Olga Mangoni

Structural and functional properties of sympagic communities in the annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

Abstract Studies on the chemical and biological properties of annual pack ice at a coastal station in Terra Nova Bay (74°41.72′S, 164°11.63′E) were carried out during austral spring at 3-day intervals from 5 November to 1 December 1997. Temporal changes of nutrient concentrations, algal biomasses, taxonomic composition, photosynthetic pigment spectra and P–E relationships were studied. Quantity, composition and degradation rates of organic matter in the intact sea ice were also investigated. In addition, microcosm experiments were carried out to evaluate photosynthetic and photo-acclimation processes of the sympagic flora in relation to different light regimes. High concentrations of ammonia were measured in four ice-cores (weighted mean values of the cores ranged from 4.3 ± 1.9 μM to 7.2 ± 3.4 μM), whereas nitrate and phosphate displayed high concentrations (up to 35.9 μM and 7.6 μM, respectively) only in the bottom layer (135–145 cm depth). Particulate carbohydrate and protein concentrations in the intact sea ice ranged from 0.5 to 2.3 mg l−1 and 0.2 to 2.0 mg l−1, respectively, displaying a notable accumulation of organic matter in the bottom colored layer, where bacterial enzymatic activities also reached the highest values. Aminopeptidase activity was extremely high (up to 19.7 μM l−1 h−1 ± 0.05 in the bottom layer), suggesting a rapid turnover rate of nitrogen–enriched organic compounds (e.g. proteins). By contrast, bacterial secondary production was low, suggesting that only a very small fraction of mobilized organic matter was converted into bacterial biomass (<0.01‰). The sympagic autotrophic biomass (in terms of chlorophaeopigments) of the bottom layer was high, increasing during the sampling period from 680 to 2480 μg l−1. Analyses of pigments performed by HPLC, as well as microscope observations, indicated that diatoms dominated bottom communities. The most important species were Amphiprora sp. and Nitschia cfr. stellata. Bottom sympagic communities showed an average PBmax of 0.12 mgC mg Chl−1 and low photoadaptation index (Ek=18 μE m−2 s−1, Em=65 μE m−2 s−1). Results of the microcosm experiment also indicated that communities were photo-oxidized when irradiance exceeded 100 μE m−2 s−1. This result suggests that micro- autotrophs inhabiting sea ice might have a minor role in the pelagic algal blooms.

Implementing and Innovating Marine Monitoring Approaches for Assessing Marine Environmental Status

Marine environmental monitoring has tended to focus on site-specific methods of investigation. These traditional methods have low spatial and temporal resolution and are relatively labor intensive per unit area/time that they cover. To implement the Marine Strategy Framework Directive (MSFD), European Member States are required to improve marine monitoring and design monitoring networks. This can be achieved by developing and testing innovative and cost-effective monitoring systems, as well as indicators of environmental status. Here, we present several recently developed methodologies and technologies to improve marine biodiversity indicators and monitoring methods. The innovative tools are discussed concerning the technologies presently utilized as well as the advantages and disadvantages of their use in routine monitoring. In particular, the present analysis focuses on: (i) molecular approaches, including microarray, Real Time quantitative PCR (qPCR), and metagenetic (metabarcoding) tools; (ii) optical (remote) sensing and acoustic methods; and (iii) in situ monitoring instruments. We also discuss their applications in marine monitoring within the MSFD through the analysis of case studies in order to evaluate their potential utilization in future routine marine monitoring. We show that these recently-developed technologies can present clear advantages in accuracy, efficiency and cost.

Light environment and seasonal dynamics of microalgae in the annual sea ice at Terra Nova Bay, Ross Sea, Antarctica

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

The 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.

Phytoplankton production in Italian freshwater and marine ecosystems: State of the art and perspectives

The present work aims at evaluating the state of art of phytoplankton production research in Italy. We present a synthesis of the main results achieved in three ecosystems where primary production studies have been carried out most intensively: a large subalpine lake (Lago Maggiore, LM), a shallow marine ecosystem with strong fluvial influence (the Northern Adriatic Sea, NAS), and a coastal area of the Southern Tyrrhenian Sea (the Gulf of Naples, GoN). The present yearly production values are around 150 g C m−2 yr−1 in LM and GoN; this ranges between 80 (offshore) and 150 g C m−2 yr−1 (coast) in the NAS. The temporal and spatial variations of phytoplankton production appeared, in each ecosystem, in accordance with the trophic changes. Significant correlations between production, chlorophyll, and light were generally observed for LM and for GoN. On the contrary, these parameters were poorly correlated in the NAS, hampering the use of predictive models in this ecosystem. Discrepancies between primary production and the actual phytoplankton biomass changes were observed across trophic gradients: the largest part of the carbon that is photosynthetically produced does not seem to be transformed into new phytoplankton biomass, strongly affecting the interpretation of the production figures in the ecosystems.

