George Kehayias

Feeding and predation impact of chaetognaths in the north Aegean Sea (Strymonikos and Ierissos Gulfs)

The feeding of the most important chaetognath species (Sagitta eqflata, Sagitta minima, Sagitta setosa and Sagitta serratodentata) found in a grid of 35 stations in the north Aegean Sea (Strymonikos and Ierissos Gulfs) was investigated through gut content analysis during five sampling periods from June 1997 to May 1998. Sagitta enflata and S. minima were the most abundant species in summer autumn 1997 and in spring 1998, respectively. Copepods were the main food for all chaetognath species in spring 1998, while cladocerans in summer autumn 1997 dominated the diet, especially of S. enflata. In September 1997, the juvenile specimens of cladocerans were the most important prey of the immature Stage I specimens of S. enflata. which resulted from the major breeding period in late summer. The estimated impact of chaetognath predation on the copepod and cladoceran communities ranged between 0.02 2.76% and 0.01 1.29% of the copepod and cladoceran standing stock, respectively. Stage 1 specimens of S. enflata accounted for nearly 90% of the total copepod and cladoceran standing stock consumed per day by the total population of this species in September 1997.

Lipid production by the filamentous cyanobacterium Limnothrix sp. growing in synthetic wastewater in suspended- and attached-growth photobioreactor systems

The main objective of this study was the production of biotechnological oil/biodiesel from a filamentous cyanobacterium Limnothrix sp. with simultaneous treatment of a model wastewater. A novel attached-growth photobioreactor was designed to facilitate the harvesting of cyanobacterial biomass and to maximize biomass and lipid production compared to suspended-growth cultivation systems. Kinetic experiments with different initial nitrate and phosphate concentrations were performed in both suspended- and attached-growth cultivation modes to define the biomass and lipid concentration as well as the capability of Limnothrix sp. to remove nutrients from the artificial wastewater. The removal of nitrate and phosphate was high in both suspended- and attached-growth systems. The results of this study also demonstrated that the proposed attached-growth photobioreactor system ensured higher biomass productivity compared to the suspended-growth cultivation system. The absence of long aliphatic chain fatty acids as well as the high amount of saturated and monounsaturated fatty acids (almost 80 %) in cyanobacterial lipid make the oil produced a promising feedstock for biodiesel production.

Seasonal vertical distribution and diel migration of zooplankton in a temperate stratified lake

The investigation of the vertical distribution of the zooplankton community in the temperate Lake Trichonis during four seasons in 2005, showed the existence of vertical segregation among species, ontogenetic stages and sexes within and between the major groups. In each season, the two or three more abundant rotifer species distributed at separate depth layers, while this feature was maintained during the entire 24 h period, since no diel vertical migrations (DVM) were performed. In contrast, the crustacean community, comprised mainly by the calanoid copepod Eudiaptomus drieschi and the cladoceran Diaphanosoma orghidani, showed various patterns of DVM, being more pronounced in spring and summer. Females of E. drieschi distributed deeper than males, while the copepod nauplii were found mainly in the surface layer in all four seasons. Temperature was the most important abiotic factor affecting directly and indirectly the vertical distribution and migration of various species. During stratification, the metalimnion was the most productive layer in Lake Trichonis, having maximum values of dissolved oxygen and low transparency due to high concentration of organic matter and phytoplankton. The DVM patterns of the crustaceans indicate that the metalimnion acts probably as a daylight refuge against predation by Atherina boyeri, which is the dominant planktivorous fish in the lake.

Zooplankton dynamics in the upstream part of Stratos reservoir (Greece)

The investigation of the zooplankton community in the upstream part of Stratos reservoir during a 24 months survey (September 2004–August 2006) revealed 26 invertebrate species (14 rotifers, 6 cladocerans, 5 copepods and one mollusk larva). The mean abundance of the total zooplankton was higher in the first sampling period (2004–2005) and ranged between 8.81 and 47.74 ind. L−1, than the second period (2005–2006) when fluctuated between 1.91 and 43.09 ind. L−1. The seasonal variation was strongly influenced by the presence of rotifers, which accounting on average for 68.4% in total. Among them Keratella cochlearis and the order Bdelloidea were numerically the most important, while Macrocyclops albidus prevailed among the copepods and Bosmina longirostris among the cladocerans. Dreissena polymorpha was the only mollusk found in the zooplankton community. Rotifers, copepods and cladocerans showed a seasonal succession with the former preceding in the abundance having their first maximum in spring, while copepods and cladocerans followed, having peaks of abundance in early summer and in autumn, respectively. No seasonal succession among the cladoceran species was observed. The intense water flow in the upstream part of the reservoir, as well as temperature, conductivity, DO, pH, phosphates and silicates, were significant parameters controlling abiotic and biotic elements of the ecosystem and consequently influencing the seasonal variation and the dynamics of the zooplankton community.

