Even creatures at the bottom of the ocean aren’t sheltered from the detritus of human civilization. Underwater surveys conducted at dozens of sites in the northeast Atlantic and Acrtic oceans and the Mediterranean Sea found fishing gear, plastic, metal, glass and other bits of garbage in shallow and deep waters both near and close to shore. 
 
 The research, led by Christopher Pham of the University of the Azores in Portugal, was published today in PLOS ONE. Similar studies have documented trash lining the seafloor in other areas, such as Monterey Canyon off California and the more than 7000-meter-deep Ryukyu trench off the coast of Japan [PDF]. Our trash is everywhere. 
 
 Around 14 billion pounds of litter makes its way into the world’s oceans every year. Some is created when fishing gear is lost. More comes when our trash washes off streets and down through waterways to the sea. Whole containers of goods may be swept overboard from the numerous ships plying the waves. And plenty of trash was deliberately dumped from barges and ships (a practice only recently banned by international convention). 
 
 The trash that floats on top of the ocean—often in great garbage patches at the center of gyres—or that washes onto beaches is most visible and gets the most attention. But plenty of it ends up on the seafloor. It’s just harder to see. 
 
 “The large quantities of litter reaching the deep ocean floor is a major issue worldwide, yet little is known about its sources, patterns of distribution, abundance and, particularly, impacts on the habitats and associated fauna,” Pham and colleagues write. 
 
 Pham’s team collected data from surveys at 32 underwater sites in the northeast Atlantic and Acrtic oceans and the Mediterranean Sea that took place between 1999 and 2011. These surveys either trawled the seafloor or sent down still and/or video cameras to image what was on the ocean bottom. The surveyed sites were located near as well as thousands of kilometers from shore, at depths of 35 to 4,500 meters, and were located on continental shelves and slopes, ocean ridges, banks, mounds and seamounts and within submarine canyons and deep basins. 
 
 Not one site was free of human garbage. 
 
 The surveys turned up trash along the mid-Atlantic ridge, 2,000 kilometers from shore. It was found in the shallowest waters as well as the deepest. Actually, the deepest areas, such as the Lisbon and Blanes canyons, had the highest densities of garbage, the researchers calculated. 
 
 “Such records were not surprising,” Pham’s team noted in their paper, “as litter is known to be present in all seas and oceans of the planet, as remote as the Southern Ocean and at depths as deep as 7,216 m in the Ryuku trench, south of Japan.” 
 
 The most common items were the ubiquitous plastic bags now banned in some cities. There were also glass bottles, fishing lines and nets, wood, cardboard, bits of clothing, pottery and a material called clinker. Clinker is the residue of burnt coal, and it was common in the late 18th to 20th centuries for steam ships to dump this waste material overboard, so most of this type of trash is more than 100 years old. 
 
 The abundance of plastic might be a surprise for some as plastic floats. But about 70 percent of it eventually sinks to the seafloor, the researchers note. 
 
 Abandoned, derelict fishing lines and nets were most often found in areas such as seamounts and banks that host dense communities of fish and shellfish. Those are the regions, of course, where fishing vessels are most likely to ply their trade. 
 
 Scientists are still figuring out the global patterns of distribution of all this garbage. But they do know quite a lot about its effects on marine life. Some organisms eat the trash, thinking its food. Others—especially turtles, marine mammals and birds—get entangled in it, and sometimes die. Fish get caught up in drifting nets, in what’s known as “ghost fishing.” And chemicals such as dioxins get consumed by small organisms and concentrated in organisms further up the food web, where these poisons can reach lethal levels. 
 
 This has to make us wonder: Is there any pristine place left on Earth? ||||| Abstract Anthropogenic litter is present in all marine habitats, from beaches to the most remote points in the oceans. On the seafloor, marine litter, particularly plastic, can accumulate in high densities with deleterious consequences for its inhabitants. Yet, because of the high cost involved with sampling the seafloor, no large-scale assessment of distribution patterns was available to date. Here, we present data on litter distribution and density collected during 588 video and trawl surveys across 32 sites in European waters. We found litter to be present in the deepest areas and at locations as remote from land as the Charlie-Gibbs Fracture Zone across the Mid-Atlantic Ridge. The highest litter density occurs in submarine canyons, whilst the lowest density can be found on continental shelves and on ocean ridges. Plastic was the most prevalent litter item found on the seafloor. Litter from fishing activities (derelict fishing lines and nets) was particularly common on seamounts, banks, mounds and ocean ridges. Our results highlight the extent of the problem and the need for action to prevent increasing accumulation of litter in marine environments. 
 
