1. Introduction

Figure 1. Bathymetry of (a) Thermaikos Gulf (TG), divided in three basins (Inner TG, Central TG and Outer TG), and (b) Inner TG, divided in two basins (Thessaloniki Bay and Central Gulf of Thessaloniki). The main topographic characteristics (e.g., rivers, capes, Natura 2000 areas) and anthropogenic pressures (e.g., urban, industrial, agriculture etc.) are marked (Krestenitis et al., 2012). The insert map in (a) shows the location of TG in Mediterranean Sea.

Figure 1. Bathymetry of (a) Thermaikos Gulf (TG), divided in three basins (Inner TG, Central TG and Outer TG), and (b) Inner TG, divided in two basins (Thessaloniki Bay and Central Gulf of Thessaloniki). The main topographic characteristics (e.g., rivers, capes, Natura 2000 areas) and anthropogenic pressures (e.g., urban, industrial, agriculture etc.) are marked (Krestenitis et al., 2012). The insert map in (a) shows the location of TG in Mediterranean Sea.

2. Statistical Analysis of the Studies About Thermaikos Gulf

3. Main Research Findings

3.1. Hydrography and Circulation

The first publication simulating the hydrographic conditions of TG was authored by Ganoulis and Krestenitis (1982), presenting the development of a numerical model to simulate the transport, dilution and degradation of the pollutant discharges from the sewerage system of Thessaloniki city. However, the earliest monitoring effort, with hydrographic and current measurements that covered the Inner and Central TG, took place in the mid-1970s (Voutsinou and Balopoulos, 1989). This was the first campaign that described all the major physical processes of the gulf: the dominance of riverine waters in the western zone due to northerly winds and the Coriolis effect, the meteorological effect on the vertical structure, the main circulation patterns, and the water mass exchanges with the Aegean Sea. Since then, various oceanographic campaigns and numerical studies were undertaken (analysed in the following Sections), leading to a deeper understanding of the dynamics and dominant forcing factors in the area.

3.1.1. Main Circulation Patterns

The distribution of physical properties and the general circulation of TG are controlled by four major environmental factors: (i) the air-sea interactions and especially the wind forcing (Kontoyiannis et al., 2003; Androulidakis et al., 2021; 2023a), (ii) the exchanges with the northern Aegean Sea through the southern boundary (Hyder et al., 2002), (iii) the river plume dynamics (Kourafalou, 2001), and (iv) the morphological setting of the enclosed basin (Kourafalou, 2001; 2004; Kontoyiannis et al., 2003). The tidal amplitudes are small in the TG, ranging up to a few tens of centimetres (Poulos et al., 2000; Tsimplis et al., 1995; Kontoyiannis et al., 2003), leading to very weak corresponding tidal currents (<0.02 m/sec; Hyder et al., 2002). The river plume waters affect both the physical characteristics (density currents) and the biochemical properties of TG coastal waters, due to their high concentrations of nutrients (Karageorgis et al., 2005a; see Section 3.3). The formation of the river plumes that control the expansion of the riverine discharge loads is also influenced by the prevailing wind-induced circulation and the proximity of the TG’s east and west coasts (Kourafalou et al., 2004).

The morphological separation of TG into three main sub-basins of Inner, Central and Outer TG (Figure 1a) and the further separation of the Inner TG into two smaller coastal areas (Figure 1b) control the hydrodynamic circulation conditions. Distinct circulation patterns may form at each sub-basin, controlling the connectivity pathways, the transport across the sub-basins’ entrances, and finally the renewal of the water masses. Wind forcing may induce different circulation patterns among the gulf’s sub-basins. Winds from the north-northwestern sector (Mistral type, “Vardaris” and “Hortiatis” local ravine winds) are the most dominant (combining strength and frequency) over the region as derived by a 30-years investigation of the ERA5 Reanalysis database (Figure 5a), in agreement with older studies (e.g., Poulos et al., 2000). This wind regime may form a cyclonic ocean circulation pattern in the Central Gulf of Thessaloniki (Androulidakis et al., 2023a; Figure 6a). They also enhance the southward transport of near-surface waters towards the Outer TG (Kourafalou and Tsiaras, 2007), removing the riverine brackish masses away from the confined northern parts of the gulf (Hyder et al. 2002; Krestenitis et al., 2012) (Figure 6a). This type of wind-induced circulation is commonly evidenced during the winter months, following the general cyclonic circulation along the northern Aegean coasts (Zervakis and Georgopoulos, 2002; Kourafalou et al., 2004). It also allows the northward cyclonic intrusion of denser Aegean Sea Waters (ASW) in the deeper layers (Karageorgis and Anagnostou, 2001) that facilitates the renewal of the Inner TG with clearer waters (Krestenitis et al., 2012; Androulidakis et al., 2021). Such wind conditions can prevail during the entire annual cycle and enhance the renewal of the Inner TG, limiting the eutrophication events (Androulidakis et al., 2021), process that is crucial for the quality of the Thermaikos’ water masses. During these periods, a two layer-flow is formed mainly along the eastern coasts and across the entrances of the Inner TG (Cape Megalo Emvolo; Figure 1b) and Thessaloniki Bay (Cape Mikro Emvolo; Figure 1b). The two-layer flow consists of southward currents over the near-surface layer and northward streaming over the near-bottom layer (Androulidakis et al., 2023a). A clear southward connectivity pathway, between the more polluted western Thessaloniki Bay (Christophoridis et al., 2009; see Section 3.3) and the Central Gulf of Thessaloniki (Figure 6a), also affects the usually clearer waters along the eastern coasts under northerly winds (Androulidakis et al., 2023a). The cyclonic general circulation along the Aegean coasts may further evolve along the western coasts, and becomes more intense under northerly winds, thus connecting the northern parts of TG with the southern coasts and the Aegean Sea (Kourafalou et al., 2001; Kontoyiannis et al., 2003). The hyposaline signal of the Black Sea Waters has also been detected in the TG, following the same cyclonic circulation of the northern Aegean Sea, with a peak inflow during summer months (Kontoyiannis et al., 2003; Androulidakis and Kourafalou, 2011; Kourafalou and Tsiaras, 2007).

Contrastingly, the southeast winds (Sirocco type; “Eurus” in Greek shipping notation), which are usually weaker but also very frequent over the TG (Figure 5a), may reduce the renewal capacity of the gulf (Androulidakis et al., 2021), spread the freshwater plume over the Inner TG (Krestenitis et al., 2012) and induce an anticyclonic circulation pattern over the Central Gulf of Thessaloniki (Androulidakis et al., 2023a) (Figure 6b). An anticyclonic pattern, formed in front of the Axios and Aliakmonas deltas over the Central TG (Figure 1a), is associated with the Coriolis force effect on the river plume (forming an “anticyclonic bulge”; Kourafalou, 2001; Kourafalou et al., 2004). The narrowness of the basin near the freshwater discharge sources (Cape Megalo Emvolo; Figure 1b) allows the offshore expansion of the plume towards the eastern coasts (Kourafalou, 2001), especially under the influence of southerly winds (Krestenitis et al., 2012; Androulidakis et al., 2023a). Southerly winds may also spread river plume waters towards the Inner TG, even reaching Thessaloniki Bay (Krestenitis et al., 2012). The ASW intrusion is weaker along the eastern coasts, evolving mainly over the Outer and Central TG. The two-layer flow is weaker and can even become reversed in comparison to the northerlies’ case (e.g., Cape Mikro Emvolo; Figure 6b).

Figure 6. Schematic 3-d representations of general circulation features (Cyclonic and Anticyclonic patterns) of TG under the prevailing (a) Northerly (cold period) and (b) Southerly (warm period) winds. River plume spreading, 2-layer flows, Aegean Sea Water (ASW) inflow, Deep Water Formation (DWF) under buoyancy loss conditions, and wind-induced (Northwesterlies: NW, Southerlies: S, Southeasterlies: SE) upwelling and downwelling processes are also marked.

Figure 6. Schematic 3-d representations of general circulation features (Cyclonic and Anticyclonic patterns) of TG under the prevailing (a) Northerly (cold period) and (b) Southerly (warm period) winds. River plume spreading, 2-layer flows, Aegean Sea Water (ASW) inflow, Deep Water Formation (DWF) under buoyancy loss conditions, and wind-induced (Northwesterlies: NW, Southerlies: S, Southeasterlies: SE) upwelling and downwelling processes are also marked.

3.1.2. Thermohaline Variability and Stratification

The vertical structure of the water column reveals significant spatial and temporal variability, with periods of stratified or homogenised conditions. The characteristics of the surface layer vary considerably, although the lowest-salinity waters are usually concentrated in the western gulf (Hyder et al., 2002). Increased riverine outflows hinder vertical mixing, resulting to haline stratification (Tragou et al., 2005), especially from December to April (Hyder et al., 2002). Strong cold northerly winds, enhance vertical mixing and the homogenisation of the water column, especially in the shallower Thessaloniki Bay (Krestenitis et al., 2012), contributing on the formation of a southward-flowing, dense, near-bed current (Hyder et al., 2002; see Section 3.1.3). The seasonal pycnocline is stronger during summer (thermal stratification) and starts to recede in early autumn. Generally, the formation of the pycnocline starts in spring and the highest density gradients occur in summer. It is shown that the winter thermocline in the Inner TG develops at greater depths (~15–20 m) than the rest of the domain, forming wider mixed layers, mainly due to the lower sea depths in the semi-enclosed northern part of the gulf (Krestenitis et al., 2012). The vertical homogenization during winter months results to a prevailing barotropic circulation, in contrast with the summer conditions, when the water circulation is mainly baroclinic (Kontoyiannis et al., 2003; Zervakis et al., 2005). Strong pycnonclines (combining diverse thermoclines and haloclines) may also form in the near-bottom layer due to the intrusion of colder and more saline ASW, that either remain within the Central TG under southerly winds, or enter into the Inner TG under the effect of northerly winds (Poulos et al., 2000; Karageorgis and Anagnostou, 2001). It has been established that salinity presents a strong interannual variability, with intense short-term fluctuations. Field measurements after 2020 showed significantly higher salinities (often related to exceptionally high temperatures) at all depths of the Inner TG (Androulidakis et al., 2023a) than values measured during previous monitoring campaigns (e.g., 1994-2007; Krestenitis et al., 2012). Pertaining to this, sea temperature of the TG has also revealed significantly high peaks, especially during the last decade, and strengthened the formation of Marine Heatwaves (MHW), designating the TG as a MHW “hot spot” (Androulidakis and Krestenitis, 2022; see Section 4.2).

