Danijela Šantić

Institute of Oceanography and Fisheries | IZOR · Laboratory of Marine Microbiology

Telonemia are one of the oldest identified marine protists that for most part of their history have been recognized as a distinct incertae sedis lineage. Today, their evolutionary proximity to the SAR supergroup (Stramenopiles, Alveolates, and Rhizaria) is firmly established. However, their ecological distribution and importance as a natural predat...

Background Aerobic anoxygenic phototrophs are metabolically highly active, diverse and widespread polyphyletic members of bacterioplankton whose photoheterotrophic capabilities shifted the paradigm about simplicity of the microbial food chain. Despite their considerable contribution to the transformation of organic matter in marine environments, re...

In this communication, we present an innovative approach leveraging advanced Machine Learning (ML) and Artificial Intelligence (AI) techniques, specifically the Non-Negative Matrix Factorization (NMF) method, to analyze downward and upward light spectra collected by Hyperspectral Ocean Color Radiometer (HyperOCR, HOCR) sensors in the water column....

In this communication, we present an innovative approach leveraging advanced Machine Learning (ML) and Artificial Intelligence (AI) techniques, specifically the Non-Negative Matrix Factorization (NMF) method, to analyze downward and upward light spectra collected by Hyperspectral Ocean Color Radiometer (HyperOCR, HOCR) sensors in the water column....

By combining qualitative 16S metabarcoding and quantitative CARD-FISH methods with neural gas analysis, different patterns of the picoplankton community were revealed at finer taxonomic levels in response to changing environmental conditions in the Adriatic Sea. We present the results of a one-year study carried out in an oligotrophic environment w...

Recent advances in new molecular biology methods and next-generation sequencing (NGS) technologies have revolutionized metabarcoding studies investigating complex microbial communities from various environments. The inevitable first step in sample preparation is DNA extraction which introduces its own set of biases and considerations. In this study...

Artificial neural network analysis (ANN) is used to study the seasonal distribution of viruses and microbial food web (MFW) components in the open Adriatic Sea. The effect of viruses within the MFW is often overlooked, although viruses play an important role in microbial community dynamics. The results showed that the strongest influence is found i...

Aerobic anoxygenic phototrophs are a newly discovered member of the bacterial community in the Adriatic Sea. During the last seven years, when we started to study these organisms, we have collected a considerable number of samples from different environments, from the coast, the estuary, and the open sea. Here we have compiled data from 34 georefer...

Human-induced climate change is expected to increase the frequency and severity of vegetation fires. The Mediterranean region is considered particularly prone to fire episodes in summer. It is well known that pyrogenic particles are an important source of external nutrients for the marine environment, especially in oligotrophic areas. In this study...

Atmospheric deposition (AD) of nutrients and its impact on the sea surface requires consideration of interfacial processes within the sea surface microlayer (SML), the ocean-atmosphere boundary layer of major importance for many global biogeochemical and climate-related processes. This study comprised a comprehensive dataset, including dissolved NO...

The mechanisms responsible for the development of various structural and functional features of the microbial food web (MFW) and their dynamics at spatial and temporal scales, which are important for predicting their responses to future environmental changes, are largely unknown. More than 3000 datasets of environmental and microbial variables coll...

Marine bacterioplankton represent a diverse assembly of species differing largely in their abundance, physiology, metabolic activity, and role in microbial food webs. To analyze their sensitivity to bottom-up and top-down controls, we performed a manipulation experiment where grazers were removed, with or without the addition of phosphate. Using am...

Bacteria are an active and diverse component of pelagic communities. The identification of main factors governing microbial diversity and spatial distribution requires advanced mathematical analyses. Here, the bacterial community composition was analysed, along with a depth profile, in the open Adriatic Sea using amplicon sequencing of bacterial 16...

Laboratory of Microbiology at the Institute of Oceanography in Split, founded in 1947, covers numerous research in the field of marine microbial ecology. Marine microorganisms, heterotrophic bacteria, cyanobacteria Prochlorococcus and Synechococcus, heterotrophic nanoflagellates, aerobic anoxygenic phototrophs and viruses, are investigated in terms...

We analyzed a widely used barcode, the V9 region of the 18S rRNA gene, to study the effect of environmental conditions on the distribution of two related heterotrophic protistan lineages in marine plankton, kinetoplastids and diplonemids. We relied on a major published dataset (Tara Oceans) where samples from the mesopelagic zone were available fro...

