## 1 Introduction  
The Black Sea, which is nearly entirely isolated from the rest of the world's oceans and contains an abyssal basin with a maximum depth of 2300 m next to a large continental shelf area, notably in the north-western half, is one of the most amazing regional seas. Under the effect of fresh water supplied by large rivers, of which the Danube has the greatest influence, and the entrance of Mediterranean water through the Bosphorus and Dardanelles Stratis, the Black Sea waters are permanently stratified [1]. Its size and geographical, geological, and ecological peculiarities render the Black Sea the character of a Large Marine Ecosystem (LME) [2]. When compared to the Mediterranean, it exhibits distinct physical, chemical, and ecological properties [3]. In this exceptional ecosystem, life is supported by a 100 m upper layer of lighter marine water with lower salinity and density. A pycnocline divides this layer from the deeper, more dense layers of water, which are saturated with hydrogen sulfide and result in permanent anoxic conditions between 100 and 200 m depth [4]. The coastline and shelf zones of the Black Sea comprise a mosaic of intricate, interconnected ecosystems with significant economic value, abundant natural resources and ecological communities, and a high concentration of human activity [5, 6]. The biodiversity of the Black Sea is approximately three times lower than that of the Mediterranean due to the difficult oceanographic circumstances [7], and its unique characteristics (oceanography, location, and climate) render it extremely vulnerable to disruptions of its habitats and ecosystems [8]. An area of particular interest in the north-western part is the Marine Zone of the Danube Delta Biosphere Reserve, a Marine Protected Area (MPA) declared under the Habitats Directive (ROSCI0066). The MPA has its own administration, who elaborated in the past a Management Plan and related Regulations, both currently undergoing a revision process. However, regarding beam trawling, none of the mentioned documents regulates this activity in the extended area (beyond 20 m), this being one of the rationales for performing this study. The Black Sea habitats off the Danube Delta experience constant change in conditions brought on by the Danube's inputs and anthropogenic influence, just as the species. The salinity, temperature, transparency, and nutrient content of coastal waters are all impacted by freshwater supplies that are transferred south. Due to the muddy substrata, the Danube's plume area really forms a circaltitoral phonomic zone (even at depths less than 20 m), which is known as the boundary between the infralittoral and circaltitoral zones [9; 10]. Since the 1960s, when researchers first described the communities of _Lentidium_ in the infralittoral and _Spisula-Syndesmia_ (_Abra nitida_)-_Cardium_ (_Acanthocaria paucicostata_), as well as the community of _Mytiilus_ for the circaltitoral unit, the benthic communities in front of the Danube Delta have been thoroughly studied [11; 12]. Later, [PERSON] [13; 14] describes a new community formed by the leading species _Melima palmata_, which we still meet today in extensive areas in the studied area [9]. The Danube inputs and anthropogenic pressures continuously place stress on the benthic communities. These caused the Black Sea's environmental characteristics to deteriorate between 1970 and 1990. Thus, from the reference 1960-1970 period, when the benthic community numbered about 75 species, Tiganus [15] and Gomoiu [13; 16] recorded only about 45 species in the 1980s. At the beginning of the 2000s--a period of relaxation of anthropogenic pressures--the condition of the benthic communities experienced a slight improvement [9; 17; 18; 19]. At greater depths, the North-Western Black Sea shelf is of tremendous interest due to its singularity in terms of habitats--it shelters mussel beds on Pontic circaltitoral terrigenous muds, which form a unique biocoonosis: deep-sea black mussel biogenic reefs [20].