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Concentrations of polycyclic aromatic hydrocarbons (PAH) were studied in 36 sediment samples collected from 29 sites in the central Adriatic Sea. The total concentration of PAH showed high variability, ranging from 42.85 µg kg−1 in open sea sediments to 28, 662 µg kg−1 in the sediments of Šibenik Bay. Unsubstituted, parent PAH were dominant PAH compounds in the entire area of Šibenik Bay and most of the stations in the coastal area. In Kaštela Bay, methyl PAH concentrations were higher than the concentrations of unsubstituted PAH, whereas in the sediments along the mid-Adriatic transect, similar concentrations of both PAH fractions were determined. PAH sources were investigated by applying the Positive Matrix Factorization software developed by the U.S. Environmental Protection Agency (USEPA). The results indicate the presence of four sources, two of which can be considered petrogenic and two pyrogenic. The contribution of the sources to the total concentration PAH at each station indicates the dominance of pyrogenic sources in Šibenik Bay and at most stations in the coastal area. In the sediments along the mid-Adriatic transversal, as well as in Kaštela Bay, PAHs originate mainly from petrogenic sources. The obtained results show that PMF can be a suitable tool for control of PAH pollution and thus, for the management of various activities in the Adriatic region. Seasonal differences between the contributions of sources in the Kaštela and Šibenik bays indicate that the contribution of traffic to the total concentration of PAH was higher during the tourist season. The carcinogenic risk of PAH determined by toxicity equivalent (TEQ) calculations showed an increased carcinogenic risk in the whole area of Šibenik Bay, regardless of the number of PAH compounds considered for the calculations. A low PAH-related carcinogenic risk was found for the rest of the study area.

Polycyclic aromatic hydrocarbons (PAH) were investigated in the bottom sediments on 25 locations in the coastal area of Adriatic Sea. Total PAH concentrations ranged from 14, 98 to 23970, 92 µg kg-1 . The highest PAH levels were determined in sediments from the Sibenik Bay and the lowest PAH levels were determined in sediment near Island of Pag. Unsubstituted, parent PAHs predominated in sediments from the Sibenik Bay and the Coastal area, while methyl-substituted PAHs were dominant in sediments of the Kastela Bay. In order to estimate the possible toxicological significance of PAH concentrations, Sediment Quality Assessment was done according to three different guidelines: Canadian Sediment Quality Guidelines, North America Sediment Quality Guidelines and OSPAR commission quality Guidelines. According to all three applied criteria, high environmental risk was calculated for each station in Sibenik Bay ; for the station in vicinity of the Industrial port of Split and for the two stations in Coastal zone. Low environmental risk was calculated for the remote areas such as Island of Pag, whereas moderate environmental risk was calculated for the majority of stations in Kastela Bay and Coastal area. Sediment extracts were further analysed for acute toxicity using the Microtox® bioassay. Obtained results show disagreement between sediment toxicity calculated upon total PAH levels in sediment and experimentally obtained sediment toxicity. Sediment extracts with low PAH levels were highly toxic indicating that only concentrations of PAH were not accurate indicators of sediment toxicity.

Koncentracije partikularnog fosfora (PP) istraživane su sezonski u vodenom stupcu priobalja srednjeg Jadrana na 7 postaja tijekom 2009. godine te jednokratno u površinskom sloju duž estuarija rijeke Krke. U svim uzorcima morske vode, uz PP, određeni su i standardni oceanografski parametri te koncentracije otopljenih hranjivih soli dušika, fosfora i silicija. Određene koncentracije PP u istraživanom području bile su u rasponu od 0, 011 µmol dm-3 (ušće Neretve) do 0, 589 µmol dm-3 (Šibenski zaljev) i više od koncentracija otopljenog anorganskog P. Statističkom analizom rezultata određena je značajna pozitivna korelacija PP s klorofilom a i hranjivim solima silicija te negativna korelacija sa salinitetom. Koncentracije PP, određene u površinskom sloju duž estuarija rijeke Krke, upućuju na njegovo nekonzervativno ponašanje u odnosu na salinitet. U gornjem dijelu estuarija zabilježeno je pozitivno, a u donjem dijelu negativno odstupanje od teoretske raspodjele partikularnog fosfora.