Metabolic coupling between phytoplankton and bacteria determines the fate of dissolved organic carbon in aquatic environments, and yet how changes in the rate of primary production affect the bacterial activity and community composition remains understudied. Here, we experimentally limited the rate of primary production either by lowering light int...

In order to detect the possible regulatory effect of non-native C. gigas on the native O. edulis, under aquaculture conditions, feeding interactions between them were investigated in a highly productive environment of Lim Bay (Adriatic Sea). The present study uses a multi-methodological approach, including stomach content, DNA barcoding and stable...

Oceanographic measurements carried out in the middle Adriatic during summer 2017 revealed anomalous conditions in both physical and microbial properties. High salinities were observed throughout the entire water column, with an ‘inverse’ salinity profile in August and a maximum in the surface layer, recorded for the first time in the middle Adriati...

A recent analysis of the Mediterranean Sea surface temperature showed significant annual warming. Since small picoplankton microorganisms play an important role in all major biogeochemical cycles, fluxes and processes occurring in marine systems (the changes at the base of the food web) as a response to human-induced temperature increase, could be...

Vertical mixing and stratification are among the most important physical processes controlling nutrient dynamics, the dominant category of primary producers and consequently the dominant types of food web, and are therefore important for the assessment of the marine ecosystem's response to global climate change. This study showed consistent short-t...

Southern Adriatic (Eastern Mediterranean Sea) is a region strongly dominated by large-scale oceanographic processes and local open-ocean dense water formation. In this study, picoplankton biomass, distribution, and activity were examined during two oceanographic cruises and analyzed in relation to environmental parameters and hydrographic condition...

Although Aerobic Anoxygenic Phototrophs (AAPs) are widespread in aquatic environments, relatively little is known about their dynamics in the Adriatic Sea. Therefore, we investigated their distribution along the trophic gradient from coast to the open sea over a year-round period, for the first time, as well as the factors that influenced the spati...

Danas su mora izložena rastućim antropogenim pritiscima koji utječu na promjene njihovih bioloških, kemijskih i fizikalnih svojstava na lokalnoj i globalnoj razini. Najveća nesigurnost u procjenama antropogenih klimatskih pritisaka povezana je s aerosolima zbog nedovoljnog poznavanja njihovih fizikalno-kemijskih svojstava te atmosferskih (trans)for...

Temperature and phosphorus positively interacted in controlling picoplankton biomass production and its transfer towards higher trophic levels. Two complementary approaches (experimental and field study) indicated several coherent patterns: (1) the impact of temperature on heterotrophic bacteria was high at temperatures lower than 16oC and levelled...

Microbial transformations of toxic monomethylmercury (MMHg) and dissolved gaseous mercury (DGM) at the lower levels of the marine food web are not well understood, especially in oligotrophic and phosphorus-limited seas. To examine the effects of probable phosphorus limitation (PP-limitation) on relations between mercury (Hg) fractions and microorga...

An assessment of the temperature increase effect on processes within the microbial food web provides a better insight into the carbon transfer and energy flow processes in marine environments in the global warming perspective. Modified laboratory dilution experiments that allow simultaneous estimates of protozoan grazing and viral lysis on picoplan...

Distribution and abundance of two Synechococcus ecotypes, phycocyanin-rich cells (PC-SYN) and phycoerythrin-rich cells (PE-SYN) were studied in the surface layer of the central Adriatic Sea during the 2015-2016 period. The studied area included several estuarine areas, and coastal to open sea trophic gradients, covering a wide range of seawater tem...

U radu je istražena raspodjela i brojnost dva ekotipa roda Synechococcus, tzv. stanice bogate fikocijaninom (PC-SYN) i stanice bogate fikoeritrinom (PE-SYN) u površinskom sloju vodenog stupca, tijekom 2015. i 2016. godine. Područje istraživanja obuhvaćalo je nekoliko estuarijskih područja te područje trofičkog gradijenta od obale prema otvorenom mo...

Global and atmospheric climate change is altering the thermal conditions in the Adriatic Sea and, consequently, the marine ecosystem. Along the eastern Adriatic coast sea surface temperature (SST) increased by an average of 1.03 °C during the period from 1979 to 2015, while in the recent period, starting from 2008, a strong upward almost linear tre...

