Spatial and seasonal variability of fractionated phytoplankton biomass and primary production in the frontal region of the Northern Adriatic Sea

Spatial and seasonal patterns of variation of fractionated phytoplankton biomass and primary production and their relationships with nutrient concentrations were analyzed along an inshore - offshore gradient and in relation to the presence of a frontal system in the Northern Adriatic Sea. Sampling was carried out in winter and summer during four oceanographic cruises (June 1996 and 1997, February 1997 and 1998) as part of the PRISMA II project. Water samples for determining nutrient concentrations, phytoplankton biomass (as Chla) and primary production (as 14 C assimilation) were collected at five optical depths. Sampling stations were located along 2 or 4 parallel transects arranged perpendicularly to the shoreline and the frontal system. The transects were located at such a distance from the coast that the frontal system crossed them at their halfway point. Total dissolved nitrogen (TDN) and total dissolved phosphorus concentrations (TDP) were 12.41 ± 3 .95 mM and 0.146 ± 0 .070 mM, respectively. The values in the two seasonal periods were similar, decreasing along the inshore-offshore gradient. Values for phytoplankton biomass and primary productionwere higher in the winter than the summer cruises, and decreased, in both seasonal periods, along the inshore / offshore gradient. Moreover, in both seasonal periods, picophytoplankton dominated both biomass and productivity, (56% and 44%, respectively) at stations beyond the frontal system, while microphytoplankton was more important at stations inside it (44% and 44%, respectively). Total phytoplankton biomass and primary production were directly related to nutrient concentrations. Regarding size classes, significant patterns of variation with nutrients were observed particularly for biomass. The results indicate that the size structure and function of phytoplankton guilds seem to be mediated by nutrient inflow, as well as by competitive interaction among size fractions

Biovolume determination of phytoplankton guilds in transitional water ecosystems of Mediterranean Ecoregion

1 - Conceptually, morphometric measurements of phytoplankton guilds seem to have major advantages as descriptors of the ecological status of transitional water ecosystems (TW) with respect to classical taxonomic descriptors. However, at present, standardized or common methodologies for the use of morphometric descriptors do not exist. 2 - This paper aims to provide a starting point for the activation of standardized methods for the determination of morphometric descriptors of phytoplankton as a quality element in TW in accordance with the new directive of WFD 2000/60/EU. 3 - Phytoplankton biovolume is one of the most studied morphometric descriptors. It can be estimated by associating the algae with similar geometric forms and determining the volume of these by measuring the linear dimensions required for its calculation under the microscope. However, the lack of a standardized set of geometric forms and equations for calculating biovolume causes difficulties and produces data that are not comparable. 4 - A set of geometric models is suggested here for calculating the cell biovolumes of 201 phytoplankton genera found in transitional water ecosystems of Mediterranean Ecoregion. The equations were designed to minimize the effort of microscopic measurements. The main methodological problems, and the similarities and differences between our own and previously published proposals are discussed

Interruption of torus doubling bifurcation and genesis of strange nonchaotic attractors in a quasiperiodically forced map : Mechanisms and their characterizations

A simple quasiperiodically forced one-dimensional cubic map is shown to exhibit very many types of routes to chaos via strange nonchaotic attractors (SNAs) with reference to a two-parameter $(A-f)$ space. The routes include transitions to chaos via SNAs from both one frequency torus and period doubled torus. In the former case, we identify the fractalization and type I intermittency routes. In the latter case, we point out that atleast four distinct routes through which the truncation of torus doubling bifurcation and the birth of SNAs take place in this model. In particular, the formation of SNAs through Heagy-Hammel, fractalization and type--III intermittent mechanisms are described. In addition, it has been found that in this system there are some regions in the parameter space where a novel dynamics involving a sudden expansion of the attractor which tames the growth of period-doubling bifurcation takes place, giving birth to SNA. The SNAs created through different mechanisms are characterized by the behaviour of the Lyapunov exponents and their variance, by the estimation of phase sensitivity exponent as well as through the distribution of finite-time Lyapunov exponents.Comment: 27 pages, RevTeX 4, 16 EPS figures. Phys. Rev. E (2001) to appea

Nutrient loading and spatial-temporal dynamics of phytoplankton guilds in a Southern Italian coastal lagoon (Lake Alimini Grande-Otranto, ITALY).

The importance of external and internal P-loading to the structural organization and dynamics of phytoplankton guilds in a Southern Italy coastal lagoon (Lake Alimini Grande) was investigated. To this end, phosphorus external loading through localized freshwater inputs was measured, P-release through detritus decomposition on sediments was evaluated, and phytoplankton abundance, biomass and taxonomic composition were quantified at 33 sites and 12 sampling times from September 1998 to September 1999. P-loading in the area was greater in the winter (26.5 µM P m−2 d−1) than in the summer (18.4 µM P m−2 d−1). In the winter, external inputs were 61.7% of the total, while in summer, internal inputs accounted for 99.8% of the total. Phytoplankton biomass was related to P inputs. In particular, the spatial distribution of phytoplankton biomass was related to external inputs in winter-spring, and to internal inputs in summer-autumn. A total of 228 phytoplankton taxa were identified of which 13 taxa accounted for more than 80% of phytoplankton abundance. The spatial and temporal dynamics of 13 taxa were related to P-availability and habitat heterogeneity