 Citation: Pham CK, Ramirez-Llodra E, Alt CHS, Amaro T, Bergmann M, et al. (2014) Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins. PLoS ONE 9(4): e95839. doi:10.1371/journal.pone.0095839 Editor: Andrew Davies, Bangor University, United Kingdom Received: August 23, 2013; Accepted: March 31, 2014; Published: April 30, 2014 Copyright: © 2014 Pham et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was supported by the European Community's Seventh Framework Programme (FP7/2007∧2013) under the HERMIONE project, Grant agreement (GA) no. 226354. The authors would like to acknowledge further funds from the Condor project (supported by a grant from Iceland, Liechtenstein, Norway through the EEA Financial Mechanism (PT0040/2008)), Corazon (FCT/PTDC/MAR/72169/2006; COMPETE/QREN), CoralFISH (FP7 ENV/2007/1/21314 4), EC funded PERSEUS project (GA no. 287600), the ESF project BIOFUN (CTM2007-28739-E), the Spanish projects PROMETEO (CTM2007-66316-C02/MAR) and DOS MARES (CTM2010-21810-C03-01), la Caixa grant "Oasis del Mar", the Generalitat de Catalunya grant to excellence research group number 2009 SGR 1305, UK's Natural Environment Research Council (NERC) as part of the Ecosystems of the Mid-Atlantic Ridge at the Sub-Polar Front and Charlie-Gibbs Fracture Zone (ECOMAR) project, the Marine Environmental Mapping Programme (MAREMAP), the ERC (Starting Grant project CODEMAP, no 258482), the Joint Nature Conservation Committee (JNCC), the Lenfest Ocean Program (PEW Foundation), the Department for Business, Enterprise and Regulatory Reform through Strategic Environmental Assessment 7 (formerly the Department for Trade and Industry) and the Department for Environment, Food and Rural Affairs through their advisors, the Joint Nature Conservation Committee, the offshore Special Areas for Conservation programme, BELSPO and RBINS-OD Nature (Belgian Federal Government) for R/V Belgica shiptime. The footage from the HAUSGARTEN observatory was taken during expeditions ARK XVIII/1, ARK XX/1, ARK XXII/1, ARK XXIII/2 and ARK XXVI/2 of the German research icebreaker “Polarstern”. The authors also acknowledge funds provided by FCT-IP/MEC to LARSyS Associated Laboratory and IMAR-University of the Azores (R&DU #531), Thematic Area E, through the Strategic Project (PEst-OE/EEI/LA0009/2011∧2014, COMPETE, QREN) and by the Government of Azores FRCT multiannual funding. CKP was supported by the doctoral grant from the Portuguese Science Foundation (SFRH/BD/66404/2009; COMPETE/QREN). AP was supported by Statoil as part of the CORAMM project. MB would like to thank Antje Boetius for financial support through the DFG Leibniz programme. JNGP was supported by the doctoral grant (M3.1.2/F/062/2011) from the Regional Directorate for Science, Technology and Communications (DRCTC) of the Regional Government of the Azores. ERLL was supported by a CSIC-JAE-postdocotral grant with co-funding from the European Social Fund. Publication fees for this open access publication were supported by IFREMER. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. 
 
