The expedition, conducted in the summer of 2025 aboard a research cruise funded by the Schmidt Ocean Institute, marked the first time scientists had captured images of the seafloor within the Mar del Plata Submarine Canyon. Using a remotely operated submersible, the team carried out seventeen dives into the canyon system, revealing a landscape teeming with life as well as litter. Among the discoveries were approximately forty species that may be new to science, a reminder of how little is known about deep-sea biodiversity even as human refuse arrives there. The same dives that documented unfamiliar organisms also recorded twenty-nine identifiably manmade objects across ten of the dives, a striking proportion for a habitat so far from any coastline.

The technical details of the debris survey are sobering. The vast majority of the objects were plastic, accompanied by a smaller number of rubber items. The catalog ranged from fishing gear to plastic bags, food wrappers, snack wrappers, a tissue paper wrapper, a nylon cord with a hook, a white plastic cup, and a rubber boot. Depth records for individual items read like a descent into the abyss: a plastic wrapper at 2,109 meters, a food wrapper at 1,920 meters, a snack wrapper at 3,231 meters, a sediment-filled plastic bag at 3,739 meters, a highly degraded plastic fragment at 3,709 meters, and a plastic cup and bag at 3,243 meters. The boot, resting at 2,598 meters, offered perhaps the most vivid illustration of how ordinary consumer items can end up kilometers beneath the waves.

Equally significant was the spatial pattern the researchers observed. Litter was more abundant inside the canyon than in the surrounding seafloor, suggesting that the canyon’s topography and the currents flowing through it act as a funnel, concentrating drifting debris into the fissure. Submarine canyons are known to channel sediments and organic material from the continental shelf into the deep ocean, and the new evidence indicates that buoyant and neutrally buoyant trash follows the same routes. Items were found in a variety of states: some were partially buried in sediment, others were trapped among rocks, and a few were still drifting, indicating that debris continues to arrive rather than representing only a legacy of past pollution.

The study also recorded how deep-sea animals interact with the waste, and the picture is more complicated than simple avoidance. Mobile creatures such as crustaceans showed transient interactions with the debris, passing over or briefly investigating the foreign objects. More sedentary organisms, including starfish and corals, were observed attached to some items, with plastic packaging and fishing ropes often partially subsumed by the animals growing on them. To a filter-feeding coral or an anchored starfish, a length of sunken rope may present a surface resembling the hard substrate that is otherwise scarce on soft sediment plains. The researchers cautioned, however, that these observations should not be mistaken for evidence that the debris provides suitable habitat. The long-term consequences of colonization on plastic in the deep sea remain unknown.

The discovery in the Mar del Plata Submarine Canyon is not an isolated case. Just a few months before this expedition, a plastic bag was found in the Mariana Trench, the deepest fissure on the planet, demonstrating that no ocean depth is beyond the reach of human waste. The sinking of organic material from the surface is essential to sustaining life in the darkness below, where sunlight never penetrates and food must arrive from above. The new study adds to emerging evidence that this vertical rain of nutrients is not the only matter being pulled to the ocean floor. Debris generated on land and at sea follows the same gravitational and oceanographic pathways, settling into the very environments that depend on the steady delivery of material from the surface ocean.

For the scientists involved, the expedition carried a profound emotional weight alongside its technical achievements. The authors reflected on the experience of exploration in the deep: “Unveiling a species previously unknown to science in the endless darkness of the deep sea may be one of the most extraordinary experiences a marine biologist can have.” That sense of wonder makes the presence of trash all the more jarring. The same dives that revealed organisms never before seen by human eyes also revealed the unmistakable fingerprints of consumer culture, from snack wrappers to plastic cups, resting among creatures that evolved over hundreds of millions of years without any contact with synthetic materials.

The research was a genuinely international effort, with authors from Argentina, Ecuador and the United States, and it was supported by a broad coalition of funders including the Schmidt Ocean Institute, the Nippon Foundation-Nekton Ocean Census Programme, the CORDAP Coral Accelerator Program, the AZARA Foundation, Argentina’s Agencia I+D+I and CONICET, and Fundación ProyectoSub. The expedition designation FKt250712 will likely be remembered as a milestone in the documentation of the southwestern Atlantic’s deep-sea environments. All images of the litter were captured by the ROV SuBastian and released under a Creative Commons license, allowing the public to see for themselves what lies nearly four kilometers beneath the surface of the Atlantic.

