Taksonomija i ekologija planktonskih dijatomeja iz porodice Chaetocerotaceae (Bacillariophyta) u Jadranskom moru

The cosmopolitan diatom family Chaetocerotaceae abounds in the phytoplankton of coastal regions, comprising ca. 170 species, belonging to two genera, Chaetoceros and Bacteriastrum. In the Adriatic Sea the group is ecologically important represented with ca. 50 species whose identification is often problematic. The species morphology was assessed by analysing the material from cultured strains and the field plankton samples collected at 8 locations along the eastern Adriatic coast from 2006 to 2012. All taxa were studied with light, scanning and transmission electron microscopy. Ecological relationships were investigated: (i) in the coastal area of northern Adriatic (biweekly in 2008 – 2009) (ii) in Krka River estuary (twice a day during six days in July 2010). 49 morphologically distinct taxa were recorded, of which six were affiliated with the genus Bacteriastrum and 43 with genus Chaetoceros with 41 species, two varieties, two tentatively identified and four unknown morphotypes. Five taxa have been reported for the first time for the Adriatic and three emended diagnoses were proposed for Chaetoceros vixvisibilis, Bacteriastrum jadranum and B. mediterraneum. The morphological analysis helped to clear previously common misidentifications of species Bacteriastrum delicatulum/B. furcatum, Chaetoceros contortus/C. compressus, C. decipiens/C. lorenzianus and C. lauderi/C. teres where that in all observed material only first species from the given pair could be identified. The individual morphological characters were classified according to their identification significance with the particular emphasis on comparison and establishing species-specific traits such as resting spore morphology, ultrastructure of the setae and valves. We distinguished 9 different setae structural types in the subgenus Chaetoceros and the same number in the subgenus Hyalochaete. A novel and unique type of colony formation in planktonic marine diatoms was discovered and characterized with the atomic force microscopy (AFM) for Bacteriastrum jadranum which forms colonies by enclosing the cells within the organic network (cell jacket). The phylogenetic analysis of 28S rDNA separated Bacteriastrum furcatum and B. hyalinum in one clade and B. jadranum and B. mediterraneum in the other one. In relation to other Chaetoceros species results imply that that Bacteriastrum species form a lineage within the genus Chaetoceros, but for the drastic changes in the taxonomy there is still a need for a more thorough investigation. The multivariate analysis of seasonal dynamics and ecological relationships showed the permanent presence of chaetocerotacean species in the phytoplankton with with a change in dominance and clear annual succession. The pattern can be partially explained by the environmental parameters, with the temperature, silicate, salinity and phosphate as most important factors driving the community succession.Kozmopolitska porodica dijatomeja Chaetocerotaceae je brojna u morskom fitoplanktonu obalnih područja te obuhvaća oko 170 vrsta svrstanih u dva roda Chaetoceros i Bacteriastrum. U Jadranu skupina je vrlo raznolika i ekološki značajna te zastupljena s oko 50 vrsta čija je identifikacija često problematična. Morfologija vrsta je određena analizirajući materijal izoliranih kultura stanica i uzoraka planktona prikupljenih na terenu, na 8 lokacija duž istočnojadranske obale u razdoblju 2006 – 2012. Sve svojte su analizirane pomoću svjetlosne, skenirajuće i transmisijske elektronske mikroskopije te vrsta Bacteriastrum jadranum dodatno s mikroskopom atomskih sila (AFM). Ekološki odnosi su istraženi: 1) na jednoj postaji (RV001) u obalnom području sjevernog Jadrana (2008 – 2009, svaka dva tjedna) 2) u području ušća rijeke Krke (dva puta dnevno, tijekom šest dana u srpnju 2010). Određeno je 49 morfološki različitih svojti od kojih 6 pripadaju rodu Bacteriastrum a 43 rodu Chaetoceros, s 41 vrsta, dva varijeteta dvije uvjetno identificirane svojte i četiri nepoznata morfotipa. Tri nadopunjene dijagnoze su predložene za vrste: Chaetoceros vixvisibilis, Bacteriastrum jadranum i B. mediterraneum. Pet vrsta je zabilježeno po prvi put u Jadranu. Razjašnjena je prethodna pogrešna identifikacija kod Bacteriastrum furcatum/B. delicatulum, Chaetoceros contortus/C. compressus, C. decipiens/C. lorenzianus and C. lauderi/C. teres. Analiza je pokazala da je samo prva vrsta iz svakog navedenog para prisutna u analiziranom materijalu. Procijenjena je taksonomska važnost pojedinih morfoloških obilježja s posebnim naglaskom na morfologiju mirujućih spora, ornamentaciju valve i strukturu seta. Razlikuje se 9 različitih tipova struktura seta kod vrsta podroda Chaetoceros i isto toliko kod Hyalochaete. Kod vrste Bacteriastrum jadranum otkriven je i opisan jedinstven i novi način formiranja kolonija kod planktonskih morskih dijatomeja, gdje stanice nisu povezane pomoću fuzije silikatnih struktura nego pomoću optički transparentnog organskog matriksa. Rezultati molekularne filogenetske analize odvojila su Bacteriastrum furcatum i B. hyalinum u jednu grupu te B. jadranum i B. mediterraneum u drugu. U odnosu na ostale vrste Bacteriastrum vrste se grupiraju unutar roda Chaetoceros, ali za drastične taksonomske promjene potrebna su daljnja istraživanja. Multivarijantna analiza sezonske dinamike i ekoloških odnosa pokazala je da su vrste skupine Chaetocerotaceae stalno prisutne u fitoplanktonu a sukcesivno se izmjenjuju tijekom godine. Sukcesijski obrazac se može djelomično objasniti okolišnim parametrima, sa temperaturom, silikatima, salinitetom i fosfatima. Opisi vrsta dijatomeja će olakšati buduću ispravnu identifikaciju u planktonskim uzorcima što će u budućnosti pridonijeti boljoj biogeografskoj rezoluciji i ekološkoj interpretaciji u pelagijalu