3.1.3. Vertical Water Fluxes

The Inner TG also appears amongst the regions of Dense Water Formation (DWF) in the Eastern Mediterranean Sea, process taking place under intense cooling by northerly gales (Estournel et al., 2005; Zervakis et al., 2005; Krestenitis et al., 2012). The phenomenon can be triggered by density gradients due to temperature, due to salinity or under the contribution of both (Shapiro et al., 2003). Despite the existence of the deltaic system in the southwestern part of the Inner TG, which could inhibit such a process, the northern TG is a favoured area for DWF. Low air temperatures, strong northerlies and weak river plume spreading in the Inner TG contribute to the formation of denser waters (Figure 6a) that typically cascade along the continental over the Outer TG and towards the Sporades basin (Estournel et al., 2005). The shallow depths of Thessaloniki Bay (10-20 m) and the topography of the area allow rapid cooling of the water masses since the shallow bathymetry favours strong heat losses and fast mixing of the waters, while the morphology reduces the interactions with the ‘open sea’. Thus, under favourable forcing conditions, a semi-secluded mass that is gradually becoming cooler and denser can be formed in the gulf. After a DWF in the Inner TG, a southward density current can be formed towards the southern gulf. The denser water masses that cascade over the TG’s continental shelf are capable to renew the North Aegean Trough’s deep water and especially the Sporades deep basin (Valioulis and Krestenitis, 1994). They can reach the southern boundary of the Outer TG, approximately 2 weeks after their formation in the Inner TG (Zervakis et al., 2005).

Upwelling in the coastal region (close to land) takes place when the wind blows parallel to the coast, especially along the western and eastern coasts of the Central and Outer TG (Dodou et al., 2002). When winds are favourable to upwelling for the west Thermaikos coast (southerlies), large amounts of high-salinity water enter the surface (Figure 6b), as the buoyancy-driven circulation is reversed (Kourafalou, 2001). Downwelling may evolve periodically on a diurnal time scale, especially in summer at the northwestern Gulf (Figure 6b) during onshore southeasterly winds (Kourafalou, 2001; Savvidis et al., 2019); note that such winds are very frequent in TG (Figure 5a). The prevailing and usually stronger northwesterly winds (Figure 5a) may reduce temperature at the surface after the coastal upwelling of colder waters over the eastern coasts of the Central and Outer TG (Kourafalou and Tsiaras, 2007; Figure 6a).

3.4. Biological Elements of the Water Column - Plankton

Plankton - named from the Greek “πλαγκτόν”, meaning to “wander“- is a vital component of the marine environment. Bacterioplankton comprising the highest abundance of pelagic biota, has key roles in global processes, influencing ecosystem structure and functioning as well as biogeochemical cycles. Marine phytoplankton contributes approximately 50% of global primary production plays a crucial role in removing CO2 from the elevated atmospheric levels via carbon pumping to the deep sea. Protozooplankton is highly important for carbon and energy transfer in the microbial loop and plankton food web. Metazoan zooplankton is an important component of the pelagic food web, contributing to many ecosystem functions, such as the transfer of primary production to higher organisms.

3.4.1. Bacterioplankton

Although the view on ecology of marine plankton has changed remarkably since the 1980’s (Azam et al., 1983, Fenchel, 1988) recognizing the significant role of bacteria in plankton food-webs (microbial loop), there is a lack of publications on bacterioplankton structure and dynamics in the TG. The first relevant work in the Inner TG (Mihalatou and Moustaka-Gouni, 2002) indicated high numbers of bacteria (from 0.9 to 6.8·10⁶ cells mL-1), reaching maximums in May, within the water layer between 50% and 20% of the incident Photosynthetic Active Radiation (PAR). This bacterial maximum coincided with high primary productivity (13.0 mg C m^-3h^-1) indicating strong trophic coupling of bacterioplankton and phytoplankton. Another work, recently published by Genitsaris et al. (2023), aimed at the response of bacterioplankton communities from the Inner and the Outer TG to PAHs’ exposure under experimental conditions (mesocosms). No negative effects of the contaminants were apparent in the experiments and net growth rates of both bacterioplankton communities were always positive. The bacterioplankton community composition was also examined for the first time. High Operational Taxonomic Unit (OTU) numbers were observed in both communities. In total, 841 and 693 OTUs were retrieved from the Inner and Outer TG, respectively. A high functional-response diversity of PAHs degrading OTUs reflected a high potential for acute mitigation responses of bacteria in TG. The Outer TG contained bacterioplankton communities with higher resistance sustaining bottom-up ecosystem stability.

3.4.2. Phytoplankton

Several studies on phytoplankton in the TG have been carried out, although long timeseries are lacking. The existing studies provide important information on phytoplankton composition, abundance and biomass, seasonal and spatial distributions, molecular diversity, and Harmful Algal Blooms (HABs). The earlier studies on phytoplankton have focused on composition, abundance and biomass. Diatoms and dinoflagellates were the richest groups in morphospecies of the diverse phytoplankton community of the Inner TG (Nikolaides and Moustaka-Gouni, 1990). The phytoplankton seasonal succession was dominated by Leptocylindrus, Chaetoceros, Skeletonema, Pseudo-nitzschia, Thalassiosira, Cylindrotheca, Cerataulina (diatoms) and Gymnodinium, Prorocentrum, Scrippsiella, Gonyaulax, Heterocapsa (dinoflagellates) species forming phytoplankton biomass peaks up to 6.7 mgL^-1. Focusing on spatial phytoplankton distribution in the entire TG, Gotsis-Skretas and Friligos (1990) showed a spatial variation of phytoplankton along the pollution gradient with maximal total abundance of 7,600 cells mL^-1. Most of the dominant phytoplankters of the Inner TG, mentioned above, also dominate the phytoplankton communities of the broader TG. New findings from works spanning the entire Aegean Sea (including TG), indicate that circulation patterns leading to broad-scale compartmentalization, might also have an important impact on the diversity and composition of phytoplankton assemblages in the coastal system of Thermaikos (Spatharis et al., 2019). Androulidakis et al. (2021) indicated that the phytoplankton species of the different habitat communities of the Inner, Central and Outer TG were highly connected via circulation (see Section 3.1), while the largest species pool, including nutrient opportunists, was recorded in the phytoplanktonic community of a station located closest to the river deltas (see Section 3.3).

Genitsaris et al. (2020), based on an eDNA analysis, showed that the temporal scale rather than the small-spatial scale, was the main signal for shaping phytoplankton assemblages in the Inner TG. This metabarcoding analysis has detected phytoplankton groups frequently observed in the Inner TG, dominated by diatoms and dinoflagellates. The most abundant molecular species were Chaetoceros tenuissimus, Chaetoceros cf. wighamii, Skeletonema pseudocostatum, Thalassiosira sp., (diatoms), Scrippsiella trochoidea, Gonyaulax fragilis, Alexandrium margaelefii (dinoflagellates), the cryptophyte Teleaulax sp., the pico-chlorophyte Micromonas pusilla and the haptophyte Haptolina sp. Dominant OTUs were closely related to species known to form harmful blooms and mucilage aggregates, together with rare taxa having potential negative impacts on human health not detectable with traditional microscopy. Among the potentially harmful species of the TG’s phytoplankton (Genitsaris et al., 2019), Dinophysis species was found responsible for mussel intoxication in aquaculture areas (Koukaras and Nikolaidis, 2004; Varkitzi et al., 2013). Dinophysis bloom occurrence had been documented several decades ago (Athanassopoulos, 1931; Gotsis-Skretas and Friligos, 1990; Nikolaides and Moustaka-Gouni, 1990; Nikolaidis and Evagelopoulos, 1997). Cysts of potentially toxic dinoflagellate species, such as Alexandrium cf. tamarense, A. cf. affine, A. cf. minutum, as well as Gymnodinium catenatum, were detected in the sediment of the Central and Outer TG (Giannakourou et al., 2005).

Comprehensive long-term studies on red tides and algal blooms are scarce. The first study that examined the seasonal shift and described the responsible phytoplankton for the formation of these phenomena in the Inner, Central and Outer TG was conducted by Petala et al. (2018). By applying traditional microscopy, they divided Thermaikos into two subregions based on phytoplankton abundance and, hence, the eutrophic status. The study estimated significantly higher abundance in the Inner and Central TG compared to the Outer TG. Algal bloom and red tides formation (Figure 8) by several mucilaginous diatoms (i.e. Chaetoceros sp., Cylindrotheca closterium etc.) and dinoflagellates (i.e. Gonyaulax fragilis) including the heterotrophic dinoflagellate Noctiluca scintillans (Figure 9) and its relative Spatulodinium pseudonoctiluca were observed. Furthermore, the study found considerably lower plankton abundance in the Outer TG, demonstrating its oligotrophic state. A thorough study documenting the weekly phytoplankton species succession and identifying the responsible taxa for the formation of phytoplankton blooms and red tides at the urban marine environment of the Inner TG was conducted by Genitsaris et al. (2019). The study classified this subregion of Thermaikos as heavily eutrophic, indicating persistent phytoplankton blooms that were dominated by known mucilaginous species such as C. closterium, Chaetoceros spp., Leptocylindrus spp. and Skeletonema costatum (Figure 9). The accumulation of the organic mucilaginous material from the successive algal blooms and red tides resulted in the formation of an excessive mucilage aggregate phenomenon in June and July 2017 (Figure 8), extending from the Inner to the Outer TG (Genitsaris et al., 2019), attributed to the same mucilage-producing diatoms, together with the mucilaginous haptophyte Phaeocystis sp. and the dinoflagellate G. fragilis.

The trophic conditions of TG were assessed using the multiparametric Eutrophication index (E.I.; Primpas et al., 2010) by some studies. Based on nutrients and chlorophyll-a (chl-a) data of the period 1995-2007 an improvement in the trophic status of Thessaloniki bay and of the area near the Axios river estuary was observed. The trophic status of both areas which was classified as “Poor” till 2000, was improved and classified as “Moderate” in 2007 (Zachioti et al., 2022). In addition, data collected in five samplings during 2012–2014 for the implementation of the WFD showed that the “Moderate” trophic status of the two areas is maintained (Pavlidou et al., 2015).

Figure 8. Eutrophication events in Thermaikos Gulf (TG) in July 2017 (Photo courtesy: Eurokinissi.gr), February 2017 (Photo courtesy: Thes.gr), March 2017, and December 2017. The plankton species associate with the red tide events in March and December 2017 are also shown.

Figure 8. Eutrophication events in Thermaikos Gulf (TG) in July 2017 (Photo courtesy: Eurokinissi.gr), February 2017 (Photo courtesy: Thes.gr), March 2017, and December 2017. The plankton species associate with the red tide events in March and December 2017 are also shown.

Several studies in the prism of monitoring activities in the framework of the implementation of WFD 2000/60/EC (WFD) and Marine Strategy Framework Directive 2008/56/EU (MSFD), evaluated the Inner TG, and particularly the Thessaloniki Bay, with “Moderate” or “Poor” status (Pavlidou et al., 2012; 2015; Simboura et al., 2016). Recently, a study on eutrophication assessment of TG capitalized on current advances in remote sensing, and employed satellite image analysis in order to evaluate the spatial distribution of chl-a levels (Androulidakis et al. 2021). In order to have more accurate evaluation of chl-a levels, the authors combined microscopy with satellite ocean color image analysis and attempted to associate the chl-a with the “actual” plankton biomass during eutrophication events in the TG. It was found that chl-a concentrations evaluated using satellite imagery correlated well with phytoplankton biomass, measured with the time consuming microscopy, revealing similar patterns. Thus, they concluded that by coupling the two methods it is possible to determine the extent, as well as the responsible taxa, for the formation of these eutrophication phenomena. For instance, they found that during an annual cycle, chl-a peaked at 45 mgm^-3 in December 2017 (Figure 8) under the prevalence of southerly winds (weak renewal; Section 3.1), when an extensive red tide caused by the photosynthetic ciliate Mesodinium rubrum expanded throughout the Inner and Central TG (Androulidakis et al., 2021). On the contrary, low chl-a levels were detected during periods with northerly winds that enhanced the renewal of the enclosed basins.

