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Il genere Cocconeis (Bacillariophyta) nella comunità epifita a diatomee di Posidonia oceanica: analisi tassonomica, ultrastrutturale ed ecologica
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McMurdo Sound summer phytoplankton revisited: a comparison between 1984 and 2010
Full text linkDuring January 2010, participants of the 9th International Graduate Training Course in Antarctic Biology (sponsored by the US National Science Foundation) conducted an investigation of the phytoplankton in McMurdo Sound (77°50'S, 166°36'E). Sample sites were established along a transect from open ocean to the inland limit of the annual sea ice at the edge of the Ross Ice Shelf. Hydrographic data (e.g., vertical profiles of temperature and salinity; attenuation of ultraviolet and photosynthetically active radiation (PAR); nutrient concentrations) and biological parameters (e.g., community taxonomic structure, chlorophyll a concentrations) were quantified. The transect corresponded to the December 1984 study area of Palmisano et al. (1986), and a comparison of data across the 25-year period was undertaken. In both studies, the prymesiophyte Phaeocystis was dominant (~99% of cells). Chlorophyll maxima were 12 μg/L in 1984 and 11 μg/L in 2010. Mean nutrient concentrations in 2010 (55.7±2.8 μM silicate and 0.76±0.43 μM phosphate) were also comparable to 1984 means (58.0±11.3 μM silicate and 1.52±0.52 μM phosphate). The 2010 extinction coefficients for PAR ranged from 0.2 in the open water at the ice edge to 0.6 in areas under the annual sea ice, supporting conclusions by Palmisano et al. that Phaeocystis can be productive under a large gradient of light regimes as cells are transported under the ice. The close correlation between data obtained in 1984 and 2010 suggests long-term consistencies in the physical and biological characteristics of McMurdo Sound
Biodiversity of epiphytic diatom community on seagrasses and corals from Saudi Arabian coasts of the Arabian Gulf: a taxonomical, ecological and environmental approach (oral presentation)
Full text linkThe microphytobenthic community significantly contributes to primary production in shallow waters, mainly along continental shelves where it can reach values exceeding phytoplankton biomass in the overlying water column. Diatom communities are among the dominant components in the microphytobenthos and their species composition is strongly influenced by the nature of substrate and by their biogeographic distribution. On the other hand, these communities appear to be composed by a limited number of genera, belonging to different growth forms that can be considered fully adapted to the epibenthic lifestyle. In spite of the important ecological
role played in the food chain, the biodiversity of diatom communities on seagrasses and seaweeds is still poorly studied and highly underestimated while that on corals results virtually neglected as in the literature there are only two studies on this topic.
Our study aimed to decrypt and document for the first time the hidden biodiversity of diatoms associated to seagrasses and hard corals along the Saudi coasts of Arabian Gulf. The diatom assemblages have been identified exclusively by electron microscopy so that their community structure has been analyzed in depth and the diversity have been documented at genus/species level.
Preliminary results demonstrated that both seagrasses and corals collected along the Saudi Arabian coasts hosted benthic diatom communities, which in both the case constituted the major element of their epibenthic microalgal flora. Significant differences in terms of cell density, species composition and community structure were observed between the diatom communities of seagrasses and corals and within the different sampling locations analyzed. More in detail, cell densities of seagrass diatom communities resulted more than one hundred times higher than those of corals with mean values approximately of 6000-7000 cell/mm2 in the former vs 100-300 cell/mm2 in the latter. Noteworthy is that the specie composition of seagrasses diatom communities was characterized by the almost full dominance of adnate genus Cocconeis (represented by four species) exhibiting cell densities mean values more than one hundred times higher than those of all the other diatom genera present in the communities. The cell density values showed by Cocconeis communities epiphytic on Saudi Arabian gulf seagrasses analyzed in the present study are up to my knowledge the higher
registered in any other environment and host organism studied, comparable only to some peculiar monospecific communities found onAntarctic macroalgae. Undoubtedly, the particularly challenging environmental conditions occurring in the different sampling stations selected along the Saudi coastal areas of Arabian Gulf could be responsible of some specific changes in the abundances and specie composition observed in the diatom communities of seagrasses
Tassonomia e distribuzione nel Mediterraneo di specie del genere Cocconeis Ehr. (Bacillariophyta)epifite sulle foglie di Posidonia oceanica
No full textCaratteristiche morfologiche di transizione fra le Monoraphideae (Achnanthales, Bacillariophyceae, Bacillariophyta): il caso di specie atipiche appartenenti al genere Cocconeis
No full textNell’ambito delle diatomee provviste di raphe (Bacillariophyceae), un discreto numero di generi è caratterizzato dalla assenza di tale struttura in una delle due valve che, per tale motivo, viene definita arafidica. Uno sviluppo eterovalvare, pertanto, accomuna i rappresentanti di tali generi che nel complesso sono noti come diatomee monorafidee. Secondo la più recente revisione tassonomica dei generi delle diatomee (Round et al., 1990), 3 famiglie (Cocconeidaceae, Achnanthaceae, Achnanthidiaceae) con rispettivamente 3 (Anorthoneis, Cocconeis, Campyloneis) 1 (Achnanthes) e 2 (Achnanthidium, Eucocconeis) generi costituiscono il raggruppamento delle monorafidee.
