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The threat of anthropogenic marine litter, particularly plastic pollution, to marine ecosystems and human health, has spurred mitigation initiatives and global scientific research. Following the Marine Strategy Framework Directive guidelines, this study evaluated marine litter distribution, cleanliness, and plastic pollution indices along Bulgarian Black Sea beaches in 2023. The survey integrates visual assessment, manual sampling, and drone mapping, distributing the beaches along the coastline to encompass a broader range, totaling 45, including 28 remote/natural, 10 semi-urban, and 7 urban beaches. Results indicate a 48% decrease in marine litter distribution on beaches from 1462 ± 147 items/100 m in 2021 to 753 ± 97 items/100 m in 2023, with Artificial polymer materials/plastic materials constituting 88.62% of the total litter amount. A comprehensive plastic macro litter pollution assessment was carried out along Bulgarian beaches using PAI for the first time. In 2023, the average cleanliness status of Bulgarian beaches was classified as "moderate" (CCI: 7.61 ± 1.00), with clean northern and central beaches contrasting with dirty southern beaches. Urbanized beaches were assessed with the highest level of pollution (PAIAV,23: 5.51; CCIAV,23: 18.16). In the long term, cleanliness and plastic pollution maintain "moderate" values with CCIAV,18-23: 8.81 ± 0.89, and PAIAV,18-23: 2.35 ± 0.32, persisting throughout the period, necessitating ongoing monitoring and intervention strategies. Despite identifying a significant number of clean beaches, none meet the EU threshold value of 20 litter items/100 m. This study highlights the urgent need for effective interventions to combat litter accumulation and plastic pollution, particularly in urban or semi-urban beaches, emphasizing multi-stakeholder collaboration for sustainable solutions and coastal ecosystem preservation. [ABSTRACT FROM AUTHOR]

Coastal sand dunes are amongst the world’s most sensitive and dynamic landforms. Unfortunately, during the last thirty years, heavy anthropogenic alterations have been observed, encompassing the greater part of the Bulgarian Black Sea coast (BBSC), which has changed the land-sea interactions significantly. As a consequence, the depositional coast has shrunk to 131 km or 25% of the aggregate Bulgarian Black Sea shoreline length. Although our research reveals that 86% of BBSC dunes are included in the Natura 2000 network of protected sites established under the Habitats Directive (Council Directive 92/43/EEC 1992), they are often heavily modified, subjected to environmental vandalism and destroyed due to mismanagement or lack of accurate information and prevention. These facts were the main reason for carrying out an inventory of the Bulgarian Black Sea coastal dune systems in 2021-2022. Our research aimed to identify all dune systems/ sand dunes, update their spatial distribution and classify the observed coastal sand dunes landforms along the BBSC. The article demonstrates a successful methodology for combining unmanned aerial systems (UAS), Structure-from-Motion (SfM) photogrammetry, in situ sediment sampling, video imaging and verification and GNSS-RTK ground control points for coastal mapping. As of June 2022, over 97% of the Bulgarian shoreline has been surveyed with this technique, excluding military areas and national security sites. Based on the acquired data, as of 2021, the shoreline length was estimated to be 518.7 km at a scale 1:5000. The integrated UAS approach includes using Digital surface models (DSM), raster orthophotomosaics (OM) and 3D models, based on SfM photogrammetry to analyse the coastal topography, detect dune forms and update their spatial distribution. Throughout the inventory, 46 beach-dune systems were identified along the BBSC, which were divided into 62 dune sectors. The area of coastal dune systems was estimated at 988.21 ha (0.0089% of Bulgaria) and a total length of 73 km (14% of the shoreline). A comprehensive geomorphological analysis of the relationships between landforms morphology, aeolian and morphodynamic processes, vegetation density and type was the basis for the coastal dune landforms (CDLs) or dune systems to be classified into primary (312 ha; 32%) and secondary (676 ha; 68%). Additionally, the CDLs were classified according to Natura 2000 habitats: fixed (grey) dunes (546.27 ha; 55.28%), wooded dunes (222.61 ha; 22.53%), shifting (white) dunes (150.30 ha; 15.21%), embryonic dunes (68.3 ha; 6.91%) and humid dune slacks (0.94 ha; 0.09%). The highest positioned CDLs on the Balkan Peninsula were registered at perched Sozopol Sand Dunes (61 m a.s.l.) and cliff-top dunes at Arkutino (50.2 m a.s.l.). The multi-temporal analysis of photogrammetric DSMs and raster OMs showed the permanent loss of five dune systems in the Pomorie-Burgas-Rosenets coastal sector. The accrued UAS data approach allowed us to identify and map eight dune systems for the first time: Zlatni Pyasatsi (Panorama), Asparuhovo (Varna), Byala, Atanasovska Kosa, Central Beach (Burgas), Chernomorets, Kavatsite (partly) and Rezovo-Kastrich. A high anthropogenic footprint was registered on 50.7 ha (5.1%) of the entire dune surface. In the final stage of the study, human interventions that caused degradation and permanent loss of dunes (12 ha) over the last 15 years along the BBSC were shown. The main causes for dune degradation along BBSC have been documented, such as massive tourism development after the socialist period, road construction, recreational pressure exerted on the dunes, human trampling, lack of designated footpaths in areas with fixed and mobile dunes, off-road vehicles and parking lots (especially at camping sites), dumping of garbage and anthropogenic marine litter on the sand dunes etc. [ABSTRACT FROM AUTHOR]

