Phytoplankton blooms during austral summer in the Ross Sea, Antarctica: Driving factors and trophic implications

During the austral summer of 2014, an oceanographic cruise was conducted in the Ross Sea in the framework of the RoME (Ross Sea Mesoscale Experiment) Project. Forty-three hydrological stations were sampled within three different areas: the northern Ross Sea (RoME 1), Terra Nova Bay (RoME 2), and the southern Ross Sea (RoME 3). The ecological and photophysiological characteristics of the phytoplankton were investigated (i.e., size structure, functional groups, PSII maximum quantum efficiency, photoprotective pigments), as related to hydrographic and chemical features. The aim was to identify the mechanisms that modulate phytoplankton blooms, and consequently, the fate of organic materials produced by the blooms. The observed biomass standing stocks were very high (e.g., integrated chlorophyll-a up to 371 mg m-2 in the top 100 m). Large differences in phytoplankton community composition, relative contribution of functional groups and photosynthetic parameters were observed among the three subsystems. The diatoms (in different physiological status) were the dominant taxa in RoME 1 and RoME 3; in RoME 1, a post-bloom phase was identified, whereas in RoME 3, an active phytoplankton bloom occurred. In RoME 2, diatoms co-occurred with Phaeocystis antarctica, but were vertically segregated by the upper mixed layer, with senescent diatoms dominating in the upper layer, and P. antarctica blooming in the deeper layer. The dominance of the phytoplankton micro-fraction over the whole area and the high Chl-a suggested the prevalence of non-grazed large cells, independent of the distribution of the two functional groups. These data emphasise the occurrence of significant temporal changes in the phytoplankton biomass in the Ross Sea during austral summer. The mechanisms that drive such changes and the fate of the carbon production are probably related to the variations in the limiting factors induced by the concurrent hydrological modifications to the Ross Sea, and they remain to be fully clarified. The comparison of conditions observed during summer 2014 and those reported for previous years reveal considerably different ecological assets that might be the result of current climate change. This suggests that further changes can be expected in the future, even at larger oceanic scales

Assessing the quality of biogeochemical coastal data: a step-wise procedure

Coastal areas host valuable but vulnerable marine ecosystems subjected to increasing anthropogenic pressure and climate change consequences. To assess the impact of these pressures, monitoring programs have proliferated in coastal areas, but most of them follow locally established procedures for quality control (QC). The well-established QC procedure of open ocean data cannot simply be extended to the highly variable coastal area, for which there is the need to develop ad hoc QC approaches. This is particularly crucial for long-term time series, where different instrumentation and analytical methods have been applied over time. This study, based on the biogeochemical dataset collected over 30 years at the LTER MareChiara station (LTER-MC, Gulf of Naples, Mediterranean Sea), addresses potential discrepancies in a long-term dataset, identifying criteria and methods that could also be applied to other coastal datasets. We developed a serial step-wise procedure to characterize the quality of ~ 84,000 data-points, merging statistical tests and expert knowledge. The procedure included nine tests, each addressing potential problems in data generation and management, some of which of general application and others tailored to specific subsets of data. Based on these test, quality flags were assigned to individual data. Critical tests applied to two other independent datasets, showed that the procedure is not dataset dependent. These results contribute to bridge the gap between the need of objective QC criteria and the intrinsic noise of coastal datasets, promoting the discussion on this topic, and improving a proper management and sharing of coastal data

The New Carotenoid Pigment Moraxanthin Is Associated with Toxic Microalgae

The new pigment “moraxanthin” was found in natural samples from a fish mortality site in the Inland Bays of Delaware, USA. Pure cultures of the species, tentatively named Chattonella cf. verruculosa, and natural samples contained this pigment as a dominant carotenoid. The pigment, obtained from a 10 L culture of C. cf. verruculosa, was isolated and harvested by HPLC and its structure determined from MS and 1D- and 2D-NMR. The data identified this pigment as a new acylated form of vaucheriaxanthin called moraxanthin after the berry like algal cell. Its presence in pure cultures and in natural bloom samples indicates that moraxanthin is specific to C. cf. verruculosa and can be used as a marker of its presence when HPLC is used to analyze natural blooms samples

Photosynthetic rate and size structure of the phytoplankton community in transitional waters of the Northern Adriatic Sea