What emerges from the study is a revised mental map of human influence on the ocean. On average, the oceans are only a few miles deep, and as the researchers note, the sea floor is not as distant from human activity as it may seem. Every wrapper, bag and fragment of fishing gear that escapes into the sea has a destination, and increasingly that destination is the deep. The Mar del Plata Submarine Canyon, with its newly documented species and its accumulated debris, offers a preview of what awaits other unexplored canyon systems around the world. The findings underscore that protecting deep-sea ecosystems requires addressing plastic pollution at its sources, because once trash reaches these environments, monitoring it is difficult and removing it may be impossible with current technology.

The open access publication of the study in PLOS One ensures that the evidence is freely available to researchers, policymakers and the public alike. As deep-sea exploration technology becomes more accessible and remotely operated vehicles descend into more canyons, trenches and abyssal plains, scientists expect that similar discoveries will follow. The deep ocean, it turns out, is not a separate world insulated from the one above. It is connected by currents, by sinking particles, and now demonstrably by our garbage. The question raised by the Mar del Plata survey is not whether human debris can reach the deepest corners of the sea, but how much is already there, unseen, in the darkness waiting to be explored.

Subject of Research: Marine litter accumulation in the deep-sea Mar del Plata Submarine Canyon

Article Title: The depths of the ocean aren’t immune to human debris

Article References: The depths of the ocean aren’t immune to human debris. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: deep sea, marine litter, plastic pollution, submarine canyon, ROV survey, PLOS One, southwestern Atlantic, biodiversity, Mariana Trench, ocean currents, deep-sea ecosystems, Argentina

Mesophotic ecosystems occupy the dimly lit zone of the ocean, roughly between 30 and 150 meters in many subtropical regions, where light is too scarce for most photosynthetic reef builders but where life still flourishes in remarkable abundance. In many oceanic archipelagos, these communities are dominated by black corals of the order Antipatharia, a group of more than 300 species characterized by proteinaceous skeletons, an almost universal lack of symbiotic algae, slow growth and long lifespans. Whip black corals are a distinctive form within this group: they grow as a single unbranched stem that can extend several meters in length, spiraling and swaying in areas of strong current. Where they aggregate in high densities, they form what ecologists call Marine Animal Forests, three-dimensional structures built by suspension-feeding animals that alter water flow, trap sediments, generate shade and create an architectural complexity comparable to that of terrestrial forests.

These animal forests are far more than scenic curiosities. Scientists regard them as biodiversity hotspots, nursery grounds and refugia for a vast array of associated species, from crustaceans to fish, and as key regulators of biogeochemical cycling in the sediments beneath their canopies. Yet because mesophotic depths require expensive equipment to explore, black coral forests remain among the least studied and least protected ecosystems on the planet. The new research, conducted as part of the Ocean Citizen project, a marine restoration initiative funded through Horizon Europe, set out to map benthic habitats along a stretch of Tenerife’s rocky coastline between La Arena and the southern end of San Juan Beach, and in doing so captured an unexpected ecological relationship on camera.

Between June 16 and 25, 2024, the research team, which included scientists from the University of Salento in Italy and the non-profit organization Oceana, deployed a remotely operated vehicle to survey the seabed. The vehicle, a Sibiu Pro model from Nido Robotics rated to 300 meters, was equipped with 4K cameras, LED lights and eight thrusters. It crawled along the bottom at an average speed of just 0.2 to 0.3 knots, its camera field of view spanning roughly 185 centimeters. Of 61 planned dives, 55 were completed, covering a total surveyed area of 31,217 square meters at depths ranging from 7 to 157 meters. The resulting footage was cut into 1,502 one-minute sample units, yielding 26 hours of analyzable video from which the team identified 169 distinct taxa.

The statistical analysis revealed a striking pattern. The bearded fireworm co-occurred with whip coral forests in 40 percent of the transects, appearing in the algae at the base of the black corals or in their immediate vicinity. Peak abundances of both the fireworm and the two whip coral species studied, Stichopathes gracilis and Stichopathes setacea, fell between 80 and 120 meters depth. Pearson correlation analysis confirmed that the association was not coincidental: the relationship between fireworm occurrence and S. gracilis produced a correlation coefficient of 0.895 with a p-value of 0.0027, a strong and statistically significant positive association, while the relationship with S. setacea yielded a coefficient of 0.715 with a p-value of 0.0464, also significant. All three species showed unimodal distributions across depth, peaking in the 80 to 100 meter range, with polynomial trendlines suggesting a partial overlap of their ecological niches.

