NE Aegean Sea Research Articles

Holocene records of oyster reefs in a shallow semi-enclosed island embayment of the Aegean Sea

A high-resolution survey in the semi-enclosed Kalloni Gulf (Lesvos Island, NE Aegean Sea) revealed a plethora of oyster reef structures. The reefs have a relief of up to 6 m high and a length of 1.4 km at the deepest part (∼17 m) of the surveyed area and are developed in a fine-grained seabed. Acoustic backscatter variations caused by the presence and the type/distribution of different reef structures were mapped, resulting in the identification of four backscatter types. Sub-bottom acoustic information revealed the presence of similar buried features, which were classified in three types according to their characteristics. The seismic stratigraphy also showed the Holocene highstand and the transgressive system tracts as well as a deeper-seated distinct erosional surface with numerous buried channels, most likely corresponding to the surface flooded during the Holocene marine transgression. Starting at around 9700 years BP, the Kalloni paleo-landscape was progressively submerged and gradually transformed into a shallow, land-locked marine environment, allowing the establishment, and thriving of oyster reefs. The buried reefs presumably began to grow during the early stages of the gulf's transgression, whereas most of the modern reefs were developed/maintained by the modern hydrodynamic/sedimentary regime. It is the first time that such a large occurrence of well developed, diachronic oyster reef assemblage has been documented in the transgressive coastal environments of the microtidal Mediterranean Sea, but further research is required to determine the exact mode of their development.

An Insight into the Factors Controlling Delta Flood Events: The Case of the Evros River Deltaic Plain (NE Aegean Sea)

The present contribution aims to give an insight into the main terrestrial and marine processes leading to delta flooding in the case of the transboundary Evros delta, located at the microtidal NE Aegean Sea, on the basis of recorded flood events in the Evros deltaic plain. The prevailing weather conditions at the onset of the event, along with sea-level rise above the mean state, portray the mechanism for the development of compound flood events and subsequent riparian flooding. This system blocks the riverine water’s seaward exit, resulting in the flooding of the lower deltaic plain. The river discharge is recognized as a secondary factor acting mainly toward the persistence of the events. Several limitations restrict the quantification potential of the relative contribution of the key factors to the development, onset, and duration of a flood. Mitigation of the impacts of such flood events requires intercountry cooperation and a management plan based on a network of environmental monitoring.

Fault-controlled gas escapes in the shelf sediments of the Saros Gulf, NE Aegean Sea

Fault-controlled gas escapes in the shelf sediments of the Saros Gulf, NE Aegean Sea

Middle-late Holocene climate and hydrologic changes in the Gulf of Saros (NE Aegean Sea)

A multi-proxy analyses was applied on the sediment core from the Gulf of Saros (GoS) to identify and characterize climate and hydrological changes during the middle-to-late Holocene. The formation of two discrete Holocene sapropel layers in the GoS sediments was documented for the first time in the sediment core based on total organic carbon analysis. According to our paleo-proxy records, the lower Holocene sapropel was deposited under warm and humid climate conditions that gave rise to high delivery of terrestrial organic matter by numerous rivers in the northern catchment of the GoS. Biomarker and μ-XRF data were used to decipher climate variations during the middle to late Holocene. The general trends of sea-surface temperature records from the GoS and Sea of Marmara (SoM) at the beginning of late Holocene are in good agreement, underlying the influence of the Black Sea inflow. A relatively warm and wet climate together with a high sedimentation rate during the mid-Holocene Climatic Optimum resulted in high organic productivity and ensuing formation of the younger Holocene sapropel between 5.4 and 3.0 cal ka BP. Late Holocene European climate periods are evident in the Saros core records. The Roman Humid Period is represented by high variation in climate, indicating an earlier (2.5–2.3 cal ka BP) dry and a later (2.3–1.55 cal ka BP) wet periods. The abrupt return to drier condition during the Dark Ages Cold Period (1.6–1.3 cal ka BP) was followed by a wetter Medieval Climate Anomaly (1.1–0.7 cal ka BP). The paleo-proxy record of the core indicates a passage from a wetter to drier climate during the cold Little Ice Age period (730–110 cal yr BP), and highlights the influence of deforestation in the catchment of the GoS as a result of human activities during the last three centuries.

