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The Dardanelles Straits – North Aegean Sea mixing zone is the area where the less saline waters of Black Sea origin supply organic material to the oligotrophic Mediterranean Sea. The objective of this work was to assess the seasonal dynamics of dissolved organic matter (DOM) in this region based on the optical properties (absorbance and fluorescence). By combining excitation-emission fluorescence with parallel factor analysis (EEM-PARAFAC), four fluorescent components were identified corresponding to three humic – like components and one amino acid – like. The latter was dominant during all seasons. Chromophoric DOM (CDOM) and dissolved organic carbon (DOC) were found to be strongly coupled only in early spring when conservative conditions prevailed and the two water masses present (Black Sea Waters – BSW and Levantine Waters – LW) could be identified by their absorption coefficients (a 300 ) and spectral slopes S 275–295 . In summer and autumn the relationships collapsed. During summer two features appear to dominate the dynamics of CDOM: i) photodegradation that acts as an important sink for both the absorbing DOM and the terrestrially derived fluorescent humic substances and ii) the release of marine humic like fluorescent substances from bacterial transformation of DOM. Autumn results revealed a source of fluorescent CDOM of high molecular weight, which was independent of water mass sources and related to particle and sedimentary processes. The removal of the amino acid-like fluorescence during autumn provided evidence that although DOC was found to accumulate under low inorganic nutrient conditions, dissolved organic nitrogenous compounds could serve as bacterial substrate. [ABSTRACT FROM AUTHOR]

Aim To study the variation in the species turnover and nestedness components of compositional dissimilarity in a multi-taxa and multi-island-group system. In addition, to examine the influence of several biogeographical drivers on compositional dissimilarity and discuss the findings in the light of the ecological characteristics of taxa and the palaeogeographical histories of island groups. Location A small-scale system of island groups within the Aegean Sea, namely the Astypalaia, Kalymnos and Nisyros groups, with different palaeogeographical histories. Methods We examined community variation of predatory ground spiders, omnivorous ground beetles and detritivorous terrestrial isopods. Compositional dissimilarity was decomposed for each group, by disentangling all compositional differences (βtotal) into two components, species turnover (βjtu) and nestedness (βjne). Partial Mantel tests were used to test the effects of island area, island elevation and inter-island distances on βjtu and βjne. Results Compositional dissimilarity levels of all arthropod communities varied among island groups and were primarily dominated by the species turnover component of compositional dissimilarity. Species turnover of spider communities was lower within the old and isolated Astypalaia group compared to the younger and less distant from mainland Kalymnos and Nisyros groups. Elevation differences between islands did not affect compositional dissimilarity. In contrast, area and inter-island distances significantly affected compositional dissimilarity between islands, albeit only in island groups of continental origin and only in some of the examined arthropod groups. Main conclusions Despite their geographical proximity, the three island groups show differences in compositional dissimilarity patterns which are more pronounced in the predatory arthropod communities. Using multiple taxa and clearly defined palaeogeographical and topographical elements, i.e. island groups, we show that the ecological characteristics of organisms and idiosyncrasies in geography and palaeogeography can be reflected in compositional dissimilarity patterns at small geographical scales. [ABSTRACT FROM AUTHOR]

The short-time scale evolution of plankton carbon partitioning and downward flux in the modified Black Sea water (BSW) mass entering the northeast Aegean Sea was studied using a Lagrangian approach (6–10 April 2008). The free-drifting sediment trap positioned at the bottom of the BSW layer and the control drifter, followed the same path within the anticyclone that circulates the BSW in the area. Ζooplankton biomass increased (from 159 to 292 mg C m−2), as did faecal pellet production (from 5 to 8 mg C m−2 day−1), whereas a generally decreasing trend was displayed by particulate organic carbon (POC) (from 2099 to 1440 mg C m−2), net primary production and biomass of plankton cells >5 µm (from 32 to 11 mg C m−2 day−1 and from 153 to 124 mg C m−2, respectively). At the same time, the organic carbon flux increased (from 131 to 311 mg C m−2 day−1), due to the contribution of zooplankton detritus (from 30 to 165 mg C m−2 day−1). Normalized biomass-size spectra slopes suggest an elevated grazing pressure upon microplankton cells and a non-steady-state ecosystem. Moreover, both the overall shallow slope values and their high correlation to organic carbon flux indicate an increased efficiency of energy transfer to higher trophic levels. [ABSTRACT FROM PUBLISHER]