Transitional waters are among the most productive systems of the earth, supporting high rates of metabolism and primary production processes and providing important ecosystem services. In this study, we have investigated the effects of the freshwater input of the Po river on primary production processes in a coastal area influenced by the plume dispersion, using overall data derived from seven oceanographic cruises performed in seven different periods.In order to do this, PvsE (maximum rate of photosynthesis, P - vs light irradiance, E) curves with 14C were made for the determination of photosynthetic parameters, in association with the analyses of total phytoplankton biomass and size structure of the phytoplankton community, salinity and inorganic nutrient concentration. Stations were positioned according to salinity distribution from the coast to the off-shore waters.Data revealed that the water stratification mainly influenced the maximum Chl-a normalized photosynthetic rate (PBmax), total biomass and inorganic nutrients concentration. In the surface layer (0m), where the highest values of phytoplankton biomass were recorded, the micro- (>20µm) size class showed the highest photosynthetic rate and decreased toward off-shore waters. In the sub-surface layer, the nano- (>2 and <20µm) size class displayed the highest PBmax, probably linked to its capability to well photosynthesize under low light irradiance. The structure of the community in terms of size-classes was similar in both surface and deeper layer

Phytoplankton blooms below the Antarctic landfast ice during the melt season between late spring and early summer

Antarctic regions are known to be mainly dominated by diatoms in the water column under sea ice. In this study, we report for the first time two distinct phytoplankton blooms dominated by nanoflagellates (< 15 µm) under the landfast ice in Terra Nova Bay during the late spring-early summer 2015-2016. The taxa included the pelagic Bolidophyceae Pentalamina corona, the Chrysophyceae Ochromonas spp. and the Chlorophyceae Chlamydomonas spp., typically found in fresh waters, and the Prymnesiophyceae Phaeocystis antarctica usually observed dominating in polynya areas. These species represented from 40% to 91% of the total phytoplankton community, a percentage contrasting with the prevalence of diatoms found previously. The dominance of nanoflagellates, rather than diatoms, during late spring and early summer may have important implications for trophic relationships in Antarctic waters and the presence of typical freshwater species could indicate a great input of continental waters related to environmental changes

A review of past and present summer primary production processes in the Ross Sea in relation to changing ecosystems

We analyse primary production processes during austral summer 1996 and 2001 in different environmental conditions such as ice-free waters and extensive ice-covered areas. Spatio-temporal distribution of phytoplankton biomass and functional groups along with photosynthetic parameters are presented. Production vs irradiance (PvsE) experiments were performed using 14C incubations at several stations and three or four different depths to define the eco-physiology of phytoplankton communities. The results of the oceanographic campaign conducted in ice-free waters of the Ross Sea (summer 1996) emphasize that these ecosystems are characterized by high nutrient low chlorophyll (HNLC) conditions due to limiting factors (eg. Fe). Conversely, the results of the oceanographic cruise in extensively packice-covered areas (summer 2001) indicate that the average phytoplankton biomass (estimated from Chla) was about three times the values recorded in ice-free conditions, but the primary production was relatively lower. In fact, in situ primary production and PvsE experiments over few days show that high primary production values occurred in most of the area, but only within the first five meters of the water column and the melting pack ice. Notwithstanding some high values of phytoplankton biomass during the 2001 campaign, water column stability, similar irradiance levels along the water column, photosynthetic capacity was suppressed in deeper layers, indicating a low carrying capacity of the pelagic ecosystem due to iron limitation, as shown by low values of the photo-chemical efficiency of photosystem II (PSII), variable fluorescence and maximal fluorescence ratio (Fv/Fm). In contrast with a very high variability in phytoplankton biomass at several temporal and spatial scales, photosynthetic parameters (PB max , α, Ek) varied within narrow ranges. Relevant changes in phytoplankton abundance and species composition are reported in this study although the environmental factors that drive these changes in primary production processes and prevalence of principal functional groups of phytoplankton communities compared to the past (1996 and 2001) are still unknown. The effect of these changes on the carrying capacity of Ross Sea ecosystems, carbon export and the potentially new asset of the food web will need to be determined

TROPHIC CHARACTERIZATION OF THE PELAGIC ECOSYSTEM IN VLORA BAY (ALBANIA)

Phytoplankton assemblages were studied to characterize the trophic status of the semienclosed Vlora Bay (Albania) and to evaluate the influence of terrestrial inputs on its pelagic ecosystem. The study was carried out as part of the European Project CISM (INTERREG IIIA Italy–Albania) and conducted during two oceanographic cruises (spring 2007, winter 2008). The size-fractionated chlorophyll a concentrations, primary production rates, and the chemotaxonomic composition (high-performance liquid chromatography) of the phytoplankton assemblages were measured. The spatial variability of primary production rates and chlorophyll a concentrations both showed a pronounced E-W gradient in the surface layer, with the highest values along the eastern coast. In spring, a deep chlorophyll maximum was observed in the central western part of the bay, whereas in winter a homogeneous vertical distribution was observed. The phytoplankton assemblages were quite similar in both seasons and were dominated by the picophytoplankton fraction (<46% and 53% in spring and in winter, respectively). Haptophytes and pelagophytes were the major phytoplankton groups, and accounted, respectively, for 50% and 15% in spring, and 40% and 25% in winter. The results showed that Vlora Bay was characterized by generally oligotrophic conditions and that the influence of the southern Adriatic open waters was negligible. The trophic characteristics of the pelagic ecosystem of the bay were essentially driven by terrestrial inputs

