The current distribution of Zostera spp. seagrass meadows along the Bulgarian Black Sea coast was studied using a combination of historical and recent observations of the habitat along the studied coastline, confirmed by georeferenced drop camera observations, scuba diving sampling and georeferenced scuba diving photo and video transects. Once the presence of seagrass beds in a certain location was confirmed, the most recent and clearly visible satellite images available in the Google Earth Pro libraries were used for creating polygons of the actual outline and distribution of the studied Zostera meadows. In certain locations ( e.g. Sozopol Bay), these methods were combined with high resolution side scan mosaics, where the borders of the seagrass meadows were outlined based on the clearly visible differences in texture of vegetated and non-vegetated sediments. The actual ground truthing and mapping methods are marked in the attributive table of the database under the column ‘map_method’. The date of the in-situ observation is noted in the column ‘dive_date’, and the date of the satellite image/side scan used for the mapping is noted in the ‘Sat_date’ column. In total over the period of the whole study (2011-2020) a total of 1859 video and photo observations were filmed and analyzed, as well as 129 samples were collected and processed.

The total area of the habitat type classified in the EUNIS habitat types list ( 2019) as ‘MB548- Black sea seagrass meadows on lower infralittoral sands’ in the study area is 916.9 ha, of which only 17.9 ha are in man-made sheltered environments ( harbours). We have not mapped some some small seagrass meadows in Varna Bay and in the vicinity of the towns of Kavarna and Balchik, which may further increase the overall area of this habitat along the Bulgarian Black Sea coast.

Mapping done in the framework of the following research projects: ''Enlargement of the Natura 2000 ecological network within the Bulgarian Black Sea sector".Contract 7976/04.04.2011 between MoEW and IO-BAS" ; FP7 Perseus ; FP7 Coconet; BalkanMed Reconnect; FEMA-MARE; MSFD National monitoring program 2017;