Figure 9. Micrographs of common planktonic organisms of TG as seen by microscopy. Epifluorescence micrographs were taken by UV excitation for (A) DAPI-fluorescence cells or by green excitation (B) and blue excitation for (C) Chl-a red auto-fluorescence. Light - phase contrast (D, E, F, G) micrographs. (A) Heterotrophic bacteria. (B) Pico- cyanobacteria. (C) Pico-chlorophytes. (D) The diatoms Chaetoceros sp. and Leptocyllindrus sp. along with the dinoflagellate Ceratium cf. horridum. (E) The red-tide forming ciliate Mesodinium rubrum. (F) The bloom forming dinoflagellate Karenia with other plankton species. (G) Cells of the red-tide forming heterotrophic dinoflagellate Noctiluca scintillans along with the pelagic tunicate Oikopleura dioica. Scale bars in μm.

Figure 9. Micrographs of common planktonic organisms of TG as seen by microscopy. Epifluorescence micrographs were taken by UV excitation for (A) DAPI-fluorescence cells or by green excitation (B) and blue excitation for (C) Chl-a red auto-fluorescence. Light - phase contrast (D, E, F, G) micrographs. (A) Heterotrophic bacteria. (B) Pico- cyanobacteria. (C) Pico-chlorophytes. (D) The diatoms Chaetoceros sp. and Leptocyllindrus sp. along with the dinoflagellate Ceratium cf. horridum. (E) The red-tide forming ciliate Mesodinium rubrum. (F) The bloom forming dinoflagellate Karenia with other plankton species. (G) Cells of the red-tide forming heterotrophic dinoflagellate Noctiluca scintillans along with the pelagic tunicate Oikopleura dioica. Scale bars in μm.

3.4.3. Protozooplankton

Protozooplankton community is underappreciated in plankton studies in the TG. The early study by Mihalatou and Moustaka-Gouni (2002) focused on protozooplankton components (heterotrophic nanoflagellates, heterotrophic dinoflagellates and ciliates) as grazers of bacteria. The ciliate M. rubrum as member of protozooplankton was assigned to the photosynthetic functional category, supported by organelle robbery. Several heterotrophic dinoflagellates (e.g., species of the genera Protoperidinium, Gyrodinium) even the red-tide forming omnivorous feeder N. scintillans, have been considered members of phytoplankton community in earlier plankton studies (Nikolaides and Moustaka-Gouni, 1990; Gotsis-Skretas and Friligos, 1990). Investigating the underexplored diversity of marine unicellular eukaryotes, Genitsaris et al. (2020) identified phytoplankton heterotrophic unicellular eukaryotes frequently observed in TG. In addition, they also revealed protozooplankton taxonomic groups previously undetected in the area (MALVs, MAST and Cercozoa). The protozooplankton community showed temporal patterns rather than small-scale spatial separation responding to the variability of physical and chemical environmental factors. The specific functional characterization of protozooplankton, that had previously been taxonomically characterized by 18S rRNA gene amplicon sequencing, showed a diverse range of trophic preference of picograzers, nanograzers, micrograzers, phagotrophs, decomposers and parasites (Genitsaris et al., 2020).

3.4.4. Metazooplankton

The metazooplankton community of TG is also poorly known resulting to lack of data on trophic interactions occurring in the pelagic food web and the resource efficiency of zooplankton in relation to phytoplankton richness and harmful blooms. An early study on zooplankton (Siokou-Frangou and Papathanasiou, 1991) indicated that the spatial-temporal variability in the Gulf is highly affected by riverine water inflow, pollution and ocean circulation. Copepods and cladocerans were the most abundant groups, with high numbers of copepods in the Inner TG. The dominant species were Acartia clausi followed by Oithona nana and Podon polyphernoides. In the Central TG, dominant species were Acartia clausi followed by Paracalanus parvus and Penilia avirostris. Appendicularians were well represented, in terms of species richness and number of individuals, in the Outer and Central TG. Another early study on metazooplankton focused on the annual cycle of neritic cladocera (Alvanou, 1999). The distribution of mesozooplankton resting eggs was studied in the sediments of TG and indicated higher abundance of eggs at locations close to the river mouths, with water column rich in zooplankters (Siokou-Frangou et al., 2005). Recent research on metazooplankton reported the presence of the non-indigenous calanoid copepod Pseudodiaptomus marinus (Kourkoutmani and Michaloudi, 2022). One of the very few studies dealing with marine rotifers across the Mediterranean Sea investigates the temporal distribution patterns of four coexisting Synchaeta species in the Inner TG. This work contributed to our understanding of the dynamics of this group of micrometazoans, previously underestimated among marine zooplankton, given that rotifers are lost when using larger mesh size nets in sampling (Kourkoutmani et al., 2023).

3.4.5. Planktonic Response to Climate Change and Pollutants

During the last decade, Inner TG unicellular plankton community has been used in mesocosm experiments to explore the species response to multiple variables of climate change (Stefanidou et al., 2018a), and phytoplankton response to pollutants discharged in the seawater from exhaust gas cleaning systems on ships, known as scrubbers (Genitsaris et al., 2023). In regard to the climate change variables, the impacts of elevated temperature (see Section 4.2) in the form of an intense heat shock, together with changes in salinity, were examined on the natural phytoplankton community of TG and demonstrated adverse effects on species diversity, resource use efficiency and productivity (Stefanidou et al., 2018a). The lower productivity and resource use function after the heat shock and the changes in salinity were supported by the lower inferred activity of the major phytoplankton taxonomic groups, as evidenced by the lower ratio of rRNA sequences to rDNA sequences (rRNA : rDNA) under these circumstances (Stefanidou et al., 2018b), which has been used as a proxy of metabolic activity in the literature. The major outcome of these studies was the synergistic negative effects on phytoplankton community caused by the elevated temperature and increased salinity, which was also confirmed by measurements of physical properties by Androulidakis et al. (2023). Taking into consideration that climate change is associated with concurrent shifts in several variables, besides temperature and salinity, in the marine environment, it could also lead to more intensified and complex effects on primary producers; this may modify the energy flow and consequently the biogeochemical cycles, therefore impacting ecosystem functioning. The potential impacts of scrubber effluents, containing several chemical compounds such as PAHs and metals, and particularly vanadium and nickel, was examined in mesocosms using natural phytoplankton communities of the Inner and Outer TG. Adverse effects were observed only under high, 10% (v/v) dilutions of scrubber effluent exposure while no adverse effects were observed in communities exposed at 1% dilutions. Effluent discharge at 50 m along the ships’ wake is diluted 2000 times for vessels with established open-loop scrubbers sailing in open sea (Genitsaris et al., 2023).

4. Discussion and Concluding Remarks

4.2. Thermaikos Gulf under Climate Change

Evidence of a changing climate can be recognized in the recent evolution of physical properties in the seawater of TG. Figure 14 shows the prevailing ocean warming conditions in the gulf as derived from daily satellite Sea Surface Temperature (SST; Copernicus Reprocessed Mediterranean L4 dataset; 0.05° resolution grid) between 1982 and 2023. The annual mean SST, averaged over the entire TG, reveals a strongly increasing Sen’s Slope (0.52°C/decade; Figure 14a), higher than the general trend of the broader Aegean, Ionian and Cretan Seas (0.49°C/decade; Androulidakis and Krestenitis, 2022). The TG is characterized as a “hot spot” area for MHWs, with events that do not only occur near the sea surface, but extend through the entire water column, especially in the shallower Inner TG (Androulidakis et al., 2023a). A statistically significant (p_value<0.0001) SST shift of around 1.2°C was computed after 2006, based on the Pettitt Homogeneity test (Pettitt, 1979), while the mean SST increased from around 17.5°C in 1982 to 19.5°C in 2023. The SST trend follows the respective air temperature interannual increase (0.43°C/decade) that also showed a clear shift after 2006 (Figure 5b). The highest SST peaks of the maximum values (99^th Percentiles) were observed in 2021 and 2023 (>29°C; Figure 14a). The summers of these two years were the warmest of the entire period, affecting several environmental and socioeconomic factors of the area (e.g., aquaculture; Androulidakis and Krestenitis, 2022). The related trend slope of the maximum levels is even steeper than the annual mean (0.67^oC/decade), increasing by approximately 2.5^oC during the 1982-2023 period. The respective MHWs were computed based on the satellite-derived SSTs and the methodology, introduced by Hobday et al. (2016); the annual MHW cumulative intensity (^oCxdays), averaged over the entire TG, is presented in Figure 14b. The events were defined using the 90^th percentile climatology (1982-2023) as threshold baseline, and a 5-days minimum duration for each event. Very high intensities successively occurred after 2018 confirming the intensification of the warming impact in the TG. Intensity peaks were computed for 2012 (related mainly to winter MWHs as derived from the high mean SST and relatively low 99^th percentiles; Figure 14a) and in 2021. Especially in 2021, the TG’s MWHs had significant biochemical implications, affecting the marine environment and imposing mass mortality events of prominent biota with considerable impacts (e.g., on aquaculture, fishing, tourism, human health, etc.; Androulidakis and Krestenitis, 2022; Lattos et al., 2022; Antoniadou et al. 2023). The importance of MHWs raises the need of accurate prediction tools for both short-term (e.g. a few days based on operational hydrodynamic modeling) and interim-future periods (e.g., weeks to months forecasts based on artificial intelligence techniques; Krestenitis et al., 2024).

An increase has also been observed in salinity that reached the highest measured levels after 2020, associated with elevated temperatures and possible changes in precipitation rates and river discharge outflows (Androulidakis et al., 2023a). Temperature increases together with changes in salinity may also affect species diversity, resource use efficiency and productivity (Stefanidou et al., 2018a). Experiments in the TG (Stefanidou et al., 2018a) showed how changes in the species inventory driven by a MHW would influence the ability of the resultant phytoplankton communities to cope with salinity changes, especially in the context of climate change, where short term temperature changes during heatwaves are expected to increase in frequency and magnitude during the 21^th century (Darmaraki et al, 2019).

Figure 14. Annual (a) mean and 99^th Percentile Sea Surface Temperature (SST; ^oC) and (b) cumulative intensity of Marine Heatwaves (MHWs), derived from the satellite-derived daily fields and averaged over the TG during 1982-2023. The linear trends, the Sen’s Slopes, and the μ1 and μ2 levels of the Pettit homogeneity test for the mean values are also shown.