Mesozooplankton group composition was examined in the Northeastern Aegean Sea (NEA) over a grid of 30 stations sampled during July 2004. The surface water layer influenced by the low salinity Black Sea waters (BSW) is considered in this paper. We attempted to study horizontal distribution patterns of major mesozooplankters within a more comprehensive framework, taking into account not only hydrology but also available, concurrently collected data on lower trophic levels (autotrophic and microbial heterotrophic communities). BSW was mainly restricted in the eastern part of the surveyed area where it was entrapped in a ca. 50-km wide anticyclone (the “Samothraki” gyre). High Chl α concentrations, autotrophic biomass as well as abundance and biomass of mesozooplankton were associated with the BSW, with the highest values recorded inside the gyre as well as at its coastal northern periphery and the lowest values towards the western and offshore part of the surveyed area characterized by high salinity waters of Levantine origin. Among mesozooplankters, cladocerans (mainly Penilia avirostris) showed a high abundance within the gyre in contrast to the very low abundance of copepods and appendicularians. Low salinity-high temperature gyre waters were characterized by the dominance of cyanobacteria of the genus Synechococcus in autotrophic biomass and the significant contribution of heterotrophic nanoflagellates in microbial heterotrophic biomass. Based on existing knowledge on ecophysiological traits and prey size-spectra selectivity, we discuss the observed distribution patterns of major mesozooplankton groups in terms of ambient abiotic parameters and the possible biological interactions among these groups as well as with lower or upper trophic levels. [ABSTRACT FROM AUTHOR]

Abstract: The dynamics of dissolved organic matter (DOM) in the Marmara Sea–Dardanelles Straits–North Aegean Sea were investigated using measurements of dissolved organic carbon and nitrogen (DOC, DON), PARAFAC modeling of 3-D excitation–emission fluorescence spectra and bacterial production (BP) and respiration (BR) rates. In the surface brackish waters, chemical parameters showed an increase from the Aegean to the Marmara (DOC: 65–217μmolL−1; DON: 3.08–9.34μmolL−1; Dissolved Inorganic Nitrogen (DIN): 0.044–1.38), followed by an increase in BP rates (7.2–195nmolL−1 d−1). In the subsurface waters, DIN also showed an increase in the Marmara basin (0.085–9.79μmolL−1) followed by an increase in BP rates (3.3–17.4nmolL−1 d−1). PARAFAC modeling revealed three fluorescent components: λex/λem: <260(330)/464nm, humic-like; λex/λem: <(260) 285/364nm, quinone-like; λex/λem: 270/308nm, tyrosine-like. DOC:DON ratios were found similar for the Marmara (21±3) and the N. Aegean Sea (19±2). The slopes ΔDOC:ΔDON suggested that in the Marmara Sea mineralization processes require more carbon relative to nitrogen (22.3), whereas in the N. Aegean there is preferential removal of nitrogen over carbon (5.66). The lack of significant correlation between DOC and AOU (apparent oxygen utilization) in the deep Marmara waters indicates that particulate organic matter is important in deep mineralization processes. [Copyright &y& Elsevier]

Abstract: The Mediterranean and the Black Seas are connected through Bosphorus, Marmara Sea and Dardanelles (Turkish Straits System, TSS). In this study, we examined the spatial distribution of copepods and investigate their production and grazing. The aim was to understand the transfer of phytoplankton/microzooplankton production up the food chain in TSS and Aegean Sea during spring. The phytoplankton and microzooplankton biomass and production showed a clear decreasing trend from Bosphorus to the Aegean Sea, whereas copepod biomass did not reveal any distinct trend and only the number of copepod species increased from Bosphorus to the Aegean Sea. Production of copepods and egg production showed similar trends except for the Bosphorus, where production of copepods was very low due to the low copepod biomass in this area. In all areas, the copepod carbon demand was largely met by phytoplankton and microzooplankton production. However, only a low amount of primary production was consumed by copepods and production appeared to flow mostly through other pathways (microbial loop) and/or sediment on the bottom. The results of this study confirm the hypothesis that there is a substantial differentiation within pelagic food web structure and carbon flow from Bosphorus to the Aegean Sea. [Copyright &y& Elsevier]

This work is a study of plankton food web structure and carbon flow in March and September 1997 in the Aegean Sea, area of outflow of Black Sea waters in the Mediterranean Sea. Biomass and production of autotrophs were measured by size fraction as well as bacterial biomass and production; furthermore, we studied heterotrophic nanoflagellates (HNAN), ciliates and mesozooplankton biomass, copepod production and grazing impact on phytoplankton. The obtained low values of nutrients and plankton biomass and production confirmed the oligotrophic character of this region. Despite the fact that there was no significant horizontal variability in the spatial distribution of nutrients throughout the study area, the planktonic biomass and production revealed a gradual decrease from the Northeast Aegean (NEA) towards the South Aegean (SA). In the Northeast Aegean, a large part of the fixed carbon was channelled through the microbial food web towards copepods; in contrast there was a low transfer of energy in the South Aegean where the multivorous food web was developed. Throughout the study area, almost 60–70% of autotrophic biomass and primary production was performed by cells <3 μm. [Copyright &y& Elsevier]