 Introduction Litter disposal and accumulation in the marine environment is one of the fastest growing threats for the world's oceans health. Marine litter is defined as ‘‘any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment”[1]. The issue has been highlighted by the United Nations Environment Program [1] and was included in the 11 Descriptors set by Europe's Marine Strategy Framework directive (2008/56/EC) (MSFD) [2]. The MSFD requires each Descriptor in all European marine waters not to deviate from the undisturbed state and reach Good Environmental Status (GES) by 2020. With an estimated 6.4 million tonnes of litter entering the oceans each year [1], the adverse impacts of litter on the marine environment are not negligible. Besides the unquestionable aesthetic issue, litter can be mistaken for food items and be ingested by a wide variety of marine organisms [3]–[8]. Entanglement in derelict fishing gear is also a serious threat, particularly for mammals [9]–[11], turtles [12] and birds [13] but also for benthic biota such as corals [14], [15]. High mortality of fish through “ghost fishing” is another consequence of derelict fishing gear in the marine environment [16]. Moreover, floating litter facilitates the transfer of non-native marine species (e.g. bryozoans, barnacles) to new habitats [17], [18]. Barnes et al. [19] estimated that the dispersal of alien species through marine litter more than doubles the rate of natural dispersal processes, especially during an era of global change. Although the type of litter found in the world's oceans is highly diverse, plastics are by far the most abundant material recorded [20]–[22]. Because of their persistence and hydrophobic nature, their impact on marine ecosystems is of great concern. Plastics are a source of toxic chemicals such as polychlorinated biphenyls (PCBs) and dioxins that can be lethal to marine fauna [23]. Furthermore, the degradation of plastics generates microplastics which, when ingested by organisms, can deliver contaminants across trophic levels [24]–[27]. Litter type, composition and density vary greatly among locations and litter has been found in all marine habitats, from surface water convergence in the pelagic realm (fronts) down to the deep sea where litter degradation is a much slower process [21]. The spatial distribution and accumulation of litter in the ocean is influenced by hydrography, geomorphological factors [21], [28], prevailing winds and anthropogenic activities [29]. Hotspots of litter accumulation include shores close to populated areas, particularly beaches [30], but also submarine canyons, where litter originating from land accumulates in large quantities [28], [31]. In Europe, much has been written on the abundance and distribution of litter on the coastline and in surface waters [32]–[41]. As more areas of Europe's seafloor are being explored, benthic litter is progressively being revealed to be more widespread than previously assumed [15], [28], [29], [31], [42]–[52]. The sources of litter accumulating on the seafloor are variable, depending upon interactions between distances from shore [31], [45], oceanographic and hydrographic processes [47] and human activities such as commercial shipping [29] and leisure craft [43]. Early studies used trawling to quantify litter abundance on the seafloor [53], whilst more recent studies have demonstrated the potential of remotely operated vehicles (ROV), manned submersibles or towed cameras to study litter in the deep sea [15], [31], [43], [47], [54], [55]. However, understanding spatial patterns in litter abundance and distribution in the deep sea is challenging, owing to the lack of standardization in the sampling and analytical methodologies used. Furthermore, the high cost of sampling in the deep sea has limited our ability to perform standardized surveys across large areas to understand fully the extent of this pollution issue. The problem of marine litter on the deep seafloor was addressed by the EU-FP7 project HERMIONE, recognising the need to use the surveys conducted by all partners (although designed for other purposes) to gather data on litter in the deep sea. This paper presents the results on the distribution and densities of marine litter obtained during these surveys, with additional data provided by the UK's Mapping the Deep project as well as other previous projects. It provides a unique large-scale analysis of litter on the seafloor across different physiographic settings and depths. 
 
