| Περίληψη: | The 1st chapter is the introduction of the thesis and is an overview of the present knowledge about the coralligenous formations found in the Mediterranean Sea in general and in the Greek Seas more specifically. Several aspects and the mechanisms that control the presence and growth of coralligenous formations are presented in this chapter. Coralligenous formations are under immense pressure due to the impact of human activities. These pressures and the conservation methods and acts that have been established are also part of this chapter. In order to map the coralligenous formations on the seafloor marine scientists use a plethora of different techniques. All these techniques as well as some new emerging state-of-the-art high-resolution techniques and the different seafloor classification schemes that are used are also described. The final part of the chapter is dedicated to gathering and presenting all the available information regarding the presence and status of the coralligenous formations of the Greek Seas that have been published in scientific studies.
The 2nd chapter presents the survey areas that were selected for the application of the methodologies proposed in this PhD. For the probability model, the study area is the whole span of the Greek Seas. Key features of the Ionian and the Aegean Seas are presented, in addition, a further note is given to some very important gulfs of these seas. Gyaros Island (Cyclades Archipelago, South Aegean) was selected to be the survey area for testing and application of the down-scale, high-resolution marine remote sensing survey.
In the 3rd chapter methodologies that are used for the objectives of the PhD are analysed. The first part describes the steps taken for the creation of a probability map of coralligenous formation presence in the Greek Seas. The steps are the collection of seafloor mapping data from the archive of the Laboratory of Marine Geology and Physical Oceanography, the collection of data regarding the seafloor morphology and its physico-chemical attributes for the areas mapped and the Greek Seas in general. The methodology of the applied random forest algorithm analysis is the final step of this part. The second part is the description and analysis of the downscale seafloor mapping survey techniques on Gyaros Island. This part presents both the survey planning and execution phase as well as the processing of the data collected through the survey.
Chapter 4 presents the results of the methodologies described in chapter 3. The results are also divided into two parts; the first refers to the mapped coralligenous formations and the probability model of the spatial distribution of coralligenous assemblages in Greece, while the second present the results of the high-detail mapping in Gyaros Island At first the result of the combination of the mapping data of the LMGPO archive is presented in the form of the most complete coralligenous formations presence map of the Greek Seas. The results of the statistical analysis and the creation of violin plots for the parameters collected from the open-access portals are the next part of this chapter. In this part, the violins plots are used to detect common attributes and differences between the formation found in the Greek Seas by segmenting it into three different geographical areas (Ionia, S and N Aegean Seas). The results of the probability model close the presentation of the first part of the results. In the second part, the results of the marine remote sensing and ground truthing survey are presented through thematic maps for each of the techniques applied. The combination of these maps allowed the segmentation of the seafloor based on three different seafloor classification schemes and their results are analysed. The final part of this chapter is the statistical analysis of the coralligenous formation mapped in the area of Gyaros seafloor in respect to the bathymetry and the sediment thickness.
The 5th and last chapter of the thesis is the synthesis of this thesis. The key results of each applied methodology are presented and their contribution to the process of understanding the coralligenous formation is highlighted Moreover, the limitations and/or gaps in each of the implemented methodological approaches are mentioned and ways to solve or fill them are also presented. The presentation of methodologies and instrumentations that will further enhance future mapping surveys is the last part of the PhD.
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