Deep-sea marine litter from visual surveys: New findings from offshore Al Wajh, Red Sea (Saudi Arabia)

Marine litter poses a critical threat to ocean health, yet deep-sea benthic macrolitter (> 25 mm in diameter) is still quite underassessed, mostly because of logistical and financial constraints to carry out research with camera-equipped devices for ocean floor surveys in the high seas. Despite growing research efforts on this crucial topic, our knowledge of the spatial distribution of deep-sea litter is still highly uneven. We have, therefore, summarized available data from the literature for a first synoptic view, documenting that most such studies are related to European seas, North America, and the Western Pacific. We have added also newly acquired information from a sector of the Red Sea basin that only recently has been targeted for deep-sea macrolitter, in view of its rapid coastal development and increasing tourism driven by giga-scale initiatives. In late summer 2023, the seabed off Al Wajh (Saudi Arabia) was explored using a Remotely Operated Vehicle (ROV) during mission M193 aboard the R/V Meteor. Analysis of the data collected provides new insights into the distribution of deep-sea benthic macrolitter in the region. Consistent with previous observations, litter density was low, with plastic items being the only recorded anthropogenic debris. Distribution patterns appeared to be influenced by geomorphology and hydrography, with debris accumulating in submarine canyons and topographic depressions, aligning with global patterns of litter deposition in complex seabed environments. The observed macrolitter is likely linked to maritime traffic, supporting literature findings that identify international maritime activities as the primary source of deep-sea macrolitter in the western Red Sea, with local sources playing a subordinate role. Differentiating between endogenous and exogenous litter sources is crucial for designing effective mitigation strategies, and requires long-term monitoring efforts integrating litter composition analysis, hydrodynamic modeling, and waste management assessments. This study aims to contributes establishing a baseline for future assessments of deep-sea marine litter in the northern Saudi Arabian Red Sea as basis for policies that balance economic growth with marine conservation.