Protoperidinium (Dinophyceae) from Greece as seen by scanning electron microscopy

The marine dinoflagellates Protoperidinium ventricum (Abé) Balech, P. diaholus (Cleve) Balech, P. tristylum (Stein) Balech and P. divergens (Ehrenberg) Balech, collected from neritic plankton of the gulfs of Saronikos and Korinthiakos, Greece, have been examined by SEM. Morphological characteristics of their thecae are described and evaluated. Results are compared with patterns established by earlier SEM studies on related taxa.     

Limnological survey of the warm monomictic lake Trichonis (central western Greece); II. Seasonal phytoplankton periodicity – a community approach

Phytoplankton assemblages of the warm monomictic lakeTrichoniswere studied during the period April 1985 to February 1986.Speciescomposition and biomass data are presented along withinformationon the seasonal periodicity of dominant taxa of microalgae.Multivariate methods were used to analyze community structureandannual succession. Population succession patterns correspondtochanges in environmental variables. According to thegeneralizedphytoplankton sequences Trichonis is classified as anoligotrophiclake.     

The application of a micro-algal/bacterial biofilter for the detoxification of copper and cadmium metal wastes

In the present study the potential of a biofilter containing a mixture of dried micro-algal/bacterial biomass for removing heavy metals (Cu²⁺, Cd²⁺) from dilute electroplating waste was tested. The biomass was produced in an artificial stream using the effluent of a municipal waste water treatment plant as a nutrient source, with the additional benefit of reducing phosphorus and nitrogen loadings. Baseline batch experiments determined that optimum adsorption for both metals (80–100%) were achieved with the deionized-H₂O conditioned biomass at initial pH 4.0. Other biosorption variables (contact time, initial metal concentration) were also tested. Biosorption data were fitted successfully by the Langmuir model and results showed a high affinity of the used biomass for both metals (q_max 18–31 mg metal/g.d.w). Flow-through column experiments containing Ca-alginate/biomass beads showed that metal adsorption depends also on flow-rate and volume of treated waste. Desorption of both metals with weak acids was very successful (95–100%) but the regeneration of the columns was not achieved due to the destabilization of beads.     

Probing the settlement signals of Amphibalanus amphitrite

To achieve their reproductive potential, barnacles combine tactile exploration of surface structural properties and integration of cellular signals originating from their antennular sensory setae within a developmentally defined, temporally narrow window of settlement opportunity. Behavioural assays with cyprids coupled with biometric analysis of scanning electron microscopy-acquired images in the presence of specific chemical compounds were used to investigate how settlement on a substratum is altered in response to the presence of these compounds. Impeding tactile exploration was shown which altered cellular signalling and/or induced malformation of anatomical features of the antennular sensory setae, which disrupted the settlement behaviour of the model barnacle species Amphibalanus amphitrite. It is concluded that surface exploration by the cyprids relies on mechanical and nociception-related and calcium-mediated signals while a protein kinase C signalling cascade controls the timely metamorphosis of the cyprids to sessile juveniles.     

Abundance and growth response of microalgae at Megalon Embolon solar saltworks in northern Greece: An aquaculture prospect

There is continuous interest in many countries in maintaining and manipulating the rich ecological value of hypersaline ecosystems for aquaculture. The Megalon Embolon solar saltworks (northern Greece) were studied in sites of increasing salinity of 60–144 ppt to evaluate Dunaliella salina abundance and microalgal composition, in relation to physical and chemical parameters. Cluster and ordination analyses were performed based on the biotic and abiotic data matrices. Using fresh aliquots from 60 and 140 ppt salinity waters, phytoplankton performance was appraised with flask cultures in the laboratory by varying the inorganic PO₄-P concentration at 23 °C and 30 °C. At the saltworks, among the most abundant microalgae identified were species of the genera Dunaliella, Chlamydomonas, Amphora, Navicula, and Nitzschia. Dunaliella salina populations were predominant comprising 5–22% of the total microalgal assemblages during spring, but only 0.3–1.0% during the summer, when grazing by Artemia parthenogenetica and Fabrea salina was intense. D. salina cell density in April–July was in the range of 0.4–12.5 × 10⁶ L⁻¹ with typical densities of 1.5–4.5 × 10⁶ L⁻¹. Overall, microalgal densities were high in salinities of ≥100 ppt when inorganic-P concentrations were ≥0.20 mg L⁻¹ within saltworks waters. Multivariate analysis of species abundance showed that algal growth responses were primarily related to variation in salinity and inorganic-P concentrations, but also to NO₃-N concentration. In the laboratory, experiments indicated effective fertilization and denser microalgal growth under high inorganic PO₄-P applications (4.0 and 8.0 mg L⁻¹) at 60 ppt salinity and 23 °C. The lower PO₄-P applications (0.6–2.0 mg L⁻¹) were more effective at 60 ppt salinity and 30 °C. At 140 ppt salinity, microalgal growth response was less obvious at any of the corresponding phosphorus concentrations or temperatures. In both salinity experiments, Dunaliella salina bloomed easily and was predominant among the microalgae. Our observations indicate that Dunaliella salina populations and the overall rich microalgal profile of the saltworks, along with their performance in laboratory mono–and mixed cultures hold promise for mass cultivation within the M. Embolon saltworks basins.     