Sjeverni Jadran je plitko područje pod jakim utjecajem dotoka rijeke Po. Karakteriziraju ga brojni prostorno-vremenski gradijenti (npr. temperatura, salinitet, nutrijenti). To rezultira izrazito kompleksnom strukturom planktonskog ekosustava koja nam omogućuje praćenje prilagodbi planktonskih organizama duž navedenih gradijenata. U ovom istraživanju analizirali smo vrste roda Leptocylindrus i vrstu Chaetoceros peruvianus. Posebno smo se usredotočili na njihove fiziološke odgovore na limitaciju fosfatima. Analizirali smo njihovo ponašanje in situ te proveli eksperimentalna mjerenja ex situ. U ovom radu prikazati ćemo promjene brzine rasta pojedine vrste pri različitim koncentracijama nutrijenata, brzine unosa fosfata, podatke o aktivnosti, lokalizaciji i načinima aktivacije enzima alkalne fosfataze, te morfološke prilagodbe pojedine vrste na stres fosfatima. Uočene fiziološke promjene uključuju promjene dužine generacijskog vremena i različitu ekspresiju enzima alkalne fosfataze. Uz fiziološke, uočene su i morfološke promjene kao reakcija na stres fosfatima. Kod roda Leptocylindrus uočene su promjene u dužini stanica i lanaca u uvjetima smanjene koncentracije fosfata, dok su kod C. peruvianus uočene morfološke promjene koje nalikuju prijelazu između dva već opisana oblika te vrste (C. peruvianus i C. peruvianus var. gracilis). Naši rezultati upućuju na to da morfološke analize in situ uzoraka mogu biti dobar pokazatelj trenutnog stanja u okolišu kao što je limitacija fosfatom.

The northern Adriatic is characterized by a multitude of steep and quickly-changing gradients (e.g. nutrients), both temporal and spatial. The current systems and the major freshwater input (River Po), in particular, generate strong gradients in nutrient concentrations with an expressed N/P imbalance and sustained phosphate limitation. This results in a highly structured planktonic ecosystem that allows us to investigate the performance of planktonic species along those gradients and in contrasting conditions. We analyzed several diatom species with respect to their metabolic reaction towards phosphate limitation. Here we report data on species specific growth rates under different nutrient regimes, phosphate uptake rates, alkaline phosphatase activity, localization and activation patterns and characteristics of alkaline phosphatase activity as well as on morphological reactions to phosphate stress. The Leptocylindrus danicus Cleve species complex and Chaetoceros peruvianus Brightw. are two common taxa/species in the northern Adriatic. We compared their performance in situ as well as performed phosphate limitation experiments ex situ. Physiological changes observed include changes in generation time, expression of alkaline phosphatase as well as morphological reactions to phosphate limitation. L. danicus species complex showed cell and chain elongation in phosphate limitation, while C. peruvianus showed elongation of setae and apical axis. We could demonstrate that both morphological changes are increasing volumes and surface areas, where alkaline phosphatase activity is localized and thus increase the species’ capability to make use of organic phosphate resources. In the case of C. peruvianus, the morphological changes resemble the transition between two described variabilities, (C. peruvianus var. peruvianus and C. peruvianus var. gracilis Schröd.). Our results show that careful morphological analysis of in situ samples can be a good indicator for the detection of specific and complex ecological circumstances like e.g. phosphate limitation. We furthermore combine the results of our physiological experiments and in situ performance analyses into a model for the life strategies of L. danicus species complex and C. peruvianus.