Figure 14. Annual (a) mean and 99^th Percentile Sea Surface Temperature (SST; ^oC) and (b) cumulative intensity of Marine Heatwaves (MHWs), derived from the satellite-derived daily fields and averaged over the TG during 1982-2023. The linear trends, the Sen’s Slopes, and the μ1 and μ2 levels of the Pettit homogeneity test for the mean values are also shown.

Temperature also greatly affects the equilibrium constants of the CO₂-carbonate system and particularly the solubility coefficient of CO₂; warming and increasing salinity decrease the solubility of CO₂ (e.g., for a temperature increase of 1°C, pCO2 rises by ~4%, Takahashi et al., 1993), which may induce CO₂ oversaturation in many cases and change of the character of the area, acting finally as a CO₂ source to the atmosphere. High-resolution simulations of the physical and biogeochemical state of the Mediterranean were used to study the climate change-related impacts on the marine ecosystems of the basin under different future CO₂ emissions scenarios (Solidoro et al., 2022; Reale et al., 2022). The projections showed a DIC concentration increase as well as an acidification signal in the upper water column, as a result of increased respiration, but also because of the increase in atmospheric CO₂ and of the changes in CO₂ solubilization driven by changes in temperature and salinity, with stronger changes in the eastern basin than in the western one. Even though future projections are unfavourable and the TG is a coastal ecosystem that is already subject to climate change and characterized by complex biogeochemical processes that are directly linked to the CO₂-carbonate system, there is a lack of regular monitoring of related parameters.

The limitation of freshwater and sediment discharge has led to erosion of the protected deltas and coastline retreat in more recent years (Poulos et al., 2000). To this regard, the risk of intensification of coastal retreat and flooding under rising sea levels in the future may have severe environmental and socioeconomic impacts, especially over the western coastal area of the TG. The interannual variability of the sea level anomaly over the TG is also characterized by a strong increasing trend of approximately 4 cm/decade during the last 30 years, resulting to increasing flooding frequencies over the low-lying coastal areas (Androulidakis et al., 2023b). Climate change is also associated with concurrent shifts in several variables of the marine environment and not only in physical parameters (temperature, salinity, sea level), leading to more complex effects on primary producers and impacts on the biochemical cycles and ecosystem functioning. Despite these alarming signs, it is noted that climatic studies analysing long-term future projections of physicochemical and biological features, based on diverse climatic scenarios combining atmospheric input from ensemble modeling, are absent for the TG, while the research over past climate-scale periods forming the present day situation corresponds to only the 2% of the entire research activity in the gulf.