Limnological survey of the warm monomictic lake Trichonis (central western Greece); I. The physical and chemical environment

The physical and chemical status of Trichonis – the largestanddeepest natural lake in Greece – is examined over two annualcycles (1985–86 and 1988–89). A correlation between lakenutrientpatterns and phytoplankton biomass is attempted. Limnologicalfeatures are compared with data from other warm and temperatelakes.With regard to its thermal regime, Trichonis is classified asawarm monomictic lake. The lake's stratification pattern andannualheat budget resemble those of other temperate lakes. Trichonisisa carbonate type, low conductivity lake (class II, lowsalinitywarm lake). Nitrogen and phosphorus concentrations were ratherlow.The inorganic nitrogen content fluctuated widely over the twoannual cycles examined. On the contrary, phosphorusconcentrationsshowed no significant changes. The limiting factor during1985–86was P, while N was limiting during stratification in 1988–89.Aweak correlation was found between the plankton communityfeatures(species abundance, biomass, chlorophyll-a) and lightpenetration. At present the eutrophication process fromoligotrophytowards mesotrophy has not been essentiallyaccelerated.     

Dynamics of potentially harmful microalgae in a confined Mediterranean Gulf—Assessing the risk of bloom formation

The population dynamics of potentially harmful microalgae was investigated in the semi-enclosed shallow Gulf of Kalloni, Greece (Aegean Sea, Eastern Mediterranean), during a 2-year period from August 2004 to March 2006. A total of 21 potentially harmful microalgae (bloom-forming and/or toxic) were identified including 3 diatoms and 18 dinoflagellates. The densities of each species were analyzed in time and space and in relation to environmental parameters. Some species such as Alexandrium insuetum, Heterocapsa circularisquama, Karlodinium veneficum, Scrippsiella trochoidea, and Ceratium spp. developed high cell concentrations, particularly during a Pseudo-nitzschia calliantha winter bloom. Other species such as Dinophysis caudata, Ostreopsis ovata, Prorocentrum minimum, and Protoperidinium crassipes were rare or appeared in small numbers. Densities of the most abundant species were closely associated with freshwater nutrient-rich inputs during winter, being negatively correlated with temperature and salinity and positively correlated with nitrogen. The spatial distribution of the abundant species exhibited a marked increase towards the inner part of the gulf, close to the main freshwater inputs, whereas some species were mainly concentrated in the dilute surface layer (1 m depth). Examination of the abundance–occupancy relationship revealed that the species more prone to bloom are those with wide spatial distribution and frequent presence throughout the year such as the diatom P. calliantha. Although blooms of cyst-forming species are rarer, an increased risk can be foreseen under favorable resource supply and environmental conditions during winter.     

Screening for marine nanoplanktic microalgae from Greek coastal lagoons (Ionian Sea) for use in mariculture

Mediterranean mariculture uses imported strains of marine phytoplankton, raising questions of ecological risk and ability to adapt to local conditions for mass culture outdoors. In this context, we report here on the mass-culture potential and chemical composition of six strains of Prasinophyceae (five strains of Tetraselmis sp. and one Pyramimonas sp.) isolated from a Greek coastal lagoon. Proximate composition had a pattern of 10–20% ash, 35–65% protein, 6–10% lipids, and 25–45% other organics including carbohydrates. The amino acid profiles were typical for the marine representatives of the class. All strains had a high PUFA content with dominant the ω3 fraction in four of them. The fatty acid profiles indicated a Tetraselmis strain with high EPA (14%) and a Pyramimonas strain with high DHA (6%). These strains might be a good alternative for the common commercial strains used in Mediterranean aquaculture.