Antonella Gesuina Laura Lugliè

Paleoecological evidence for diatom response to metal pollution in Lake Orta (N. Italy)

Diatom remains were analysed in two short sediment cores from a subalpine Italian lake (Lake Orta), known for its major industrial pollution dating from the late 1920s, which has only recently been stopped. Copper was recognised as the main toxic agent for diatoms during the first 30 years of pollution (peak value: 100 μg l-1 in the late 1950s). A diatom community similar to other deep subalpine lakes existed in the past, and was disrupted by the pollution events. Acute and long-term effects of Cu contamination were tracked by changes in three distinct groups of species around the sharp boundary corresponding to the onset of the pollution. These groups were respectively composed of: (1) Species quickly extirpated by the discharge, mostly belonging to Fragilaria and Cyclotella and never reappearing; (2) Species apparently not affected, or not immediately affected, by the pollution, showing no definite trends with time. Synedra species, with various deformities, were conspicuous among these; (3) Species with accumulation rates increasing with time irrespective of pollution, mostly belonging to Achnanthes. Properties and tolerances of these groups (e.g. Synedra and Achnanthes) are discussed in detail.

Phylogenetic relationships among the Mediterranean Alexandrium (Dinophyceae) species based on sequences of 5.8S gene and Internal Transcript Spacers of the rRNA operon

A phylogenetic analysis of the genus Alexandrium, including both the most common and rare species from coastal areas of the Mediterranean Sea was carried out. Nucleotide sequences of 5.8 S gene and Internal Transcribed Spacer regions of the rRNA operon were examined and analysed together with isolates of Alexandrium spp. from elsewhere in the world. These rDNA ribosomal markers were useful in delineating the phylogenetic position of species in the genus, as well as in determining relationships among isolates within each species collected from different localities. Results of phylogeographical analyses within the ‘Alexandrium tamarense’ species complex identified three lineages in the Mediterranean Sea: the Mediterranean (ME), Western European (WE) and Temperate Asian (TA) clades. The phylogenetic grouping of the isolates is consistent with the ribotype clades, but not with the morpho-species that constitute the complex. Additional non-toxic isolates were included in the ME clade. The NA (North Atlantic) clade is the fourth group within the ‘Alexandrium tamarense’ species complex identified by phylogenetic analyses. Based on its higher genetic diversity and phylogeographical relationships, it can be hypothesized that the NA clade represents the ancestral group of the ‘Alexandrium tamarense’ species complex. Alexandrium minutum isolates of the NW Mediterranean clustered with strains from Brittany and Australia. Alexandrium minutum constituted a sister clade of A. tamutum, which is another species strongly associated with the Mediterranean area. Another typical Mediterranean species, A. taylori, was placed as a sister clade of A. pseudogoniaulax by the phylogenetic analysis. Finally, the phylogenetic relationships of some Alexandrium morpho-species that were infrequently observed in the Mediterranean Sea have been resolved.

Effects of trophic status on microcystin production and the dominance of cyanobacteria in the phytoplankton assemblage of Mediterranean reservoirs.

The aim of our study was to evaluate the abundance of cyanobacteria and microcystins in four Sardinian reservoirs (Italy) characterised by different trophic status to define a reference picture for future changes. Increasing levels of eutrophication and the abundance of cyanobacteria are expected to occur due to climate change, especially in the southern Mediterranean. Consequently, an in-depth study of the occurrence of harmful cyanobacteria is important to develop appropriate management strategies for water resources at a local scale. Monthly samples were collected at one station in each reservoir over an 18-month period. The Analysis of similarity indicated that cyanobacterial abundance and species composition differed significantly among the reservoirs. The Redundancy analysis highlighted their relationship to trophic, hydrological and seasonal patterns. Spearman’s analysis indicated that there were significant correlations among the most important species (Planktothrix agardhii–rubescens group, Aphanizomenon flos-aquae and Dolichospermum planctonicum), nutrients and microcystins. We highlighted that the species composition during periods of maximum microcystin concentrations differed from those typically reported for other Mediterranean sites. We found new potential microcystin producers (Aphanizomenon klebahnii, Dolichospermum macrosporum and Dolichospermum viguieri), which emphasised the high diversity of cyanobacteria in the Mediterranean area and the need for detailed research at the local scale.

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. Pearsons correlations indicate temperature, salinity and nutrients as the environmental parameters that most influenced the phytoplankton composition and dynamics.

Potentially toxic dinoflagellates in Sardinia

ABSTRACT Four coastal areas in Sardinia where bivalve molluscs are farmed or collected were checked for the presence of potentially toxic dinoflagellate species from 1992 to 1993. The study showed the presence of four potentially toxic species (Dinophysis sacculus Stein, Dinophysis caudata Saville-Kent, Gymnodinium cf. catenatum Graham and Cochlodinium polykrikoides Margalef). The four species showed a different frequency and density in every site. The Gulf of Olbia, which produces over 90% of the marketed bivalves in Sardinia, was the most affected of the studied areas.

Nutrient-flux evaluation by the LOICZ biogeochemical model in Mediterranean lagoons: the case of Cabras Lagoon (Central-Western Sardinia)

In this study, the Land-Ocean Interactions in the Coastal Zone (LOICZ) budgeting procedure was used to evaluate the main nutrient pathways and ecosystem functions within Cabras Lagoon (Central-Western Sardinia, Italy) in 2004. The results of a simple one-box and one-layer model showed that nutrient accumulation prevailed over mobilisation for both dissolved inorganic phosphorus (annual mean of 675.69 mol d−1) and dissolved inorganic nitrogen (mean of 6120.05 mol d−1). Net ecosystem metabolism (NEM) was always positive, implying that production predominated over respiration throughout the year (mean of 3.3 mmol C m−2d−1). Estimates obtained from the model also highlighted the fact that nitrogen fixation prevailed over denitrification (mean of 0.14 mmol m−2d−1). Finally, extended water-residence times (mean of 192 days) were observed in the lagoon, particularly in the summer. An approach based on the improvement of water exchange with the sea would provide a relatively simple and short-term interim strategy, until more comprehensive actions aimed at reducing the anthropogenic nutrient loads in the watershed can be implemented.