References

1. Albanis, T.A. Herbicide losses in runoff from the agricultural area of Thessaloniki in Thermaikos Gulf, N. Greece. Sci. Total. Environ. 1992, 114, 59–71. [CrossRef]
2. Alexandridis, T.K.; Monachou, S.; Skoulikaris, C.; Kalopesa, E.; Zalidis, G.C. Investigation of the temporal relation of remotely sensed coastal water quality with GIS modelled upstream soil erosion. Hydrol. Process. 2014, 29, 2373–2384. [CrossRef]
3. Alvanou, L., 1999. Annual cycle of cladocerans in the Thermaikos Gulf and the Gulf of Thessaloniki (North Aegean Sea) (No. RefW-14-58897). Aristotle University of Thessaloniki.
4. Anagnostopoulou, C.; Zanis, P.; Katragkou, E.; Tegoulias, I.; Tolika, K. Recent past and future patterns of the Etesian winds based on regional scale climate model simulations. Clim. Dyn. 2013, 42, 1819–1836. [CrossRef]
5. Androulidakis, Y.; Kolovoyiannis, V.; Makris, C.; Krestenitis, Y.; Baltikas, V.; Stefanidou, N.; Chatziantoniou, A.; Topouzelis, K.; Moustaka-Gouni, M. Effects of ocean circulation on the eutrophication of a Mediterranean gulf with river inlets: The Northern Thermaikos Gulf. Cont. Shelf Res. 2021, 221, 104416. [CrossRef]
6. Androulidakis, Y.; Makris, C.; Kolovoyiannis, V.; Krestenitis, Y.; Baltikas, V.; Mallios, Z.; Pytharoulis, I.; Topouzelis, K.; Spondylidis, S.; Tegoulias, I.; et al. Hydrography of Northern Thermaikos Gulf based on an integrated observational-modeling approach. Cont. Shelf Res. 2023, 269. [CrossRef]
7. Androulidakis, Y.; Makris, C.; Mallios, Z.; Krestenitis, Y. Sea level variability and coastal inundation over the northeastern Mediterranean Sea. Coast. Eng. J. 2023, 65, 514–545. [CrossRef]
8. Androulidakis, Y.S.; Kourafalou, V.H. Evolution of a buoyant outflow in the presence of complex topography: The Dardanelles plume (North Aegean Sea). J. Geophys. Res. 2011, 116. [CrossRef]
9. Androulidakis, Y.S.; Krestenitis, Y.N. Sea Surface Temperature Variability and Marine Heat Waves over the Aegean, Ionian, and Cretan Seas from 2008–2021. J. Mar. Sci. Eng. 2022, 10, 42. [CrossRef]
10. Antoniadou, C. and Chintiroglou, C., 2005. Response of polychaete populations to disturbance: an evaluation of methods in hard substratum. Fresenius Environmental Bulletin 14, 1066-1073.
11. Antoniadou, C. and Chintiroglou, C., 2009. Temporal variability of zoobenthos inhabiting the photophilic algae community in Thermaikos Gulf (Eastern Mediterranean). Proceedings of the 11th International Congress on the Zoogeography and Ecology of Greece and Adjacent Regions, Heraklion, Crete, p 94.
12. Antoniadou, C.; Pantelidou, M.; Skoularikou, M.; Chintiroglou, C.C. Mass Mortality of Shallow-Water Temperate Corals in Marine Protected Areas of the North Aegean Sea (Eastern Mediterranean). Hydrobiology 2023, 2, 311–325. [CrossRef]
13. Antoniadou, C., Krestenitis, Y. and Chintiroglou, C., 2004. Structure of the “Amphioxus sand” community in Thermaikos bay (Eastern Mediterranean). Fresenius Environmental Bulletin, 13(11a), 1122-1128.
14. Antoniadou, C.; Sarantidis, S.; Chintiroglou, C. Small-scale spatial variability of zoobenthic communities in a commercial Mediterranean port. J. Mar. Biol. Assoc. United Kingd. 2010, 91, 77–89. [CrossRef]
15. Arditsoglou, A.; Voutsa, D. Partitioning of endocrine disrupting compounds in inland waters and wastewaters discharged into the coastal area of Thessaloniki, Northern Greece. Environ. Sci. Pollut. Res. 2009, 17, 529–538. [CrossRef]
16. Arditsoglou, A.; Voutsa, D. Occurrence and partitioning of endocrine-disrupting compounds in the marine environment of Thermaikos Gulf, Northern Aegean Sea, Greece. Mar. Pollut. Bull. 2012, 64, 2443–2452. [CrossRef]
17. Athanassopoulos, G., 1931. Microfaune du golfe de Salonique, etc. Bull. Inst. Oceanogr., 588, 1–24.
18. AUTh, 2018a. Monitoring the marine environment of Thermaikos Gulf. Technical Report (in Greek).
19. AUTh, 2018b. Monitoring the marine environment of Thermaikos Gulf. Technical Report (in Greek).
20. AUTh, 2019. Monitoring the marine environment of Thermaikos Gulf. Technical Report (in Greek).
21. AUTh, 2020a. Monitoring the marine environment of Thermaikos Gulf. Technical Report (in Greek).
22. AUTh, 2020b. Environmental status of the seabed on existing and new installations of mussel farms in the Allocated Zone for Aquaculture of Thermaikos. Technical Report (in Greek).
23. AUTh, 2023. Distribution of the invasive Callinectes sapidus (blue crab) in the Hellenic Seas: population study, ecological impacts and management plans to control and commercially exploit the crab’s populations. Technical Report (in Greek).
24. Azam, F.; Fenchel, T.; Field, J.G.; Gray, J.S.; Meyer-Reil, L.A.; Thingstad, F. The Ecological Role of Water-Column Microbes in the Sea. Mar. Ecol. Prog. Ser. 1983, 10, 257–263. [CrossRef]
25. Azaria, A., Karavasilis, G., Kehris, E. and Vrana, V., 2019. The impact of financial crisis on university students in Greece. South-Eastern Europe Journal of Economics, 17(2).
26. Balopoulos, E.T.; Friligos, N.C. Water circulation and eutrophication in the northwestern Aegean Sea: Thermaikos Gulf. Toxicol. Environ. Chem. 1994, 41, 155–167. [CrossRef]
27. Balopoulos, E.T.; Collins, M.B.; James, A. Satellite images and their use in the numerical modelling of coastal processes. Int. J. Remote. Sens. 1986, 7, 905–919. [CrossRef]
28. Baltas, E.A.; Mimikou, M.A. Climate Change Impacts on the Water Supply of Thessaloniki. Int. J. Water Resour. Dev. 2005, 21, 341–353. [CrossRef]
29. Borja, .; Franco, J.; Valencia, V.; Bald, J.; Muxika, I.; Belzunce, M.J.; Solaun, O. Implementation of the European water framework directive from the Basque country (northern Spain): a methodological approach. Mar. Pollut. Bull. 2004, 48, 209–218. [CrossRef]
30. Centre for the Development of Educational Policy, 2015, 2015 Key indicators on education. Centre for the Development of Educational Policy of the General Confederation of Workers of Greece. www.kanep-gsee.gr/sitefiles/files/2015_ekth.pdf Accessed on 23 October 2023 (in Greek).
31. Chalari, M., 2016. Education in the midst of Greece's socio-economic crisis. Is there room for new stories, another way of thinking and a notion of hope? (Doctoral dissertation, UCL (University College London)).
32. Chester, R.; Voutsinou, F. The initial assessment of trace metal pollution in coastal sediments. Mar. Pollut. Bull. 1981, 12, 84–91. [CrossRef]
33. Chintiroglou, C., Antoniadou, A., Damianidis, P. and Kourelea, E., 2007. Surrogate measures of biodiversity in macrobenthic communities in Thermaikos Gulf. Greece. Rapp. Comm. int. Mer Médit, 38, p. 449.
34. Chintiroglou, C., Antoniadou, C. and Krestenitis, Y., 2006. Can polychaetes be used as a surrogate group in assessing ecological quality of soft substratum communities (NE Thermaikos Gulf)? Fresenius Environmental Bulletin 15, 1199-1207.
35. Chintiroglou, C.-C.; Antoniadou, C.; Baxevanis, A.; Damianidis, P.; Karalis, P.; Vafidis, D. Peracarida populations of hard substrate assemblages in ports of the NW Aegean Sea (eastern Mediterranean). Helgol. Mar. Res. 2004, 58, 54–61. [CrossRef]
36. Christophoridis, C.; Bourliva, A.; Evgenakis, E.; Papadopoulou, L.; Fytianos, K. Effects of anthropogenic activities on the levels of heavy metals in marine surface sediments of the Thessaloniki Bay, Northern Greece: Spatial distribution, sources and contamination assessment. Microchem. J. 2019, 149, 104001. [CrossRef]
37. Christophoridis, C.; Dedepsidis, D.; Fytianos, K. Occurrence and distribution of selected heavy metals in the surface sediments of Thermaikos Gulf, N. Greece. Assessment using pollution indicators. J. Hazard. Mater. 2009, 168, 1082–1091. [CrossRef]
38. Damianidis, P., Karachle, P. and Chintiroglou, C., 2016. Population structure of clam Venus verrucosa Linnaeus, 1758 harvested in Thermaikos Gulf, NW Aegean Sea, Greece. Int. J. Fish. Aquat. Stud, 4, 393-401.
39. Darmaraki, S.; Somot, S.; Sevault, F.; Nabat, P.; Narvaez, W.D.C.; Cavicchia, L.; Djurdjevic, V.; Li, L.; Sannino, G.; Sein, D.V. Future evolution of Marine Heatwaves in the Mediterranean Sea. Clim. Dyn. 2019, 53, 1371–1392. [CrossRef]
40. Dassenakis, M., Zeri, C., and Kaberi H. 2005. Heavy metals in seawater. In: ‘State of the Hellenic Marine Environment (SoHelME 2005)’, E. Papathanassiou & A. Zenetos (eds) 360 p., HCMR Publ., Athens, Greece. 148-152. https://epublishing.ekt.gr/el/8303.
41. Dimou, A.D.; Sakellarides, T.M.; Vosniakos, F.K.; Giannoulis, N.; Leneti, E.; Albanis, T. Determination of phenolic compounds in the marine environment of Thermaikos Gulf, Northern Greece. Int. J. Environ. Anal. Chem. 2006, 86, 119–130. [CrossRef]
42. Dodou, M.; Savvidis, Y.; Krestenitis, Y.; Koutitas, C. Development of a two-layer mathematical model for the study of hydrodynamic circulation in the sea. Application to the Thermaikos gulf. Mediterr. Mar. Sci. 2002, 3, 5. [CrossRef]
43. de Madron, X.D.; Nyffeler, F.; Balopoulos, E.; Chronis, G. Circulation and distribution of suspended matter in the Sporades basin (northwestern Aegean sea). J. Mar. Syst. 1992, 3, 237–248. [CrossRef]
44. Estournel, C.; Zervakis, V.; Marsaleix, P.; Papadopoulos, A.; Auclair, F.; Perivoliotis, L.; Tragou, E. Dense water formation and cascading in the Gulf of Thermaikos (North Aegean), from observations and modelling. Cont. Shelf Res. 2005, 25, 2366–2386. [CrossRef]
45. Feidas, H.; Kokolatos, G.; Negri, A.; Manyin, M.; Chrysoulakis, N. A TRMM-Calibrated infrared technique for rainfall estimation: application on rain events over eastern Mediterranean. Adv. Geosci. 2006, 7, 181–188. [CrossRef]
46. Fenchel, T., 1988. Marine plankton food chains. Annual Review of Ecology and Systematics, 19(1), 19-38.
47. Flocas , A. A. and Arseni-Papadimitriou , A., 1974 . On the annual variation of air temperature in Thessaloniki. In Sci. Annals, Fac. Phys. and Mathem. , Vol. 14 , 129 – 150 . Univ. Thessaloniki .
48. Friligos, N., Kondylakis, J.C., and Psyllidou-Giouranovits, R., 1997. Eutrophication and phytoplankton abundance in the Thermaikos Gulf, Greece. Fresenius Environmental Bulletin, 6, 27–31.
49. Friligos, N., and Koussouris, T., 1984. Preliminary observations on sewage nutrient enrichment and phytoplankton ecology in the Thermaikos Gulf, Thessaloniki, Greece. Vie et Milieu/Life & Environment, 35-39. https://hal.sorbonne-universite.fr/hal-03019801.
50. Fytianos, K.; Vasilikiotis, G. Concentration of heavy metals in seawater and sediments from the Northern Aegean Sea, Greece. Chemosphere 1983, 12, 83–91. [CrossRef]
51. Fytianos, K.; Vasilikiotis, G.; Weil, L. Identification and determination of some trace organic compounds in coastal seawater of Northern Greece. Bull. Environ. Contam. Toxicol. 1985, 34, 390–395. [CrossRef]
