Phytoplankton Assemblage over a 14-Year Period in the Adriatic Sea: Patterns and Trends.

Considering the role of phytoplankton in the functioning and health of marine systems, it is important to characterize its responses to a changing environment. The central Adriatic Sea, as a generally oligotrophic area, is a suitable environment to distinguish between regular fluctuations in phytoplankton and those caused by anthropogenic or climatic influences. This study provides a long-term perspective of phytoplankton assemblage in the central eastern Adriatic Sea, with 14 years of continuous time series data collected at two coastal and two offshore stations. The predominant phytoplankton groups were diatoms and phytoflagellates, but their proportion varied depending on the vicinity of the coast, as evidenced also by the distribution of chlorophyll a. In the coastal environment, the phytoplankton biomass was substantially higher, with a higher proportion of microphytoplankton, while small phytoplankton accounted for the majority of biomass in the offshore area. In addition, a decreasing trend in diatom abundance was observed in the coastal waters, while such trend was not so evident in the offshore area. Using a neural gas algorithm, five clusters were defined based on the contribution of the major groups. The observed increase in diversity, especially in dinoflagellates, which outnumber diatom taxa, could be a possible adaptation of dinoflagellates to the increased natural solar radiation in summer and the increased sea surface temperature.

Assessment of the eutrophication status at Mediterranean sub-basin scale, within the European Marine Strategy Framework Directive.

The aim of this work is to define harmonized reference conditions and assessment thresholds for selected criteria elements of the Marine Strategy Framework Directive (MSFD) Descriptor 5 (Eutrophication) in the Eastern Mediterranean Sea and to test if a tool for integrated assessment of the status of marine systems can be used as a common methodological approach. In this frame, we tested two statistical approaches in order to set threshold values for four criteria of Descriptor 5: nutrients, chlorophyll a, transparency and dissolved oxygen in the bottom waters. It is noteworthy that this work revealed the need to apply common procedures in data treatment and assessment evaluation. This is the first attempt to set common methods for the assessment of eutrophication in the Eastern Mediterranean, which is essential in marine environments, especially those shared by several countries. To this end, we have applied common criteria and metrics and established thresholds "Good" and "Moderate" for nutrients, chlorophyll a, transparency and dissolved oxygen in the bottom waters for the different Water Types of the Adriatic and Aegean Seas (I, II, IIIW, IIIE), based on datasets provided by Italy, Slovenia, Croatia and Greece. The selected criteria elements were common for all countries, providing a unified approach to GES assessment of two case study areas: the Adriatic Sea and the Saronikos Gulf. Dissolved Inorganic Nitrogen (DIN) threshold values of 15.6, 6.85, 1.61 and 2.11 µmol L-1 were set for the Water Types I, II, IIIW and IIIE, respectively. We also tested if an aggregation tool for GES assessment, such as Nested Environmental status Assessment Tool (NEAT), could be used as a common methodological approach. The comparison of NEAT with TRIX showed good comparability. In this end, NEAT can be used as a useful and much needed assessment tool for assessing eutrophication status of the marine.

How do open coastal fire episodes' impact sea surface microlayer neuston communities?

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, the plankton components of the sea surface layers were integrated to evaluate, for the first time, their dynamics over six months and their response to fire events in a typical coastal area of the Adriatic Sea. Concentrations of nutrients and organic compounds, together with plankton communities were significantly higher in the sea surface microlayer (SML, < 1 mm thick), than in the underlying water from 1 m depth. The piconeuston community and chlorophyll a responded with extreme abundance and concentration to the most intense fire event that enriched the SML with NH4+. Phytoneuston abundance increased with a delay of 2 weeks, while diversity indices decreased slightly after the fire events. The large abundances of the studied piconeuston parameters could be explained by the high availability of organic compounds and the immediate availability of NH4+, while the phytoneuston community responded to an increased NO3- concentration, triggered by the fire events. We confirmed that fast-acting marine heterotrophs are important members of biogeochemical cycles associated with fire events and that, together with phytoplankton, they are unavoidable parameters to detect environmental changes.

Variabilities of biochemical properties of the sea surface microlayer: Insights to the atmospheric deposition impacts.