 Discussion The occurrence of litter on the seafloor has been far less investigated than in surface waters or on beaches, principally because of the high cost and the technical difficulties involved in sampling the seafloor at bathyal and abyssal depths [21], [60]. Considering such limitations and poor knowledge on litter accumulation in deep waters, every survey is of great value for obtaining information on litter density and distribution. In the present study, we integrated data collected during numerous cruises over a large regional scale into a single analysis, providing insight on the density and composition of litter across a wide variety of seafloor settings and over a large geographical area in European waters. Although standardisation of the data permitted comparisons between sites, dissimilarities in the sampling equipment implies that the results should be treated with caution. Furthermore, differences in the areas of the seafloor surveyed between locations may lead to overestimations or underestimations of the litter density. Also, studying litter from trawls introduces the issue of quantification units (number vs. weight), with no correct solution. When using number of items, certain litter categories may be overestimated such as plastic or glass that can break into many small pieces. As a counterpart, if weight is used, the abundance of litter type with different weights (e.g. heavy clinker vs. light plastic) cannot be compared. Ideally, both units for litter quantification will help to understand better trends, but the EU Marine Strategy Framework Directive stresses that for monitoring litter in the marine environment, number is mandatory whilst weight is only recommended [2]. Litter was found at all the locations surveyed, from sites close to population centres such as the Gulf of Lion or the Lisbon Canyon to as far as the South Charlie-Gibbs Fracture Zone on the Mid-Atlantic Ridge, located at about 2000 km from land. Litter was found from shallow waters (35 meters in Gulf of Lion) down to 4500 meters (Cascais Canyon). Such records were not surprising, as litter is known to be present in all seas and oceans of the planet, as remote as the Southern Ocean [21] and at depths as deep as 7216 m in the Ryuku trench, south of Japan [61]. The range of litter densities found on our study sites was within the same order of magnitude to the ones found on the seabed in other parts of the globe (North America [55], [62], [63], China [54], Japan [64], [65]) and for other locations in Europe [28], [44], [45], [47], [48]. On the other hand, macro litter densities on the seabed were higher than reported for surface waters [32], [66]–[69]. At the surface, floating litter tends to accumulate in frontal areas but eventually reaches the seabed when heavily covered by fouling organisms [70] or loaded with sediments. Contrary to a common notion that most plastic items float at the sea surface it has been estimated that 70% of the plastic sinks to the seafloor [23]. This results in macro litter accumulation on the seabed rather than in the open sea [21]. For example, on the seafloor of the Mediterranean Sea, our data showed much higher litter densities (0.4 to 48 litter items ha−1) than that estimated to float at the surface (0.021 items ha−1; [1]). Alternatively, floating litter may be transported for considerable distances and get washed ashore [71], [72]. Litter density on the coastline is typically higher than on the seafloor given that there is an additional input of waste coming from inland sources (e.g. man-made drainage systems, recreational usage, rivers, winds, etc.) [71], [73]. On European coasts, litter densities can exceed 30,000 litter items per linear km [1], [41], [74], while much higher densities have been reported for beaches in Indonesia [75] or on the beaches along Armaçao dos Buzios, Rio de Janeiro, Brazil [76]. However, comparisons between studies are challenging considering differences in the size of the litter items sampled and the sampling methodology used [77]. Our data showed a general increase in litter density in locations closer to the shore, a pattern previously reported for the French Mediterranean coast [47] and off California [55]. Nevertheless, low litter densities in some near-shore sites (e.g. Gulf of Lion or Faroe-Shetland channel) suggest that many other factors (such as geomorphology, hydrography and human activity) affect litter distribution and accumulation rates [29]. In the Gulf of Lion, Galgani et al. [47] suggested that low litter density on the shelf was caused by strong water flow from the Rhone River, transporting litter down south to deeper waters. A similar situation occurs in Monterey Bay where sediment and litter are being swept off the continental shelf down into Monterey Canyon [78]. Such phenomena may explain why continental shelves were the settings with overall lowest litter density, whilst submarine canyons had the highest litter concentration. Litter levels on seamounts, banks, mounds and ocean ridges were characterised by intermediate levels when compared to other physiographic settings. They are typically located far away from coastal areas where the main anthropogenic activities include fishing [79] and seabed mining [80], [81]. The presence of litter on these settings is of concern because they harbor Vulnerable Marine Ecosystems (VMEs) (such as cold-water corals and hydrothermal vents) that have reduced capacity to recover from disturbance events and for which conservation is a global priority [82]. The types of accumulated litter can provide an indication on the human activities impacting a particular location. However, one must be cautious and consider the differences in the buoyancy and longevity of the different types of litter. For example, while some plastics sink to the seafloor, others float on the surface and are able to travel great distances before eventually sinking far from their initial dumping locations, following biofouling and degradation [23]. On the other hand, glass, metal and clinker will sink rapidly and are expected to be recovered from the seafloor close to sites where they were initially released. Cardboard and fabrics (of organic origin) will break down quickly, implying that such items will not reach the deep ocean with the frequency of more resistant materials such as plastic and negatively buoyant items such as glass, metal and clinker. Although it is difficult to determine the exact source of the litter observed on the seafloor, the dominant litter category can be used as an indicator to separate ocean and terrestrial sources [15], [29], [31], [78]. Plastic (other than derelict fishing gear) was the most abundant litter category in submarine canyons, continental shelves and continental slopes. The predominance of plastics in submarine canyons reaffirms that litter accumulation in these habitats comes from coastal and land sources and that submarine canyons act as conduits for litter transport from continental shelves into deeper waters [21], [28], [29], [31], [47], [78]. Therefore, submarine