Mentre i caratteri diagnostici distintivi dei generi inclusi nelle famiglie Cocconeidaceae e Achnanthaceae risultano ben definiti non altrettanto si puo affermare riguardo ai generi della famiglia Achnanthidiaceae, oggetto di recenti revisioni tassonomiche (Round & Bukhtiyarova, 1996). Nell’ambito di un’approfondita revisione ultrastrutturale effettuata sulle specie mediterranee del genere Cocconeis, in alcune di esse sono stati individuati caratteri diagnostici ritenuti non tipici del genere. Alcuni di questi mostrano carattere di transizione con quelli presenti in altri generi della famiglia Cocconeidaceae (Campyloneis) o di quella Achnanthidiaceae (Planothidium). Ciò conferma la necessità di una più ampia revisione del genere Cocconeis
Comparison of Cocconeis pseudonotata sp nov with two closely related species, C-notata and C-diruptoides, from Posidonia oceanica leaves
No full textThree Cocconeis Ehrenberg species, epiphytic on the leaves of Posidonia oceanica (L.) Delile, were studied by light and electron microscopy. A new species, C. pseudonotata, is described which is closely related to C. notata Petit and C. diruptoides Hustedt. Gross morphology and the presence of a sigmoid raphe and sternum are the characters shared by the three species, whereas the central areas of sternum and raphe-sternum valves, and the stria and areola densities are the main distinctive characters for the species when observed by light microscopy. Scanning and transmission electron microscopic observations revealed that the fine structure of areolae must be also considered in order to identify the species. Comparison among the three species has been carried out by observations on material from our samples, as well as on the type material of C. diruptoides and cleaned samples from the Hustedt collection. The study also provides new information on the geographical distribution of these species
Morphology and taxonomy of Amphicocconeis gen. nov. (Achnanthales, Bacillariophyceae, Bacillariophyta) with considerations on its relationship to other monoraphid diatom genera
No full textSEM and TEM observations on the cleaned material used by Hustedt for the preparation of the type of the marine diatom Cocconeis disculoides Hustedt and on living specimens of the species scraped from Posidonia oceanica (L.) Delile leaves collected in different coastal areas of the Mediterranean Sea revealed structures that differentiate this species from the genus Cocconeis Ehrenberg. The external apical raphe endings have marked terminal fissures; valvocopulae extend over a large part, or all, of the valve surface and bear rounded perforations arranged differently in the two bands; areolae are occluded by simple hymenes with irregularly distributed, rounded perforations. Recently, C. disculoides Hustedt was transferred to Psammococconeis Garcia, a new genus found in sediment samples from Port Belo Peninsula (Brazil), as P. disculoides (Hustedt) Garcia. However, the genus Psammococconeis lacks the raphe terminal fissures, shows two types of areolae in the sternum valve mantle and an extended valvocopula with perforations only in the raphid valve. Furthermore, in P. disculoides, the areolae are occluded by fimbriate hymenes in both valves. These observations lead us to propose the new genus Amphicocconeis, which at present includes only A. disculoides (Hustedt) comb. nov. The elements of Hustedt's type material examined by Garcia should be the lectotype of a new species of Psammococconeis
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