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 NO3-, NH4+ and PO43- in ambient aerosol particles, wet deposition and sea surface samples collected from February to July 2019 at a central Adriatic coastal site. The aerosol mean concentration of dissolved nitrogen (DIN = NO3- + NH4+) and PO43- were 48.8 ± 82.8 µmol m-3 and 0.8 ± 0.6 µmol m-3, respectively, while their total fluxes (dry + wet) ranged from 24.2 to 212.3 µmol m-2 d-1 (mean 123.2 ± 53.2 µmol m-2 d-1) and from 1.2 to 2.1 µmol m-2 d-1 (mean 1.5 ± 0.3 µmol m-2 d-1), respectively. Intensive local episodes of open biomass burning (BB) significantly increased aerosol DIN concentrations as well as DIN deposition fluxes, particularly altering the molar DIN/PO43- ratio of atmospheric samples. The DIN temporal patterns showed high variability in the SML (range 0.2-24.6 µmol L-1, mean 5.0 ± 7.1 µmol L-1) in contrast to the underlying water samples (range 0.5-4.2 µmol L-1, mean 1.9 ± 1.2 µmol L-1), with significant increases during BB periods. Variability in abundance of heterotrophic bacteria and autotrophs in the SML along with concentrations of bulk dissolved and particulate organic carbon as well as dissolved and particulate lipids and carbohydrates, gel particles and surfactants followed DIN enhancements with a two-week delay. This study showed that AD can affect the short-term scale enrichments of organic matter in the SML, especially when accompanied by BB emissions typical of the overall Mediterranean coastal environment. This could have strong implications for global air-sea exchange processes, including those of climate relevant gases, mediated by the SML.

The relationship between toxic phytoplankton species occurrence and environmental and meteorological factors along the Eastern Adriatic coast.

In this study, the time series of toxic phytoplankton species collected between 2004 and 2018 from the Northern Adriatic, Sibenik Bay, and Mali Ston Bay was analyzed in relation to environmental (temperature, salinity, water column stability, and river flow) and meteorological parameters (precipitation and wind). Because of the mostly non-linear relation between biotic and abiotic parameters, self-organizing maps (SOM) were used to identify these relationships. SOM analysis distinguished species of the genus Dinophysis from Gonyaulax spinifera and Lingulodinium polyedrum species, which better tolerate wind-induced disturbance. Among the Dinophysis species, Dinophysis fortii, Dinophysis tripos, and Dinophysis acuta preferred higher precipitation rate and river flow in addition to optimal temperatures. The abundances of Alexandrium species, which occurred more frequently in estuarine areas, were associated with river flow and maximum stable water column. Regardless of the ecological preferences of individual harmful algae, freshwater inflow-caused stratification is present in all clusters of environmental conditions associated with increased abundances of harmful algae in the SOM analysis. It is highly likely that stratification represents an important factor for the development and maintenance of HABs. The non-linear relationship between the NAO index and rainfall was noted, of which the most important for the development of harmful algae is the proportional correlation between the positive phase of the NAO index and higher rainfall, especially in winter and spring. Such conditions are conducive to the development of harmful algae because, with the increase in temperature accompanying the positive phase of the NAO index, increased rainfall further stimulates their growth. This can be achieved either through nutrient yields or through higher freshwater inflow that further stabilizes the water column.

Non-indigenous species refined national baseline inventories: A synthesis in the context of the European Union's Marine Strategy Framework Directive.

Refined baseline inventories of non-indigenous species (NIS) are set per European Union Member State (MS), in the context of the Marine Strategy Framework Directive (MSFD). The inventories are based on the initial assessment of the MSFD (2012) and the updated data of the European Alien Species Information Network, in collaboration with NIS experts appointed by the MSs. The analysis revealed that a large number of NIS was not reported from the initial assessments. Moreover, several NIS initially listed are currently considered as native in Europe or were proven to be historical misreportings. The refined baseline inventories constitute a milestone for the MSFD Descriptor 2 implementation, providing an improved basis for reporting new NIS introductions, facilitating the MSFD D2 assessment. In addition, the inventories can help MSs in the establishment of monitoring systems of targeted NIS, and foster cooperation on monitoring of NIS across or within shared marine subregions.

Massive Occurrence of the Harmful Benthic Dinoflagellate Ostreopsis cf. ovata in the Eastern Adriatic Sea.

In September 2015, a massive occurrence of the Ostreopsis species was recorded in central Adriatic Kastela Bay. In order to taxonomically identify the Ostreopsis species responsible for this event and determine their toxin profile, cells collected in seawater and from benthic macroalgae were analyzed. Conservative taxonomic methods (light microscopy and SEM) and molecular methods (PCR-based assay) allowed the identification of the species Ostreopsis cf. ovata associated with Coolia monotis. The abundance of O. cf. ovata reached 2.9 × 104 cells L-1 in seawater, while on macroalgae, it was estimated to be up to 2.67 × 106 cells g-1 of macroalgae fresh weight and 14.4 × 106 cells g-1 of macroalgae dry weight. An indirect sandwich immunoenzymatic assay (ELISA) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) were used to determine the toxin profile. The ELISA assay revealed the presence of 5.6 pg palytoxin (PLTX) equivalents per O. cf. ovata cell. LC-HRMS was used for further characterization of the toxin profile, which showed that there were 6.3 pg of the sum of ovatoxins (OVTXs) and isobaric PLTX per O. cf. ovata cell, with a prevalence of OVTXs (6.2 pg cell-1), while the isobaric PLTX concentration was very low (0.1 pg cell-1). Among OVTXs, the highest concentration was recorded for OVTX-a (3.6 pg cell-1), followed by OVTX-b (1.3 pg cell-1), OVTX-d (1.1 pg cell-1), and OVTX-c (0.2 pg cell-1).

