## 4 Discussion
### Impact of Beam Trawling on Benthic Habitats  
Bottom-trawl fishing, in general, and beam trawling, in particular, disturb benthic species and habitats and can reduce ecosystem biomass, production, and diversity [58]. Incomparison to communities in locations that are not exploited in this manner or are fished at low levels of effort, benthic communities in extensively fished areas using towed gears typically have lower biomass and productivity [59]. It has been established that intensive trawling typically causes major changes in the composition of the infauna, as well as losses in the infauna and epifauna's biomass [60]. The research carried out in the Danube Delta--Marine Zone shows that the benthic communities, despite the high variability of the natural conditions of the area, are well developed and play an important role in the area's bioeconomy, fully aligned with the purpose for which it was established as a protected area for migratory fishes' populations. In general, overfishing effects, by using any kind of trawling gears and especially in such an environment heavily impacted by a high input of sediments and nutrient enrichment, are difficult to detect, and selected habitats and communities thriving in the area are already adapted to have great ecological resilience for recovery. Still, the natural recovery is limited and depends on non-impacted adjacent healthy benthic communities, which can contribute by the larval dispersion of core engineering species. The analysis of the extent of trawl marks detected on the seabed raises doubts that the recovery can properly take place at the same parameters or change to other statuses/habitats as proven in other human activities on the Romanian coast [18]. The main habitat that confers to the area a unique status is represented by the mussel biogenic reefs on the muddy substrata (soft bottoms). Usually, the _Mytilus_ \"clumps\" are widely distributed in the study area, starting from the infralittoral up to the offshore circaltitoral biomomic zone [20; 21]. No such biogenic structures were found during the study period, except for a few solitary mussel individuals close to the outer deeper part of the trawling area (Station MN207/6-40) in the habitat of Circaltitoral mud dominated by _Melinna palmata_. The low number of taxa also suggests that the habitats are threatened and affected by constant physical disturbance. A number of 26 taxa recorded in the habitat of Circaltitoral mud with _Spisula_ and _Mytilus_ beds is extremely low, basically half of the potential biodiversity which can be supported by the habitat. More recent and denser beam trawl marks (finding also supported by VMS lines--Figure 3) are concentrated in the north-western area of the MPA, which corresponds to the lowest recorded number of taxa. Secondarily, eutrophication is another negative effect of intensive trawling through which water quality decreases in the area due to the excavation of nutrients trapped in the sediments and their relocation in the water mass. In our investigation, in the areas where intensive trawling was carried out, the community-level indicators of species richness (S), Shannon diversity (H\({}^{\prime}\)), total abundance (A), and biomass all decreased. Relevant references consulted showed that under intense trawling conditions the rates for the depletion of biota (density and biomass combined) have been estimated at \(\sim\)6% per pass of an otter trawl [61]. The efficacy of A as an indicator of trawling impacts in gradient studies has been demonstrated in a number of regions: the Irish Sea [62] and the Mediterranean [63]. Furthermore, total biomass has been shown to persistently decline in highly traveled areas [64], while AMBI and M-AMBI indicators were found to be unresponsive to trawling [65]. Despite this, in our study we observed a decrease in the values of the M-AMBI*(n) index with increasing trawling disturbance. However, we point out that we analyzed the available data from the area in order to obtain a first regional image of the potential impact that _R.