Long-term phytoplankton dynamics in a Mediterranean eutrophic lagoon (Cabras Lagoon, Italy)

Abstract

The temporal variations in phytoplankton abundance and diversity were analysed from 1999 to 2009 in Cabras Lagoon, a shallow eutrophic Mediterranean lagoon (west coast of Sardinia). It is one of the aquatic ecosystems listed in the ''Marine Ecosystems of Sardinia'' by the Italian Network of Long-Term Ecological Research (LTER Italy). The objectives of this work were to assess the general features of phytoplankton succession and its dynamics in relation to environmental factors along the decade 1999-2009, and to identify the main forces driving phytoplankton variability in terms of the general trends in Mediterranean transitional waters. Our results highlight several important aspects: a shift in the annual peak density from the summer-autumn season, observed in 1999-2002, to the winter-spring season in subsequent years; simultaneous reductions in chlorophyll a concentrations and cell size from 1999 to 2008; and the modification of the structure of the phytoplankton assemblages, from a more differentiated class composition in 1999-2002 to the subsequent dominance of the Cyanophyceae. Moreover, analysis of similarity on both abiotic and phytoplanktonic data shows significant differences among the hydrological years considered. Pearson's correlations indicate temperature, salinity and nutrients as the environmental parameters that most influenced the phytoplankton composition and dynamics.

Plankton dynamics across the freshwater, transitional and marine research sites of the LTER-Italy Network. Patterns, fluctuations, drivers

“…This period was characterized by very severe droughts (Zanchettin et al, 2008), with an estimated decrease of nutrient discharge in the sea of 50% -70 % with respect to previous years (Cozzi et al, 2012). Cabras, a salinity decrease since the early 2000s, resulted in a shift in phytoplankton community composition, which became dominated by cyanobacteria (Pulina et al 2012). Salinity changes were mainly due to the precipitation regime and inputs of freshwater from the watershed, which increased in relation to the increased frequency of exceptional climatic events (Pulina et al, 2016).…”

Effects of warming on a Mediterranean phytoplankton community

“…Water for phytoplankton analyses was collected every 3 days (day 0, T0; day 3, T1; day 6, T2, day 9, T3; day 13, T4; day 16, T5) from each incubation unit; 100 mL water samples were fixed with acid Lugol's solution and analyzed according to Utermöhl (1958), using an inverted microscope (Zeiss, Axiovert25), and 5 mL of water was settled for at least 4 h, after which larger and more easily identifiable cells were counted at 100 × magnification by scanning the entire bottom of the sedimentation chamber, whereas smaller species were counted at 200 × or 400 × magnification in an adequate number of fields (at least 10 % of the total bottom area of the settling chamber). Species were identified according to the taxonomic literature listed in Pulina et al (2012). Carbon biomass was estimated after determination of biovolume based on standard geometric shapes, by using the specific conversion factors indicated by Menden-Deuer and Lessard (2000).…”

First detection of Mnemiopsis leidyi (Ctenophora, Bolinopsidae) in Sardinia (S’Ena Arrubia Lagoon, Western Mediterranean): a threat for local fishery and species recruitment

“…Cell counts were made at a magnification of 100X on the entire bottom of the sedimentation chamber for the larger and more easily identifiable species, and at magnifications of 200X, and 400X in an adequate number of fields for the smaller cells. The species were determined according to the literature listed in Pulina et al (2012).…”