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Diatoms are unicellular, photoautotrophic eukaryotic microorganisms, often forming colonies and can be found in most aquatic and moist terrestrial habitats. All known diatoms today have specific golden-brown pigment fucoxanthin that masks chlorophylls in diatom plastid, but one genus represents an exception, having the additional specific pigment marennine due to whom the cells appear blue. Blue diatoms from genus Haslea cause a global phenomenon of ˝greening˝ in shellfish (mostly oysters) affecting them in both positive and negative ways. In this study, historical and recent review regarding blue diatoms and physiological and behavioural effect of marennine as well as challenges in shellfish farming from diatom perspective is addressed. This study is also a first record of blue Haslea diatom in the South Adriatic Sea during BIOTA (Bio-tracing Adriatic Water Masses) cruise in March 2016. Investigated blue diatom was cultured in laboratory and morphologically analysed with light microscopy. Diatom investigations are very important for better understanding of the ecology of specific marine area, but also for the economy, aquaculture and tourism. The emergence of green coloured flesh of shellfish in the Adriatic Sea has not been recorded yet, but this finding of the blue diatom from genus Haslea does not rule out this possibility in the future. [ABSTRACT FROM AUTHOR]

The planktonic diatoms belonging to two genera Chaetoceros and Bacteriastrum , included within the family Chaetocerotaceae, are ecologically important as they represent an important component of the phytoplankton in the coastal regions and are often among bloom-forming taxa. We analysed the chaetocerotacean species composition and abundances in the coastal area of northeastern Adriatic in a biweekly study conducted from September 2008 to October 2009 with the aim of investigating seasonal dynamics and species succession on a fine temporal scale and determining the most important ecological factors influencing their distribution. The study identified seven Chaetoceros and three Bacteriastrum species as major phytoplankton components showing the clear annual succession and two types of blooms (one species/multi species) governed by differing ecological conditions. Autumn bloom was composed of 20 chaetocerotacean species with Chaetoceros contortus and Chaetoceros vixvisibilis alternating in dominance. The summer period was characterized by spreading of freshwater from the Po River up to the eastern coast increasing availability of phosphate which triggered the monospecific Chaetoceros vixvisibilis bloom. We explained the chaetocerotacean dominant species succession pattern by the environmental parameters, with the temperature, salinity and phosphate availability as most important factors driving the species seasonality. [ABSTRACT FROM AUTHOR]

This work describes the dynamics of the autotrophic plankton community in Lim Bay in the north-eastern part of the Adriatic Sea from June 2008 to September 2009. There was an evident shift between microphytoplankton and picophytoplankton domination in summer and autumn periods, while nanophytoplankton contributed negligibly. Picophytoplankton dominated in June 2008 and September 2009 (contributing up to 84 % of the total phytoplankton biomass), while the micro-fraction dominated in September 2008 and June 2009 (contributing up to 97.2 % of the total biomass). The pico- fraction was dominated by Synechococccus in terms of abundance and biomass, with the highest abundances in September of 2009. Picoeukaryotes were not that prominent in terms of abundance or biomass, but they exceeded Synechococcus in terms of biomass in November 2008 and February 2009, and proved to be an important and consistent component of the Lim Bay phytoplankton community. Our results indicate that seasonal variability in the community structure was more affected by specific environmental perturbations occurring in Lim Bay than by availability of nutrients. [ABSTRACT FROM AUTHOR]