Imbalanced nutrient supply is a general and common challenge to marine microalgae. The competition for the limiting resource quickly becomes a shaping pressure for microalgae community structures. Nitrogen and phosphorous are often key nutrients and limiting supply of phosphorous is hypothesized to be a global trend in marine systems. The northern Adriatic is a model system with respect to this trend and marine microalgae can be observed under a variety of steep ecological gradients. We observed the in situ “behavior” of microalgae with respect to competition for phosphorous, generally the limiting nutrient. Our results suggest a number of key strategies for the successful competition for this element: Increased phosphate uptake rates, specialization on organic phosphate sources at high or low concentrations by the use of alkaline phosphatases, delayed bloom initialization, phosphate pool formation, morphological adaptations and alternations of cellular nutrient requirements. This results in the characterization of a multitude of spatiotemporal niches across ecological gradients. We performed in vitro experiments on monoclonal algal cultures to quantify the performances of microalgal species in phosphate limited conditions. Here we present the relative performances of harmful algae with respect to the abovementioned mechanisms in the context of other common northern Adriatic microalgae and explain the spatio-temporal distribution of harmful algae from the genera (Skeletonema, Chaetoceros, Pseudo-nitzschia, Prorocentrum and Ostreopsis).

The unusual and prolonged occurrence of rare and poorly known dinoflagellate Prorocentrum arcuatum in the phytoplankton of the shallow aquaculture site in Medulin Bay was recorded from July 2013 to October 2014. This enabled us to investigate changes in abundance and environmental drivers of P. arcuatum population dynamics in natural conditions, and to provide first detailed description of P. arcuatum from field samples based on SEM images. During 15 months of observations we also recorded seasonal variability in P. arcuatum cell size. The optimum physical conditions for P. arcuatum proliferation were reached in autumn 2013, during the narrow temperature range between 19.6oC – 20.4oC, and salinity between 36.7 - 37.7. Despite the general similarity in physical conditions in autumn 2014, this increase in the abundance of P. arcuatum was not repeated, which might be connected to higher competition due to observed interannual changes in phytoplankton population structure.

The northern Adriatic is a very convenient ecosystem to observe phytoplankton under a variety of different conditions. Steep gradients of nutrient concentration/availability in this shallow basin allow the observation of the very same species under changing nutrient regimes on small temporal and spatial scales. After studying the in situ behavior of marine phytoplankton along the aforementioned gradients, we set out and isolated key species for in vitro experiments, where we analyzed their reactions to contrasting nutrient regimes. An imbalanced N/P ration in the basin and a resulting overall phosphate limitation appear to be a major driver and determining factor of the ecosystem. The reaction of key species to phosphate limitation and the resulting efficiency in niche formation and competition for ecological niches explain most of the in situ observations regarding abundance and spatio-temporal distribution of phytoplankton species. This study shows that in vitro characterization of phytoplankton species metabolic capabilities allows the prediction of their relative performance in in situ competition for resources.

The northern Adriatic is characterized by a multitude of steep and quickly changing gradients (e.g. nutrients), both temporal and spatial. The current systems and the major freshwater input (River Po) in particular generate strong gradients in nutrient concentrations with an expressed N/P imbalance and sustained phosphate limitation. This results in a highly structured planktonic ecosystem that allows for a high level of sympatric congeneric species diversity. We analyzed several such sympatric congeneric species with respect to their metabolic reaction towards phosphate limitation. Here we report data on species specific growth rates under different nutrient regimes, phosphate uptake rates, alkaline phosphatase activity, localization and activation patterns and characteristics of alkaline phosphatase activity. Our results demonstrate a high interspecific variation in metabolic responses to phosphate limitation in sympatric congeneric species. The ecological significance and function appears hence to be defined on species level and appears far from homogeneous within genera.

