| 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.
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Διαβάθμιση βιοποικιλότητας και περιβαλλοντικών παραμέτρων σε θαλάσσιο σπήλαιο της Κρήτης
