Biomedical subjects

Cecilia Totti

Publications and source records attributed to Cecilia Totti.

4 recordsLinked to original sources

PubMed2005

Relevance of the dinoflagellate Gonyaulax fragilis in mucilage formations of the Adriatic Sea.

Oceanographic cruises were carried out monthly from June 1999 to July 2002 to follow the mucilage formation process in the Northern Adriatic Sea. Results show that in correspondence with these events the dinoflagellate Gonyaulax fragilis (Schütt) Kofoid was observed both in the water column and within mucilage aggregates. In the water column, increasing abundances were observed from May until July, with values never exceeding 8500 cells l(-1). Much higher densities were observed within superficial gelatinous aggregates (22800-3400000 cells l(-1)). In mucilage samples, a large number of decomposing cells were present, together with abundant alive cells, enveloped in exudates. G. fragilis isolated from mucilage samples was cultured in three different culture media; it was characterized by a low growth rate but it produced a high amount of polysaccharides. The highest yield both in terms of cell number and carbohydrate production was observed in the medium having the highest nitrogen and phosphorus content and the lowest N/P ratio. The monomeric composition of G. fragilis carbohydrates, compared with that of mucilage samples, showed that in both natural and cultured samples galactose was the most abundant sugar; in addition, an overall good correlation, especially between the monomeric carbohydrate composition of G. fragilis grown in f/2 medium and that of a mucilage sample in which this species was present in high density, was observed.

Animals↗

PubMed2005

Inter-annual variations of planktonic food webs in the northern Adriatic Sea.

The temporal dynamics of microphytoplankton, microzooplankton and mesozooplankton were monitored over 37 months in the Adriatic Sea in order to identify alterations in the plankton structures, which can lead to, or enhance the production of macro-aggregates, that affected the entire northern basin in summers 2000 and 2002, and to assess any negative effects of mucilage on plankton temporal patterns. Samples were collected monthly, from June 1999 to July 2002, on three transects at 9 stations across the northern and central Adriatic Sea. Besides the high year-to-year variations in abundances and taxonomical composition, plankton communities only showed a clear seasonal succession during 2001, when since April a grazing food web developed and was able to control large sized phytoplankton increase. In spring-summer 2000 and 2002 consumer abundances remained quite low and the dominant mesozooplankton summer species (Penilia avirostris) did not reach its usual summer maximum. The lack of an efficient top control was more evident on the northernmost transect, where generally grazing food web prevails over the microbial one. A large part of the microphytoplankton blooms, although not particularly intense, was exported to the bottom in the particulate phase, where it was processed by bacteria, enhancing the production of refractory dissolved material.

Animals↗

PubMed2005

Mucilage microcosms.

In the summers of 2000, 2001 and 2002, large amounts of sticky mucilaginous material aggregated to form masses of impressive dimensions over large areas of the Adriatic Sea, particularly in its northern part. Aggregates differing in size were sampled by SCUBA divers and submitted to chemical (nutrient and organic matter concentrations) and biological analysis (virus, bacteria and phytoplankton abundances and bacterial metabolism). Suspended and sinking mucilaginous aggregates were biota-rich environments where the abundance of planktonic organisms and the concentration of nutrients were orders of magnitude higher than in the surrounding seawater. The embedded phytoplankton was mostly composed of diatoms, but the dinoflagellate Gonyaulax fragilis, previously reported in association with the aggregates, was also present. A variety of processes occurred within the mucilaginous aggregates which resulted in the transformation of the organic matter composition and lability and contributed to a partial degradation of mucilage. For an efficient degradation of mucilage, several conditions are necessary: high bacterial abundance and activity and an efficient recycling of nutrients within the aggregates. Most of these conditions, appear to change depending on the type and age of the aggregate. During the first phase of aggregation (cobwebs and ribbons), bacterial activities addressed the degradation of organic matter, particularly that of the nitrogen fraction. The degradation products were rapidly taken up by bacteria, supporting an increase in their abundance and production. In aged mucilage (clouds), the degradation processes decreased and the bacterial metabolism suggested the presence of new organic labile compounds probably due to phytoplankton production. On the basis of our results, stringers, generally considered the first step of the aggregation process, seemed to be the result of a mechanical disruption of other types of aggregates.

Analysis of Variance↗

PubMed2005

Phytoplankton size-distribution and community structure in relation to mucilage occurrence in the northern Adriatic Sea.

The spatial and temporal variations of pico-, nano- and microphytoplankton abundance and composition were investigated over a 37 month period, focusing on the ecological role of different size classes of phytoplankton, and on the changes of the community structure that might occur during periods when large mucilage macroaggregates appear. Samples were collected monthly from June 1999 to July 2002 at 11 stations, along three transects covering the northern Adriatic basin. Highest abundances were observed in late-winter/spring for microphytoplankton (mainly diatoms), in spring-summer for nanophytoplankton, and in summer for picophytoplankton. The autotrophic component was more abundant in the summers of 2000 and 2002 (when large mucilage aggregates occurred) than in the summers of 1999 and 2001 (when a massive phenomenon was not observed). This increase was statistically significant for pico-, nano- and, among microphytoplankton, only for dinoflagellates. Blooms of picophytoplankton were often observed at the bottom layer during mucilage summers. The microphytoplankton community during mucilage phenomena was characterized by a species composition (Chaetoceros spp., Cerataulina pelagica, Pseudo-nitzschia delicatissima, P. pseudodelicatissima, Cylindrotheca closterium, Dactyliosolen fragilissimus) comparable to that observed in summers without extensive mucilage occurrence. However, some species appeared with significantly higher densities in the summers of 2000 and 2002: Ceratium furca, C. closterium, Oxytoxum spp., Hemiaulus hauckii and Gonyaulax fragilis. Microscopic observation of aggregates revealed that the microphytoplankton species composition inside the aggregates was comparable to that observed in the water column, with an enrichment of opportunistic species such as C. closterium and P. delicatissima. The presence of mucilage aggregates affects the phytoplankton populations in the water column, even when aggregates are at early stages. It seems that there is a mutual relationship between phytoplankton and aggregates, i.e., several diatom and dinoflagellate species may contribute to the aggregate formation and enlargement, but mucilage aggregates themselves may also affect the phytoplankton populations, allowing the development of a rich diatom community and in general enhancing nanophytoplankton growth.

Demography↗