The northern Adriatic is a very suitable ecosystem for observing phytoplankton under a variety of different ecological conditions. This shallow basin is characterized by steep gradients of nutrient concentrations with an expressed N/P imbalance and sustained phosphate limitations. Here we characterize the non bloom forming, omnipresent, planktonic diatom Chaetoceros peruvianus Brightwell, 1856 with respect to its presumed life strategy in the northern Adriatic. Long term data of phytoplankton monitoring suggests omnipresence of C. peruvianus. To further understand the metabolic adaptation of C. peruvianus we report growth rates, phosphate uptake rates, alkaline phosphatase activity, alkaline phosphatase localization and activation patterns and characteristics of alkaline phosphatase enzyme activity. We observed cell cycle durations of about 24 h and only little differences between growth rates in F/2 medium and in P-limited medium. P uptake rates around 1.13 pm/cell/day could be perceived in F/2 medium as well as in P-limit medium. However, during the adaptation phase to P-limited conditions significantly lower P-uptake rates where observed. Cellular alkaline phosphatase activity was up to 20 am/s/cell. In P-limited conditions we could measure Km values of 64 μM. Observed morphological adaptations include the transition between different forms. All results combined suggest C. peruvianus to be a generalistic/opportunistic phytoplankton species

In this paper we investigated the organic and inorganic P in sediments collected during the 2004-2014 period at fish farms, bays, estuaries, open sea areas, military harbors and nautical marinas to evaluate the environmental status impact on the P distribution in sediments. Granulometric composition, organic matter content and carbonate content as geochemical characteristic were also obtained. Environmental status indexes (CARLIT, that presents the state of coastal biocenosis of macroalgae ; TRIX, that is description of trophic state in the water column and LUSI index, that presents group of anthropogenic pressures in some area) were determined for certain locations. Total P determined for all investigated sediments was 16.0±12.8 μmol g-1 with highest concentrations obtained at fish farm sites. Higher portion of inorganic P (66%) in relation to organic P (34%) was found. Positive correlation was established between total P and sediment organic matter content as well as between organic P and organic matter. Negative correlation was obtained between organic P and carbonate content. These associations were in accordance to previous investigations of P and geochemical parameters in sediment. In sediments at fish farm sites, beside the organic P, inorganic P forms were examined (P in biogenic, authigenic and detrital apatite and P bound to iron oxides and hydroxides). Under the fish farm cages elevated portion of P in biogenic apatite and P bound to iron oxides and hydroxides was found. Obtained portions were attributed to fish farm impact. Association between total P in sediment and environmental indexes (CARLIT, TRIX and LUSI) was established that confirm thesis of the environmental state impact on P in sediment. These results present the basis of the potential implementation of P from the sediment, together with environmental indexes, in assessment of the ecological status of some marine environment.

Fitoplanktonska zajednica je zbog svog brzog odgovora na promjene u okolišu pouzdan pokazatelj stanja okoliša i jedan je od bioloških elemenata koje za procjenu kvalitete vode propisuje Okvirna direktiva o vodama (ODV). Kako bi se testirao odgovor fitoplanktonske zajednice na antropogene pritiske s kopna, multivarijatne statističke metode korištene su za analizu koncentracije klorofila a, brojnosti i sastava fitoplanktonske zajednice u odnosu na antropogeni utjecaj i ekološke varijable kao što su temperatura, slanost i hranjive soli. Analizom su obuhvaćene postaje različitog stupnja opterećenja, a preliminarna procjena antropogenog utjecaja na istraživanim postajama je određena preko LUSI indeksa (Land Use Simplified Indeks). Multivarijatna analiza je pokazala da su koncentracije hranjivih soli nitrata i silikata pouzdan pokazatelj utjecaja slatke vode, dok su biomasa i brojnost fitoplanktonske zajednice pouzdan pokazatelj antropogenog utjecaja. Odgovor bioraznolikosti fitoplanktonske zajednice nije bio linearan, a najveća biorazmolikost zabilježena je u srednje eutrofnim odnosno mezotrofnim područjima. Kanonička analiza korespondencije identificirala je sljedeće vrste kao indikatore porasta eutrofikacije: Skeletonema costatum, Scrippsiella trochoidea, Guinardia flaccida, Leptocylindrus spp., Prorocentrum spp., Proboscia alata, Eutreptiella spp. i Pseudonitzschia spp.