canyons can be considered to be accumulation zones of land-based marine litter in the deep sea. In fact, submarine canyons are areas where macrophyte detritus that originates from coastal areas accumulates in high quantities. This results in a localised increase of organic matter and high abundances of associated fauna, dominated by deposit and suspension-feeding invertebrates [83]–[85]. Since some deposit-feeders (e.g. holothurians) have been shown to select plastic fragments over sediment grains under laboratory conditions [7], the accumulation of plastics in submarine canyons could have detrimental effects for these ecologically important deep-sea organisms. Furthermore, plastic fragments contain a wide variety of persistent organic pollutants (POPs) that may accumulate in the consumer's tissues and can be transferred upwards in the trophic webs to predators, including humans [86]. Derelict fishing gear was the main litter item found on seamounts, banks, mounds and ocean ridges implying that, unlike submarine canyons, fishing activities are the major source of litter at those settings. Seamounts and banks are targeted by commercial fishing activities as they are often highly productive areas supporting dense aggregations of commercially valuable fish and shellfish [87]. At other locations where recreational [55], [88] and commercial [28], [54], [62], [89] fishing activities are intense, derelict fishing gear dominated the litter on the seabed. It was beyond the scope of this study to evaluate the impacts caused by derelict fishing gear, but numerous studies have shown diverse impacts including ghost fishing [16], [90] and entanglement by sessile invertebrates such as corals [15], as well as causing damage to fishing equipment [91]. Discarded trawl gear can also have a compounding effect by trapping more mobile litter resulting in a litter ‘depot’ that has a greater impact than single pieces of litter [31]. Since most fishing equipment (lines and nets) is made mostly of highly resistant plastics, such negative effects will likely persist for a long time. Sites located in deep basins and continental slopes were dominated by clinker. Clinker, the residue of burnt coal, was commonly dumped from steam ships from the late 18th century and well into the 20th century. In the Mediterranean Sea, its occurrence on the deep seafloor has been shown to coincide with such shipping routes [29]. However, it is important to acknowledge that in this study, deep basins and continental slopes were principally sampled by trawling and it is difficult to determine if the differences in litter composition with other physiographic settings are the results of differences in the sampling methodology, particularly since clinker is difficult to identify from underwater footage. Indeed, clinker was present in non-quantitative trawls undertaken at HAUSGARTEN (Bergmann, unpublished data), but could not be detected on images from the seafloor. Similarly, a high abundance of clinker was recovered from trawl surveys in Blanes Canyon that could not be identified in analysis of ROV footage from the same area (Table 3). Given that most of the clinker present on the seafloor was dumped over 100 years ago, sedimentation will have buried it, which would explain the differences in clinker quantification between images and trawl data. The deep seafloor is a passive accumulation area for litter, integrating information over long-time periods. If trawls are able to recover heavy clinker deposited on the seafloor over a century ago, these gears must be retrieving at the same time all of the lighter and most recent litter items, such as plastic for example, that have been accumulating only in the last 50 years. Overall, the composition of litter found on the seafloor showed some dissimilarity with the composition found on the coasts or in surface waters. Although plastics are dominant in all settings [70], some areas of the seafloor investigated here and elsewhere [28], [44], [45], [54], [78] harbour significant quantities of non-buoyant litter such as glass, metal and clinker, directly dumped from ships but that are seldom found in surface waters [41], [68] or on the coasts [41], [72]. The coasts and surface waters are a source of litter items for the open seas and all this litter, sooner or later, will sink to the seafloor where it accumulates. The most common method used to provide data on benthic marine litter has been trawling, typically as a parallel objective to surveys directed to fish or benthic organism sampling [53]. With the recent development of optical methods fitted to platforms such as submersibles, ROV and drop-down systems, the use of underwater imaging technology has greatly increased our ability to quantify deep-sea litter. Both methods (imaging technology and trawling) have distinct assets for studying benthic litter that should be used in conjunction to best understand the dynamics of pollution on the seafloor. Video surveys can provide data for areas where topography is complex (e.g seamounts or canyon walls), habitats made by structure-building organisms (e.g. cold-water corals), or dynamic systems (e.g. hydrothermal vents and cold seeps), that cannot be accessed with a trawl [53]. Furthermore, imaging is a non-intrusive method that does not remove benthic organisms or damage the environment. On the other hand, a trawl has the advantages of recovering litter items of very small size (e.g. small plastic fragments) or that are buried in the sediments (e.g. clinker), which otherwise would not be detected through imaging technology. In addition, litter items collected with a trawl can be analysed in the laboratory to obtain further important information, such as state of degradation or colonisation by fouling organisms [92]. Such data will help understand sinking processes of plastic, facilitate the identification of their location of arrival into the ocean and provide information on the impacts of litter on marine organisms. The large quantities of litter reaching the deep ocean floor is a major issue worldwide, yet little is known about its sources, patterns of distribution, abundance and, particularly, impacts on the habitats and associated fauna [1]. At present, density of litter in the deep sea is lower than found on some heavily polluted beaches [33], [93], but unlike the coastal zone, only a tiny fraction of the (deep) seafloor has been surveyed to date. Furthermore, microplastic accumulation may become an important component of pollution in deep-sea ecosystems [94] that urgently needs to be evaluated. Our results for European waters show that litter sources are distinct across different physiographic settings and that their abundance is variable, most probably guided by a complex set of interactions between physiography, anthropogenic activities and hydrography. It is important that in the future, large-scale assessments are done in a standardised manner to understand fully the scale of the problem and set the necessary actions to prevent the accumulation of litter in the marine environment. 
 
