Mapping marine habitats in the Gulf of Guinea: A contribution to the future establishment of Marine Protected Areas in Principe Island

Abstract

Accurate mapping of marine benthic habitats, using acoustic technologies such as Side-Scan Sonar (SSS), is a useful tool for marine conservation and management, as well as to support zoning processes of maritime activities in the coastal environment. Georeferenced habitat maps can improve management of isolated tropical coastal and marine ecosystems, where rapid unsustainable anthropogenic coastal development often occurs. In this study, SSS was employed to map subtidal marine habitats of Principe Island (Gulf of Guinea, West Africa) to determine areas of especial interest for biodiversity or marine resource conservation. The SSS methodology was applied, during the BIO-Principe Scientific Expedition (2016), in four target areas, both inside and outside its UNESCO Biosphere Reserve, covering 675 ha between 3 and 30 m depth, also combining SCUBA diving and video transects. These areas were chosen based on their geographical location and habitat information, provided by the local stakeholders. Over the total surface mapped, five main habitats were recorded: sandy seabeds (flat sandbanks and rippled sandbanks), rhodolith seabeds (rhodoliths interspersed with scleractinian coral colonies and macroalgae), biogenic (mud/sedimentary) seabeds, and rocky seabed (bedrock and rocky reefs). In the northern, eastern, and southern areas of the island, sandy bottoms with ripples, interspersed with small biogenic sedimentary beds and rhodolith bottoms predominated. The southwestern area, Baia das Agulhas, concentrated the greatest variability and richness of habitats, including the largest rhodolith seascape. This study provided a consistent and detailed dataset to support the creation and design of future MPAs, already planned by the Principe's government, adding including essential information on areas containing key habitats (e.g. rhodoliths) not detected in previous reports.