First recording of the non-native species Beroe ovata Mayer 1912 in the Aegean Sea

A new alien species Beroe ovata Mayer 1912 was recorded in the Aegean Sea. It is most likely that this species spread on the currents from the Black Sea. Beroe ovata is also alien to the Black Sea, where it was introduced in ballast waters from the Atlantic coastal area of the northern America. The species is established in the Black Sea and has decreased the population of another invaderMnemiopsis leidyi, which has favoured the recovery of the Black Sea ecosystem.We compare a new 1 species with the native species fam. Beroidae from the Mediterranean and predict its role in the ecosystem of the Aegean Sea using the Black Sea experience

Zooplankton community dynamics in the N. Aegean front (E. Mediterranean) in the winter spring period

Zooplankton community composition was studied in the North Aegean frontal area in the winter-spring period along a trophic gradient going from the less saline and cold modified Black Sea water to the high salinity and temperature waters of Levantine origin. Samples were collected at the upper 100 m of three stations positioned along this gradient by using three nets with different mesh sizes (45 μm, 200 μm and 500 μm). Τhe community composition (all sizes) was differentiated along the gradient with smoother seasonal succession and higher diversity with increasing oligotrophy and salinity. The temporal variability of the community composition revealed significant changes in the January-April period as well as gradual decrease of diversity index values at the station positioned within the front.  The major characteristic at this station was the abrupt increment and dominance of Centropages typicus in April, especially within the layer occupied by the modified Black Sea water. Significant difference in the community composition between March and April was a common feature in the whole study area and for all zooplankton fractions, though not of the same strength. The inflow of the Black Sea water and the trophic gradient were found to be important factors for the observed temporal variability and its spatial differentiation, while changes in the phytoplankton and protozoa abundance and community composition could account for the seasonal succession in species dominance

Zooplankton of the Black Sea and the Eastern Mediterranean: Similarities and dissimilarities

A synthesis of data on abundance and biomass of zooplankton in the Eastern Mediterranean (EMED) and the Black Sea shows major differences in the composition and structure of pelagic communities in the two basins. Few Mediterranean planktonic animals have invaded and acclimatised in the Black Sea. The great bulk of Black Sea species is represented by coastal inhabitants that spread throughout the whole basin. This process has been called “neritization” of the Black Sea fauna. Peculiarities in zooplankton assemblages of the Black Sea have been further strengthened over the last few decades due to increasing eutrophication and the massive invasion of the ctenophore Mnemiopsis leidyi. The relative contribution of copepods, cladocerans, chaetognaths, and appendicularians to total zooplankton biomass has notably decreased , whereas gelatinous groups (mainly represented by Mnemiopsis and Aurelia aurita) contributed up to 99% of total wet weight in 1995 in the Black Sea.The basic features of planktonic fauna in the Black Sea are mainly due do the geo-morphological characters of the basin and the limited exchanges with the EMED, that are confined to the surface-subsurface layers in the Dardanelles and Bosphorus Straits. However, the dramatic changes that recently occurred in the structure of zooplankton assemblages seem to have been caused by heavy anthropogenic impact on the pelagic system

Distribution of mesozooplankton resting eggs in seabottom sediments of Thermaikos gulf (NW Aegean Sea, Greece) and possible effects of sediment resuspension.

The distribution of mesozooplankton resting eggs was studied in the bottom sediments of Thermaikos Gulf (Aegean Sea, Greece), to study possible effects of sediment resuspension on egg assemblages, due to physical forcing (storm events) and/or anthropogenic activity (trawling). The total abundance of eggs in sediments was higher at stations located close to the rivers’ mouths, with muddy sediments, and with the water column richer of zooplankton, than at stations located at greater depths and with muddy-sand bed sediments. At the former stations the vertical distribution of eggs has revealed a trend of homogenization within the sediment column, from September to February. This is related probably to the sediment re-suspension. At the latter stations, no clear temporal variability in the vertical distribution was detected. The eggs found in the bottom sediments of Thermaikos Gulf were assigned to 16 morpho-types. Amongst these, those assigned to Paracartia latisetosa and Labidocera wollastoni (as well as one type called Calanoida 3), were found to be dominant at all the stations and during all the sampling periods, both as full and empty eggs