Kaštelanski zaljev, s površinom od 61 km2, najveći je zaljev u središnjim obalnim vodama Hrvatske. Uslijed pojave eutrofikacije i povišenih koncentracija žive u sedimentima i organizmima uzrokovane intenzivnom industrijalizacijom i urbanizacijom, ovaj je zaljev tijekom 80.-tih godina prošlog stoljeća dobio status "vruće točke". Izgradnjom sustava odvodnje za okolne gradove i zatvaranjem nekoliko industrijskih pogona u razdoblju između 1990 i 2009, pritisci na morski ekosustav Kaštelanskog zaljeva su se značajno smanjili, naročito u njegovom istočnom dijelu. Rezultati znanstvenog istraživanja i programa monitoringa provedeni u nekoliko proteklih desetljeća ukazuju da su se dogodile velike pozitivne promjene u vodenom stupcu, dok razine nekih kontaminanata u sedimentu i bioti još uvijek pokazuju rastući trend.

This report represents the result of the scientific and technical review of Commission Decision 2010/477/EU in relation to Descriptor 9. The review has been carried out by the EC JRC together with experts nominated by EU Member States, and has considered contributions from the GES Working Group in accordance with the roadmap set out in the MSFD implementation strategy (agreed on at the 11th CIS MSCG meeting). The report is one of a series of reports (review manuals) including Descriptor 1, 2, 5, 7, 8, 9, 10 that conclude phase 1 of the review process and, as agreed within the MSFD Common Implementation Strategy, are the basis for review phase 2, towards an eventual revision of the Commission Decision 2010/477/EU. The report presents the state of the technical discussions as of 30 April 2015 (document version 8.0: ComDecRev_D9_V8), as some discussions are ongoing, it does not contain agreed conclusions on all issues. The views expressed in the document do not necessarily represent the views of the European Commission., JRC.H.1-Water Resources

Jadran je poluzatvoreno more koje je zbog svog položaja duboko uvučenog u europsko kopno vrlo osjetljivo na atmosferski stres te na nagle i postupne promjene klime. U sjevernom Jadranu, zbog njegovih kontinentalnih osobina, utjecaj klimatskih promjena, a posebno ekstremnih situacija jače je izražen nego u srednjem, odnosno južnom Jadranu, gdje je taj utjecaj donekle umanjen i usporen. No, činjenica je kako se zadnjih desetljeća uočavaju znatne promjene temperature zraka i oborine kao posljedica promjena atmosferske cirkulacije nad sjevernom hemisferom što se povezuje s klimatskim promjenama globalnog karaktera. Efekti tih promjena uočljivi su u cijelom vodenom stupcu Jadranskog mora, posebno na promjenama temperature, saliniteta i kisika srednje-dubokih slojeva Jadrana. Analizirajući višegodišnje promjene temperature zraka i oborine, temperature mora i saliniteta dubljih slojeva te uspoređujući ih s procesima na hemisferskoj skali, uočen je kontinuirani porast prizemne temperature zraka i nelinearni trend oborine od kasnih 80-ih godina prošlog stoljeća. Uz temperaturu mora i salinitet, sadržaj otopljenog kisika dobar je pokazatelj starosti vodenih masa pa time i atmosferom uvjetovanog prozračivanja Jadrana. U promatranom razdoblju uočeno je više ekstremnih meteoroloških situacija, od kojih je ona zabilježena zimi 1987. godine bila odgovorna za promjenu režima termohaline cirkulacije Jadrana.