First record of straight-needle pteropodCreseis aciculaRang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)

AbstractPteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropodCreseis aciculaRang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered theC. aciculabloom, rather than global atmospheric CO2levels.

A webGIS Application to Assess Seawater Quality: A Case Study in a Coastal Area in the Northern Aegean Sea

The assessment of seawater quality in coastal areas is an important issue as it is related to the welfare of coastal ecosystems, a prerequisite for the provision of the related ecosystem services. During the last decades, marine eutrophication has become an important problem in coastal waters as a result of nutrient inputs increase. Consequently, there is need for appropriate methods and tools to assess the eutrophication status of seawater which should be user-friendly to coastal managers and support the adoption of effective plans for the protection and sustainable development of the coastal environment. In this framework, a user-friendly webGIS application has been developed and the Strait of Mytilene at the southeastern part of the Island of Lesvos in the NE Aegean Sea, Greece, was used as a case study. The methodology includes, as a first step, the evaluation of the accuracy of spatial interpolators widely applied in oceanographic studies for assessing the spatial distribution of relevant variables. The most appropriate interpolator revealed for each variable is subsequently applied for the production of the representative thematic layer. The second step involves the integration of the information from the optimal thematic layers representing the spatial distributions of the variables under study; as a result, a new thematic layer illustrating the eutrophication status of the study area is produced. The webGIS application is fully available via a web browser and provides a number of geoprocessing modules developed in Python which implement the user interface, the application of the interpolation analytical tasks, the statistical evaluation toolset and the integration of the optimal interpolated layers. Suggestions for further improvement of the proposed webGIS application are discussed.

Modelling and assessment of 137-Cs and of heavy metals impact on marine ecosystems

Modelling is an important and useful tool for predicting the behaviour and the impact of pollutants on the local ecosystem parameters. More specifically, simulation and computational methods can be used for estimating the environmental impact on marine ecosystems.The paper presents a three-dimensional general deterministic model, developed to simulate and study the time-dependent behaviour of 137Cs in marine environments. The model capabilities are demonstrated by applying it at the northeast region of the island of Lemnos, in the NE Aegean Sea, Greece. Full Navier-Stokes equations for transient, three-dimensional turbulent flow, heat and mass transfer are solved numerically. The solution method is the finite-volume method and the general CFD code in which the present model is implemented is Phoenics.

Using spatial indicators to investigate fish spawning strategies from ichthyoplankton surveys: A case study on co-occurring pelagic species in the NE Aegean Sea

Multispecies ichthyoplankton associations are believed to be adaptive and their objective definition can be useful in designating species with similar or contrasting spawning strategies. In this case study, a suite of indicators, recently developed to characterize the spatial patterns of animal populations, are applied on egg abundance data of summer-spawning European anchovy (Engraulis encrasicolus), round sardinella (Sardinella aurita) and chub mackerel (Scomber colias), in an effort to identify common or contrasting spawning patterns in the North-East Aegean Sea (NEA) and their relation to the major oceanographic features of the area. A considerable increase in abundance and area of presence was observed between the early (May) and advanced (July) phase of the 2010 spawning period. The definition of major spatial patches revealed a persistent multispecies spawning location associated with the outflow of Black Sea water (BSW). A second major patch was defined for anchovy and chub mackerel in July, clearly associated with the Samothraki gyre (SG). In contrast, round sardinella spawned in coastal waters outside the SG. Surprisingly, in May 2010, the spawning intensity of anchovy was very low in the SG which was attributed to unfavorable conditions caused by the bloom of mucilage-producing phytoplankton cells. The levels of aggregation and occupation of space seemed to be adequately described by the indices of Positive, Equivalent and Spreading Area. Conclusively, many of the spatial indicators applied in this study have the potential to become important tools for studying egg distributions and the changing priorities of adult fish in selecting spawning sites.

