Maria Rosaria Vadrucci

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.

Quantitative relationships among phytoplankton body size classes and production processes in the North Adriatic frontal region

The variation patterns of phytoplankton standing crop and productivity in the North Adriatic frontal region and the relative importance of pico-, nano-, micro-phytoplankton are shown. Data of standing crop (chlorophyll a - Chl a ) and productivity ( 14 C assimilation) and PAR radiation ( w Em m 2 r s m 1 ) were collected during the four oceanographic cruises of the PRISMA II project. Average standing crop and productivity in the study area were 1.41 - 0.42 r mg r m m 3 Chl a and 1.23 - 0.37 r mg r C r m m 3 r h m 1 ; average assimilation number (P/B) was 0.872 - 0.589 r mg r C (mg-Chl a ) m 1 h m 1 and average photosynthetic efficiency (PE) was 0.020 - 0.054 (mg r C(mg-Chl a ) m 1 r h m 1 ) [ w Em m 2 r s m 1 ] m 1 . Phytoplankton biomass and productivity showed significant patterns of variation with the distance from the coast, with increasing depth and decreasing light intensity. The same patterns were shown by the three phytoplankton size classes. The spatio-temporal variations were significantly larger within the microplankton than within the pico- and nano-plankton size classes. Planktonic guilds were dominated by picoplankton, both as standing crop and productivity, in the northern stations (0.539 - 0.21 r mg r m m 3 Chl a and 0.572 - 0.25 r mg r C r m m 3 r h m 1 ) and in those more offshore, while microplankton was more important in the coastal and southern stations (0.727 - 0.58 r mg r m m 3 Chl a and 0.63 - 0.28 r mg r C r m m 3 r h m 1 ). In relative terms, picoplankton accounts for the 53% and 46% of biomass and primary production, while the microplankton account for the 43.6% and 48%. Assimilation number and photosynthetic efficiency did not show spatio-temporal variations but PE was inversely related with PAR radiation for all the size classes. Data suggest that the spatio-temporal patterns observed in this study are affected by the competitive relationships among body size classes in the phytoplankton guilds.

PhytoNumb3rs: An easy-to-use computer toolkit for counting microalgae by the Utermöhl method

Abstract Phytoplankton is recognised as a biological quality element and a biological descriptor in European Directives (WFD, MSFD) and several national laws. To determine the biodiversity and abundance of phytoplankton assemblages, the Utermohl method, using an inverted light microscope, is the most widely used. Nevertheless, the Utermohl method, standardised as UNI EN 15204 (2006), is time-consuming and labour intensive. We developed and tested PhytoNumb3rs, a tool for supporting microscope-based analysis of phytoplankton. PhytoNumb3rs is designed to make cell density calculation easier and to take account of qualitative and quantitative aspects regarding data precision, bias and method sensitivity. Specifically, it makes it possible to assess the performance characteristics of single analyses. PhytoNumb3rs is a user-friendly computing system based on a combination of Excel® spreadsheets. It allows the user to count phytoplankton cells, at various magnifications using various counting strategies, and to obtain the relative cell density, uncertainty and detection limit for each taxon. PhytoNumb3rs enables analysts to adopt a suitable counting strategy, run the analyses and easily perform all the steps associated with conventional microscope-based phytoplankton procedures (counting, data entry, computation, and data storage in a structured database). It allows the user to calculate the performance characteristics associated with the analytical results in accordance with UNI EN 15204 (2006) quality control procedures. Finally, it represents a useful tool for data harmonisation and data standardisation which in turn, are needed in order to increase the quality, comparability and accessibility of intra- and inter-laboratory data over time.