Abstract: The population dynamics of Pseudo-nitzschia in relation to environmental factors was investigated from March 2002 to July 2008 in Lim Bay, in the north-eastern Adriatic Sea. Domoic acid was monitored in the breeding population of Mytilus galloprovincialis from 2005 to 2008. The principal-component analysis of environmental parameters showed that the system is mostly temperature driven. The phytoplankton community was mainly composed of diatoms. Pseudo-nitzschia was the dominant diatom, present in 60% of samples, with a maximum (1.6×106 cellsL−1) contribution up to 97% of the total diatom abundance. Morphological analysis revealed Pseudo-nitzschia manii and potentially toxic Pseudo-nitzschia pseudodelicatissima, Pseudo-nitzschia pungens, Pseudo-nitzschia fraudulenta and Pseudo-nitzschia calliantha as the dominant species in blooms. Pseudo-nitzschia abundance positively correlated to temperature, phosphate and ammonia in accordance with its maximal abundance in the summer/autumn period when fish farms had a maximum impact on the environment. Domoic acid was detected in M. galloprovincialis in concentrations below regulatory limits, ranging from 0.097 to 0.8721μgg−1 in five cases from April to October 2005 in Lim Bay, but so far it is not clear which of the species was responsible for DA production. This study is also the first record of P. manii, P pungens and P. fraudulenta species in the Adriatic Sea. [Copyright &y& Elsevier]

The Velebit and Pag Channels form a 40 km long and 4-14 km wide system running parallel to the northeastern Adriatic coast. The aim of this study was to investigate phytoplankton abundance, composition and distribution along the system in the autumn period. Sampling was carried out at 8 stations in November 2008. The spatial distribution of physico-chemical parameters indicated the existence of a pronounced horizontal thermohaline and trophic gradient. From the inner part of the Velebit Channel, which is an extension of the karstic Zrmanja River estuary, to the outer end of the Pag Channel, which communicates with the open sea, the temperature and salinity ranged from 11.0 to 16.0 °C and from 23.4 to 38.2, respectively. Nutrient concentrations ranged from 0.001 to 0.1 µmol L-1 for orthophosphates, from 0.85 to 7. 0 µmol L-1 for total inorganic nitrogen and from 0.3 to 15.4 µmol L-1 for silicates. Total abundance of phytoplankton decreased from 5.5 x 105 cells L-1 to 8.5 x 104 cells L-1 along the trophic gradient. Diatoms dominated the phytoplankton with maximum abundances from 7.3 x 104 cells L-1 (85% of total phytoplankton) at the most oligotrophic stations up to 9.6 x 105 cells L-1 (96% of total phytoplankton) at the nutrient enriched stations. Statistical analysis on the basis of environmental and biological parameters clustered the stations in three main groups. The first group represented the southern Velebit Channel with higher nutrient levels and phytoplankton dominated by Thalassionema nitzschioides. The second group included stations from the middle Velebit Channel with significantly lower levels of nutrients, and phytoplankton mostly dominated by Bacteriastrum sp. with a contribution by various diatom species. The third group represented the stations from the Pag Channel and associated with the exclusive domination of Bacteriastrum sp. and a greater contribution of coccolithophorids. This paper also gives the first checklist of species present in the extremely oligotrophic area of the Velebit and Pag Channels. 148 taxa were identified." 91 diatoms, 47 dinoflagellates and 10 other flagellate morphotypes. Detailed electron microscopy analysis revealed three potentially toxic diatoms of Pseudo-nitzschia genus: P. calliantha, P. pseudodelicatissima and P. manii. The results of this work represent a valuable contribution to the knowledge of phytoplankton species composition and distribution relative to prevailing physico-chemical conditions in this poorly investigated transition zone. [ABSTRACT FROM AUTHOR]

We present the first insight to the oceanography of the southeastern Adriatic Sea, where coastal water influenced by Albanian rivers comes into contact with the inflowing oligotrophic Eastern Adriatic Current (Ionian Surface Water and Levantine Intermediate Water). A distinct plankton distribution was observed on each side of the shelf break hydrographic boundary in May 2009, during gradual warming of the surface waters. The prochlorophytes accumulated along the nutricline above the shelf and continental slope. The phosphorus limited inshore waters were dominated by a small diatom Chaetoceros circinalis, dinoflagellates, cryptophytes, autotrophic picoplankton, and heterotrophic nanoplankton. The offshore surface layer was characterized by bigger nanoplankton (coccolithophorids, green flagellates). Low nutrient concentrations influence relatively low productivity not only above the Albanian shelf but also further to the north along the Montenegrine and Croatian coastal Adriatic Sea. [ABSTRACT FROM AUTHOR]