Consideration of modern sendimentary processes of the Evros river delta front and prodelta, NE Aegean sea

Gravity cores data from the Evros River delta front and prodelta confirm the aspect that the Evros River deltaic deposits tend to west-northwest, along the main direction of the local hydrodynamic regime, preventing the construction of a symmetrical Holocene prism. In the delta front, the terrigenous sediment consists mostly of fine-grained material. Its vertical succession is monotonous with slight differences in grain size or colour, and lack of internal structure or current-produced laminae, indicating almost immutable sedimentary processes as well as long-term discharge fluctuations. The river-borne sand is limited because of its entrapment in the river mouth but sometimes, during extreme conditions (periods of high river discharge, short-lived catastrophic events etc.), can be transported seawards covering an extensive area of the Alexandroupolis Gulf. The negligible biogenic content and the absence of bioturbation effects are attributed to the high rates of deposition. Some bioturbated horizons are produced when sedimentation rates decrease temporarily. The prodelta sediment distribution patterns occur a distinctive zonation along an east-southeast to westnorthwest trend. In the central part, mud dominates, while on both sides of this area, the content of sand gradually increases and becomes the prevalent facies near the coast and in the outer plateau of the gulf. The vertical facies sequences of the upper sedimentary cover are complicated, with many variations in grain size, colour and biogenic content reflecting a complicated manner of deposition. The major feeder of this area is the Evros River providing great amounts of suspended load. Another remarkable source of sand is derived from the coastline, which during storm conditions provides coarse-grained material in the shoreface area. Finally, a sediment supplier of local importance, Loutros River, affects the eastern area of Alexandroupolis building up a small subaqueous fan. In the open sea, the consequences of the modern sedimentation are negligible. The sandy character of the surface and sub-surface sediments, the analysis of biogenic fragments, the long distance from the present-day terrigenous sources are some evidences which lead to the view that the upper sediment body of the southwestern part of the study area has a presumable relict origin. 210Pb profiles are, more of less, consistent showing a sedimentation rate more than 2 cm/yr in the delta front, which decreases to 0.2 cm/yr at about 8 km seaward.

A GIS methodology to support sea water quality assessment in coastal areas

The development of methodologies for assessing water quality in coastal areas including mapping of eutrophication levels is a research area of high interest. A wide range of methodological approaches can be found in the literature, including multivariate techniques, since marine eutrophication is a multi-parametric phenomenon. In this context, statistical analysis and in particular Principal Component Analysis (PCA) have been widely applied. However, no attempt has been presented so far for mapping eutrophication levels based on information acquired from PCA results in integration with spatial analysis methods. The rapid development of Geographical Information Systems provides the appropriate framework for the development and application of methodologies integrating statistical analysis, spatial analysis methods and mapping techniques. This paper proposes such a methodological approach for assessing sea water quality in coastal areas. The methodology is clearly described and the Strait of Mytilene at the east of the Island of Lesvos in the NE Aegean Sea, Greece is used as a case study.

Transparent Exopolymer Particles (TEP) in the NE Aegean Sea frontal area: Seasonal dynamics under the influence of Black Sea water

