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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Seasonal blooms of the HAB dinoflagellate Alexandrium taylori Balech in a new Mediterranean Area (Vulcano, Aeolian Islands)
No full textHigh-biomass blooms of A. taylori Balech have recently been spreading over new Mediterranean areas, with evident adverse effects on the marine ecosystem. In 1999-2000, a new Mediterranean locality was affected by blooms of A. taylori: the West Bay of Vulcano (Aeolian Islands, Tyrrhenian Sea), with maximum cell densities of 1.2 x 10(7)cells 1(-1) in August 1999 and 4.0 x 10(6) cells 1(-1) in August 2000 observed together with yellowish water discoloration. The seawater samples contained high concentrations of nutrients as DIN (Dissolved Inorganic Nitrogen), especially NH3-N with values of 14.4 mu M and TOT-P (Total Phosphorus) with values of 3.2 mu M due to the anthropic presence and discharge of untreated sewage. The climatic conditions also seem to influence the occurrence and spreading of the A. taylori blooms in the Vulcano Bay. Clonal cultures of A. taylori, established from Italian and Spanish seawater samples, were used for the sequence analyses of the 5.8S rDNA gene and ITS regions in order to study the genetic variability of different geographical populations of Alexandrium species in the Mediterranean area and to further develop the molecular markers for HAB key-species
Taxon-specific analysis of growth and mortality rates of harmful dinoflagellates during bloom conditions
Full text linkGrowth and mortality rates of natural single Alexandrium spp. cells were measured by the Landry-Hassett dilution technique during different phases of blooms. Taxon-specific experiments were conducted between May and October 2002 during 3 intense blooms of A. taylori and A. catenella at different locations of the Mediterranean Sea. In addition, dilution experiments using chlorophyll a as a proxy for total phytoplankton biomass were used to estimate daily rates of net growth and mortality of the total phytoplankton community. A. taylori growth rates ranged from 0.04 to 0.67 d(-1) and mortality rates from -0.20 to -0.65 d(-1). Growth rates of Gyninodinium sp., an accompanying dinoflagellate species during the A. taylori bloom studied, were similar to those measured for A. taylori, whereas their mortality rates (-0.58 to -0.82 d(-1)) were slightly higher. A. catenella growth and mortality rates were balanced (0.24 and 0.44 d(-1) compared with -0.25 and -0.44 d-1, respectively). The highest mortality rates (-0.65 d(-1)) were measured during the decline phase of 2 A taylori blooms. At the decline of the blooms, A. taylori and A. catenella showed considerable mortality, but microzooplankton grazing was not confirmed to be the main cause of the bloom termination. In general, growth was not limited by nutrients in the experiments. There were a few cases of a potential nutrient limitation in these areas and, in general, blooms were not conditioned by nutrients. When changes in biomass (chlorophyll a) were measured, non-linearity of data due to saturation was observed. The interpretation of these results required a split-function model. Saturated grazing (G(s)) was 28.9 mu g chl a 1(-1) d(-1), during which the saturating phytoplankton population represented a chl a concentration of 16 mu g 1(-1) (P-s)
Plankton toxicity and shellfish contamination by phycotoxins in a new Mediterranean locality
No full textDinoflagellate cyst assemblages as repertoire of species diversità: main results of the EU-SEED Project related to Mediterranean sites.
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