To understand the activity of marine viruses, experiments on viral production, viral decay and the percentage of lytic and lysogenic bacterial cells among the total number of bacterial cells were carried out seasonally at two stations in the Adriatic Sea with different trophic conditions. Additionally, we are providing an insight on the enrichment...

Viruses are the most abundant and ubiquitous component of marine microbial plankton. To understand their dynamics, experiments on viral production, viral decay, and the percentage of lytic and lysogenic bacterial cells among the total number of bacterial cells were carried out at two stations in trophically different areas. Additionally, we gave th...

The spatial patterns of aerobic anoxygenic phototrophs abundances were investigated, for the first time, in the Adriatic Sea. Also, the spatial patterns of the whole picoplankton community as well as the environmental factors that potentially influence these patterns were highlighted. AAP abundances was in average 66.9 ± 66.8 × 10³ cell mL⁻¹, and t...

We investigated the effect of intravalvular liquid loss on changes in Escherichia coli (E. coli) levels in mussels (Mytilus galloprovincialis) harvested in different seasons and refrigerated (5°C) for 72 hours. A positive effect of seawater temperature at the time of harvesting on intravalvular liquid loss was found. No changes in E. coli levels in...

Mediterranean Sea (including Adriatic Sea) has been identified as a ‘hotspot’ for climate change, with prediction of the increase in water temperature of 2-4 °C over next few decades. Being mainly oligotrophic, and strongly phosphorus limited, Adriatic Sea is characterised by important role of microbial food web in production and transfer of biomas...

This book provides an overview of scientific activities of the scientists from Laboratory for Marine Microbiology (Institute of Oceanography and Fisheries in Split, Croatia) and collaborators during the last 15 years, which are presented through the number of case studies performed in different marine habitats of the Adriatic Sea. The main topics o...

The dynamics of the prokaryotic picoplankton community were studied at six stations of three embayments in Boka Kotorska Bay from January 2010 to January 2011. The abundance of non-pigmented bacteria, high nucleic acid content (HNA) bacteria, low nucleic acid content (LNA) bacteria, bacterial production and heterotrophic nanoflagellates was determi...

The structure of the microbial food web was studied in six estuary areas along the eastern Adriatic coast during March, July and October 2012. Limitation by phosphorus, not nitrogen, was a common feature for all studied estuaries. Heterotrophic bacteria and autotrophic picoplankton (APP) (particularly picoeukaryotes and Synechococcus ) can reach no...

Flow cytometry was used to describe seasonal cycles of Prochlorococcus (Prochl), Synechococcus (Syn), picoeukaryotes and heterotrophic bacteria in the central Adriatic Sea along the trophic gradient from January to December 2010. All picoplankton parameters decreased from eutrophic to oligotrophic areas, while the biomass ratio of bacterial to auto...

The response of phytoplankton community structure to anthropogenically-derived nutrients from the submarine sewage outflow was analysed in a shallow coastal area of the middle Adriatic Sea. The study was conducted during an eight-year period (2002-2010) at six stations in the Brač Channel, aiming to assess the potential change in the state of biolo...

The response of phytoplankton community structure to anthropogenically-derived nutrients from the submarine sewage outflow was analysed in a shallow coastal area of the middle Adriatic Sea. The study was conducted during an eight-year period (2002-2010) at six stations in the Brač Channel, aiming to assess the potential change in the state of biolo...

The seasonal distribution of marine viruses and their relationship with heterotrophic bacteria in the coastal and offshore area of the central and southern Adriatic were studied. Additionally, the percentage of high (HNA) and low (LNA) nucleic acid bacteria between the total number of bacteria and the distribution of heterotrophic nanoflagellates (...

The microbial abundances, including bacteria, viruses, and heterotrophic nanoflagellates, were determined for two anchialine caves located on the Island of Mljet (Adriatic Sea): Bjejajka Cave and Lenga Pit. Both caves are situated approximately 100 m from the coast with extensive subter-ranean connections to the sea, resulting in noticeable marine...

This paper addresses the dynamics of the prokaryotic picoplankton community in the coastal and open sea areas of the central Adriatic and in the coastal area of the southern Adriatic. This involved the study, from January to December 2005, of bacteria (total number of non-pigmented bacteria ; high nucleic acid content (HNA) bacteria ; low nucleic a...