The abundance of Transparent Exopolymer Particles (TEP) was determined on a seasonal basis (autumn, spring and summer) along a north-south transect in the NE Aegean Sea and the vicinity of the Dardanelles Straits. Their distribution patterns were studied in respect to hydrographic conditions and water mass characteristics in the area, as well as particulate organic carbon (POC) concentrations, changes in standing stocks of chlorophyll-α and bacterial production. TEP concentrations ranged from 15.4 to 188µg GX eqL-1. Their spatial distribution patterns within the euphotic zone displayed significant seasonal variability, which appears to closely reflect the temporal variation of the water column structure, resulting from the encounter and interplay of the Black Sea and Levantine Water masses, and the associated biogeochemical processes. Minimum TEP concentrations during autumn could be likely attributed to a minor quantity of TEP and/or its dissolved precursors exuded by phytoplankton and their enhanced degradation due to their long residence time in the water column. During spring, high TEP production was mediated by actively growing phytoplankton, while during summer a positive link to the intense stratification of the water column and the enhanced bacterial growth within the Black Sea Water layer was observed. The results reported in this study highlight the fact that TEP carbon represents a significant fraction of the POC pool. Moreover, TEP production is critical in promoting particle coagulation rates, playing an important role in carbon cycling/transportation out of the euphotic zone.

Particle characterization and composition in the NE Aegean Sea: Combining optical methods and biogeochemical parameters

The NE Aegean Sea constitutes a challenging sector of the world ocean in studying optical and biogeochemical properties and processes due to a dynamic frontal regime resulting from the continuous mixing of Black Sea waters (BSW) and waters of Levantine origin (LW), which are characterized by substantially different physical, chemical and biological properties. In the framework of Perseus and AegeanMarTech projects, inherent optical properties (IOPs; beam attenuation, optical backscattering, chlorophyll-α fluorescence), particle size, and discrete bottle data (particulate matter, particulate organic carbon, and chlorophyll-α concentrations) were measured during October 2013, March and July 2014. Black Sea water enters into the Aegean Sea through the Dardanelles and disperses to the west-northwest, as traced by characteristic salinity minima. The core of the BSW to the east of Lemnos Island was occasionally particle-enriched, showing maxima in cp, bbp, D50, PMC, POC, and TChl-α, the latter, however, detected primarily at sub-surface layers. Particle composition was chiefly organic, associated with phytoplanktonic communities (BSW and LW), heterotrophic planktonic organisms and detrital organic matter primarily originating in the BSW and forming aggregates often >100µm in diameter. A discrepancy between particle and TChl-α abundance was observed, with cp local maxima occurring in surface waters (BSW) and TChl-α maxima in mid-waters (LW). This pattern was attributed to phytoplankton photo- acclimation with depth leading to increased cell- chlorophyll content deeper, not necessarily matched by a similar biomass increase, thus, using TChl-α as an absolute proxy for phytoplankton biomass may not be appropriate, when considering water bodies encompassing the entire euphotic zone. Primarily in surface waters, the in situ optically measured median particle diameter primarily corresponds to large particles/aggregates, contrary to the findings obtained by laboratory analysis of cell counts in discrete water samples; this inconsistency was attributed to the fragile nature of aggregates that usually break up during sample processing and other methodological issues. The particulate backscattering ratio as well as the estimated bulk particulate index of refraction revealed a 2-layer structure, with biogenic particles and organic detritus occupying the upper ~65m of the water column, whereas deeper waters were enriched in lithogenic/organic particles resuspended from the seabed. Overall, the NE Aegean Sea is characterized by low particulate matter concentrations and low chlorophyll biomass during the sampling periods, exhibiting rather open-sea characteristics, reflected on all optical properties studied, as evidenced by their very low values and also by the POC:cp regression parameters. The present work contributes to a better understanding of bio-optical properties of the Aegean Sea, which by extension may improve regional satellite algorithms applied to retrieve chlorophyll-α concentration from space.

Evaluation of sediment contamination by monoaromatic hydrocarbons in the coastal lagoons of Gulf of Saros, NE Aegean Sea

The concentrations and distribution of monoaromatic hydrocarbons (benzene, toluene, ethyl benzene and the sum of m-, p- and o-, xylenes) were determined in the sediments of coastal lagoons of the Gulf of Saros, using a static headspace GC–MS. The total concentrations of BTEX compounds ranged from 368.5 to below detection limit 0.6μgkg−1 dw, with a mean value of 61.5μgkg−1 dw. The light aromatic fraction of m-, p-xylene was the most abundant compound (57.1% in average), and followed by toluene (38.1%)>ethylbenzene (4.1%)>o-xylene (2.5%)>benzene (1.1%). The factor analysis indicated that the levels and distribution of BTEX compounds depend on the type of contaminant source (mobile/point), absorbance of compounds in sediment, and mobility of benzene compound and degradation processes. Point sources are mainly related to agricultural facilities and port activities while the dispersion of compounds are related with their solubility, volatility and effect of sea/saline waters on lagoons.