Phytoplankton in Sardinian reservoirs

Abstract A picture of the studies carried out in the past 20 years on phytoplankton from the 36 reservoirs and one natural lake in Sardinia is presented. Processing of the 1994 seasonal data shows that the dominant or subdominant algal species in the 36 reservoirs in terms of density belong to only 8 genera, with species of the genus Microcystis in 17 reservoirs, Chlorella in 15, Cyclotella in 12, Ankistrodesmus and Anabaena in 9, Aphanizomenon in 8, Melosira in 7 and Oocystis in 6. Processing of the data from the 16 reservoirs in which annual or plurennial surveys were carried out, shows that on the basis of the biomass the most likely floristic pattern is Microcystis aeruginosa Kg., Microcystis flos-aquae (Wittr.) Kichn., Anabaena flos-aquae (Lyngb.) Breb., Anabaena planctonica Brunnth., Aphanizomenon flos-aquae (L.) Ralfs., Melosira granulata (E.) Ralfs and Closterium aciculare T. West. In general terms this means that most of these reservoirs are eutrophic. In fact the species are capable of describin...

Phytoplankton dynamics in relation to environmental changes in a phytoplankton-dominated Mediterranean lagoon (Cabras Lagoon, Italy)

In Mediterranean lagoons, macrophytes often surpass phytoplankton as the most important primary producers. Less frequently, phytoplankton dominates throughout the year, thus knowledge of its dynamics is relatively limited and scattered. In this study, we assessed over two years the dynamics of phytoplankton assemblages, including potential harmful algal species (HAS), in relation to environmental changes in the phytoplankton-dominated Cabras Lagoon (Sardinia, Italy). The lagoon was characterised by uniform spatial conditions, wide temporal variations in salinity (40 PSU) and high nutrient availability. Phosphorus was highest in summer, possibly recycled within the system, while dissolved inorganic nitrogen increased in winter and spring due to watershed discharge. Chlorophyll a, positively correlated with nutrients and rainfall, showed a typical bimodal pattern with summer-winter blooms. Modifications in phytoplankton composition strongly correlated with extreme weather events, such as intense rainfall. This generated an abrupt salinity decrease that, combined with high nutrient availability, favoured the dominance of Cyanophyceae of reduced cell size, such as Cyanobium and Rhabdoderma species. We suggest that the prolonged and intense dominance of Cyanophyceae, added to other HAS, has a negative impact on the primary economic activities of the lagoon, such as fishery, and generally on the whole lagoon functioning.

First record of planktonic crustaceans in Sardinian reservoirs

Sardinian man-made lakes are reservoirs of species richness, hosting zooplankton taxa from the Mediterranean region and North Africa. To provide a first record of the taxa composition and diversity of zooplankton communities, we sampled 15 reservoirs during 2008–2009, from the north of the island to the south, representative of a range of size, depth, renewal time, and trophy. The survey was complemented by seasonal sampling in one of the largest lakes studied. Water samples collected from surface to bottom provided data on hydrochemistry and trophy. Crustacean dormant stages were inspected from sediments of the richest, and most diverse, Lake Sos Canales. RDA suggested that productivity, water depth, renewal time and altitude were the main variables related to taxa composition. The ubiquitous Copidodiaptomus numidicus, and its persistence in the water column, resulted from the production of subitaneous eggs throughout the year, an adaptive strategy in perennial water bodies. Genetic analyses of DNA sequences of the diagnostic gene ND5 placed the Sardinian Daphnia pulex in the North American group. Moreover, the ND5 sequence found in Sardinia was identical with that of an asexual hybrid clone between the American D. pulex and American D. pulicaria that replaced native D. pulex throughout Africa. The presence of this ND5 haplotype in Sardinia shows that this invasive clone also poses an invasive threat to native populations in Europe.

Epilithic diatom assemblages and environmental quality of the Su Gologone karst spring (centraleastern Sardinia, Italy)

Abstract Karst springs are considered among the most vulnerable groundwater-dependent ecosystems. Despite their ecological value and importance as strategic water sources, Mediterranean karst springs are still poorly investigated. The aim of this study was to analyse the epilithic diatom assemblages and to test their usefulness as indicators of environmental quality on the Su Gologone spring (central-eastern Sardinia, Italy), a biotope of great natural value and a precious source of drinking water. A total of 89 diatom taxa were found with 25 new records for Sardinian running waters. Species richness, Shannon-Wiener and Pielou indices showed good biotic integrity. The dominant taxa were alkaliphilous, halophobous-oligohalobous exigent, xeno- oligosaprobic and characteristic of oligotrophic waters. The eutrophication/pollution index − diatom based (EPI-D) and the Navicula Nitzschia Surirella indices indicated respectively an excellent/good biological water quality and a low physical disturbance. However, the biological and chemical oxygen demand, and the microbiological variables (E. coli, fecal and total coliforms) revealed an organic contamination of the water, although moderate. The judgment provided by the EPI-D should be verified after updating of the index. In fact, 10 taxa found in this study are not currently considered by the EPI-D method.