A one-year survey of HNA and LNA heterotrophic bacteria abundance and its relation to bacterial production was conducted in the middle and southern Adriatic. The average abundance of heterotrophic bacteria in the central and southern coastal areas of the eastern coast of the Adriatic Sea ranged from 0.24×106 to 2.39×106 cells mL-1 and in the open s...

The abundance of Synechococcus and Prochlorococcus were determined at twenty-one stations located along the eastern coast of the central and southern Adriatic and at three stations located in the open central Adriatic Sea. Synechococcus abundance ranged from 10 2 to 10 5 cells mL -1 in the coastal area, and from 10 3 to 10 4 cells mL -1 in the open...

Variability in the bottom-up (BU) and top-down (TD) regulation of bacteria was analysed on non-seasonal (inter-annual) scales in the coastal and open middle Adriatic Sea during one decade (1997-2006). Decomposition of time series was performed to eliminate seasonal variability and to isolate non-seasonal (inter-annual) changes in the relative impor...

Vranjic Basin, in the eastern part of Kaštela Bay (middle Adriatic Sea), received municipal wastewater until offshore submarine outfalls were finished in November 2004. To identify the responses of the microbial community to changes in the trophic status of the marine environment, two 4-year periods were compared: A "eutrophic" period (2001-2004) w...

Due to the unsolved system for collection and treatment of urban and industrial wastewater of the towns Trogir, Kaštela, Solin and Split, the Kaštela Bay has long been one of the Mediterranean bays with the highest loads and significantly negative occurrences of eutrophication and pollution. With the aim of improving the ecological status in the ba...

Variability in the bottom-up (BU) and top-down (TD) regulation of bacteria was analysed on trophic and temporal (seasonal and inter-annual) scales in the middle Adriatic Sea during 1997–2006 using 3 empirical models. The analyses showed the tendency for bacteria to be TD controlled in oligotrophic open sea stations, and BU controlled in more eutrop...

Flow cytometry was used for the first time to determine the abundance of pico-and nanophototrophic plankton in the northern Adriatic during five cruises, from June to December 2006, along the west-east trophic gradient from the Po River delta (Italy) to Rovinj (Croatia). The firstly recorded occurrences of Prochlorococcus were obtained. Synechococc...

The paper describes a finding of photoautotroph cyanobacteria Synechococcus in deep Adriatic waters during the spring of 2006. The maximum abundance in early May was positioned at 800m, being of order of the values referred for the surface waters in the Adriatic Sea. The deep abundance maximum has been associated to the fast ventilation of deep Adr...

Month-to-month fluctuations in the abundance of bacteria and heterotrophic nanoflagellates (HNF) and bacterial production, as well as various chemical (nutrients, oxygen) and physical (salinity, temperature) parameters were analysed at a station located in the open middle Adriatic Sea during one decade (1997-2006). Being influenced by both coastal...

Two direct heterotrophic bacterioplankton counting methods, epifluorescence microscopy (EM) and flow cytometry (FCM) were compared using samples collected in two geographically different oceanic regions, the Adriatic Sea and the English Channel. A statistically significant correlation was found between results obtained by these two methods for samp...

The presence of sunlight was the major factor controlling the survival of faecal coliforms (FC) in seawater. The response of FC survival to intensity of solar radiation and temperature were inversely proportional. The combined effect of solar radiation and temperature on the survival of FC was expressed by multiple linear regression. The coefficien...

The effects of different temperatures (12oC, 18 oC, 24 oC) on the rate of concentration of faecal coliforms (FC) in mussels were studied in experimental conditions at different concentrations of FC in seawater. At low initial concentrations of FC in mussels the rate of FC concentration increased with concentration of FC in seawater and with increas...

Two direct heterotrophic bacterioplankton counting methods, epifluorescence microscopy (EM) and flow cytometry (FCM) were compared using samples collected in two geographically different oceanic regions, the Adriatic Sea and the English Channel. A statistically significant correlation was found between results obtained by these two methods for samp...

Vertical variations of autotrophic picoplankton, hetero-trophic bacteria, pigmented (PNAN) and non-pigmented (HNAN) nanoflagellates, and their activity were studied in a small-eutrophicated meromictic saline lake (eastern Adriatic Sea). The variations of heterotrophic filamentous cells exhibited similar patterns to that of HNAN, pointing out the ec...