A CHEMTAX‐derived phytoplankton community structure during 12‐year observations in the Gulf of Naples (LTER‐MC)

The rapid response of phytoplankton communities to environmental changes makes this compartment one of the most important biological variable to consider in dealing with ecology and trophodynamic of coastal areas, especially in relation with ongoing climate changes and increased human pressures. In the last 30 years, the use of chemotaxonomy has improved the capability to detect phytoplankton community composition in terms of chemofunctional groups, especially for small size species requiring specific expertise and techniques, as well as time-consuming observation with light microscope. In this study, the temporal variability of chemotaxonomic functional groups has been investigated in surface waters of a LTER station in the Gulf of Naples over 12-year weekly sampling activities (2003–2015). Data reveal increasing trends in the percentage contribution of diatoms, prasinophytes, cryptophytes to the total phytoplankton biomass, while other groups show a decreasing trend. Nevertheless, strong differences in the intervals of periodicity for each chemofunctional group have emerged, both in terms of timescale and strength of periodicity over time, implying that temporal dynamics of groups were not stationary over the time and that they have different relationships with environmental variability. Our results contribute to enrich scientific knowledge on the ecology of this LTER site and underline the importance of chemotaxonomy as a monitoring tool in coastal marine systems

All-aqueous emulsions as miniaturized chemical reactors in the food and bioprocess technology

All-aqueous emulsions are conventionally formed at bulk scale by mild shaking of aqueous two-phase systems. They can be used to carry out reactions both in droplets (compartmentalized) and on droplet surfaces in conditions free of synthetic surfactants and organic solvents. The use of all-aqueous emulsions for extractive bioconversion is a routine application; however, these emulsions hold many more promises. A renowned, rapidly evolving application is bio-microgel synthesis through biopolymer crosslinking within the emulsion internal phase. When polyelectrolyte crosslinking is achieved at the interface rather than in droplets, microcapsules can be formed, and when in situ colloidal particle generation at the droplet surface is obtained, colloidosomes are produced. The use of microfluidics to control the formation of all-aqueous emulsions offers many advantages in reactions monitoring and partitioning of reactants

Spatial-Related Community Structure and Dynamics in Phytoplankton of the Ross Sea, Antarctica

The Ross Sea exhibits the largest continental shelf and it is considered to be the most productive region in Antarctica, with phytoplankton communities that have so far been considered to be driven by the seasonal dynamics of the polynya, producing the picture of what is considered as the classical Antarctic food web. Nevertheless, the Ross Sea is made up of a complex mosaic of sub-systems, with physical, chemical, and biological features that change on different temporal and spatial scales. Thus, we investigated the phytoplankton community structure of the Ross Sea with a spatial scale, considering the different ecological sub-systems of the region. The total phytoplankton biomass, maximum quantum efficiency (Fv/Fm), size classes, and main functional groups were analyzed in relation to physical\u2013chemical properties of the water column during the austral summer of 2017. Data from our study showed productivity differences between polynyas and other areas, with high values of biomass in Terra Nova Bay (up to 272 mg chl a m\u20132) and the south-central Ross Sea (up to 177 mg chl a m\u20132) that contrast with the HNLC nature of the off-shore waters during summer. Diatoms were the dominant group in all the studied subsystems (relative proportion 65 50%) except the southern one, where they coexisted with haptophytes with a similar percentage. Additionally, the upper mixed layer depth seemed to influence the level of biomass rather than the dominance of different functional groups. However, relatively high percentages of dinoflagellates ( 3c30%) were observed in the area near Cape Adare. The temporal variability observed at the repeatedly sampled stations differed among the sub-systems, suggesting the importance of Long-Term Ecological Research (L-TER) sites in monitoring and studying the dynamics of such an important system for the global carbon cycle as the Ross Sea. Our results provide new insights into the spatial distribution and structure of phytoplankton communities, with different sub-systems following alternative pathways for primary production, identifiable by the use of appropriate sampling scales