Blue Diatoms: Global Phenomenon of ˝Greening˝ in Shellfish and Record of Planktonic Haslea Species in the South Adriatic Sea

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

Morphological study of Chaetoceros wighamii Brightwell (Chaetocerotaceae, Bacillariophyta) from Lake Vrana, Croatia

Chaetoceros wighamii Brightwell is a planktonic diatom species originally described from brackish waters. Since its original description, the species has been reported in a wide variety of habitats, ranging from freshwater to marine. Varying descriptions exist in the taxonomic literature and several taxa have been considered as synonyms, including freshwater species Chaetoceros amanita. In this study we provide morphological and ultrastructural information on a cultured strain isolated from freshwater sample collected in the Lake Vrana (Vransko jezero) in Croatia, in April 2011. The cells form short and robust chains with very narrow apertures, often partially occluded by silica membranes. Other distinctive features observable in light microscopy are the shape and orientation of the setae which are very long, straight and robust, diverging in various directions from the chain axis and the single parietal chloroplast extending from valve to valve. Distinct ultrastructural characteristics are the absence of processes either in intercalary or terminal valves and the ornamentation of the valve face with densely distributed ribs spreading from an irregular eccentric hyaline area without a clearly defi ned annulus. The outer surface of the terminal valve is ornamented with small spines and setae are composed of flat longitudinal filaments interconnected with short bars and ornamented with small spines tightly arranged around the setae. Our description agrees well with that reported for the freshwater morphotypes of C. wighamii (syn. C. amanita) and contributes for a reliable distinction of this intriguing taxon from similar morphotypes. This finding supports the interpretation of Chaetoceros wighamii as a freshwater/brackish species and represents the first report of a Chaetoceros species in lacustrine environment in Croatia and possibly in any Central European habitats

Seasonal distribution of plankton diatoms in Lim Bay, northeastern Adriatic Sea

The seasonal distribution of planktonic diatoms is presented in relation to the hydrographic and chemical parameters in Lim Bay, a 10 km long fjord-like embayment situated in the north east Adriatic Sea. Water samplings for physicochemical and biological variables were conducted fromMarch 2002 to November 2007 at three stations along the bay. The phytoplankton was dominated by diatoms throughout the year, with the minimum species diversity in summer and the maximum in autumn. A total of 100 diatoms were identified and classified according to their seasonal occurrence in the plankton; some were consistently present throughout the whole year, but a large fraction showed a distinct seasonal cycle. The inner two stations differed significantly in terms of phytoplankton biomass and nutrient content from the outer station, indicating a higher nutrient input in the inner part. The majority of the dominant diatoms recorded in this study prefer nutrient- enriched conditions. Due to the anticipated increase of human impact in the area, this study can serve as a base for future environmental studies in Lim Bay

A novel type of colony formation in marine planktonic diatoms revealed by atomic force microscopy

Diatoms have evolved a variety of colonial life forms in which cells are connected by organic threads, mucilage pads or silicate structures. In this study, we provide the first description of a novel strategy of colony formation among marine planktonic diatoms. Bacteriastrum jadranum is a chain‐forming centric diatom in which sibling cells are enclosed within the optically transparent organic matrix instead of fusing of silica between setae as it is the case in all other members of the family Chaetocerotaceae. This cell jacket structure was detected by staining procedures (Alcian Blue and Coomassie Brilliant Blue G), which showed that the polysaccharides are predominant matrix constituents and revealed that the jacket reaches the span of the setae. The scanning electron microscopy (SEM) observations showed distinguishable fibrillar network firmly associated with cells. Using atomic force microscopy (AFM), we were able to visualise and characterise the cell jacket structure at molecular resolution. At nanoscale resolution, the cell jacket appears as a cross‐linked fibrillar network organised into a recognisable structure. It is composed of non‐evenly distributed high density domains (patches) surrounded and interconnected by thicker fibrils. Inside the patches are the hexagonally shaped pores decreasing in size from the patch edge towards the center. The large pore openings found between the patches are formed by the robust branching fibrils and these represent the backbone of the fibrillar network. Such structure is porous, but at the same time highly flexible and mechanically stable. We conclude that the Bacteriastrum polysaccharide jacket represents an essential part of the cell, as such specific and unique patterns have never been found in self‐assembled polysaccharide gel networks, which are usually encountered in the marine environment