Sastav i prostorna raspodjela fitoplanktona u sjeveroistočnom kanalu Jadranskog mora u jesen 2008. godine

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.Velebitski i Paški kanal čine 40 km dug i 4-14 km širok sustav koji se proteže usporedno sa sjeveroistočnom obalom Jadranskog mora. Cilj ovog istraživanja je bio istražiti abundanciju, sastav i raspodjelu fitoplanktona duž sustava u jesenskom razdoblju. Uzorkovanje je obavljeno na 8 postaja u studenom 2008. Prostorna raspodjela fizikalno kemijskih parametara upućivala je na postojanje izrazitog horizontalnog termohalinog i trofičkog gradijenta. Od unutrašnjeg dijela Velebitskog kanala, koji je produžetak estuarija krške rijeke Zrmanje do vanjskog dijela Paškog kanala koji se spaja s otvorenim morem, raspon površinske temperature mora iznosio je 11.0 do 16.0 °C, a saliniteta 23.4 do 38.2. Koncentracije nutrijenata kretale su se u rasponu 0.001 - 0.1 μmol L-1 za fosfate, 0.85 - 7.0 μmol L-1 za otopljeni anorganski dušik i 0.3 - 15.4 μmol L-1 za silikate. Dijatomeje su prevladavale u fitoplanktonu s maksimalnom abundancijom u rasponu od 7.3 x 104 stanica L-1 (85% ukupnog fitoplanktona) na najviše oligotrofnim do 9.6 x 105 stanica L-1 (96% ukupnog fitoplanktona) na postajama s većom koncentracijom nutrijenata. Statistička analiza na osnovi bioloških i fizikalno kemijskih parametara podijelila je postaje u tri glavne grupe. Prva grupa predstavljala je južni dio Velebitskog kanala s većom koncentracijom nutrijenata i prevladavajućom vrstom Thalassionema nitzschioides. Druga grupa uključila je postaje iz središnjeg dijela Velebitskog kanala s nižim razinama nutrijenata i s prevladavajućom dijatomejom Bacteriastrum sp.. Treća grupa uključila je postaje u Paškom kanalu u kojima gotovo isključivo prevladava Bacteriastrum mannii sp. i prisutan je veći udio kokolitoforida. Ovaj rad također donosi prvi popis vrsta fitoplanktona prisutnih u ekstremno oligotrofnom području Velebitskog i Paškog kanala. Identificirano je 148 taksona od čega 91 dijatomeja, 47 dinoflagelata i 10 taksona raznih flagelata. Detaljna analiza pomoću elektronskog mikroskopa otkrila je tri vrste iz potencijalno toksičnog dijatomejskog roda Pseudo-nitzschia: P-n. calliantha, P-n. pseudodelicatissima i P-n. mannii. Rezultati ovog rada predstavljaju značajan doprinos poznavanju sastava i raspodjele fitoplanktona u odnosu na prevladavajuće fizikalno kemijske uvjete u ovom slabo istraženom tranzitnom području

Phytoplankton diversity and chemotaxonomy in contrasting North Pacific ecosystems

Background Phytoplankton is the base of majority of ocean ecosystems. It is responsible for half of the global primary production, and different phytoplankton taxa have a unique role in global biogeochemical cycles. In addition, phytoplankton abundance and diversity are highly susceptible to climate induced changes, hence monitoring of phytoplankton and its diversity is important and necessary. Methods Water samples for phytoplankton and photosynthetic pigment analyses were collected in boreal winter 2017, along transect in the North Pacific Subtropical Gyre (NPSG) and the California Current System (CCS). Phytoplankton community was analyzed using light and scanning electron microscopy and photosynthetic pigments by high-performance liquid chromatography. To describe distinct ecosystems, monthly average satellite data of MODIS Aqua Sea Surface temperature and Chlorophyll a concentration, as well as Apparent Visible Wavelength were used. Results A total of 207 taxa have been determined, mostly comprised of coccolithophores (35.5%), diatoms (25.2%) and dinoflagellates (19.5%) while cryptophytes, phytoflagellates and silicoflagellates were included in the group “others” (19.8%). Phytoplankton spatial distribution was distinct, indicating variable planktonic dispersal rates and specific adaptation to ecosystems. Dinoflagellates, and nano-scale coccolithophores dominated NPSG, while micro-scale diatoms, and cryptophytes prevailed in CCS. A clear split between CCS and NPSG is evident in dendogram visualising LINKTREE constrained binary divisive clustering analysis done on phytoplankton counts and pigment concentrations. Of all pigments determined, alloxanthin, zeaxanthin, divinyl chlorophyll b and lutein have highest correlation to phytoplankton counts. Conclusion Combining chemotaxonomy and microscopy is an optimal method to determine phytoplankton diversity on a large-scale transect. Distinct communities between the two contrasting ecosystems of North Pacific reveal phytoplankton groups specific adaptations to trophic state, and support the hypothesis of shift from micro- to nano-scale taxa due to sea surface temperatures rising, favoring stratification and oligotrophic conditions