Biogeochemical and ecological variability during the late summer–early autumn transition at an ice‐floe drift station in the Central Arctic Ocean

As the annual expanse of Arctic summer ice‐cover steadily decreases, concomitant biogeochemical and ecological changes in this region are likely to occur. Because the Central Arctic Ocean is often nutrient and light limited, it is essential to understand how environmental changes will affect productivity, phytoplankton species composition, and ensuing changes in biogeochemistry in the region. During the transition from late summer to early autumn, water column sampling of various biogeochemical parameters was conducted along an ice‐floe drift station near the North Pole. Our results show that as the upper water column stratification weakened during the late summer–early autumn transition, nutrient concentrations, particulate dimethylsulfoniopropionate (DMSPp) levels, photosynthetic efficiency, and biological productivity, as estimated by ΔO2/Ar ratios, all decreased. Chemotaxonomic (CHEMTAX) analysis of phytoplankton pigments revealed a taxonomically diverse picoautotrophic community, with chlorophyll (Chl) c3‐containing flagellates and the prasinophyte, Pyramimonas spp., as the most abundant groups, comprising ~ 30% and 20% of the total Chl a (TChl a) biomass, respectively. In contrast to previous studies, the picoprasinophyte, Micromonas spp., represented only 5% to 10% of the TChl a biomass. Of the nine taxonomic groups identified, DMSPp was most closely associated with Pyramimonas spp., a Chl b‐containing species not usually considered a high DMSP producer. As the extent and duration of open, ice‐free waters in the Central Arctic Ocean progressively increases, we suggest that enhanced light transmission could potentially expand the ecological niche of Pyramimonas spp. in the region

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

Bacterioplankton diversity and distribution in relation to phytoplankton community structure in the Ross Sea surface waters

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cordone, A., D’Errico, G., Magliulo, M., Bolinesi, F., Selci, M., Basili, M., de Marco, R., Saggiomo, M., Rivaro, P., Giovannelli, D., & Mangoni, O. Bacterioplankton diversity and distribution in relation to phytoplankton community structure in the Ross Sea surface waters. Frontiers in Microbiology, 13, (2022): 722900, https://doi.org/10.3389/fmicb.2022.722900.Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. However, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here, we report data on the bacterial diversity in relation to phytoplankton community structure in the surface waters of the Ross Sea during the Austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay (TNB) coastal waters and the Ross Sea Open Waters (RSOWs), with a dominance of members belonging to the bacterial phyla Bacteroidetes and Proteobacteria. In the TNB coastal area, microbial communities were characterized by a higher abundance of sequences related to heterotrophic bacterial genera such as Polaribacter spp., together with higher phytoplankton biomass and higher relative abundance of diatoms. On the contrary, the phytoplankton biomass in the RSOW were lower, with relatively higher contribution of haptophytes and a higher abundance of sequences related to oligotrophic and mixothrophic bacterial groups like the Oligotrophic Marine Gammaproteobacteria (OMG) group and SAR11. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provide new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters, suggesting that specific rather than random interaction contribute to the organic matter cycling in the Southern Ocean.Samples were collected in the framework of Plankton biodiversity and functioning of the Ross Sea ecosystems in a changing Southern Ocean [P-ROSE – (PNRA16_00239)], and CDW Effects on glacial mElting and on Bulk of Fe in the Western Ross sea [CELEBeR – (PNRA16_00207)] projects – Italian National Antarctic Program – funded by the Ministry of Education, University and Research (MIUR), awarded to OM and PR, respectively. MM was supported by an Earth-Life Science Institute (Tokyo, Japan) visiting fellowship. This work was partially supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948972) to DG

Effect of light, iron and vitamin B12 co-limitation on phytoplankton species of the Ross Sea (Antarctica). Ecological implications.

This thesis aimed at understanding the ecophysiological mechanisms implied in primary production processes in the Ross Sea waters (Antarctica), addressing aspects related to structural and functional biodiversity of phytoplankton, their production efficiency and the limiting role of iron and vitamin B12 in determining rates and timing of production. The information gathered during this thesis has confirmed some fundamental points on which is based the present paradigm on the role of the primary component in structuring the Antarctic food web. The results obtained show a richer picture of production mechanisms, thanks to adequate scales covering the coupling between water and the different coastal features or with the open waters of the Southern Ocean. Diatoms and haptophytes represent the dominant groups of phytoplankton community, although new ecological evidence emerges from the research performed in situ and on phytoplankton species isolated and cultivated in laboratory under manipulative conditions (iron and vitamin B12 limitation). Data, in fact, highlight the necessity of looking to the significant contributor of heterotrophic pathways to autotrophic primary production processes in a changing Southern Ocean

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

Presence of the Eurasian otter Lutra lutra (Linnaeus, 1758) (Mammalia Mustelidae) in the Foce Sele-Tanagro Nature Reserve (Campania, Southern Italy)

In Italy, the Eurasian otter, Lutra lutra (Linnaeus, 1758) (Carnivora Mustelidae), occurs with two separated populations in the southern regions and recently it has also re-colonized the north-eastern fluvial networks. Here, we present the first photographic evidence of the Eurasian otter presence along a stretch of the Calore river (Campania region, Southern Italy), where this species was generically reported in previous study. Our findings enlighten that the Calore river network might play an important role for the conservation and expansion of this species in Campania

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

Chlamydomonas Responses to Salinity Stress and Possible Biotechnological Exploitation

Salinity is among the main drivers affecting growth and distribution of photosynthetic organisms as Chlamydomonas spp. These species can live in multiple environments, including polar regions, and have been frequently studied for their adaptation to live at different salinity gradients. Upon salinity stress (hypersalinity is the most studied), Chlamydomonas spp. were found to alter their metabolism, reduce biomass production (growth), chlorophyll content, photosynthetic activity, and simultaneously increasing radical oxygen species production as well as lipid and carotenoid contents. This review summarizes the current literature on salt stress related studies on the green algae from the genus Chlamydomonas considering physiological and molecular aspects. The overall picture emerging from the data suggests the existence of common features of the genus in response to salinity stress, as well as some differences peculiar to single Chlamydomonas species. These differences were probably linked to the different morphological characteristics of the studied algae (e.g., with or without cell wall) or different sampling locations and adaptations. On the other hand, molecular data suggest the presence of common reactions, key genes, and metabolic pathways that can be used as biomarkers of salt stress in Chlamydomonas spp., with implications for future physiological and biotechnological studies on microalgae and plants