Spatial and temporal distribution of zooplankton in Lake Trichonis (Greece)

The investigation of the zooplankton community in Lake Trichonis during a two‐year survey (September 2003–August 2005) revealed 37 invertebrate species (26 rotifers, three copepods, seven cladocerans and one mollusc larva). The seasonal distribution followed a biacmic pattern in the first year and a monoacmic in the second. Copepoda prevailed, with the calanoid Eudiaptomus driesci being the dominant species. No differences in the horizontal distribution of the zooplankton community were found. The maximum abundance of the zooplankton community was recorded in the surface 0–10 m layer and abundance decreased with depth. The most important species of rotifers follow a vertical separation pattern, while the cladocerans revealed either a seasonal succession of dominance, or a vertical separation. Although Lake Trichonis holds the basic characteristics of an oligotrophic lake, the presence of certain species typical of eutrophic lakes, could reflect a possible alteration of its trophic state.

Zooplankton dynamics in a gypsum karst lake and interrelation with the abiotic environment

Zooplankton species composition and abundance variation was studied in Lake Amvrakia, which is a deep, temperate, gypsum karst lake situated in the western Greece. The two year survey of zooplankton revealed 33 species (23 rotifers, five cladocerans, four copepods and one mollusc larva). The mean integrated abundance of the total zooplankton ranged between 83.6 and 442.7 ind. L−1, with the higher density to be recorded in the surface 0–20 m layer. Small numbers of specimens of almost all species were found also in the hypoxic or anoxic hypolimnion. Copepods and especially the calanoid Eudiaptomus drieschi dominated the zooplankton community throughout the sampling period, followed by Dreissena polymorpha larvae, rotifers and cladocerans. Seasonal succession among the cladocerans and the most abundant rotifer species was observed. The concentration of chlorophyll-a was the most important factor for the variation of total zooplankton, as well as for the rotifers’ community. Dissolved oxygen affected copepods and cladocerans, water level correlated mainly with the molluscs larvae of D. polymorpha, while temperature influenced the variation of several rotifers, the cladoceran Diaphanosoma orghidani and the mollusc larvae. Negative correlation of conductivity with the cladoceran Daphnia cucullata and the copepods E. drieschi and Macrocyclops albidus was found. The differences in species composition found in Lake Amvrakia in comparison to the nearby lakes are probably ought to the geographical isolation and perhaps to its particular chemistry (e.g., elevated conductivity).

Abundance, vertical distribution and feeding of chaetognaths in the upper 50 m layer of the eastern Aegean Sea

The present study presents data on the abundance, vertical distribution and feeding of chaetognaths found in the 0–50 m column in a neritic area of the eastern Aegean Sea during July 2004. The abundance of total chaetognaths ranged between 7.76 and 35.92 ind m−3. The highest values were recorded in the uppermost 20 m and values decreased with depth. The chaetognath community comprised nine species with Sagitta enflata, Sagitta minima, Sagitta serratodentata and Sagitta setosa being numerically the most important. Copepods were the main prey for most chaetognath species, while S. minima showed a higher preference for cladocerans. An evident relation between the presence of food of chaetognaths and their horizontal and vertical distribution in the area of study was found. In the surface 0–50 m of this typical oligotrophic area of the eastern Mediterranean, the chaetognath species occupied different depth strata possibly in order to reduce the interspecific competition.

A Light Trap for Sampling Atherina boyeri Larvae in Lake Trichonis, Greece

ABSTRACT In order to sample the larvae of Atherina boyeri in the large and deep lake (Lake Trichonis), we devised a simple Plexiglas™ light trap in which the light was produced by five colors of Cyalume™ light sticks. In trials during July 2006, 957 larvae were caught, with greater numbers of larvae recovered from the traps with the green and blue light sticks. These two colors also attracted large numbers of the dominant copepod, Eudiaptomus drieschi.

A Simple and Inexpensive Light Trap for Lake Zooplankton

ABSTRACT Various types of light traps have been used in aquatic ecosystems to attract fish larvae, zooplankton, and benthic invertebrates. However, most of these devices have been cumbersome and expensive. I devised a simple and inexpensive light trap using a modified Ruttner water sampler and green Cyalume® light sticks. Repeated trials in Kastraki Lake (Greece) demonstrated that the light trap was efficient in attracting zooplankton, notably the cladoceran Bosmina longirostris.

Monitoring and Modeling of Metal Concentration Distributions in Anoxic Basins: Aitoliko Lagoon, Greece

The balance between physicochemical processes, influencing vertical and temporal distributions of metal compounds in one relatively isolated anoxic environment, constitutes the objective of the present work. Ion activity product (IAP) was calculated for manganese and iron sulfides, in order to define the metal sulfide forms that control Fe and Mn solubility in the bottom waters of anoxic lagoons. Iron solubility depended on amorphous FeS formation, while manganese sulfides were a minor component in a solid solution lowering its solid-phase activity. A theoretical physicochemical model was developed for the iron speciation, based on experimental pH and redox potential data. A very good match was achieved for the measured and the theoretical total dissolved iron, at all depths. The dominance of oxidant iron species Fe(OH)3− in the surface waters and their sequence by FeSH+ and FeSaq in the deeper layers brings out the influence of physicochemical parameters (dissolved oxygen, sulfide, pH and Eh) in vertical distribution of dissolved metal species, in anoxic/hypoxic basins. Based on these findings, we can conclude that the distribution of manganese and iron is of special interest, not only because these are the indicators of redox conditions but also for the role of their oxidized/reduced forms in the formation of the biogeochemical structure of redox zone.