 Supporting Information Table S1. Results of analyses of similarity (ANOSIM) evaluating variation in the composition of litter among physiographic settings. RIDGE: ocean ridges; CANY: submarine canyons; SHELF: continental shelves; SLOPE: continental slopes; SBM: seamounts, banks and mounds; BASIN: deep basins. doi:10.1371/journal.pone.0095839.s001 (DOCX) Table S2. Similarity percentage analysis (SIMPER) of litter composition for each pooled physiographic settings (based on similarities revealed by ANOSIM) and the contribution of litter category to group similarity. doi:10.1371/journal.pone.0095839.s002 (DOCX) 
 
 Acknowledgments The authors would like to thank the captains, crews and scientific parties of all cruises for their help and support during the data collection. PT would like to thank Gideon Mordecai for analytical work and Doug Masson. Finally, the authors would like to thank Martin Thiel and two other anonymous reviewers, whose suggestions and comments greatly improved the manuscript. This is publication number 33575 of the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung.
– In the depths of European oceans, you'll find coral, sand—and old Heineken cans. Yup, human litter can be found even in the most far-reaching places on the planet, according to one of the biggest scientific surveys ever done of the seafloor. Using video and trawling surveys between 1999 and 2011, scientists analyzed 32 sites in the Atlantic Ocean, Arctic Ocean, and Mediterranean Sea. They found everything from bottles to plastic bags, clothing, and fishing nets—even more than 1,200 miles from land and nearly three miles below the water's surface, the Guardian reports. Not a single site was litter-free. That means your garbage is on continental shelves, ocean ridges, and deep canyons—the worst spot for garbage build-up, the study says. Plastic was most common at 41% of the garbage found, while 34% was related to fishing—think nets and lines. Also spotted: wood, pottery, glass, paper, cardboard, and even burnt coal residue left from steam ships more than 100 years ago. "This survey has shown that human litter is present in all marine habitats, from beaches to the most remote and deepest parts of the oceans," a researcher says. "Most of the deep sea remains unexplored by humans and these are our first visits to many of these sites, but we were shocked to find that our rubbish has got there before us." Smithsonian notes some 14 billion pounds of garbage enter the oceans each year, some of which animals eat, get tangled in, and often die.