The Srebarna Lake was designated as a Monument of World Cultural and Natural Heritage (1983), UNESCO biosphere reserve (1977), Ramsar site (1975) and Important Bird Area (1990) because of its extremely rich ornithofauna and mainly because of the breeding of globally threatened species Dalmatian Pelican (Pelecanus crispus), Pygmy Cormorant (Phalacrocorax pygmeus) and Ferruginous Duck (Aythya nyroca). During the last years the lake ecosystem underwent significant changes towards strong eutrophication and anthropogenically speeded-up succession. The main reasons were the interrupted connection with the Danube River (because of a dyke built in 1948) together with the pumping-out of the underground waters, as well as the agricultural changes and activities in the watershed basin. The restoration activities carried out in 1993-1994 and especially the canal which connected the lake with the Danube lead to the beginning of lake recovery. All these events influenced the biodiversity of the reserve. The dominant plant association is that of the Reed (Phragmites australis), which occupies about two-thirds (400 ha) of the Reserve's total surface area. Gray Willow (Salix cinerea) and Purple Willow (Salix purpurea) bushes grow in some places. The second widest spread plant species after the Reed is the Lesser Reedmace (Typha angustifolia), and it is more abundant than the Great Reedmace (Typha latifolia). Of all 139 vascular plant species hosted by the Reserve, 11 are rare or endangered. Some 19 fish species occurred in the lake until 1948. There are 21 reptile and amphibian species, and 41 mammal species. The avifauna numbered a total of 230 bird species. The nesting colony of Dalmatian Pelican (Pelecanus crispus) is the pearl of the Reserve.

The current distribution of Zostera spp. seagrass meadows along the Bulgarian Black Sea coast was studied. We used a combination of historical and recent observations of the habitat along the studied coastline. Remote sensing data (satellite images, sonar side-scans) was groundtruthed with georeferenced drop camera observations, scuba diving sampling and georeferenced scuba diving photo and video transects.

We provide long-term data for the water level of Srebarna Lake (2010-2020).

Long-term monitoring of chlorophyll-a, ammonium, dissolved total nitrogen, nitrate, nitrite and phosphate concentrations in the water column at Sozopol, Bulgaria (2013-2021).

Abundance (individuals/m2) and biomass (g/m2) of macrozoobenthic taxa at soft-bottom stations along the Southern Bulgarian Black Sea coast (Burgas Bay), collected during field surveys of IBER-BAS in 2013-2014 as part of project PERSEUS. The dataset also contains measurements of several environmental parameters at the stations: sediment grain size (% gravel, sand, and silt/clay); sediment moisture content (%) and total organic matter (% loss on ignition); temperature, salinity and dissolved oxygen in the water column and near the bottom.

Long-term data for the number of breeding pairs of Dalamatian Pelican, Pelecanus crispus for the period 1955-2020 in Srebarna Lake.

Monitoring of chlorophyll-a, ammonium, dissolved total nitrogen, nitrate, nitrite and phosphate concentrations in the water column in Burgas Bay, Bulgaria (2009-2011).

Abundance (individuals/m2) and biomass (g/m2) of macrozoobenthic taxa from seagrass meadows along the Southern Bulgarian Black Sea coast (Burgas Bay), collected during field surveys of IBER-BAS in 2013-2014 as part of project PERSEUS. Due to the sampling method (hand corer), the dataset represents the infauna associated with the seagrasses. The dataset also contains measurements of several environmental parameters at the stations: sediment grain size (% gravel, sand, and silt/clay); sediment moisture content (%) and total organic matter (% loss on ignition); temperature and salinity of the water.

Soft bottom and hard bottom habitats within the BB0000146 'Gradina-Zlatna ribka' SCI area. Mapped and created by IBER-BAS within the BalkanMed RECONNECT project (2017-2020).

Daily total precipitation (sum) data series from 2003 to 2013 for the Bulgarian LTER site Belasitsa