Ioanna Varkitzi

• PhD
• Research Scientist at Hellenic Centre for Marine Research

This study investigates the intricate dynamics of siliceous plankton species within the open marine regions of the Greek Seas, focusing on their seasonal and spatial variability. For this purpose, vertical export fluxes of diatoms (DtF), silicoflagellates (SF), and radiolaria (RF) were analyzed in three sediment trap time series obtained from the N...

Phytoplankton is a fundamental component of marine food webs and play a crucial role in marine ecosystem functioning. The phenology (timing of growth) of these microscopic algae is an important ecological indicator that can be utilized to observe its seasonal dynamics, and assess its response to environmental perturbations. Ocean colour remote sens...

The present review aims to assess the overall marine environmental status of the Pagassitikos, a semi-enclosed gulf off the eastern Greek mainland which is very important in terms of ecological significance and national economy. According to older and more recent physical, chemical, and biological data, the gulf can be separated into three distinct...

This work offers an overview description of the natural environment and anthropogenic pressures in the Thermaikos Gulf along the land-sea continuum, encompassing coastal areas and hinterlands, shaped by major rivers and diverse geological formations. Coastal zones experience anthropogenic pressures from urbanization, industry, agriculture, and tour...

HABs pose a threat to coastal ecosystems, the economic sector and human health, and are expanding globally. However, their influence on copepods, a major connector between primary producers and upper trophic levels, remains essentially unknown. Microalgal toxins can eventually control copepod survival and reproduction by deterring grazing and hence...

Anthropogenic activities have transformed the pelagic habitat in the last decades with profound implications for its essential functions. While the EU-Marine Strategy Framework Directive 2008/56/EC and the Commission Decision (EU) 2017/848 have set criteria and methodological standards for the assessment and determination of Good Environmental Stat...

We developed a zooplankton-based water-quality evaluating method using indices of alpha diversity. Two key objectives were set: (i) the comparison of two—different quality—samples from different areas, and the verification of their differentiation, based on mesozooplankton biodiversity indices; and (ii) the development of a methodology, which was a...

Harmful Αlgal Βlooms (HABs) play a central role as traits for ecological/environmental status assessment. Phytoplankton species that produce HABs are therefore considered as key elements for marine monitoring. Some coastal areas in the Mediterranean Sea are listed as "hot spots" due to the formation of blooms with toxic species or high biomass prod...

Many phytoplankton metrics are known to provide valuable insights on population dynamics, however they are not operational for the pelagic habitat assessment yet. In the Mediterranean Sea, not all eight European member states have defined Good Environmental Status (GES) targets for plankton communities and pelagic habitats till now in the context o...

An ongoing decline of the climax communities of canopy-forming algae along the Mediterranean shallow rocky reefs is increasingly documented, reportedly driven by a multitude of stressors. Apart from alleviating local or global pressures to reverse this alarming trend, basic knowledge of these key species' reproductive phenology, embryology and grow...

In this work, nutrient and chlorophyll-a data were used, to assess the trophic status in Thermaikos Gulf (North Aegean Sea), which is impacted by both natural and anthropogenic pressures. The Eutrophication Index and the Chl-a classification scheme were applied at two sites, one in the inner part of the gulf and the other near the estuaries of Axio...

In this study, we examine the growth of four microalgae strains of Phaeocystis sp., Pleurochrysis sp., Chlorella sp. and Nannochloropsis sp. with Mediterranean origin, which have been poorly addressed in laboratory studies under autotrophic against mixotrophic and heterotrophic conditions. Our results demonstrate that in autotro-phic conditions, th...

The present review constitutes an updated and integrated assessment of phytoplankton spatiotemporal dynamics in the Aegean Sea, based on data compiled from numerous oceanographic surveys of the Hellenic Centre for Marine Research (HCMR), conducted over the last 34 years (1987–2020). Phytoplankton properties, namely chlorophyll a (Chl a) concentrati...

This study presents the impacts of dredge spoil dumping in the pelagic habitat during a 27-month monitoring survey in eastern Mediterranean coastal waters (Saronikos Gulf, Aegean Sea), with a focus on changes in trophic status and eutrophication levels, phytoplankton diversity and bloom dynamics. A number of environmental parameters and phytoplankt...

Faecal pellet production and content along with egg production of the dominant copepod species Acartia clausi were studied in the Thermaikos Gulf (NW Aegean Sea) during a pre-bloom and a bloom of the toxic dinoflagellate Dinophysis acuminata. Both faecal pellet production (6.8–8.6 ind⁻¹ d⁻¹) and egg production (15.8–47.6 ind⁻¹ d⁻¹) appeared unrelat...

Marine primary producers are highly sensitive to environmental deterioration caused by natural and human-induced stressors. Following the Water Framework Directive and the Marine Strategy Framework Directive requirements, the importance of using the different primary producers of the coastal marine ecosystem (pelagic: phytoplankton and benthic: mac...

The loss of Mediterranean macroalgal populations dominated by Cystoseira sensu lato is driven by a multitude of pressures. In the eastern Mediterranean Sea, climate change and the establishment of Lessepsian herbivore species have further intensified the ongoing decline of these canopy-forming algae. Knowledge of the reproductive phenology, embryol...

Highlights •We show that microalgae demonstrate a range of responses to foreign exometabolites. •Biomass suppression caused by Tetraselmis was linked to L-histidinal. •Biomass enhancement was only observed in Heterosigma akashiwo. •Luxurious P uptake can also occur as a response to foreign species exometabolites. •Tiliacorine is reported for t...