Biogeochemistry and algal communities in the annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

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

Quantitative histopathology of the Mediterranean mussel (Mytilus galloprovincialis L.) exposed to the harmful dinoflagellate Ostreopsis cf. ovata

Ostreopsis cf. ovata is a benthic dinoflagellate that produces palytoxin-like compounds that adversely affect both marine vertebrates and invertebrates and are reported to be responsible for human intoxication in aerosol form. In this work, a histopathological analysis accompanied by quantitative evaluation of tissue injury in mussels (Mytilus galloprovincialis) exposed to O. cf. ovata cells under natural and experimental conditions, provided baseline data on the health status of the mussels in terms of defensive and regressive pathological changes. We recorded a total of 15 health parameters in the digestive system, muscle, kidney and gills in mussels exposed to O. cf. ovata both in the laboratory and at sea. Animals exposed to different concentrations of O. cf. ovata cells (300, 500 and 1000cellsml(-)(1)) for 48h showed activation of the inflammatory response, which increased with the cell concentration, mainly characterized by haemocyte aggregates actively enclosing the algae, while mussel mortality was also recorded in some cases. Moreover the use of image analysis for the evaluation of digestive tubule damage revealed a pronounced increase in the lumen in terms of its area, perimeter and circularity, with a shift in a high percentage of tubules from an adsorbing profile to an atrophic profile. Animals collected from the natural environment during a summer bloom of O. cf. ovata in the Gulf of Naples (Italy) showed comparable lesions in terms of types and severity. This is the first quantitative study assessing damage to the digestive epithelia in terms of lumen modifications in mussels exposed to O. cf. ovata. The presented methodology provides a new technique for automating the evaluation of epithelial tubule modifications. Our results highlight the importance of monitoring the presence of O. cf. ovata in this area, taking into account the effects on the residing marine species.

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.

Phylogeny and morphology of a Chattonella (Raphidophyceae) species from the Mediterranean Sea: what is C. subsalsa?

We analysed the molecular and morphological features of strains of Chattonella subsalsa isolated from the western Adriatic coast (Mediterranean Sea), with the aim of confirming their classification and elucidating their phylogenetic positions within the Raphidophyceae. We sequenced parts of the ribosomal operon, including the small subunit (SSU), the internal transcribed spacer region (ITS) and the large subunit (LSU) of the rDNA. Additionally, we analysed sequences of the chloroplast-encoded subunit psaA of Photosystem I (PSI) and rbcL, encoding the large subunit of the Rubisco gene. For three phylogenetic markers (LSU, ITS, rbcL), the sequences of the strains from the Adriatic Sea were identical and for two markers (SSU, psaA) only minor differences occurred. All strains were sister to, but well separated from, sequences from isolates in culture collections and from GenBank, thus far classified as belonging to C. subsalsa. Light and electron microscopy provided evidence for morphological differences between a strain of C. subsalsa (CCMP217) from the Gulf of Mexico and the isolates from the Adriatic Sea. Differences concerned the shape and arrangement of chloroplasts and the presence of mucocysts and other surface microstructures, which were only observed in isolates from the Adriatic Sea. This is the first evidence for two different taxa classified as C. subsalsa, which are clearly separated on the basis of several genetic markers and also show morphological differences. As compared with strains assigned to C. subsalsa from the NCMA (formerly CCMP) culture collection, the Adriatic strains more closely match the original species description. This would imply that strain CCMP217 and other genetically similar strains should be described under a new species name. Nevertheless, given the high morphological plasticity of Chattonella species, the definition of the true C. subsalsa must be decided based on detailed morphological and molecular analysis of more strains from other geographical areas.

Phytoplankton uptake of 15N and 14C in the Ross Sea during austral spring 1994

Abstract In spring 1994, within the ROSSMIZE research project, combined measurements of nitrogen (15N) and carbon (14C) uptake were made in the Ross Sea, passing from the McMurdo polynya to the ice-covered area in the north, in order to study the effect of environmental conditions (light availability, ice cover, vertical stability) on the coupling of N and C cycles. Nitrogen (nitrate and ammonium) and carbon uptakes were measured under simulated in situ conditions. The obtained results revealed, in most situations, much higher C:N uptake ratios than the Redfield ratio for phytoplankton composition; only in the inner part of the pack ice C:N uptake was lower than the balanced composition ratio. The high uptake ratios are ascribed to a larger C requirement during early phases of bloom evolution and to a greater importance of nitrogen sources, such as urea and other dissolved organic compounds, which were not measured in this study. In contrast, the lower C:N ratios in most of the pack-ice environment are ascribed to reduced photosynthesis in comparison to nutrient assimilation at low irradiances and to an increased importance of bacterial processes.