Understanding why a fireworm would seek out a black coral forest requires appreciating the peculiar biology of both partners. Hermodice carunculata is a large amphinomid polychaete armed with brittle, venom-filled bristles that deliver painful stings to anything that handles it. It is an omnivorous, opportunistic feeder and scavenger, consuming decaying organic matter, and preying on corals, sea urchins, sponges and ascidians. It can also act as a reservoir for coral pathogens. Crucially, it is thermophilic and highly tolerant of environmental variation, coping with swings in temperature, salinity and oxygen. As ocean waters warm, the species has been expanding northward through the Atlantic and the Mediterranean, attacking fish caught in nets, degrading catch quality and injuring fishers, swimmers and divers. In shallow water it favors structurally complex habitats, hiding in rock cavities and algal canopies to evade predators and reduce exposure to current and light.

The whip corals, meanwhile, are ecosystem engineers of a very particular kind. Antipatharians require strong currents to feed, extending their polyp-covered stems into the flow to capture passing particles. Those same currents that sustain the forest also create a hostile hydrodynamic environment for a soft-bodied worm. The study’s authors propose a dual function for the forest: the whip corals are a product of strong currents, yet their dense stems and algal understory simultaneously provide shelter from the current’s sheer force. At the base of the corals, accumulated algae offer both refuge and a foraging ground rich in decaying organic matter, precisely the kind of organically enriched, microbially active habitat to which fireworms are known to be attracted. In essence, the fireworm appears to exploit a contradiction engineered by the corals themselves, benefiting from the very conditions that made the forest possible while escaping the conditions that make it formidable.

Perhaps the most consequential observation is what the researchers did not see. In all the analyzed video, fireworms were detected only at the base of the coral colonies, never climbing the stems. No feeding or predation behavior against the whip corals was recorded, and the coral populations appeared healthy, with no signs of damage or necrosis, despite their high density throughout the study area. This stands in contrast to recent reports of fireworms actively feeding on branching black coral colonies, concentrating on the colony tips. The evidence from Tenerife instead suggests a commensal or opportunistic relationship, in which the fireworm uses the forest as shelter and a feeding ground on associated algae and detritus rather than as prey, although the authors caution that the possibility of occasional coral consumption cannot be ruled out without further observation.

The finding carries implications well beyond the natural history of a single worm. The detection of H. carunculata at mesophotic depths extends its known vertical distribution, echoing a similar recent discovery in the same study area in which the green alga Caulerpa prolifera was recorded down to 80 meters, far deeper than previously acknowledged. As climate change pushes thermophilic, adaptable species into new depths and latitudes, understanding which habitats will harbor them, and whether vulnerable ecosystem engineers such as black corals will face new pressures, becomes a matter of urgency. Black corals are already listed in Appendix II of CITES, which regulates their international trade, and are used as indicator species for ecosystem vulnerability by regional fishery management organizations.

The authors argue that expanding knowledge of these deep, dim ecosystems is essential for conservation and for effective monitoring guidelines. Marine Animal Forests are among the most extensively distributed ecosystems on Earth, spanning from shallow mussel beds to deep cold-water coral habitats in both tropical and polar seas, yet the mesophotic black coral forests remain largely unmapped and unprotected. Determining the foraging advantages, potential risks and patterns of association between vagile species like the fireworm and the ecosystem engineers that structure these communities is, the study concludes, a necessary step toward safeguarding them. For now, the image of a venomous worm coiled in the algal shadows at the foot of a swaying black coral whip serves as a reminder that the ocean’s twilight zone is neither empty nor simple, and that its most surprising residents are only now coming into view.

Subject of Research: Co-occurrence of the bearded fireworm Hermodice carunculata with whip black coral forests in mesophotic ecosystems off Tenerife, Spain

Article Title: Co-occurrence of Hermodice carunculata (Polychaeta, Annelida) and Stichopathes spp. (Hexacorallia, Cnidaria) off Punta Blanca (SW Tenerife, Spain)

Article References: Fraissinet, S., Aguilar, R., Blanco, J., Arduini, D., Anglano, M., & Rossi, S. (2026). Co-occurrence of Hermodice carunculata (Polychaeta, Annelida) and Stichopathes spp. (Hexacorallia, Cnidaria) off Punta Blanca (SW Tenerife, Spain). Discover Conservation, 3(1), Article 23. https://doi.org/10.1007/s44353-026-00092-0

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00092-0

Keywords: Hermodice carunculata, bearded fireworm, Stichopathes, black corals, mesophotic ecosystems, Marine Animal Forests, Tenerife, Canary Islands, ROV survey, biodiversity hotspots, ecosystem engineers, climate change