Plankton Dynamics and Distributionin the Eastern Mediterranean Sea

The similarities and differences in phytoplankton response to anthropogenic nutrient enrichment were studied in an open system (North Aegean Sea) and a coastal site of Saronikos gulf and in the Eastern Mediterranean. Although by physico-chemical parameters two different environments have been compared, the two regions exhibited similar features. The analysis of the data provides information on the contribution of each size class to the total autotrophic biomass and how nutrients and hydrographical variability of the water column affects the picophytoplankton assemblage composition. Phytoplankton size structure depends on a variety of factors, which ultimately are controlled by hydrodynamics of the system (Riegman et al., 1993). In general, the food web structure is also dependent on the nutrient availability. At low nutrient concentration, the picophytoplankton is supposed to be the relatively most important group, whereas under extensive nutrient supply larger size fractions dominate the phytoplankton. These larger organisms can be eaten directly by the mesozooplankton, which is the main component of the diet of the planktivorous fish. Picophytoplankton is not directly consumed by the mesozooplankton but is mainly consumed by protists. Some authors have pointed out that stability-instability conditions in the water column play a major role in controlling phytoplankton size structure. On one hand, hydrodynamical forcing controls nutrient supply to the euphotic layer. High nutrient concentrations cause an increase in the biomass and primary production of larger phytoplankton (Chisholm, 1992; Agawin et al., 2000). On the other hand, water column stability determines the size-differential residence time of phytoplankton cells within the euphotic layer, either favouring large-sized phytoplankton losses by passive sinking or accumulating them through the effect of vertical motion (Margalef, 1985; Malone, 1980; Rodrigues et al., 2001)

Large-scale testing of phytoplankton diversity indices for environmental assessment in Mediterranean sub-regions (Adriatic, Ionian and Aegean Seas)

Abstract 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 in species composition and functional characteristics. Previous research has shown that phytoplankton diversity indicators are efficient for reliable environmental assessments, although more effort has been recommended to test these indicators on a wide spatial scale to cover wider gradients of natural and anthropogenic pressures. In this work, a set of eight diversity indices was tested against the pressure levels within a common data set of the structure and abundance of phytoplankton communities from the Adriatic, Ionian and Aegean Seas. Expert knowledge was used to define four categories of impacts that take into account partial pressures, such as point and non-point pollution, industry, ports and fisheries. At the level of the common data set, most of the diversity, evenness and dominance indices could only distinguish between the highest level of impact and the rest of impact categories. These indices maintained the distinction between two levels of subsequently dichotomised impacts (no to low impact vs. high impact) across latitudinal and longitudinal gradients. On average, the indices were less sensitive to impacts in the northernmost and westernmost areas than in the southernmost and easternmost areas, although they still showed a significant response. The results also suggest that phytoplankton communities become more uniform and less dominated by a single taxon as sampling depth increases at sites with low impact, while evenness and dominance at impacted sites remain similar at all depths. In order to establish meaningful definitions of good environmental status and targets for pelagic habitats in the Mediterranean Sea, it is necessary to establish spatially specific thresholds by additional examination of indices of good performance

Abundance of microplankton in the Turkish Strait during Bilim 2 cruise in April 2008

The HCMR_SES_UNLUATA_CRUISES_TURKISH_STRAITS_CHLA & PP dataset was obtained on samples taken from 5 stations in the Dardanelles Straits, Marmara Sea and Bosporus Straits. These experiments were set up according to DoW of SESAME project. Microplankton species composition analysis was performed according to the Utermöhl's (1958) inverted microscope method. Samples for the identification and enumeration of larger phytoplankton cells (>5μm), were preserved in alkaline Lugol's solution