1,721,001 research outputs found
Identification of Chattonella species (Raphidophyceae) through molecular methods on fixed samples from Santa Giusta Lagoon (Sardinia, Italy).
No full textThe genus Chattonella Biecheler (Raphidophyceae) has a worldwide distribution and includes harmful species, which cause extensive kills of farmed and wild fishes, with very important ecological damage and economic losses. Only two species are currently taxonomically accepted as members of the genus: C. marina (Subrahmanyan) Hara & Chihara and Chattonella subsalsa Biecheler. These two species show very similar cell morphology, with some characters that overlap, such as the length and the width of the cell. Therefore, their certain identification can be obtained only through the ultrastructure and genetics. The mechanism of toxic action is known better for C. marina but, even if a number of different killing pathways have been described, the debate is still ongoing. Potential deleterious effects of C. subsalsa are less known and only few studies indicate the production of toxic substances (e.g. brevitoxins, peroxide radicals).
Chattonella spp. blooms associated with fish-kill events were observed in Sardinian lagoons since the middle of nineties. The first observation occurred in Santa Giusta Lagoon (Gulf of Oristano), during a massive fish mortality case, between the end of July and August 1994. The presence of Chattonella spp. was well documented also in 1998, 1999 and 2010, during further harmful blooms always in Santa Giusta Lagoon, which belongs to the LTER-Italy network. The presence of C. subsalsa was established in samples collected in Santa Giusta Lagoon in 2005 through molecular methods, when kill-fish events were absent.
The main objective of this work is to investigate on which species were present during the fish-kill events in Santa Giusta Lagoon using fixed samples (with Lugol's iodine or formalin) collected at the time of the events. The analysis is based on the method developed by Connel (2002), which allows a rapid identification of Raphidophyceae using three-primer PCR amplification of nuclear internal transcribed spacer (ITS) regions. The internal transcribed spacer region of the nuclear rRNA gene was used to discriminate among the marine raphidophyte species, so it’s a useful support especially when cells cannot be identified morphologically and fixation methods have destroyed cellular RNA content.
Our study is a first tentative to apply the method to natural samples in which only one or both the investigated Chattonella species may be present
Effects of trophic status on microcystin production and the dominance of cyanobacteria in the phytoplankton assemblage of Mediterranean reservoirs
Full text linkThe aim of our study was to evaluate the abundance of cyanobacteria and microcystins in four Sardinian
reservoirs (Italy) characterised by different trophic status to define a reference picture for future
changes. Increasing levels of eutrophication and the abundance of cyanobacteria are expected to occur
due to climate change, especially in the southern Mediterranean. Consequently, an in-depth study of
the occurrence of harmful cyanobacteria is important to develop appropriate management strategies
for water resources at a local scale. Monthly samples were collected at one station in each reservoir over
an 18-month period. The Analysis of similarity indicated that cyanobacterial abundance and species
composition differed significantly among the reservoirs. The Redundancy analysis highlighted their
relationship to trophic, hydrological and seasonal patterns. Spearman’s analysis indicated that there
were significant correlations among the most important species (Planktothrix agardhii–rubescens
group, Aphanizomenon flos-aquae and Dolichospermum planctonicum), nutrients and microcystins.
