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Identifier

000397289

Title

Μελέτη μεγέθους μεσοζωοπλαγκτού σε σχέση με τη διατροφή των μικρών πελαγικών ψαριών : συσχέτιση με την παραγωγικότητα και την ανθρωπογενή επιβάρυνση

Alternative Title

Mesozooplankton size study in relation to small pelagic fish diet: correlation with productivity and the anthropogenic disturbance

Author

Μπατζιάκας, Ευστράτιος Κ.

Thesis advisor

Κουμουνδούρος, Γεώργιος

Reviewer

Σωμαράκης, Στυλιανός
Καρακάσης, Ιωάννης

Abstract

For the study of mesozooplankton sizes in relation to the diet of small pelagic fishes, two distinct ecosystems in the broader area of Saronikos Gulf, Elefsis Bay and Aghios Kosmas, were chosen. These areas are different in relation to their geomorphology, hydrology, production and the magnitude of the anthropogenic impact. Samplings took place in December (2012) and September (2013), where organisms from bacteria to small pelagic fishes were collected and measures for temperature, salinity, fluorescence and dissolved oxygen from the water column were taken. The diet of the two most abundant small pelagic fish species (Engraulis encrasicolus and Sardina pilchardus) was estimated via prey counting from their stomach contents. The biomass spectrum analysis (NB-SS) was utilized for estimating the effect of seasonal variation, stratification through the summer period and hypoxia on the plankton community, as well as the overall differences between the two ecosystems. Steeper slopes of the NB-SS were observed in Elefsis Bay, which indicates a higher level of anthropogenic impact in the area. The acute hypoxia conditions in September below the thermocline in Elefsis Bay, induces drastic changes in the plankton community composition. The corresponding NB-SS slope is the steepest recorded in the present study (-1.353). Fish abundances per m3 are one order of magnitude higher in Elefsis Bay than in Aghios Kosmas, which indicates that small pelagic fishes chose Elefsis Bay, possibly to avoid fishing pressure. Anchovy and sardine feed on different prey sizes, with anchovies hunting for larger preys than sardines. This study was performed under the framework of PERSEUS project (grand Ν^Ο 287600, EC FP7/2007-2013).

Language

Greek

Subject

Anchovy

Biomass

Sardine

Spectrum

Βιομάζα

Γαύρος

Σαρδέλα

Σαρωνικός

Φάσματα