52. Galinou-Mitsoudi, S., Vlahavas, G., Papoutsi, O., 2006. Population study of the protected bivalve Pinna nobilis (Linnaeus, 1758) in Thermaikos Gulf (north Aegean Sea). Journal of Biological Research—Thessaloniki 5, 47–53.
53. Ganias, K.; Zafeiriadou, A.; Garagouni, M.; Antoniadou, C. High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery. Mediterr. Mar. Sci. 2023, 24, 203–210. [CrossRef]
54. Ganoulis, J. and Krestenitis, J., 1982. Rapport V. 9 Choix du site optimum d'évacuation des eaux usées dans une région côtière. Journées de l'hydraulique, 17(2), 1-6.
55. Genitsaris, S.; Kourkoutmani, P.; Stefanidou, N.; Michaloudi, E.; Gros, M.; García-Gómez, E.; Petrović, M.; Ntziachristos, L.; Moustaka-Gouni, M. Effects from maritime scrubber effluent on phytoplankton and bacterioplankton communities of a coastal area, Eastern Mediterranean Sea. Ecol. Informatics 2023, 77. [CrossRef]
56. Genitsaris, S.; Stefanidou, N.; Moustaka-Gouni, M.; Sommer, U.; Tsipas, G. Variability and Community Composition of Marine Unicellular Eukaryote Assemblages in a Eutrophic Mediterranean Urban Coastal Area with Marked Plankton Blooms and Red Tides. Diversity 2020, 12, 114. [CrossRef]
57. Genitsaris, S.; Stefanidou, N.; Sommer, U.; Moustaka-Gouni, M. Phytoplankton Blooms, Red Tides and Mucilaginous Aggregates in the Urban Thessaloniki Bay, Eastern Mediterranean. Diversity 2019, 11, 136. [CrossRef]
58. Giannakourou, A.; Orlova, T.; Assimakopoulou, G.; Pagou, K. Dinoflagellate cysts in recent marine sediments from Thermaikos Gulf, Greece: Effects of resuspension events on vertical cyst distribution. Cont. Shelf Res. 2005, 25, 2585–2596. [CrossRef]
59. Gotsis-Skretas, O. and Friligos, N., 1990. Contribution to eutrophication and phytoplankton ecology in the Thermaikos Gulf. Thalassografika, 13, 1-12.
60. Haritonidis, S., Diapoulis A., and Nikolaidis, G., 1990. First results on the localisation of the herbiers of marine phanerogams in the Gulf of Thermaikos. Posidonia Newsletter 3, 11-18.
61. Hatzianestis, I.; Sklivagou, E.; Georgakopoulou, E. Organic contaminants in sediments and mussels from Thermaikos gulf, Greece. Toxicol. Environ. Chem. 2000, 74, 203–215. [CrossRef]
62. Hatzianestis, J., Sklivagou, E., and Georgakopoulou, E., 2001. Hydrocarbons, pesticides and PCBs in sediments from Thermaikos gulf, Greece. Fresenius Environmental Bulletin, 10(1), 63-68.
63. HCMR, 2015. Samplings and analyses to monitor the ecological quality of coastal waters according to the WFD 2000/60/EC at three sampling stations of Thermaikos Gulf of EYATH interest. Technical Report (in Greek).
64. Hobday, A.J.; Alexander, L.V.; Perkins, S.E.; Smale, D.A.; Straub, S.C.; Oliver, E.C.J.; Benthuysen, J.A.; Burrows, M.T.; Donat, M.G.; Feng, M.; et al. A hierarchical approach to defining marine heatwaves. Prog. Oceanogr. 2016, 141, 227–238. [CrossRef]
65. Hyder, P.; Simpson, J.; Christopoulos, S.; Krestenitis, Y. The seasonal cycles of stratification and circulation in the Thermaikos Gulf Region Of Freshwater Influence (ROFI), north-west Aegean. Cont. Shelf Res. 2002, 22, 2573–2597. [CrossRef]
66. Jackman, P.C.; Sanderson, R.; Haughey, T.J.; Brett, C.E.; White, N.; Zile, A.; Tyrrell, K.; Byrom, N.C. The impact of the first COVID-19 lockdown in the UK for doctoral and early career researchers. High. Educ. 2021, 84, 705–722. [CrossRef]
67. Kaandorp, M.L.A.; Dijkstra, H.A.; van Sebille, E. Closing the Mediterranean Marine Floating Plastic Mass Budget: Inverse Modeling of Sources and Sinks. Environ. Sci. Technol. 2020, 54, 11980–11989. [CrossRef]
68. Kaberi, H., Zeri, C., Androulidakis, Y., Varkitzi, I., Siokou, I., Zervoudaki, S., Katsiaras, N., Drakopoulou, P., Tzempelikou, E., Reizopoulou, S. and Bray, L., 2023. Thermaikos Gulf: An Area Under Multiple Natural and Anthropogenic Pressures. In: The Handbook of Environmental Chemistry. Springer, Berlin, Heidelberg. [CrossRef]
69. Kapsimalis, V.; Panagiotopoulos, I.; Kanellopoulos, T.; Hatzianestis, I.; Antoniou, P.; Anagnostou, C. A multi-criteria approach for the dumping of dredged material in the Thermaikos Gulf, Northern Greece. J. Environ. Manag. 2010, 91, 2455–2465. [CrossRef]
70. Kapsimalis, V.; Poulos, S.E.; Karageorgis, A.P.; Pavlakis, P.; Collins, M. Recent evolution of a Mediterranean deltaic coastal zone: human impacts on the Inner Thermaikos Gulf, NW Aegean Sea. J. Geol. Soc. 2005, 162, 897–908. [CrossRef]
71. Karageorgis, A.; Anagnostou, C.; Kaberi, H. Geochemistry and mineralogy of the NW Aegean Sea surface sediments: implications for river runoff and anthropogenic impact. Appl. Geochem. 2005, 20, 69–88. [CrossRef]
72. Karageorgis, A.P.; Anagnostou, C.L. Seasonal variation in the distribution of suspended particulate matter in the northwest Aegean Sea. 2003, 108. [CrossRef]
73. Karageorgis, A.; Kaberi, H.; Price, N.; Muir, G.; Pates, J.; Lykousis, V. Chemical composition of short sediment cores from Thermaikos Gulf (Eastern Mediterranean): Sediment accumulation rates, trawling and winnowing effects. Cont. Shelf Res. 2005, 25, 2456–2475. [CrossRef]
74. Karageorgis, A.; Anagnostou, C.; Georgopoulos, D.; Albuisson, M. Distribution of suspended particulate matter determined by in-situ observations and satellite images in the NW Aegean Sea (Greece). Geo-Marine Lett. 2000, 20, 93–100. [CrossRef]
75. Karageorgis, A.P.; Anagnostou, C.L. Particulate matter spatial–temporal distribution and associated surface sediment properties: Thermaikos Gulf and Sporades Basin, NW Aegean Sea. Cont. Shelf Res. 2001, 21, 2141–2153. [CrossRef]
76. Karageorgis, A.; Nikolaidis, N.; Karamanos, H.; Skoulikidis, N. Water and sediment quality assessment of the Axios River and its coastal environment. Cont. Shelf Res. 2003, 23, 1929–1944. [CrossRef]
77. Karageorgis, A.P.; Skourtos, M.S.; Kapsimalis, V.; Kontogianni, A.D.; Skoulikidis, N.T.; Pagou, K.; Nikolaidis, N.P.; Drakopoulou, P.; Zanou, B.; Karamanos, H.; et al. An integrated approach to watershed management within the DPSIR framework: Axios River catchment and Thermaikos Gulf. Reg. Environ. Chang. 2004, 5, 138–160. [CrossRef]
78. Karymbalis, E.; Gaki-Papanastassiou, K.; Tsanakas, K.; Ferentinou, M. Geomorphology of the Pinios River delta, Central Greece. J. Maps 2016, 12, 12–21. [CrossRef]
79. Kendall, M., 1975. Rank Correlation Measures, vol. 202. Charles Griffin, London, p. 15.
80. Kermenidou, M.; Frydas, I.; Moschoula, E.; Kousis, D.; Christofilos, D.; Karakitsios, S.; Sarigiannis, D. Quantification and characterization of microplastics in the Thermaic Gulf, in the North Aegean Sea. Sci. Total. Environ. 2023, 892, 164299. [CrossRef]
81. Kevrekidis, K.; Thessalou-Legaki, M. Population dynamics of Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea). Fish. Res. 2011, 107, 46–58. [CrossRef]
82. Kevrekidis, K.; Antoniadou, C. Abundance and population structure of the blue crab Callinectes sapidus (Decapoda, Portunidae) in Thermaikos Gulf (Methoni Bay), northern Aegean Sea. Crustaceana 2018, 91, 641–657. [CrossRef]
83. Kitsos, M.S., 2003. Contribution to the study of the biodiversity of the midlittoral and supralitoral hard substratum assemblages. PhD Thesis, Aristotle University of Thessaloniki, p. 285.
84. Koletsis, I.; Giannaros, T.; Lagouvardos, K.; Kotroni, V. Observational and numerical study of the Vardaris wind regime in northern Greece. Atmospheric Res. 2015, 171, 107–120. [CrossRef]
85. Kombiadou, K.; Krestenitis, Y.N. Fine sediment transport model for river influenced microtidal shelf seas with application to the Thermaikos Gulf (NW Aegean Sea). Cont. Shelf Res. 2012, 36, 41–62. [CrossRef]
86. Kombiadou, K.; Krestenitis, Y.. Simulating the fate of mechanically eroded masses in the Thermaikos Gulf. Cont. Shelf Res. 2011, 31, 817–831. [CrossRef]
87. Kontoyiannis, H.; Kourafalou, V.H.; Papadopoulos, V. Seasonal characteristics of the hydrology and circulation in the northwest Aegean Sea (eastern Mediterranean): Observations and modeling. 2003, 108. [CrossRef]
88. Koukaras, K.; Nikolaidis, G. Dinophysis blooms in Greek coastal waters (Thermaikos Gulf, NW Aegean Sea). J. Plankton Res. 2004, 26, 445–457. [CrossRef]
89. Koulouris, A.; Moniarou-Papaconstantinou, V.; Kyriaki-Manessi, D. Austerity Measures in Greece and their Impact on Higher Education. Procedia - Soc. Behav. Sci. 2014, 147, 518–526. [CrossRef]
90. Kourafalou, V.; Tsiaras, K. A nested circulation model for the North Aegean Sea. Ocean Sci. 2007, 3, 1–16. [CrossRef]
91. Kourafalou, V.H. River plume development in semi-enclosed Mediterranean regions: North Adriatic Sea and Northwestern Aegean Sea. J. Mar. Syst. 2001, 30, 181–205. [CrossRef]
92. Kourafalou, V.H.; Savvidis, Y.G.; Krestenitis, Y.N.; Koutitas, C.G. Modelling studies on the processes that influence matter transfer on the Gulf of Thermaikos (NW Aegean Sea). Cont. Shelf Res. 2004, 24, 203–222. [CrossRef]
93. Kourkoutmani, P.; Michaloudi, E. First record of the calanoid copepod Pseudodiaptomus marinus Sato, 1913 in the North Aegean Sea, in Thessaloniki Bay, Greece. BioInvasions Rec. 2022, 11, 738–746. [CrossRef]
94. Kourkoutmani, P.; Loufi, K.; Kalantaridou, G.; Karagianni, A.; Michaloudi, E. Spatio-temporal variation of the invasive copepod Oithona davisae in the zooplankton community of Kavala harbour. Mediterr. Mar. Sci. 2023, 24, 174–181. [CrossRef]
95. Krasakopoulou, E.; Anagnostou, C.; Souvermezoglou, E.; Papathanassiou, E.; Rapsomanikis, S. Distribution of dissolved inorganic carbon and related parameters in the Thermaikos Gulf (Eastern Mediterranean). Mediterr. Mar. Sci. 2006, 7, 63–77. [CrossRef]
96. Krestenitis, Y.N.; Kombiadou, K.D.; Androulidakis, Y.S. Interannual variability of the physical characteristics of North Thermaikos Gulf (NW Aegean Sea). J. Mar. Syst. 2012, 96-97, 132–151. [CrossRef]
97. Krestenitis, M.; Androulidakis, Y.; Krestenitis, Y. Deep learning-based forecasting of sea surface temperature in the interim future: application over the Aegean, Ionian, and Cretan Seas (NE Mediterranean Sea). Ocean Dyn. 2024, 74, 149–168. [CrossRef]
98. Ladi, S., Panagiotatou, D., Angelou, A., Krieger, K., and Melchor, L., 2022. The Greek ecosystem of science for policy. Publications Office of the European Union, Luxembourg.
99. Lammel, G.; Audy, O.; Besis, A.; Efstathiou, C.; Eleftheriadis, K.; Kohoutek, J.; Kukučka, P.; Mulder, M.D.; Přibylová, P.; Prokeš, R.; et al. Air and seawater pollution and air–sea gas exchange of persistent toxic substances in the Aegean Sea: spatial trends of PAHs, PCBs, OCPs and PBDEs. Environ. Sci. Pollut. Res. 2015, 22, 11301–11313. [CrossRef]
100. Larsen, B.; Fytianos, K. Organochlorine compounds and PCB congeners in contaminated sediments. Sci. Total. Environ. 1989, 86, 273–279. [CrossRef]