Beach-dune systems are among the most dynamic and sensitive elements of coastal ecosystems in the world. They represent an intersection between human activities, flora, fauna and economic interests in tourism. The Bulgarian Black Sea shoreline spans 518.7 km and comprises 131 km (25%) of the depositional coast, including beaches and 46 dune systems. Over the past three decades, heavy anthropogenic impacts have been observed, significantly altering the cleanliness of the beach-dune systems along the Bulgarian Black Sea Coast (BBSC). The research initially began as an initial assessment of macrolitter on dunes (MLD) using Unmanned Aerial Systems (UAS). However, due to concerning data obtained in the first year, it transitioned into a mid-term monitoring program conducted between 2018 and 2022. The baseline assessment is based on a visual census, UAS mapping and manual image screening procedure in a GIS environment for litter mapping in 40 areas of litter monitoring (ALMs) along the Bulgarian Coast. Throughout the five-year monitoring period, the most abundant type of MLD was “Artificial polymer materials,” accounting for 83.4% of the total number, followed by “Paper/ Cardboard” (6.2%), “Glass/Ceramics” (2.8%), “Metal” (2.8%), “Processed/Worked wood” (1.83%), “Rubber” (1.29%), and “Cloth/Textile” (1.17%). Generally, 95% of the total litter amount was assessed from Land-based sources and 5% from Sea-based sources. The COVID-19 pandemic indirectly affected the cleanliness of the Bulgarian dunes due to restrictions on foreign travel, which increased the domestic tourist pressure on the Bulgarian beaches, resulting in a more significant amount of waste accumulating on the beaches and dunes. The abundance experienced an increase of 39% between 2018 and 2021. A similar upward trend (+41%) was observed in the density of macro-litter on the dunes. Based on visual census data, the average density was estimated to be 0.54 ± 0.35 items/m². The spatial distribution of MLD is a complex combination of anthropogenic impact and wind processes that affect various eco-geomorphological elements of the beach-dune system. The embryonic dunes retained only 16% of the total items (Dav: 0.32 ± 0.12 items/m²). The highest litter density was registered on the foredunes (Dav: 0.71 ± 0.21 items/m²; 28% of total items). The backdunes contained the highest litter abundance, accounting for 55% in larger areas (Dav:0.59 items/m²). Density litter maps established that dune vegetation acted as a natural trap, retaining 40% more macrolitter compared to areas without dune plants. A Clean Dune Index (CDI) was developed to evaluate the cleanliness of Bulgarian dunes. Based on aggregated CDI data for 2018–2022, the cleanliness of the dunes along the Bulgarian Coast was categorised as “moderate” (CDIav:10.89). Dune systems near the most visited resorts were classified as “extremely dirty”, with the highest CDI values recorded at Kavatsite (27.22), Nessebar – South (25.01), Bolata (24.69), Asparuhovo - Varna (24.33) and Slanchev bryag (24.09). On the other hand, the dune systems at Ropotamo and Lipite were rated with the lowest CDI – 0.95 and 1.2. Dunes are sensitive habitats and require minimal anthropogenic impact, which requires the intensification of the use of high-resolution remote sensing methods for litter mapping. The quality of the presented data and the results obtained outline drones as a future primary tool for beach and dune surveys. [ABSTRACT FROM AUTHOR]

