Distribution and composition of seafloor litter and associated macrofouling organisms in the Northeastern Mediterranean Sea

Assessing marine litter and its ecological impact on the seafloor of Thermaikos Gulf (NE Mediterranean Sea, Greece): Insights from ROV and diver surveys

This study investigates marine litter and its ecological impacts on the seafloor of the Thermaikos Gulf (NE Mediterranean Sea, Greece) for the first time, using data from 40 ROV dives (15-90 m depth) carried out between 2020 and 2024, and 11 scuba dives (0-5 m depth) conducted primarily at fishing ports during the same period. Plastics dominated the litter composition (80 %), with fishing-related activities contributing to 65 % of the litter at depths from 15 to 90 m, while single-use plastics comprised 46 % of the litter at nearshore locations. ROV surveys revealed litter densities decreased with depth and were likely influenced by water circulation patterns and human activities, particularly fishing. Shallow waters exhibited 50 times higher densities, highlighting the severe accumulation of litter in nearshore areas, particularly in ports. Benthic animals observed in ROV footage were identified, and their abundance was recorded, providing insights into the ecosystem's exposure to litter. Moreover, documented faunal interactions, including ghost fishing, entanglement, colonization, and the use of litter for shelter, highlight the ecological threats posed by marine litter. These findings surpass established Mediterranean litter density thresholds for the seafloor, underscoring the urgent need for stricter waste management at ports and offshore, stronger enforcement of EU directives, and targeted educational campaigns. This research establishes benchmark levels for setting environmental objectives under the Marine Strategy Framework Directive and for conducting targeted research to address litter pollution in the Thermaikos Gulf and similar coastal regions.

Eukaryotic phototrophs of the plastisphere in the Southeastern Black Sea

Plastics, as artificial substrates in water, are rapidly colonized by microorganisms, forming the plastisphere. Eukaryotic phototrophs of the plastisphere were studied on 46 seafloor plastic samples, representing 11 polymer types, in the Southeast Black Sea during March and July 2022. The plastisphere included 55 species from Heterokontophyta phylum (incl. Coscinodiscophycea (4), Mediophyceae (3), Bacillariophyceae (45), Dictyophyceae (1)), and Haptophyta (1). Common species were Bacillaria paxillifera, Tabularia parva, Cocconeis scutellum, and Licmophora flabellata. Octactis speculum and Emiliana huxleyi were newly reported for the plastisphere, and Thalassiosira curviseriata was recorded for the first time in the Black Sea. Two potentially harmful algae and five bloom-forming species were identified. Shannon Diversity Index values ranged from 0 to 2.9, with the highest diversity on PE/PVA and PES samples and the lowest on PE. Habitat preferences showed 34 species associated with plankton-benthic or benthic microalgae. PERMANOVA analysis revealed that polymer type explained 11.9 %-15.8 % of species composition variation. Transparent and black plastics hosted the most species, while multicolor plastics had the fewest. This study highlights that diverse microbial communities, particularly diatoms, colonize plastics in the Black Sea. Plastics can transport harmful species, posing ecological risks by disrupting benthic ecosystems, nutrient cycles, and ecosystem services like carbon storage and sediment stabilization. Our findings contribute understanding of the ecological and economic impacts of plastic debris at the seafloor.

The role of marine debris as a vector, dispersal agent, and substrate for non-indigenous species on Oceanic Islands (Northeast Atlantic)

Marine debris (MD) can be a transport vector for diverse marine communities, including non-indigenous species (NIS). This study assessed MD potential role as a substrate for colonization and dispersal vector for NIS in the Madeira Archipelago (NE Atlantic) by examining three MD categories: floating (FMD), seafloor (SMD), and beached (BMD). Opportunistic sampling, conducted in collaboration with local maritime stakeholders, documented MD sightings with photographs and GPS coordinates. A total of 92 MD items were inspected, revealing 108 fouling species across 11 phyla, with 13 % identified as NIS. SMD exhibited the highest proportion of NIS (9.6 %), followed by BMD (4.4 %) and FMD (3.9 %). Notably, the study provides evidence that FMD functions as both a substrate and a dispersal vector for NIS in Madeira waters. Combining biogeographic analyses, oceanographic modelling, and MD identification marks, this study highlighted the North Atlantic Subtropical Gyre's currents as key pathways, transporting MD items from the Wider Caribbean, the North American east coast, and the Iberian Peninsula to Madeira within 2-3 years. These findings emphasize Madeira's dual role as both a recipient and exporter of MD, with implications for NIS introductions and secondary spread. This study underscores the urgent need for standardized monitoring, stakeholder engagement, and proactive MD management strategies to mitigate NIS introductions and protect sensitive marine ecosystems like Macaronesia from the ecological risks of biological invasions.

Not only in the crowd: Benthic litter characterization in a low population density area still reveals widespread pollution and local malpractices

Various anthropogenic activities affect marine coastal habitats, leading to heavy litter pollution. However, whilst high litter concentrations are nowadays common in the proximity of metropolises, few studies investigated the magnitude of this phenomenon around coastal villages and small towns. We hereby characterized the benthic litter occurring in the trawlable grounds of the Gulf of Policastro (Tyrrhenian Sea, central-western Mediterranean), a low population density area that becomes a popular tourist destination during summer. We furthermore tested differences between two depths (∼100-200 and ∼500-600 m) and the impact of tourism on the shallower waters. The area was characterized by a litter abundance of 651.12 ± 130.61 item/km2, with plastic being almost totalitarian (93%). The shallower waters hosted two-thirds of the litter found. Almost all (∼95%) the litter items had a land-based origin, while the sea-based litter was mostly found at higher depths. About 14% of the litter was found to be fouled, with the development of litter-associated communities that somehow mimic the natural ones living on hard substrates. The higher litter presence noticed during the touristic peak (July-August) suggests that tourism is an important source of local litter, although it contributed to the local accumulation in a synergic way with other factors. The majority of the litter items presumably originated from the nearby coastline, while the deeper waters were or are used as a dumping site by the local trawling fleet. The discovery of such a critical waste accumulation and management in a somehow remote area contributes to widen the perspectives on the presence of benthic litter mostly in territories characterized by wide anthropization. Moreover, it confirms that appropriate local policies and communication plans are urged even at a regional level to stimulate citizen consciousness and mitigate the ever growing litter pollution.