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We studied the seasonal dynamics of phytoplankton, bacterioplankton, heterotrophic nanoflagellates, ciliates, and metazoan plankton in the highly eutrophic polymictic Lake Kastoria (Greece), which has a history of toxic cyanobacterial blooms. An acute increase in the flushing rate of the lake during spring inhibited cyanobacterial biomass accumulation. During this transient oligotrophic period, which was characterized by abundant lake snow particles, the plankton food web was an inverted biomass pyramid (low autotrophic biomass and high heterotrophic biomass). Prokaryotes played a key role in these changes (cyanobacteria during periods of autotrophy and bacteria during periods of heterotrophy). In summer and autumn, toxic cyanobacterial blooms developed, and the microbial loop was weak. The microbial loop was weak because the heterotrophic nanoflagellates and nanociliates decreased to undetectable densities during the summer, when larger bacterivores (rotifers and small cladocera) were abundant. Toxic blooms may have a dual effect on heterotrophic nanoplankton: negative during the first bloom and postbloom period and positive during a following toxic bloom. Different species (Cylindrospermopsis raciborskii, Aphanizomenon spp., and Microcystis aeruginosa) and succession phases of toxic blooms may differentially affect the microbial food web structure.In pelagic systems, phytoplankton and bacterioplankton constitute the complementary functional components that primarily produce new particulate matter by autotrophy and heterotrophy. Their carbon pool represents the base of grazing food chains and the microbial loop. Thus, the relative dominance of each functional component has significant implications for food web structure and the function and bio- AcknowledgmentsWe would like to thank the two anonymous reviewers and Associate Editor R. Bachmann for their constructive criticisms and suggestions. We are grateful to U. Sommer for his critical comments and suggestions on drafts of this manuscript and to U. Christaki for her helpful comments. We thank L. Economou for linguistic suggestions and C. M. Cook for the critical reading of sections of the manuscript concerning cyanotoxins. This work was partially funded by the Municipality of Kastoria, Research Committee, Aristotle University of Thessaloniki, project 7468. We thank all participating members of this project.

The dynamics of phytoplankton biomass were studied in an Eastern Mediterranean semi-enclosed coastal system (Maliakos Gulf, Aegean Sea), over 1 year. In particular, chlorophyll a (chl a) was fractionated into four size classes: picoplankton (0.2-2 µm), nanoplankton (2-20 µm), microplankton (20-180 µm) and net phytoplankton (>180 µm). The spatial and temporal variation in dissolved inorganic nutrients and particulate organic carbon (POC) were also investigated. The water column was well mixed throughout the year, resulting in no differences between depths for all the measured parameters. Total chl a was highest in the inner part of the gulf and peaked in winter (2.65 µg l -1 ). During the phytoplankton bloom, microplankton and net phytoplankton together dominated the autotrophic biomass (67.2-95.0% of total chl a), while in the warmer months the contribution of pico-and nanoplankton was the most significant (77.5-93.4% of total chl a). The small fractions, although showing low chl a concentrations, were important contributors to the POC pool, especially in the outer gulf. No statistically significant correlations were found between any chl a size fraction and inorganic nutrients. For most of the year, phytoplankton was not limited by inorganic nitrogen concentrations.

Published information on airborne algae and cyanobacteria worldwide and the related human health effects is scarce. Since 1844, a total of 353 morphological taxa (genera or species) have been identified in aerobiological studies. However, due to diverse methodologies and different microorganisms targeted in these studies, direct comparisons on the occurrences of airborne algae and cyanobacteria in various studies are rather dubious. Thirty-eight airborne algae and cyanobacteria were shown to induce allergy, skin irritation, hay fever, rhinitis, sclerosis and respiratory problems when aerosolized and inhaled. Another 14 airborne taxa are known toxin producers posing threat to human health. Most frequently associated with health effects are the genera Chlorella, Scenedesmus, Chlorococcum, Klebsormidium (Hormidium) and Lyngbya. In the air of the Mediterranean city of Thessaloniki, we found 63 algal and cyanobacterial taxa, with 21 reported for the first time in the air. Seven taxa were potentially harmful. Algae and cyanobacteria can contribute significantly in the total air particle load, rendering them as causative agents for health issues when inhaled.

The seasonal variations of temperature, dissolved organic carbon (DOC), chlorophyll a (chl a), and bacterial and protistan abundance were investigated in an enclosed Eastern Mediterranean embayrnent over an 8 mo period. DOC levels in the gulf were high, likely due to allochthonous input through freshwater discharge. However, after the end of spring, when allochthonous input was minimal, bacterial abundance was linearly related to chl a and DOC, suggesting that during this period the remaining DOC pool (probably autochthonous DOC) was important. Bacterial abundance was significantly correlated with the biomass of the phytoplankton at the end of spring and throughout summer A correspondence of protistan abundance with bactena, especially during the warm months, when the phytoplankton biomass was low, suggests that the microbial loop is the dominant component of the food web structure during the oligotrophic period of the ycar.

Herein, the effect of dietary inclusion of insect (Tenebrio molitor) meal on hepatic pathways of apoptosis and autophagy in three farmed fish species, gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss), fed diets at 25%, 50% and 60% insect meal inclusion levels respectively, was investigated. Hepatic proteome was examined by liver protein profiles from the three fish species, obtained by two-dimensional gel electrophoresis. Although cellular stress was evident in the three teleost species following insect meal, inclusion by T. molitor, D. labrax and O. mykiss suppressed apoptosis through induction of hepatic autophagy, while in S. aurata both cellular procedures were activated. Protein abundance showed that a total of 30, 81 and 74 spots were altered significantly in seabream, European seabass and rainbow trout, respectively. Insect meal inclusion resulted in individual protein abundance changes, with less number of proteins altered in gilthead seabream compared to European seabass and rainbow trout. This is the first study demonstrating that insect meal in fish diets is causing changes in liver protein abundances. However, a species-specific response both in the above mentioned bioindicators, indicates the need to strategically manage fish meal replacement in fish diets per species.

Spercheios River discharge rates of nutrients, suspended particulate matter (SPM) and particulate organic carbon (POC) and seawater concentrations of these parameters as well as chlorophyll a (chl a) were measured in the Maliakos Gulf, Greece, on a monthly basis between 1992-1993. From all the nutrients measured, silicate showed the highest discharge rates followed by nitrate, phosphate and nitrite. The river introduced significant amounts of SPM (8.5 -35.5 Kg d -1 ) with very low POC content (<3%). Most of the variables measured showed no gradient from the river to the outer gulf, which could be attributed to fast mixing of the incoming water. However, chl a had higher concentrations in the inner (0.3 -4.9 Ìg l -1 ) and lower in the outer gulf (0.05 -2.5 Ìg l -1 ). It is suggested that the nutrients introduced by the river are consumed faster in the inner gulf and that a number of temporal streams and non-point sources at the periphery of the gulf prevent the formation of a gradient.

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