In 2021, an abundant adult population of Flexopecten glaber was found in the Bulgarian Black Sea waters for the first time since the 1960s. The study provides original information on the distribution, habitat preference and population characteristics: size and age structure, growth coefficients, mortality, condition index and meat yield. The remarkable recovery and expansion of F. glaber is explained with the Black Sea recovery from eutrophication, reduced predatory pressure from the declining population of Rapana venosa and changing climatic conditions. The perspectives for the development of a new type of shellfish mariculture in the Bulgarian Black Sea waters are discussed. [ABSTRACT FROM AUTHOR]

European coasts suffer notably from hazards caused by low-probability and high-impact hydrometeorological events. The aim of the study is to assess in probabilistic terms the magnitude of storm‐induced flooding hazard along Varna regional coast (Bulgaria, western Black Sea) and to identify susceptible coastal sectors (hotspots). The study is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows estimation of relevant hazard intensities, extents and potential receptors’ exposure vulnerability within predefined sectors. Total water level was the chief property considered for calculation of coastal flooding hazard. It was estimated using Holman model (for sandy beaches) and EurOtop formulation (for artificial or rocky slopes). Resulting values were subjected to Extreme Value Analysis to establish that the best fitting distribution corresponds to Generalized Extreme Value distribution. Furthermore, hazard extents were modelled by means of bathtubbing or overwash estimation in order to form the flooding hazard indicator. Land use, social vulnerability, transport systems, utilities and business settings were considered as exposure indicators. Finally, potential risk was assessed by coastal indices following an index-based methodology, which combines hazard and exposure indicators into a single index, thereby providing base for comparison of coastal sectors’ vulnerability. The study found that the concentration of hotspots is highest in Varna Bay.

The study is aimed to demonstrate the relationships between the fecundity, length, weight and age of Chelon auratus and Chelon saliens from the Bulgarian Black Sea coast. Absolute fecundity of Ch. auratus varied from 327126 oocytes for age 3 (L-16.0 cm, EW-55 g) to a maximum of 4103879 for age 9 (L-32.4 cm, EW-321g). For Ch. saliens, absolute fecundity varied from 162890 oocytes for age 2 (L-16.9 cm, EW-52 g) to a maximum of 892441 oocytes for age 6 (L-33.7 cm, EW- 315 g). The mean estimated fecundity was 213642 eggs for Ch. auratus and 54882 eggs for Ch. saliens. Relationship between absolute fecundity-weight, fecundity-length was best fitted by the following equations: Ch. auratus - F=9476+10241*W, r2=0.921 and F=-2384206+152333*L, r2=0.906; Ch. saliens: F=215473+1698.7*W, r2=0.916 and F=-457777+36837*L, r2=0.924. The relationship between fecundity and age was best described by the exponential equation: Ch. auratus - F=106354e1.5475, r2=0.969 and Ch. saliens - F=103041e1.1264, r2=0.994. The average weighted relative fecundity was calculated as 492 for Ch. auratus and 272 for Ch. saliens. A more accurate indicator to describe the relative fecundity is the coefficient b from the equation F=a+b*W. For Ch. auratus the coefficient b was 10241, and for Ch. saliens was 1698. [ABSTRACT FROM AUTHOR]

The study is aimed to investigate the dynamics of age distribution, size structure and annual growth rates of Mugil cephalus from the Bay of Burgas. The species inhabits inshore marine waters, as well as estuaries, lagoons and rivers and has high economic importance. Only four age groups were determined for the recent period (2015-2018), compared to the previous period (2010 - 2013) when the flathead grey mullet population has eight age groups. For the period 2010-2013, the size classes ranged from 3.1 cm to 49 cm. For the period 2015-2018, the maximum total length registered was 27 cm. The equation describing the relationship between the length of the body and the radius of the scale is L=0.4177S + 0.376, r²=0.9769. The von Bertalanffy's equation for length growth of the flathead mullet is Lt=139.8[1-e-0.04(t+0.07)], r²=0.9996 and for the weight growth is Wt = 3139[1-e-0.1723 (t-0.372)]30654, r²=0.9328. The equation describing the length-weight relationship of Mugil cephalus is W=0.0122*L3.0961, r²=0.991. Values of Fulton's condition index for the age groups from 1 to 4 varied between 1.54 and 1.82. Comparison between the results obtained for the periods 2010-2013 and 2015-2018 shows deterioration of the population of the flathead grey mullet in the surveyed area. [ABSTRACT FROM AUTHOR]