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Title Διαβάθμιση βιοποικιλότητας και περιβαλλοντικών παραμέτρων σε θαλάσσιο σπήλαιο της Κρήτης
Alternative Title Biodiversity and environmental gradients in a marine cave of Crete
Author Διγενής, Μάρκος
Thesis advisor Κανακίδου, Μαρία
Select a value Γεροβασιλείου, Βασίλης
Αρβανιτίδης, Χρήστος
Abstract The present BSc diploma thesis aims to study the macrobenthic marine biodiversity of the submerged Elephant Cave both qualitatively and quantitatively, using different methods. Futhermore, it aims to explore potential correlations of the spatial distribution patterns of biodiversity with that of certain environmental parameters related to water and sediment within the cave. The present work was carried out at the Institute of Marine Biology Biotechnology and Aquaculture (IMBBC), of the Hellenic Center for Marine Research (HCMR) in Heraklion, Crete. The study focused on three main ecological zones of the cave: the entrance zone, the intermediate semi-dark zone and the inner dark zone. From each zone the HCMR scientific diving team collected: 1) photographic frames and sediment corers for the study of benthic communities on hard and soft substrate, respectively, 2) water samples for estimating the concentration of five constituted ions, and 3) sediment samples for estimating the concentration of chlorophyll-a, phaeophytins and organic matter. Five photographic frames were taken from each of five stations at the three different zones along the cave, on the walls and ceiling of the submerged entrance and semi-dark zone, and on the walls of the inner dark chamber. The sessile organisms that were found, were sorted and classified to the lowest possible taxonomic level while their spatial distribution was estimated using PhotoQuad software. According to the results, different taxonomic groups predominated in different cave zones and different types of substrates. Analyses on the soft substrate showed that Polychaetes were predominant in the entrance zone while Oligochaetes dominated the remaining two. Both on the hard and soft substrate, there was a decrease in abundance from the entrance zone to the inner dark zone of the cave. On the contrary, according to the soft substrate analysis, species richness increased from the entrance to the semi-dark zone and decreased again to the inner dark zone. In the hard substrate, biodiversity appeared to decrease from the entrance zone to the inner dark zone of the cave. A total of 146 species were identified in the cave (33 species of hard substrate from photographic analysis, 40 species of soft substrate analysis, and 73 species recorded visually and with additional photographic material). Analysis of the water showed that in the dark zone the concentration of silicate ions was nine times higher than the other two zones, possibly related to the presence of freshwater inputs inside the inner part of the cave. In addition, the nitrite ion concentration was thirty-six times higher in the dark chamber compared to the entrance zone. In contrast, the concentration of phosphate, nitrite and ammonium ions in seawater did not change significantly along the different zones of the cave. Concerning sediment analysis, the concentration of chlorophyll-a and phaeophytins decreased gradually inside the cave, with the highest concentration of organic matter recorded in the semi-dark zone. The granulometric analysis of the sediment showed that although all three zones are dominated by coarse-grained sand, in the semi-dark zone, a significant proportion of 28.5% were related to the fine-grained sand, which may be due to the reduced disturbance of this cave’s part by marine currents. The above findings are the first attempt to study this particular cave, which receives a large number of divers each year and is one of the few studies of this habitat type in the Eastern Mediterranean. The results of the study provided the basis for future monitoring of this particular ecosystem.
Language Greek
Issue date 2019-11-29
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Chemistry--Graduate theses
  Type of Work--Graduate theses
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