101. Lattos, A.; Papadopoulos, D.K.; Feidantsis, K.; Karagiannis, D.; Giantsis, I.A.; Michaelidis, B. Are Marine Heatwaves Responsible for Mortalities of Farmed Mytilus galloprovincialis? A Pathophysiological Analysis of Marteilia Infected Mussels from Thermaikos Gulf, Greece. Animals 2022, 12, 2805. [CrossRef]
102. Lykousis, V.; Chronis, G. Mechanisms of sediment transport and deposition: Sediment sequences and accumulation during the Holocene on the Thermaikos plateau, the continental slope, and basin (Sporadhes basin), northwestern Aegean Sea, Greece. Mar. Geol. 1989, 87, 15–26. [CrossRef]
103. Lykousis, V.; Collins, M.; Ferentinos, G. Modern sedimentation in the N.W. Aegean Sea. Mar. Geol. 1981, 43, 111–130. [CrossRef]
104. Mann, H.B. Nonparametric tests against trend. Econometrica 1945, 13, 245–259. [CrossRef]
105. Manousis, T.; Galinou-Mitsoudi, S. New gastropod records for the Eastern Mediterranean Sea and one new alien (Emarginula decorata Deshayes, 1863) for the Mediterranean Sea from NW Aegean Sea, Greece. J. Biol. Res. 2014, 21, 20–20. [CrossRef]
106. Manousis, T., and Galinou-Mitsoudi, S., 2022. Great molluscan diversity associated with a limited Cymodocea nodosa (Ucria) Ascherson, 1870 bed in Thermaikos Gulf, North Aegean Sea, Greece. Xenophora Taxonomy, 35, 20-42.
107. Manousis, T., Mpardakis, G., Paraskevopoulos, C., and Galinou-Mitsoudi, S., 2010. The Bivalvia Mollusca of Thessaloniki & Thermaikos Gulfs (North Aegean Sea, Greece) with emphasis on new species for Hellenic waters. Journal of Biological Research, 14, 161.
108. Manousis, T., Mpardakis, G., Silva, A.Z., Paraskevopoulos, K., Manios, D. and Galinou-Mitsoudi, S., 2012. New findings of Gastropods in the Hellenic seas with emphasis on their origin and distribution status. Journal of Biological Research, 18, p. 249.
109. Marty, D.; Bonin, P.; Michotey, V.; Bianchi, M. Bacterial biogas production in coastal systems affected by freshwater inputs. Cont. Shelf Res. 2001, 21, 2105–2115. [CrossRef]
110. Meijer, L., Van Emmerik, T., Van der Ent R., Lebreton, L., and Schmidt, C., 2020. Over 1000 rivers accountable for 80% of global riverine plastic emissions into the ocean. EGU General Assembly 2020, 4–8 May 2020, EGU2020-22000, . [CrossRef]
111. Mihalatou, H.M. and Moustaka-Gouni, M., 2002. Pico-, Nano-, Microplankton Abundance and Primary Productivity in a Eutrophic Coastal Area of the Aegean Sea, Mediterranean. International Review of Hydrobiology: A Journal Covering all Aspects of Limnology and Marine Biology, 87(4), 439-456.
112. Monachou, S., Alexandridis, T.K., Kalopesa, E., Antoniadis, A., Zalidis, G.C. and Misopolinos, N., 2014. Remotely sensed time series of chlorophyll-α, total suspended matter and sea surface temperature for monitoring water quality of Thermaikos gulf (Greece). Fresenious Environmental Bulletin, 23, 2636-2644.
113. Moncheva, S.; Gotsis-Skretas, O.; Pagou, K.; Krastev, A. Phytoplankton Blooms in Black Sea and Mediterranean Coastal Ecosystems Subjected to Anthropogenic Eutrophication: Similarities and Differences. Estuarine, Coast. Shelf Sci. 2001, 53, 281–295. [CrossRef]
114. Muir, G.; Pates, J.; Karageorgis, A.; Kaberi, H. 234Th:238U disequilibrium as an indicator of sediment resuspension in Thermaikos Gulf, northwestern Aegean Sea. Cont. Shelf Res. 2005, 25, 2476–2490. [CrossRef]
115. Muxika, I.; Borja, A.; Bald, J. Using historical data, expert judgement and multivariate analysis in assessing reference conditions and benthic ecological status, according to the European Water Framework Directive. Mar. Pollut. Bull. 2007, 55, 16–29. [CrossRef]
116. Nikolaides, G.; Moustaka-Gouni, M. The structure and dynamics of phytoplankton assemblages from the inner part of the Thermaikos Gulf, Greece. I. Phytoplankton composition and biomass from May 1988 to April 1989. Helgol. Mar. Res. 1990, 44, 487–501. [CrossRef]
117. Nikolaidis, G. and Evagelopoulos, A., 1997. Phytoplankton blooms in Thermaikos Bay, Greece. Harmful algae news, 16, 8-9.
118. Nikolaidis, N.P.; Karageorgis, A.P.; Kapsimalis, V.; Marconis, G.; Drakopoulou, P.; Kontoyiannis, H.; Krasakopoulou, E.; Pavlidou, A.; Pagou, K. Circulation and nutrient modeling of Thermaikos Gulf, Greece. J. Mar. Syst. 2006, 60, 51–62. [CrossRef]
119. Nödler, K.; Licha, T.; Voutsa, D. Twenty years later – Atrazine concentrations in selected coastal waters of the Mediterranean and the Baltic Sea. Mar. Pollut. Bull. 2013, 70, 112–118. [CrossRef]
120. Otero, M.D.M., Numa, C., Bo, M., Orejas, C., Garrabou, J., Cerrano, C., Kružić, P., Antoniadou, C., Aguilar, R., Kipson, S. and Linares, C., 2017. Overview of the conservation status of Mediterranean anthozoans. International Union for Conservation of Nature and Natural Resources (IUCN).
121. Pagou, K., 2005. Eutrophication in Hellenic coastal areas. In: ‘State of the Hellenic Marine Environment (SoHelME 2005)’, E. Papathanassiou & A. Zenetos (eds) 360 p., HCMR Publ., Athens, Greece, 311-317. https://epublishing.ekt.gr/el/8303.
122. Pagou, K., Siokou-Frangou, I., Catsiki, A.V., Pavlidou, A., Assimakopoulou, G., Papathanassiou, E., 2003. Assessment of the trophic conditions in the Inner Thermaikos Gulf. In: 7th Hell. Symp. Oceanogr. Fish., 6-9 May 2003, Hersonissos, Crete, 43 p.
123. Pakalidou, N.; Karacosta, P. Study of very long-period extreme precipitation records in Thessaloniki, Greece. Atmospheric Res. 2018, 208, 106–115. [CrossRef]
124. Paliogiannis, C.; Cliquet, A.; Koedam, N. The impact of the economic crisis on the implementation of the EU Nature Directives in Greece: An expert-based view. J. Nat. Conserv. 2018, 48, 36–46. [CrossRef]
125. Panayotidis, P.; Papathanasiou, V.; Gerakaris, V.; Fakiris, E.; Orfanidis, S.; Papatheodorou, G.; Kosmidou, M.; Georgiou, N.; Drakopoulou, V.; Loukaidi, V. Seagrass meadows in the Greek Seas: presence, abundance and spatial distribution. Bot. Mar. 2022, 65, 289–299. [CrossRef]
126. Pantelaki, I.; Voutsa, D. Organophosphate esters in inland and coastal waters in northern Greece. Sci. Total. Environ. 2021, 800, 149544. [CrossRef]
127. Paphitis, D.; Collins, M. Sediment resuspension events within the (microtidal) coastal waters of Thermaikos Gulf, northern Greece. Cont. Shelf Res. 2005, 25, 2350–2365. [CrossRef]
128. Pavlidou, A., 2012. Nutrient distribution in selected coastal areas of Aegean Sea (East Mediterranean Sea). Journal of Environmental Science and Engineering. A, 1(1A).
129. Pavlidou, A., Psyllidou-Giouranovits, R., Sylaios, G.K., 2005. Nutrients and dissolved oxygen in Hellenic coastal waters. In: ‘State of the Hellenic Marine Environment (SoHelME 2005)’, E. Papathanassiou & A. Zenetos (eds) 360 p., HCMR Publ., Athens, Greece. 127-136. https://epublishing.ekt.gr/el/8303.
130. Pavlidou, A.; Simboura, N.; Rousselaki, E.; Tsapakis, M.; Pagou, K.; Drakopoulou, P.; Assimakopoulou, G.; Kontoyiannis, H.; Panayotidis, P. Methods of eutrophication assessment in the context of the water framework directive: Examples from the Eastern Mediterranean coastal areas. Cont. Shelf Res. 2015, 108, 156–168. [CrossRef]
131. Pelliccia, A., 2013. Greece education and brain drain in times of crisis. IRPPS Working Papers.
132. Petala, M., Tsiridis, V., Androulidakis, I., Makris, C., Baltikas, V., Stefanidou, A., Genitsaris, S., Antoniadou, C., Rammou, D., Moustaka-Gouni, M. and Chintiroglou, C.C., 2018. Monitoring the marine environment of Thermaikos gulf. In PRE-XIV Conference, 762-774.
133. Petrakakis, M.J., Kelessis, A.G., Tzoumaka, P. and Samara, C., 2013, September. Levels of suspended particulate matter before and after the economic crisis in Thessaloniki, Greece. In 17th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region , p. 37.
134. Petropoulos, G.P.; Kalivas, D.P.; Griffiths, H.M.; Dimou, P.P. Remote sensing and GIS analysis for mapping spatio-temporal changes of erosion and deposition of two Mediterranean river deltas: The case of the Axios and Aliakmonas rivers, Greece. Int. J. Appl. Earth Obs. Geoinformation 2015, 35, 217–228. [CrossRef]
135. Pettitt, A.N. A Non-Parametric Approach to the Change-Point Problem. J. R. Stat. Soc. Ser. C (Appl. Stat.) 1979, 28, 126–135. [CrossRef]
136. Politikos, D.V.; Ioakeimidis, C.; Papatheodorou, G.; Tsiaras, K. Modeling the Fate and Distribution of Floating Litter Particles in the Aegean Sea (E. Mediterranean). Front. Mar. Sci. 2017, 4. [CrossRef]
137. Pothitou, P.; Voutsa, D. Endocrine disrupting compounds in municipal and industrial wastewater treatment plants in Northern Greece. Chemosphere 2008, 73, 1716–1723. [CrossRef]
138. Poulos, S. E., Collins, M. B., and Shaw, H. F., 1996. Deltaic Sedimentation, including Clay Mineral Deposition Patterns, Associated with Small Mountainous Rivers and Shallow Marine Embayments of Greece (SE Alpine Europe). Journal of Coastal Research, 12(4), 40–52. https://www.jstor.org/stable/4298544?seq=1.
139. Poulos, S.; Collins, M.B.; Ke, X. Fluvial/wave interaction controls on delta formation for ephemeral rivers discharging into microtidal waters. Geo-Marine Lett. 1993, 13, 24–31. [CrossRef]
140. Poulos, S.; Papadopoulos, A.; Collins, M. Deltaic progradation in Thermaikos Bay, Northern Greece and its socio-economical implications. Ocean Coast. Manag. 1994, 22, 229–247. [CrossRef]
141. Poulos, S.E. and Chronis, G.T., 1997. The importance of the river systems in the evolution of the Greek coastline. BULLETIN-INSTITUT OCEANOGRAPHIQUE MONACO-NUMERO SPECIAL-, 75-96.
142. Poulos, S.E., Chronis, G.T., Collins, M.B. and Lykousis, V., 2000. Thermaikos Gulf Coastal System, NW Aegean Sea: an overview of water/sediment fluxes in relation to air–land–ocean interactions and human activities. Journal of Marine Systems, 25(1), 47-76.
143. Price, N.; Karageorgis, A.; Kaberi, H.; Zeri, C.; Krasakopoulou, E.; Voutsinou-Taliadouri, F.; Lindsay, F.; Assimakopoulou, G.; Pagou, K. Temporal and spatial variations in the geochemistry of major and minor particulate and selected dissolved elements of Thermaikos Gulf, Northwestern Aegean Sea. Cont. Shelf Res. 2005, 25, 2428–2455. [CrossRef]
144. Primpas, I.; Tsirtsis, G.; Karydis, M.; Kokkoris, G.D. Principal component analysis: Development of a multivariate index for assessing eutrophication according to the European water framework directive. Ecol. Indic. 2010, 10, 178–183. [CrossRef]
145. Readman, J.; Albanis, T.; Barcelo, D.; Galassi, S.; Tronczynski, J.; Gabrielides, G. Herbicide contamination of Mediterranean estuarine waters: Results from a MED POL pilot survey. Mar. Pollut. Bull. 1993, 26, 613–619. [CrossRef]