Spatial gradients of selected groups of persistent organic compounds were investigated in the surface waters of Mediterranean Hot spots: Black Sea, Adriatic Sea and Western Mediterranean.

Phosphorus (P) is very important nutrient for the eastern Adriatic Sea owing to its limiting role in the primary production. Orthophosphate concentrations are low (median HPO42- value: 0.039 µmol dm-3) as a consequence of relatively small number of freshwater inflows and cyclonic circulation of oligotrophic eastern Mediterranean water masses. Due to anthropogenic influence in coastal areas such as bays, estuaries and channel waters, P concentrations increment occurred leading to the formation of trophic gradient from the open sea towards the coast. As marine sediment presents the ultimate sink for particulate organic P from the water column, as well as for inorganic P forms, knowledge about distribution of different sediment P species is of great importance for understanding the burial, diagenesis and environmental geochemical significance of P. This paper presents results of P distribution at the eastern Adriatic sites of different trophic status (open sea, channel, estuary, semi-enclosed bay under the anthropogenic influence and fish farms) during 2002-2012. In the water column dissolved and particulate inorganic and organic P were analyzed. In all sediments total phosphorus (organic and inorganic P) was determined, while at certain sites beside organic P, inorganic P forms were examined using modified SEDEX methods (P in biogenic – P-FD ; authigenic – P-AUT and in detrital apatite - P-DET ; phosphorus bound to iron oxides and hydroxides – P-Fe). Various geochemical variables in the water column and sediment (HPO42- concentration, sediment redox potential, granulometric composition, carbonate content, iron, organic carbon and total nitrogen content) were also investigated. Results proved total P concentrations range between 3 and 161 µmol g-1, with highest values at sites under the strong anthropogenic impact including fish farms, estuaries and bay areas. Major inorganic P species in the eastern Adriatic was P-Fe form. Fish debris P species P-FD, prevailed in fish farm sediments. Detrital and authigenic apatite P concentrations were explained by either terrestrial inputs or by internal transformation from other P forms. Statistical analysis among P and geochemical parameters indicated the granulometric composition as a leading differentiation parameter in sediment P species distribution. Statistics also indicated P-Fe importance in the P flux on the sediment water interface due to correlation between orthophosphate concentration in the water column, sediment pore water, redox-potential and iron concentration.

Na stjenovitim morskim dnima priobalnog pojasa zajednice makroalgi imaju značajnu ekološku ulogu. Obzirom na svoju raznolikost, biomasu, rasprostranjenost, ulogu u ekosustavu i trajnu pričvršćenost za podlogu, makroalge su vrlo pogodan bioindikator promjena u morskom okolišu. U ovom istraživanju razmatrana je pogodnost korištenja univarijatnih pokazatelja i biotičkih indeksa (broj svojti makroalgi, biomasa makroalgi, pokrovnost makroalgi, Margalefov indeks, Shannon-Wienerov indeks, R/P indeks, indeks onečišćenja, ekološke skupine prema Boudouresqueu, EEI indeks i CARLIT indeks) koji koriste makroalge za procjenu ekološkog stanja priobalnog mora. Uzorkovanje zajednica makroalgi je obavljeno u razdoblju od 2009. do 2010. godine na šest postaja u srednjem Jadranu gdje je uzorkovano kartografskom metodom i destruktivnom metodom na dubini od 0, 5 m unutar kvadrata površine 0, 04 m2. Rezultati primjene svake bioindikatorske metode uspoređeni su s izmjerenim srednjim godišnjim vrijednostima koncentracije hranjivih soli kao pokazateljem razine onečišćenja na svakoj postaji. Na temelju rezultata istraživanja ustanovljeno je da ukupna biomasa makroalgi, ukupna pokrovnost makroalgi i EEI indeks nisu prikladni za procjenu ekološkog stanja mora na području istraživanja jer ne pokazuju povezanost s vrijednostima koncentracije hranjivih soli te se na osnovu njih ne može razlikovati onečišćeno od čistog područja. Broj svojti makroalgi, Margalefov indeks, Shannon-Wienerov indeks, R/P indeks te indeks onečišćenja mogli bi se koristiti u procjeni ekološkog stanja priobalnog mora na području istraživanja. Vrijednosti tih pokazatelja pokazivale su povezanost s razinom onečišćenja na postajama istraživanja, ali imaju i nedostatke koji onemogućuju njihovu sigurnu primjenu te su potrebna opširnija dodatna istraživanja. Ekološke skupine prema Boudouresqueu i CARLIT indeks pokazali su najbolju povezanost s razinom onečišćenja na postajama istraživanja.