The chain-forming diatom Chaetoceros vixvisibilis is one of the most abundant and frequent diatoms in the northeastern Adriatic Sea. This species had not been previously studied by electron microscopy. Its general morphology is similar to those species allocated in the subgenus Hyalochaete: cells and chains (straight, of variable length, usually 4–8 cells per chain, but can be longer) of delicate appearance, valves thinly silicified, with slightly eccentric annulus and costae radiating from it, a single rimoportula present only at terminal valves, long, thin and delicate setae perforated by tiny poroids with no spines, and one plate-like chloroplast per cell. Setae with no spines are not common among members of Hyalochaete (and the whole genus Chaetoceros), except C. socialis. The most characteristic feature is, however, the resting spores commonly found, which also show morphological variability, from solitary to paired, both valves convex to domed and surface smooth or with small granules, and one to four strong spines often branching dichotomically. Abundances of C. vixvisibilis are positively correlated to the Po River inflow. Maximum abundances (>106 cells L−1) were found in the period April–July, in the temperature range between 12 and 16°C, salinity between 33 and 38, when total phosphorus concentration is higher than 0.4 µmol L−1, but occasionally also in nitrogen limited conditions. [ABSTRACT FROM PUBLISHER]

Phytoplankton abundance and seasonality in the northeastern Adriatic Sea were directly related to the annual regime of the Po River discharge in the period 2002–2007. In 2005, 2006, and 2007, there was a shift in the timing of the annual Po River maximum discharge and of phytoplankton maxima from spring to autumn. In addition, the eastern coastal area was greatly influenced by oligotrophic karstic rivers and the Eastern Adriatic Current. Dominant phytoplankton taxa were defined on the basis of abundance and frequency of appearance. Such an approach may help in the comparison of phytoplankton communities within different environments. The dominant taxa were the diatoms Cerataulina pelagica, Chaetoceros socialis, Chaetoceros vixvisibilis and Pseudo-nitzschia spp., which appeared at maximum abundances >106 cells l-1 in more than 20% of samples. Among other phytoplankton, the most common was the coccolithophorid Emiliania huxleyi (maximum abundance of 2×105 cells l-1 in 50% of samples), and the dinoflagellate Prorocentrum minimum (maximum abundance of 3×105 cells l-1 in 12% of samples). The present state of the phytoplankton community may provide valuable information for evaluation of possible future environmental changes in the shallow Mediterranean ecosystem. [ABSTRACT FROM AUTHOR]

Phytoplankton composition and abundance were analyzed in the period January-September 2006, along the NE coastal Adriatic. In 2006, the Po River discharge was twice as low as the 90 year average. The maximum riverine water inflow did not appear in spring but in September, resulting in a shift of phytoplankton maximum from spring to autumn. Diatoms provided most abundant phytoplankton with an annual maximum of 6 × 105 cells L-1 in the west Istrian coastal region (in September-October). The annual average abundance of diatoms was low (5.1 × 104 cells L-1), but bigger than that of dinoflagellates (28x), coccolithophorids (13x), cryptophytes (6x) and green nanoflagellates (9x), respectively. A comparison was made between phytoplankton seasonality in the dry year 2006, and the year 2001 characterized by greater freshwater inputs. The drought period was characterised by the small cell size diatoms Cyclotella and Thalassiosira. Po River discharge from the west, the north-westerly ingoing current (Eastern Adriatic current) and oligotrophic karstic waters discharging along the eastern coast, strongly influence phytoplankton dynamics in the NE coastal Adriatic Sea. [ABSTRACT FROM AUTHOR]