146. Reale, M.; Cossarini, G.; Lazzari, P.; Lovato, T.; Bolzon, G.; Masina, S.; Solidoro, C.; Salon, S. Acidification, deoxygenation, and nutrient and biomass declines in a warming Mediterranean Sea. Biogeosciences 2022, 19, 4035–4065. [CrossRef]
147. Reizopoulou, S.; Strogyloudi, E.; Giannakourou, A.; Pagou, K.; Hatzianestis, I.; Pyrgaki, C.; Granéli, E. Okadaic acid accumulation in macrofilter feeders subjected to natural blooms of Dinophysis acuminata. Harmful Algae 2008, 7, 228–234. [CrossRef]
148. Sakellariou, E., 1957 Living Mollusca of Thessaloniki Gulf and their contribution in stromatography. PhD Thesis, National and Kapodistrian University of Athens.
149. Samanidou, V.; Fytianos, K.; Vasilikiotis, G. Distribution of nutrients in the Thermaikos Gulf, Greece. Sci. Total. Environ. 1987, 65, 181–189. [CrossRef]
150. Savvidis, Y.; Antoniou, A.; Moriki, A.; Stoilas, V.-O. Downwelling Events in a Coastal Mussel Farming Area, NW Thessaloniki’s Gulf (NW Aegean Sea). Ocean Sci. J. 2019, 54, 543–558. [CrossRef]
151. Shapiro, G.I.; Huthnance, J.M.; Ivanov, V.V. Dense water cascading off the continental shelf. J. Geophys. Res. Oceans 2003, 108. [CrossRef]
152. Simboura, N.; Reizopoulou, S. An intercalibration of classification metrics of benthic macroinvertebrates in coastal and transitional ecosystems of the Eastern Mediterranean ecoregion (Greece). Mar. Pollut. Bull. 2008, 56, 116–126. [CrossRef]
153. Simboura, N.; Zenetos, A. Benthic indicators to use in Ecological Quality classification of Mediterranean soft bottom marine ecosystems, including a new Biotic Index. Mediterr. Mar. Sci. 2002, 3, 77. [CrossRef]
154. Simboura, N.; Pavlidou, A.; Bald, J.; Tsapakis, M.; Pagou, K.; Zeri, C.; Androni, A.; Panayotidis, P. Response of ecological indices to nutrient and chemical contaminant stress factors in Eastern Mediterranean coastal waters. Ecol. Indic. 2016, 70, 89–105. [CrossRef]
155. Siokou-Frangou, I.; Papathanassiou, E. Differentiation of zooplankton populations in a polluted area. Mar. Ecol. Prog. Ser. 1991, 76, 41–51. [CrossRef]
156. Siokou-Frangou, I.; Zervoudaki, S.; Kambouroglou, V.; Belmonte, G. Distribution of mesozooplankton resting eggs in seabottom sediments of Thermaikos gulf (NW Aegean Sea, Greece) and possible effects of sediment resuspension. Cont. Shelf Res. 2005, 25, 2597–2608. [CrossRef]
157. Skoulikidis, N.T. The environmental state of rivers in the Balkans—A review within the DPSIR framework. Sci. Total. Environ. 2009, 407, 2501–2516. [CrossRef]
158. Skoulikidis, N.T.; Karaouzas, I.; Amaxidis, Y.; Lazaridou, M. Impact of EU Environmental Policy Implementation on the Quality and Status of Greek Rivers. Water 2021, 13, 1858. [CrossRef]
159. Solidoro, C.; Cossarini, G.; Lazzari, P.; Galli, G.; Bolzon, G.; Somot, S.; Salon, S. Modeling Carbon Budgets and Acidification in the Mediterranean Sea Ecosystem Under Contemporary and Future Climate. Front. Mar. Sci. 2022, 8. [CrossRef]
160. Spatharis, S.; Lamprinou, V.; Meziti, A.; Kormas, K.A.; Danielidis, D.D.; Smeti, E.; Roelke, D.L.; Mancy, R.; Tsirtsis, G. Everything is not everywhere: can marine compartments shape phytoplankton assemblages?. Proc. R. Soc. B: Biol. Sci. 2019, 286, 20191890. [CrossRef]
161. Stefanidou, N.; Genitsaris, S.; Lopez-Bautista, J.; Sommer, U.; Moustaka-Gouni, M. Effects of heat shock and salinity changes on coastal Mediterranean phytoplankton in a mesocosm experiment. Mar. Biol. 2018, 165, 154. [CrossRef]
162. Stefanidou, N.; Genitsaris, S.; Lopez-Bautista, J.; Sommer, U.; Moustaka-Gouni, M. Unicellular Eukaryotic Community Response to Temperature and Salinity Variation in Mesocosm Experiments. Front. Microbiol. 2018, 9, 2444. [CrossRef]
163. Strogyloudi, E.; Krasakopoulou, E.; Giannakourou, A.; Galinou-Mitsoudi, S.; Catsiki, V.-A.; Drakopoulou, P.; Kyriakidou, C.; Papathanassiou, E.; Angelidis, M.O. How environmental factors determine mussel metal concentrations? A comparative study between areas facing different pressures. Reg. Stud. Mar. Sci. 2023, 59. [CrossRef]
164. Takahashi, T.; Olafsson, J.; Goddard, J.G.; Chipman, D.W.; Sutherland, S.C. Seasonal variation of CO₂ and nutrients in the high-latitude surface oceans: A comparative study. Glob. Biogeochem. Cycles 1993, 7, 843–878. [CrossRef]
165. Tragou, E.; Zervakis, V.; Papageorgiou, E.; Stavrakakis, S.; Lykousis, V. Monitoring the physical forcing of resuspension events in the Thermaikos Gulf—NW Aegean during 2001–2003. Cont. Shelf Res. 2005, 25, 2315–2331. [CrossRef]
166. Troumbis, A.Y.; Zevgolis, Y. Biodiversity crime and economic crisis: Hidden mechanisms of misuse of ecosystem goods in Greece. Land Use Policy 2020, 99, 105061. [CrossRef]
167. Tsiaras, K.; Petihakis, G.; Kourafalou, V.; Triantafyllou, G. Impact of the river nutrient load variability on the North Aegean ecosystem functioning over the last decades. J. Sea Res. 2014, 86, 97–109. [CrossRef]
168. Tsimplis, M.N.; Proctor, R.; Flather, R.A. A two-dimensional tidal model for the Mediterranean Sea. J. Geophys. Res. Ocean. 1995, 100, 16223–16239. [CrossRef]
169. Tsompanoglou, K.; Anagnostou, C.; Krasakopoulou, E.; Pagou, K.; Karageorgis, A.; Pavlidou, A.; Albanakis, K.; Tsirambides, A. Distribution and geochemical composition of suspended particulate material in the shallow embayment of northern Thermaikos Gulf, Greece. Cont. Shelf Res. 2017, 143, 295–310. [CrossRef]
170. Tzempelikou, E.; Zeri, C.; Iliakis, S.; Paraskevopoulou, V. Cd, Co, Cu, Ni, Pb, Zn in coastal and transitional waters of Greece and assessment of background concentrations: Results from 6 years implementation of the Water Framework Directive. Sci. Total. Environ. 2021, 774, 145177. [CrossRef]
171. Vafidis, D.; Antoniadou, C. Holothurian Fisheries in the Hellenic Seas: Seeking for Sustainability. Sustainability 2023, 15, 9799. [CrossRef]
172. Vafidis, D., Antoniadou, C., Voultsiadou, E. and Chintiroglou, C., 2014. Population structure of the protected fan mussel Pinna nobilis in the south Aegean Sea (eastern Mediterranean). Journal of the Marine Biological Association of the United Kingdom, 94(4), 787-796.
173. Valioulis, I.A. and Krestenitis, Y.N., 1994, August. Modelling the water mass circulation in the Aegean Sea. Part I: wind stresses, thermal and haline fluxes. In Annales Geophysicae, 12(8), 794-807. Berlin/Heidelberg: Springer-Verlag.
174. Varkitzi, I., Pagou, K., Granéli, E., Hatzianestis, I., Krasakopoulou, E. and Pavlidou, A., 2010, November. Spatio-temporal distribution of Dinophysis spp. in relation to organic matter availability and other parameters in Thermaikos Gulf, Greece (Eastern Mediterranean). In Proceedings of the 14th international conference on harmful algae, Crete, Greece, 1-5.
175. Vasilikiotis, G.; Voulouvoutis, N.; Themelis, D.; Sofoniou, M. Preliminary study of Thessaloniki Bay for contamination by mercury and lead. Chemosphere 1982, 11, 479–496. [CrossRef]
176. Violintzis, C.; Arditsoglou, A.; Voutsa, D. Elemental composition of suspended particulate matter and sediments in the coastal environment of Thermaikos Bay, Greece: Delineating the impact of inland waters and wastewaters. J. Hazard. Mater. 2009, 166, 1250–1260. [CrossRef]
177. Vokou, D., Giannakou, U., Kontaxi, C., Vareltzidou, S., 2018. Axios, aliakmon, and Gallikos delta complex (northern Greece). The Wetland Book, 1137–1147. [CrossRef]
178. Voutsinou-Taliadouri, F.; Balopoulos, E.T. Geochemical and Water Flow Features in a Semienclosed Embayment of the Western Aegean Sea (Pagassitikos Gulf, Greece) and Physical Oceanographic and Geochemical Conditions in Thermaikos Bay (Northwestern Aegean, Greece). Water Sci. Technol. 1989, 21, 1881–1886. [CrossRef]
179. Voutsinou-Taliadouri, F.; Satsmadjis, J. Metals in polluted sediments from the Thermaikos Gulf, Greece. Mar. Pollut. Bull. 1983, 14, 234–236. [CrossRef]
180. Voutsinou-Taliadouri, F.; Varnavas, S.P. Geochemical and sedimentological patterns in the thermaikos gulf, north-west Aegean sea, formed from a multisource of elements. Estuarine, Coast. Shelf Sci. 1995, 40, 295–320. [CrossRef]
181. YPEKA, 2012. Quality of the Hellenic surface and ground waters. Reference period 2000-2008. Technical Report (in Greek).
182. YPEKA, 2017. Quality of the Hellenic surface and ground waters. 1st implementation period 2012-2014 Technical Report (in Greek).
183. YPEKA, 2023. Quality of the Hellenic surface and ground waters. 2nd implementation period 2018-2022. Technical Report (in Greek).
184. Zabetoglou, K.; Voutsa, D.; Samara, C. Toxicity and heavy metal contamination of surficial sediments from the Bay of Thessaloniki (Northwestern Aegean Sea) Greece. Chemosphere 2002, 49, 17–26. [CrossRef]
185. Zachioti, P., Rousselaki, E., Konstadinopoulou, A., Zoulias, T., Assimakopoulou, G., Fioraki, V., Varkitzi, I., Pagou, K., Pavlidou, A. (2022). Trophic status evolution in Thermaikos Gulf during 1995-2007. Proceedings of the Marine and Inland Waters Research Symposium 2022 (ISBN: 978-960-9798-31-0), p.p. 127- 130. https://symposia.gr/wp-content/uploads/2022/10/Proceedings_5.10.22.pdf.
186. Zafirakou, A.; Palantzas, G.; Samaras, A.; Koutitas, C. Oil Spill Modeling Aiming at the Protection of Ports and Coastal Areas. Environ. Process. 2015, 2, 41–53. [CrossRef]
187. Zeri, C.; Hatzianestis, I. Distribution of total dissolved and C18 extractable copper and nickel in relation to dissolved organic matter sources, in the Thermaikos Gulf (eastern Mediterranean). J. Mar. Syst. 2005, 58, 143–152. [CrossRef]
188. Zeri, C.; Adamopoulou, A.; Koi, A.; Koutsikos, N.; Lytras, E.; Dimitriou, E. Rivers and Wastewater-Treatment Plants as Microplastic Pathways to Eastern Mediterranean Waters: First Records for the Aegean Sea, Greece. Sustainability 2021, 13, 5328. [CrossRef]
189. Zervakis, V.; Georgopoulos, D. Hydrology and circulation in the North Aegean (eastern Mediterranean) throughout 1997 and 1998. Mediterr. Mar. Sci. 2002, 3, 5-19. [CrossRef]
190. Zervakis, V.; Karageorgis, A.; Kontoyiannis, H.; Papadopoulos, V.; Lykousis, V. Hydrology, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea), during September 2001–October 2001 and February 2002. Cont. Shelf Res. 2005, 25, 2332–2349. [CrossRef]
191. Zervoudaki, S.; Frangoulis, C.; Svensen, C.; Christou, E.D.; Tragou, E.; Arashkevich, E.G.; Ratkova, T.N.; Varkitzi, .; Krasakopoulou, E.; Pagou, K. Vertical Carbon Flux of Biogenic Matter in a Coastal Area of the Aegean Sea: The Importance of Appendicularians. Estuaries Coasts 2013, 37, 911–924. [CrossRef]
192. Zotou, M.; Gkrantounis, P.; Karadimou, E.; Tsirintanis, K.; Sini, M.; Poursanidis, D.; Azzolin, M.; Dailianis, T.; Kytinou, E.; Issaris, Y.; et al. Pinna nobilis in the Greek seas (NE Mediterranean): on the brink of extinction?. Mediterr. Mar. Sci. 2020, 21, 575–591. [CrossRef]