We highlighted that the species composition during periods of maximum microcystin concentrations
differed from those typically reported for other Mediterranean sites. We found new potential
microcystin producers (Aphanizomenon klebahnii, Dolichospermum macrosporum and Dolichospermum
viguieri), which emphasised the high diversity of cyanobacteria in the Mediterranean area and the need for detailed research at the local scale
Cocconeis intermedia Héribaud & Peragallo: nouvelles informations sur la morphologie et l’écologie d’une espèce de diatomée peu connue
No full textL’espèce Cocconeis intermedia a été décrite et illustrée en 1893 par Héribaud & Peragallo. Elle a été trouvée comme diatomée fossile dans des échantillons prélevés dans des dépôts situés à Randanne, Ponteix et Verneuge en Auvergne (département du Puy de Dôme, Massif central, France). La forme minor de l’espèce, également décrite par Héribaud & Peragallo dans la même région (dépôts à Randanne), ne diffère selon les auteurs que par sa taille plus petite. Cocconeis intermedia a ensuite été mentionnée comme étant une variété de Cocconeis placentula (Cocconeis placentula var. intermedia Héribaud & Peragallo) dans certains livres floristiques classiques et ce taxon a été rarement cité dans la littérature. Certaines études ont signalé sa présence dans les diatomites du district de Terrebonne en Oregon (USA) et, plus récemment, comme forme vivante dans les eaux peu profondes des écosystèmes de la mer Noire et de la mer d'Azov et dans les sources thermales et minérales du Pamir en Tadjikistan. À ce jour, les détails morphologiques et les préférences écologiques de cette espèce n’ont pas été documentés. Cocconeis intermedia a été récemment observée dans une petite source thermo-minérale appartenant aux eaux thermales de San Saturnino (Sardaigne, Italie), connues depuis l’époque romaine sous le nom de Aquae Laesitanae. Elle était présente dans six échantillons prélevés sur différents substrats en été 2016 et en hiver 2017 et elle était surtout abondante dans l’épiphyton en été (abondance relative = 13,3%) et dans l’épilithon en hiver (abondance relative = 10,6%). Nous présentons des détails morphologiques supplémentaires de l’espèce avec des images en microscopie optique et en microscopie électronique à balayage et de nouvelles informations sur son écologie et sa distribution spatiale et saisonnière en Sardaigne
Dominance of small-sized phytoplankton in a Mediterranean eutrophic coastal lagoon
No full textThe predator-prey relationship is generally size-specific in the pelagic food webs. Phytoplankton cell size structure can provide information on the successive levels of consumers and therefore on the energy that can flow towards the top consumers. This work focuses on phytoplankton cell size structure in a coastal lagoon (Cabras Lagoon, Italy) considered one of the most important for fishing productivity in the Mediterranean. The inter-annual and seasonal dynamics of picophytoplankton (Pico, cell size <3 μm) and Utermöhl Fraction of Phytoplankton (UFP, cell size >3 μm) were considered during almost three years in relation to the temporal dynamics of selected environmental variables and zooplankton. Small-sized cells with a mean linear cell size <10 μm and a mean cell volume <103 μm3 mainly represented UFP along the entire study period. This size class contributed the most to total phytoplankton biomass (up to 86%) and density (up to 99%) during the first part of the investigation period. A compositional change was detected: smaller species of Chlorophyceae, Bacillariophyceae, filamentous Cyanophyceae, and autotrophic nanoflagellates thrived in the second part of the study, replacing larger Mediophyceae that dominated UFP at the beginning. Picocyanobacteria rich in phycocyanin were the dominant taxa of Pico along the entire investigation period and this size class contributed the most to total phytoplankton biomass (up to 30%) and density (up to 96%) at the end of the study. The observed shift towards different and even smaller UFP and Pico in the second part of the study was most probably due to complex interactions between top-down and bottom-up effects. Indeed, an increased temperature, a decreased salinity and decreased concentrations of nutrients (mainly ammonium and orthophosphate), as well as an increased grazing pressure of rotifers on the larger Mediophyceae were simultaneous with the changes detected in phytoplankton. The obtained results highlight a longer planktonic trophic web in Cabras Lagoon that includes small phytoplankton at the base, ciliates, rotifers, and copepods. This suggests low energy availability for planktivorous fish, with possible future relevant consequences for fishing activities in this coastal lagoon
Indice per la valutazione della qualità ecologica dei bacini artificiali mediterranei (MedPTI) a partire dalla composizione del fitoplancton