INCORPORATING DIFFERENT SOURCE RUPTURE CHARACTERISTICS INTO SIMULATIONS OF STRONG GROUND MOTION FROM THE 1867, M7.0 EARTHQUAKE ON THE ISLAND OF LESVOS (NE AEGEAN SEA, GREECE)

We apply the stochastic method for finite-faults (Beresnev and Atkinson, 1997, 1998) to simulate strong ground motion acceleration from the 1867 earthquake that devastated the Island of Lesvos in NE Aegean Sea. Recent geological data are taken into account to construct realistic models of the earthquake source, while a first-order approximation of the site effect variation throughout the entire island of Lesvos is achieved following an empirical approach suggested by Wald and Allen (2007). We test several source models including different segments of the Agia Paraskevi fault, which is most probably the seismogenic fault of the 1867 earthquake. Stronger ground motion is predicted in the central part of the island, i.e. around the assumed seismogenic structure. A significant site effect is evident along the eastern coast of Lesvos, where the capital of Mytilene lies, strongly hit by the 1867 earthquake, and around the gulfs of Kalloni and Geras in the south and southeast parts of the island. Synthetic peak ground acceleration values are converted to macroseismic intensities through an empirical relation and discussed in comparison with available reports on the macroseismic effects of the 1867 earthquake.

Coccolithophore assemblage response to Black Sea Water inflow into the North Aegean Sea (NE Mediterranean)

This study aims to presents the species composition of living coccolithophore communities in the NE Aegean Sea, investigating their spatial and temporal variations along a north-south transect in the area receiving the inflowing surface Black Sea Water (BSW) over the deeper Levantine Water (LW) layer. Coccolithophores in the area were relatively diverse and a total of 95 species over 3 sampling periods studied were recognized using Scanning Electron Microscope (SEM) techniques. R-mode hierarchical cluster analysis distinguished two coccolithophore Groups (I, IIa, IIb, IIc) with different ecological preferences. Emiliania huxleyi was the most abundant species of Group I, whereas Syracosphaera spp., Rhabdosphaera spp. and holococcolithophores were prevailing in the highly diversified Group II assemblages. Biometric analysis conducted on E. huxleyi coccoliths from Aegean water column and Black Sea sediment trap samples, indicated that during autumn, NE Aegean specimens in samples under BSW influence were featured by unimodal distribution concerning the coccolith relative tube width, with values similar to those provided by the Black Sea specimens. In early spring, coccoliths in the stations with increased BSW influx displayed a bimodal pattern of relative tube width with smaller values found mostly in the surface layers, while the distribution became again unimodal and dominated by larger values within the deeper LW layers. In the summer period, the typical LW holococcolithophore species (Group II) presented low cell numbers in the surface layer (<20m), which is their usual ecological niche in the Aegean Sea, compared to greater depths, therefore marking LW mass flowing beneath the less saline BSW surface lid. In contrast to Black Sea early summer bloom conditions, E. huxleyi was almost absent in the NE Aegean during the summer sampling period.

