communities all over the northern sub-basin were dominated by the cladoceran Penilia avirostris in summer, and by the calanoids Paracalanus parvus, Acartia clausi and the poecilostomatoids Oncaea spp. during the rest of the year. Whereas coastal communities were more variable with time and location, we were able to identify a group of offshore stations with a similar species/taxa composition and annual dynamics. Comparing the present results with previous studies, we observed significant changes in community composition in the time scale of 20 years, mostly due to a general decrease of A. clausi as the dominant species, being replaced by P. parvus. Also, P. avirostris swarms appear to have extended their temporal occurrence, and were present for longer periods of time when compared to past records. These changes might be related to the observed general increase of the average sea water temperature in the northern Adriatic Sea.

[1] The dynamic of biogeochemical properties in a coastal area of the northern Adriatic Sea (Gulf of Trieste) is analyzed through (1) identification of a small number of water typology classes and classification of samples, obtained by means of a novel multivariate classification procedure based on a combination of Artificial Neural Networks (ANN) and “traditional” clusterization algorithms, (2) interpretation of each class based on biogeochemical properties and ecological phenomena likely to occur in the water body, and (3) discussion of time evolution and spatial distribution of water classes which summarized and provided indications on the system's space and time evolution. Basing itself on a multivariate comparison, the Self-Organizing Map (SOM) grouped 1292 samples collected in a 3-year-long monitoring program in 187 sets and identified a representative synthetic sample for each group. These groups were further classified in seven clusters, which identified the water typology. The complexity of the space and time coevolution of 12 variables was so reduced to variation of one categorical variable. Results included an objectively derived typology of water masses and their typical temporal succession, a spatial dividing based on biogeochemical processes, a conceptual scheme of biogeochemistry in the Gulf. Results clearly indicated the importance of river input in triggering plankton blooms and pointed out that trophodynamics followed current paradigms of marine ecosystem functioning, with shifts from conditions dominated by classical food chain to situations in which most of the energy flowed through the autotrophic and heterotrophic parts of the microbial food web.

Monthly sampling was carried out during a 2-year study (2003e2004) in order to analyse benthic microalgal composition, abundance (ABU) and biomass (BIOM). Temperature and photosynthetically available radiation (PAR) at the bottom were recorded during sampling. In the overlying water nitrite (NO2 ), nitrate (NO3 ), ammonium (NH4 ), phosphate (PO4� ) and silicate (SiO3 ) were analysed. The sediment consisted of 8.2% sand, 18.3% clay and 73.5% silt. BIOM showed its maximum in August 2004, while the minimum was recorded in October 2003. The microphytobenthic community was mainly composed of diatoms. Among all the 103 Bacillariophyceae taxa identified in the sediment, we distinguished 67 benthic, 8 epiphytic and 8 planktonic species. Among diatoms Nitzschia and Navicula were the most abundant genera (30.8 and 26.2%, respectively). The linear regression between total diatom ABU and PAR was statistically significant (r ¼ 0.66, p < 0.001). A seasonal pattern of monthly samplings was highlighted both from cluster analysis and principal component analysis (PCA). The latter revealed two diatom assemblages: a winter assemblage and a springesummer one. The genera Diploneis and Pinnularia showed an inverse relation against temperature. Considering the nutrient ratios the development of microphytobenthos (MPB) appeared to be potentially co-limited by Si and P almost throughout the study period. A clear inverse relation between NO2 ,N O3 and BIOM was emphasised by the moving average and the PCA. The inverse relation among nutrients and light availability suggested that the photosynthetic activity of benthic diatoms in spring and summer may be one of the processes controlling sedimentewater nutrient fluxes. 2007 Elsevier Ltd. All rights reserved.

Cluster and time series analyses were applied to a 1970–1999 data set of zooplankton collected from the Gulf of Trieste (Northern Adriatic Sea). Two time periods were compared: 1970–1980 and 1986–1999. Associations of copepod species were identified and an attempt was made to reveal their long-term dynamics and significant patterns over the study period. Two main groups with 2 and 3 subgroups each were identified. We observed a seasonal alternation of the 2 main groups, albeit with remarkably different patterns during the 2 periods. Time-series analyses suggested recent changes in the periodicity of the associations. The long-term annual mean copepod abundance showed an increase in the late 1990s in comparison to the 1970s; however, this increase was not constant. Small-sized copepods increased in the second period, indicative of changes in the phytoplankton size spectrum. Shifts in the 1990s appeared to be related to climate change in the Northern Hemisphere that appeared abruptly after 1987. Climate change is thus recognized as the most important factor (more so than anthropogenic change) affecting inter-annual and inter-decadal variability of plankton dynamics. The strong signal recorded in the zooplankton community seems to reflect this, identifying the Gulf of Trieste as one of the most sensitive areas in the Mediterranean.

This study examines multiple, long-term zooplankton time series across the Atlantic region and its inland seas. Across a broad range of geographic regions and ecological environments, the impact of the North Atlantic Oscillation (NAO) on interannual changes in the zooplankton populations was evident. Across the mid-Atlantic, a correlation between the NAO and zooplankton abundance was present and remained positive from the northwestern Atlantic through the enclosed seas of the far eastern Atlantic. Following high NAO years, these regions experienced higher total zooplankton abundance or biomass. Following low NAO years, this trend was reversed. A time lag in the zooplankton response to the NAO was also evident, influenced more by the scale of the water basin than by latitudinal or longitudinal location. For some regions, the correlation between zooplankton and the NAO was higher when the NAO was substituted with its sub-components: the Azores High (AH) and the Icelandic Low (IL) atmospheric pressure systems. This suggests that decomposition of the NAO into its components might enhance the sensitivity of the analysis of biological time series with regard to climate change.