No full textDinamica della materia organica disciolta in ambienti vulnerabili come le lagune costiere
No full textCoastal lagoons are highly vulnerable to climate change-related pressures. For instance, increasing temperatures promote higher oxygen consumption and anaerobic metabolism which may lead to dystrophic events, this being favored by shallow waters, reduced hydrodynamics and a strong benthic-pelagic coupling. Moreover, in these environments, aquaculture and fishing activities have been developed rapidly during the past few decades, contributing to nutrient over-enrichment and eutrophication. Extreme events, as a consequence of climate change, have a significant impact on the carbon cycle and the dynamics of dissolved organic matter (DOM) in coastal areas. Thus, a concurrent event of hypoxia and acidification could provide an opportunity to study DOM dynamics (and CDOM properties) and its relationship with these phenomena. The effects of oxygen depletion and decreasing pH on the absorption properties of CDOM in coastal lagoons exploited for aquaculture purposes is under-studied. For these reasons, we aim to undertake the following research: (i) to interpret the origin of DOM by comparing the hydrological and biogeochemical characteristics of various compartments (water and sediment) with surrounding geomorphological conditions; (ii) to investigate the spatial-temporal variation of DOC/CDOM; (iii) to assess the relationship between DOM dynamics and oxygen consumption and the effect of acidification on CDOM optical properties in attempt to mitigate coastal hypoxia
Long-term phytoplankton abundance, structure and diversity in the eutrophic Cabras Lagoon (Italy, W Mediterranean Sea)
No full textThe Cabras Lagoon is a shallow and eutrophic Mediterranean lagoon, located on the west coast of Sardinia, in the Gulf of Oristano. It is one of the aquatic ecosystems listed in the station “n. 14 Marine ecosystems of Sardinia” of the Italian Network of Long Term Ecological Researches (LTER Italy). In Cabras Lagoon primary production is dominated by phytoplankton, that makes studies of this biotic component crucial to understand the ecosystem dynamics.
The temporal variation of phytoplankton abundance, structure and diversity was analysed from 1999 to 2009 to assess the general features of phytoplankton succession and its long term tendencies in relation to environmental factors. The objective is to identify the main driving forces of phytoplankton variability in the light of the general trends of Mediterranean transitional waters.
The pluriannual dynamic of phytoplankton composition showed important changes during the study years. A clear dominance of Bacillariophyceae was observed until the end of 2000. In this span of time also Nanoplankton and Dinophyceae were important. From 2001, the presence of Cyanophyceae increased, with strong affirmations especially in summers. The results demonstrated that the major phytoplankton biodiversity observed from the beginning of the study until 2002 coincided with a major temporal variability of all the considered environmental parameters, in particular of nutrients and salinity. The high stability of the same parameters for more than a year, permitted the persistent affirmation of Cyanophyceae from 2007 until 2009
Epiphytic and epilithic diatom assemblages in Mediterranean karst springs: a case study from Sardinia (Italy)
No full textCocconeis intermedia peragallo & héribaud (Bacillariophyta): New information on morphology, distribution and ecology of a poorly known diatom species
No full textCocconeis intermedia was originally described by Peragallo & Héribaud in Héribaud (1893) as a fossil diatom species from samples collected in the Puy-de-Dôme department, Auvergne-Rhône-Alpes region (France). After the first brief description, the species was mostly mentioned as C. placentula var. intermedia in classic floristic books and, over time, it was reported living in a wide variety of aquatic environments. Despite this, the morphological features of C. intermedia remained poorly known: detailed information and micrographs are not available in the literature and the fine structure was never investigated. A Cocconeis species found in the thermomineral spring San Saturnino in Sardinia (Italy) was identified as Cocconeis intermedia Peragallo & Héribaud after an extensive literature search and a comparison with specimens from slides of Tempère & Peragallo collection housed in the Natural History Museum (London, United Kingdom). In this study we provide an amended description of the species with new morphological details as observed in light and scanning electron microscopy. We also provide additional information on the seasonal distribution and occurrence of the species on a variety of substrata in its habitat in Sardinia
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