Recommendations to frame problems and solutions for the pelagic habitats’ assessment

According to the methodological standards established by Marine Strategy Framework Directive, the assessment for the pelagic habitat under the Biodiversity Descriptor should be carried out at the regional or sub-regional level. In the case of Mediterranean Sea, the sub-regional assessment seems optimal to take into account biogeographic differences...

Pelagic habitats are a policy priority below Descriptor 1 (Biodiversity) of the Marine Strategy Framework Directive (MSFD). They are addressed under the D1C6 criterion, stating “the condition of the habitat type, including its biotic and abiotic structure and its functions…, is not adversely affected due to anthropogenic pressures”. The evaluation...

This report reviews the current situation as regards to the Marine Strategy Framework Directive (MSFD) Descriptor 1 (Biodiversity) for pelagic habitats and serves as a basis for a workshop with Member States experts and scientists that will be held on March 9-10 2021. Recommendations are in the concluding section. Pelagic habitats cover the 71% of...

This study attempts to elucidate the dynamics of phytoplankton biomass (as Chl-a), productivity, community structure and bloom formation in different regions of the oligotrophic Eastern Mediterranean (EMed). With this scope, several chemical and phytoplankton parameters were studied along a transect of 1300 km across different pelagic environments...

We used different spatial and decadal time series data covering 9 biological and chemical ecosystem components, 24 indicators and 8 descriptors of the Marine Strategy Framework Directive (MSFD), to test its performance under different ecosystem approaches. The results were evaluated in relation to the anthropogenic pressures affecting the study are...

MARINE-EO is a Research and Development project using a Pre-Commercial Procurement (PCP) mechanism with the scope to develop innovative beyond the state-of-the-art downstream applications which meet the demand of maritime authorities and stakeholders, leveraging on the existing services and other products from the Copernicus portfolio. More specifi...

At present there is no consistent approach for the definition of Good Environmental Status (GES) and targets in the Mediterranean Sea, especially for Biodiversity Descriptors, according to the Article 12 of the Marine Strategy Framework Directive (MSFD). The use of plankton indicators in the Mediterranean Sea refers mostly to pelagic habitats in co...

Maritime “Awareness” is currently a top priority for Europe. “Awareness” sought either in regards of maritime security, border control against irregular immigration and safety of navigation while at the same time “awareness” sought in regards of the marine environment and climate change. “Awareness” is sought both for sea-basins of traditional inte...

This paper examines the response of phytoplankton and potentially harmful species to river inflows in an eastern Mediterranean coastal area, within the context of environmental status assessment suggested by the European Commission’s Water Framework Directive (WFD, 2000/60/EC) and the Marine Strategy Framework Directive (MSFD, 2008/56/EC). The spat...

p>Biotechnological applications of toxic marine dinoflagellates include seafood safety and biomedical, pharmaceutical and research purposes of their toxins among other bioproducts and bioactive compounds that they produce. The supply of sufficient quantities of phycotoxins for investigational uses remains in demand. Some of these toxins, available...

The use of microalgae as means of bioremediation for polluted water bodies is a rising scientifc topic. This study evaluates the potential of three microalgae strains to remove nitrogen from a lagoon, which receives untreated agro-industrial wastewater. Nannochloropsis sp., Pleurochrysis sp. and Chlorella sp. were isolated from Koumoundourou lagoon...

Phytoplankton is a key element for the assessment of ecological and environmental status of aquatic ecosystems, also in the frame of the MSFD. The methods used to analyse phytoplankton communities are mainly based on time consuming cell counts, dictating a trade-off between the number of cells counted and the number of phytoplankton samples in a mo...

Atmospheric deposition is assumed to stimulate heterotrophic processes in highly oligotrophic marine systems, controlling the dynamics and trophic efficiency of planktonic food webs, and is expected to be influenced by climate change. In the course of an 8-day mesocosm experiment, we examined the channeling, of the Saharan dust (SD) and mixed aeros...

Taking into consideration the Water Framework Directive's requirements, water samples were collected monthly and/or bimonthly between 2014 and 2015 from Spercheios River, its estuary and the adjacent Maliakos Gulf in order to assess the quality of these water bodies. A study on dissolved nitrate, nitrite, ammonium, phosphate and chlorophyll-a conce...

The cyclopoid copepods of the genus Oncaea are an important component of the zooplanktonic community in the Mediterranean Sea due to their numerical abundance and distribution in coastal and open waters. Despite their importance in the marine ecosystem, the food habits of these copepods have not been clarified to date. With the aim of shedding some...

Variability is an inherent characteristic of the natural processes. We could consider natural variability any change that is not induced by human intervention. Variability affects both, the environmental factors and the biological components of the systems (changes in abundance, species composition, structure, etc.) and manifest on space (heterogen...

This work focuses on the direct measurement of the vertical flux of appendicularian houses in order to assess their importance as a component of vertical carbon flux in coastal areas. For this purpose, arrays of cylindrical sediment traps were deployed for 5 to 8 days at two depths in a coastal area of the northern Aegean Sea (inner Thermaikos Gulf...

This work focuses on the direct measurement of the vertical flux of appendicularian houses in order to assess their importance as a component of vertical carbon flux in coastal areas. For this purpose, arrays of cylindrical sediment traps were deployed for 5 to 8 days at two depths in a coastal area of the northern Aegean Sea (inner Thermaikos Gulf...

The responses of the benthic marine dinoflagellate Prorocentrum lima to nutrient stress induced by unbalanced N:P ratios were the subject of this study. Batch cultures of P. lima cells were grown under NP sufficient (N as nitrate and ammonium) and deficient conditions, and the cell growth and toxicity were followed for eight weeks. P. lima grew slo...