Luigi Lazzara

Spectral absorption and fluorescence excitation properties of phytoplanktonic populations at a mesotrophic and an oligotrophic site in the tropical North Atlantic (EUMELI program)

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

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.

Spatial and Temporal Distribution of Phytoplankton Assemblages in the Ross Sea

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

THE FUNCTION OF WANDERING IN THE SAND-BUBBLER CRAB, DOTILLA FENESTRATA

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

Agrobacterium rhizogenes rolB gene affects photosynthesis and chlorophyll content in transgenic tomato (Solanum lycopersicum L.) plants

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

Photosynthetic Parameters, Irradiance, Biooptical Properties and Production Estimates in the Western Ross Sea

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

Analysis of Chlorophyll-a and Primary Production Dynamics in North Tyrrhenian and Ligurian Coastal–Neritic and Oceanic Waters

ABSTRACT Marchese, C.; Lazzara, L.; Pieri, M.; Massi, L.; Nuccio, C.; Santini, C., and Maselli, F., 2015. Analysis of chlorophyll-a and primary production dynamics in north Tyrrhenian and Ligurian coastal–neritic and ocean waters. Properly tuned algorithms based on optical remote sensing data can provide estimates of chlorophyll-a (as a proxy for phytoplankton biomass) concentration in near real time, allowing the monitoring of phytoplankton dynamics for both neritic and oceanic areas. The main objective of this study was, through the use of ocean color satellite images, to offer a description of the interannual variability of chlorophyll-a and primary production both in coastal–neritic and in oceanic areas of the North Tyrrhenian and Ligurian Seas (NW Mediterranean). The second objective was to highlight the possible influence of land runoff on phytoplankton biomass variability in coastal–neritic waters. The results indicate that seasonal cycles of phytoplankton biomass and production were quite different in neritic areas potentially affected by freshwater runoff compared to offshore waters. Neritic areas are characterized by an anticipated bloom (winter–spring) and by higher spatial variability that appears to be linked with the distance from shore. Meanwhile, oceanic areas are dominated by a marked seasonal cycle and the typical bloom occurs in spring (March–April) in relation with vertical mixing. Finally, linear regression analysis suggests the influence of freshwater runoff in modulating the variability of chlorophyll-a in coastal–neritic areas. Overall, the results confirm previous observations on the dynamics of phytoplankton biomass and contribute to more realistic and lower estimates of both chlorophyll-a concentration and annual primary production.

Ciclo annuale del fitoplancton nelle acque costiere del Parco Naturale della Maremma II. Flora e variazioni delle comunità

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

Ciclo annuale del fitoplancton nelle acque costiere del Parco Naturale della Maremma I. Variazioni quantitative

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

Photoacclimation strategy of Prochlorococcus sp. and consequences on large scale variations of photosynthetic parameters

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