Intercomparison of five nets used for mesozooplankton sampling

Intercomparison of nets commonly used for mesozooplankton sampling in the Black and Mediterranean seas was attempted within SESAME (Southern European Seas: Assessing and Modelling Ecosystem Changes) project. Five nets were compared: three Juday nets equipped with 150 μm, 180 μm and 200 μm mesh size, Nansen net (100 μm mesh size) and WP2 (200 μm mesh size). Replicated samples were collected at one station in the western Black Sea offshore waters in April 2009. Collected samples were analyzed at species level (except for meroplankton), stages (for copepods) and size length. A decrease of total abundance values was observed with increasing mesh size, due to the significantly higher numbers of animals smaller than 1 mm in the samples obtained by fine mesh size than with coarser nets. Few comparisons were revealed significant for the abundance of animals with 1-2 mm length, while no significance was detected for specimens larger than 2 mm. The above differences resulted in discripancies between nets regarding species and stages composition. Biomass values did not differ significantly between nets, due to the strong contribution to total biomass of the large animals fraction (Calanus euxinus). The smallest and the largest animals revealed high variability between replicates collected by Nansen, Juday- 200 μm and WP2 nets. Correction factors were calculated for the conversion of abundance values between each couple of nets. The detected differences between nets regarding the abundance and biomass, the community taxonomic composition and size structure, as well as the estimated correction factors, provide useful information for the harmonization of data obtained by the above nets in the Black Sea

Temporal variability of the microbial food web (viruses to ciliates) under the influence of the Black Sea Water inflow (N. Aegean, E. Mediterranean)

Τhe entire pelagic microbial food web was studied during the winter-spring period in the frontal area of the North Aegean Sea. Abundance of viruses, heterotrophic bacteria, cyanobacteria, auto- and hetero-trophic flagellates, and ciliates, as well as bacterial production, were measured at three stations (MD1, MD2, MD3) situated along a N-S transect between the area directly influenced by the inflowing Black Sea water and the area covered by the Levantine water. Samples were collected in December 2009, and January, March, April, and May 2011. Station MD1 exhibited the highest values of abundance and integrated biomass of all microbial groups and bacterial production during all months, and MD3 the lowest. Bacteria dominated the total integrated biomass at all stations and months, followed by cyanobacteria, auto-, hetero-trophic flagellates and ciliates. On a temporal scale, the microbial food web was less important in March as all microbial parameters at all stations showed the lowest values. After the phytoplankton bloom in March, the heterotrophic part of the microbial food web (mainly) strongly increased, though the intensity of the phenomenon was diminished from North to South. Pico-sized plankton was found to be heterotrophic whereas nanoplankton was autotrophic. It seems that the influence of the Black Sea water on station MD1, permanent throughout the study period of early winter to late spring, was reflected in all microbial populations studied, and produced a more productive pelagic food web system, with potential consequences for the upper trophic levels

Mesozooplankton biomass and abundance in Cyprus coastal waters and comparison with the Aegean Sea (eastern Mediterranean)

Here we conduct the first comprehensive assessment of mesozooplankton abundance, biomass, and taxa composition in Cyprus coastal waters (Levantine Sea).  Mesozooplankton abundance and biomass sampled at several locations around the island ranged from 153 – 498 individuals m-3 and 0.7 – 5.2 mg dry weight m-3, respectively, with significantly larger biomass observed in winter-early spring (March) than in summer (September).  The community was dominated by calanoid and cyclopoid copepods throughout the year (80% of total numbers), with higher abundances of predatory taxa (chaetognaths and medusae) in winter and cladocerans in summer.  Overall, we find that coastal mesozooplankton communities around Cyprus appear to be more similar to communities in offshore waters or those around the island of Rhodes than to communities along the mainland Levantine coast.  We further highlight regional differences in the eastern Mediterranean by comparing our data with mesozooplankton in the western Aegean (Saronikos Gulf) and northeastern Aegean Sea (NEA).  Distinct spatial differences were observed, for example anthropogenic influences in the Saronikos Gulf and the outflow of Modified Black Sea Water in the NEA drove generally greater biomass and abundance in these regions.  Overall, our comparison supports the concept of a latitudinal gradient in oligotrophy in the eastern Mediterranean, with ultra-oligotrophic conditions found in the Levantine Sea