Phytoplankton diversity in Adriatic ports: Lessons from the port baseline survey for the management of harmful algal species.

An inventory of phytoplankton diversity in 12 Adriatic ports was performed with the port baseline survey. Particular emphasis was put on the detection of harmful aquatic organisms and pathogens (HAOP) because of their negative impact on ecosystem, human health, and the economy. Phytoplanktonic HAOP are identified as species, either native or non-indigenous (NIS), which can trigger harmful algal blooms (HAB). A list of 691 taxa was prepared, and among them 52 were classified as HAB and five as NIS. Records of toxigenic NIS (Pseudo-nitzschia multistriata, Ostreopsis species including O. cf. ovata) indicate that the intrusion of non-native invasive phytoplankton species has already occurred in some Adriatic ports. The seasonal occurrence and abundance of HAOP offers a solid baseline for a monitoring design in ports in order to prevent ballast water uptake and possible expansion of HAOP outside their native region.

Lipophilic toxin profile in Mytilus galloprovincialis during episodes of diarrhetic shellfish poisoning (DSP) in the N.E. Adriatic Sea in 2006.

Dinophysis spp. blooms and related shellfish toxicity events of diarrhetic shellfish poisoning (DSP) have been the most reported toxicity event through the Croatian National monitoring program. With the aim to characterize the DSP toxin profile in shellfish farmed in Croatia, for the first time a complete analysis of the toxin profile of Croatian mussels has been carried out using the LC-MS/MS technique. The obtained results showed okadaic acid (OA) as the main toxin contaminating Croatian mussels at that time. The maximum concentration of OA in shellfish tissue was recorded 12 days after the Dinophysis fortii bloom, thus suggesting that rapid growth of the toxin level in the shellfish occurred in the first week after the bloom while it was slower in the second week. Furthermore, the presence of only OA at concentrations which could endanger human health suggests D. fortii as the main organism responsible for the toxic event that occurred in Lim Bay. The presence of gymnodimine and spirolides in Croatian mussel has been detected for the first time, while the presence of yessotoxin and pectenotoxin-2 is confirmed.

Domoic acid--a new toxin in the Croatian Adriatic shellfish toxin profile.

This is the first study that presents concentrations of domoic acid detected in the whole shellfish tissue from breeding and harvesting areas along the Croatian coast of the Adriatic Sea during the period 2006 to 2008. Shellfish sample analyses after SAX cleaning procedures, using a UV-DAD-HPLC system, showed the presence of domoic acid in four species. The most prevalent of those species were the blue mussel (Mytilus galloprovincialis), followed by European flat oyster (Ostrea edulis), Mediterranean scallop (Pecten jacobaeus) and proteus scallop (Flexopecten proteus). Domoic acid, a potentially lethal phycotoxin that causes amnesic shellfish poisoning (ASP), was detected for the first time in January 2006 with the highest value of 6.5486 µg g⁻¹ in whole shellfish tissue. Pseudo-nitzschia spp. bloom events preceded these high domoic acid concentrations. According to this study, retention of domoic acid in the blue mussel M. galloprovincialis is more than 42 days. This investigation indicates the first presence of domoic acid in Croatian shellfish, but in concentrations under the regulatory limit (20 µg g⁻¹), therefore shellfish consumption was not found to endanger human health.

Is yessotoxin the main phycotoxin in Croatian waters?

With the aim of investigating whether yessotoxin (YTX) is responsible for diarrhetic shellfish poisoning (DSP) events in Croatian waters, three different methods were combined: a modified mouse bioassay (MBA) that discriminates YTX from other DSP toxins, the enzyme-linked immunosorbent assay method (ELISA) and liquid chromatography-mass spectrometry (LC-MS/MS). Among 453 samples of mussels and seawater analyzed in 2007, 10 samples were DSP positive. Results obtained by the modified MBA method revealed that most of the samples were positive for YTX, with the exception of samples from Lim Bay (LB 1) The ELISA method also identified the presence of YTX in these samples. DSP toxin profiles showed the presence of okadaic acid (OA) in three, and YTX in four out of nine samples that were analyzed by LC-MS/MS. The phytoplankton community structure pattern revealed Lingulodinium polyedrum (Stein) Dodge, which was present in the water prior to and/or during toxicity events at low concentrations (80 to 1440 cells L(-1)), as a potential YTX producing species. It is proposed that L. polyedrum cells accumulated in mussels and the subsequently observed toxicity may be related to metabolism after ingestion, resulting in carboxy YTX as the major analog in the mussel.