Biomonitoring of contaminants (Cd, Pb, Cu, Zn, Cr, HgTOT, lindane, PCBs and DDTs ) in shellfish, Mytilus galloprovincialis, was conducted at 18 sites distributed across the entire coastal area of Croatia once a year over the period 2000-2009. Based on the obtained data pertaining to metal levels in shellfish, it can be concluded that the best status was observed at sites located in the outer estuaries of the Neretva and Krka rivers as well as in the Lim Bay area under submarine freshwater influence, while the poorest status was observed in the areas under anthropogenic impact, e.g. ports, semi-enclosed bays and industrial areas. Statistical analysis of data showed an upward trend for all metals during the period of investigation. The increase in metal concentrations appears to be the result of enhanced industrial activity during the indicated time period, mostly metal production and processing industry which showed more than 190 % growth throughout the period from 2000 to 2008. Analysis of data with regard to organic pollutants in shellfish revealed lower concentrations of lindane in comparison with DDT, while concentrations of PCB compounds (Aroclor 1254 + Aroclor 1260) were significantly higher in relation to chlorinated pesticides. Highest concentrations of organic pollutants were, similar to metals, established in the areas under anthropogenic influence, however, a decreasing trend was observed at most sites. The decrease in the levels of chlorinated pesticides (lindane, DDT compounds) was more distinguished, which was to be expected considering that the use of lindane has been banned in Croatia since 2001, while the ban on the use of DDT was enforced in 1972. Moreover, there is no national legislation prohibiting the import and use of PCB compounds.

Present study describes the phytoplankton community structure and phytoplankton abundance in three bays on the eastern Adriatic coast (Šibenik Bay, Kaštela Bay and Mali Ston Bay) during 2005. The highest phytoplankton biomass (expressed as chlorophyll a) were recorded at one station in Šibenik Bay (4.73 mg m-3), and in Kaštela Bay (2.79 mg m-3), while at all other stations recorded values were generally below 1 mg m-3. At the investigated area of Šibenik Bay a total of 114 phytoplankton taxa have been determined. The most diverse were diatoms with 61 and dinoflagellates with 37 taxa. Coccolithophorids contributed with 6, cryptophytes with 3, silicoflagellates, euglenophytes and chlorophytes with 2 taxa. In the area of Kaštela Bay 193 phytoplankton taxa have been recorded. Dinoflagellate group was the most diverse with 92 taxa, followed by diatoms (80), coccolithophorids (9), silicoflagellates and euglenophytes (4), cryptophytes (2) and chlorophyte (1). In the area of Mali Ston Bay a total of 88 phytoplankton taxa have been found, with 39 diatoms, 36 dinoflagellates, 2 silicoflagellates, 4 coccolithophorids, 2 euglenophytes, 1 chllorophyte and 3 chrisophyte taxa. Abundance of dinoflagellates was very low in this area. Coccolithophorids contributed more to the community composition in Mali Ston Bay, then in other areas of research. A diverse microflagellate group was present in the whole area of investigation with a high frequency of findings. During the investigated period a relatively small number of monospecific blooms in all areas have been recorded. The largest numbers of taxa were recorded at stations that are under an influence of freshwater input from rivers and strong anthropogenic influence.