Geomorphological survey and mapping of the Giardini Botanici Hanbury and related Capo Mortola marine protected area (Liguria, Italy)

In recent times geoheritage and geodiversity studies have received a great amount of attention. Many different themes and research lines have been addressed by geoscientists, but still little attention has been given to underwater geoheritage, and its relationship with terrestrial geosites and biodiversity.

Giardini Botanici Hanbury is a small regional protected area in the westernmost part of Liguria (Northwestern Italy), at the border with France. It comprises a small (0.19 km²) terrestrial area, with a XIX century villa, the surrounding botanic gardens, the nearby coastline, and a marine area extended for 4.634 km². The protected area also includes two Special Conservation Areas (under the European Habitats Directive): Capo Mortola and Capo Mortola Seabed. The protection of these areas is linked to the presence of very rich in species and well preserved Posidonia oceanica beds and benthic communities of biogenic-geogenic reefs.

The protected area comprises stunning geological and geomorphological features, both in the terrestrial and in the underwater part. The most important terrestrial feature is the Capo Mortola geosite, which has long been recognized at a regional level and has recently been included in the Italian National Inventory of Geosites. Capo Mortola is a synform fold, that involves strata of Nummulitic limestones, which are studied since the XIX century for the notable fossil content. The fold axis plunges seaward, so the structure continues under the sea level. In the marine part, the most notable feature is the “Polla Rovereto” spring, which is a submarine stillwater spring. It discharges more than 100 l/s, and it constitutes the main spring of the adjacent karst area.

In this research we provide an original geomorphological map of the Hanbury Botanic Gardens, comprehending either the terrestrial and the marine area. To design the map, a detailed field survey was carried out in the terrestrial part of the protected area, with the support of drills and remote sensing information. The geomorphology of the underwater area has been reconstructed partly by observations from the sea surface, partly from bibliographical data and information from previous underwater surveys. The main geoheritage features have been highlighted.

This map can provide insight on the relationship between terrestrial and marine geoheritage, and its influence on the biodiversity in a protected area. Furthermore, this map could be a powerful tool to develop geotourism in one of the most distinctive Ligurian protected areas.