Diversity of macrofungi in the Greek islands of Lesvos and Agios Efstratios, NE Aegean Sea

Diversity of macrofungi in the Greek islands of Lesvos and Agios Efstratios, NE Aegean Sea

A study of the benthic community structure of Demospongiae (Porifera) in Kalloni gulf at Lesvos Island (NE Aegean Sea, Greece)

Kalloni gulf at Lesvos Island in Aegean Archipelagos is an ecosystem where, despite its small size and the poor availability of suitable substrate, macrobenthic invertebrates find a living environment that fosters the development and growth of their populations. Among these invertebrates the Demospongiae stand out with 54 different species. In this paper the structure of demosponge communities is described according to the different types of inorganic and organic substrata encountered in Kalloni gulf. The data used for this study cover a comprehensive period of ten years. Competitiveness in finding the appropriate substrate in the limited space of the gulf is an important factor, not only among individuals of the same taxon, but also among different species, explaining the considerably high proportion of sponges that live as epiphytic and epizoic organisms. During sampling outside of typical inorganic substrata, 18 species of sponges or 33.3% of total identified species were epiphytic and 31 or 57.4% of the species encountered were epizoic. 14 species or 26% demonstrated the ability to survive both as epizoic and epiphytic.Cluster analysis and taxonomic distinctness indices (Δ+ and Λ+) analysis demonstrated that the colonization of different substrata, inorganic and organic by demosponges is rather non-specific, due to the limited substrate available.

Holocene Climatic Optimum centennial-scale paleoceanography in the NE Aegean (Mediterranean Sea)

Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters.

Ostracoda as bioindicators of anthropogenic impact in salt lakes, saltpans, and a lagoon: A case study from the Gulf of Saros coast (NE Aegean Sea), Turkey

The study area consists of wetlands and semi-wetlands (saltpan and salt lakes) that are separated from the Gulf of Saros in the northeastern Aegean Sea by a littoral cordon. Twenty-four samples were collected from the Enez Salt Lake; Dalyan, Enez Gala, Kuvalak, Isik, and Tasalti Lakes; Vakif and Erikli Saltpans; and Karagol Lagoon. The overall distribution of the sediment sizes reveals that they consist predominantly of mud and sand and a mixture of mud, sand, and gravel. The average proportion of gravel size particles is 8.36%. Feldspar and mica are abundant in sand and gravel-sized materials. Ecological conditions of these coastal areas were assessed on the basis of ostracod assemblages that can be considered as useful bioindicators and depend on water depth, temperature, and salinity. In this context, the effects of physical and chemical properties of the environment, geochemistry of the sediment, and anthropogenic impact on the meiofauna, in particular ostracoda, was here evaluated. Cyprideis torosa Jones, a cosmopolitan species of ostracoda, was found in salt lakes. Other species of ostracoda were shown to be affected by environmental conditions. The toxicity of some heavy metals in the saltpans, salt lakes, and hypersaline lagoons was evaluated. Lake Dalyan and Erikli Saltpan display high toxicity for Cu and Cd levels. The distribution of hydrocarbon pollution of terrestrial origin was determined.

Spatial and temporal variability of small-sized copepod assemblages in a shallow semi-enclosed embayment (Kalloni Gulf, NE Mediterranean Sea)

The small-sized copepod community structure (&lt;1 mm) and its response to environmental variability was examined during an annual cycle in Kalloni Gulf, a semi-enclosed coastal system in the NE Aegean Sea. Α 90 µm net was used in order to adequately sample the smaller copepod fractions. In the copepod ecology the spatial patterns dominated over the seasonal. Total copepod abundance increased towards the inner gulf area while diversity indices followed the opposite trend. The inner gulf copepod assemblage area was affected by the increasing magnitude of eutrophication, characterized by high abundance values, low species richness and dominance of a single species (e.g.Oithona nana). A clear seasonal succession of species was observed, ordered by temperature, salinity, chlorophyll a, heterotrophic bacterial biomass, organic and inorganic nutrients. Freshwater inputs and the subsequent nutrient inflow was a dominant phenomenon enhancing copepod production and negatively affecting the biodiversity of the assemblage. The great contribution of copepod larval stages in the total community and their year-round presence indicate the continuous production of copepods during the annual cycle, highlight the importance of the smaller size fraction and encourage the use of finer mesh-size nets when assessing the structure and dynamics of copepod communities.