Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question—where is all the plastic?

There is growing evidence of extensive pollution of the environment by microplastic, with microfibres representing a large proportion of the microplastics seen in marine sediments. Since microfibres are ubiquitous in the environment, present in the laboratory air and water, evaluating microplastic pollution is difficult. Incidental contamination is highly likely unless strict control measures are employed. Here we describe methods developed to minimize the amount of incidental post-sampling contamination when quantifying marine microfibre pollution. We show that our protocol, adapted from the field of forensic fibre examination, reduces fibre abundance by 90% and enables the quick screening of fibre populations. These methods therefore allow an accurate estimate of microplastics polluting marine sediments. In a case study from a series of samples collected on a research vessel, we use these methods to highlight the prevalence of microfibres as marine microplastics.

We investigated the relationship between productivity and local species diversity, and the degree of species turnover, at 8 sites on the central equatorial Pacific abyssal plain. The 8 sites span a 4-fold difference in seafloor particulate organic carbon (POC) flux and, hence, community productivity. The sites are similar in water depth (4300 to 5100 m), degree of isolation from terrigenous influences, and hydrodynamic regime. Three sites lie under the influence of equatorial upwelling, and are subject to enhanced deep POC flux derived from high overlying primary production. The remaining sites lie beneath the oligotrophic north Pacific gyre. The number of polychaete species collected at a single site ranged from 14 to 113, with at least 90% apparently being new to science. We found no evidence for the purported unimodal relationship between productivity and diversity seen in other ecosystems, including deep-sea slopes, and found only weak evidence of a monotonic increase in diversity with productivity. Rates of species turnover were low over scales of ~200 to 3000 km for the dominant polychaete species in the communities, and all sites were dominated by a core group of biogeographically widespread, locally abundant species. In contrast, there was little between-site similarity in the long list of rare species found at each site, implying either a high turnover of rare species at 200 to 3000 km scales, or incomplete sampling of the rare species list at each site. More intensive sampling studies using both morphological and molecular methods are needed to resolve the distribution patterns of rare species in the Pacific abyss. Local polychaete species diversity beneath equatorial Pacific upwelling (measured by rarefaction) appears to be unusually high for the deep sea, exceeding by at least 10 to 20% that measured in abyssal sites in the Atlantic and Pacific, and on the continental slopes of the North Atlantic, North Pacific, and Indian Oceans.

a b s t r a c tThe macrofaunal assemblages from three Portuguese submarine canyons, Nazaré , Cascais and Setú bal were studied from samples collected at their upper (900-1000 m), middle (3200-3500 m) and lower sections (4200-4500 m) and at the adjacent open slopes ( $ 1000 m), during the HERMES cruises D297 (R.R.S. Discovery, 2005) CD179 (R.R.S. Charles Darwin, 2006) and 64PE252 (R.V. Pelagia, 2006). The taxonomic composition and patterns in biodiversity, abundance and community structure of the benthic macrofauna were described. Annelida (42.1% of total abundance; 137 species) and Arthropoda (20.6%; 162 species) were, respectively, the most abundant and the most species-rich Phyla among the 342 taxa identified during this study. Multivariate analyses showed significant differences between and within canyons and between canyons and open slope assemblages. At their upper section, canyons supported higher macrofauna abundance but slightly lower biodiversity than the adjacent slopes at similar depth. In all canyons abundance reached the highest value in the middle section and the lowest in the upper section, with marked fluctuations in Nazaré (474-4599 ind. m

Marine litter is a global challenge that has recently received policymakers' attention, with new environmental targets in addition to changes to old legislation. There are no global estimates of benthic litter because of the scarcity of data and only patchy survey coverage. However, estimates of baseline abundance and composition of litter are vital in order to implement litter reduction policies and adequate monitoring schemes. Two large-scale surveys of submarine geomorphological features in the Indian and Atlantic Oceans reveal that litter was found at all locations, despite their remoteness. Litter abundance was patchy, but both surveyed oceans had sites of high litter density. There was a significant difference in the type of litter found in the two oceans, with the Indian Ocean sites being dominated by fishing gear, whereas the Atlantic Ocean sites displayed a greater mix of general refuse. This study suggests that seabed litter is ubiquitous on raised benthic features, such as seamounts. It also concludes that the pattern of accumulation and composition of the litter is determined by a complex range of factors both environmental and anthropogenic. We suggest that the tracing of fishing effort and gear type would be an important step to elucidate hotspots of litter abundance on seamounts, ridges and banks.

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Societal concerns over the potential impacts of recent global change have prompted renewed interest in the long-term ecological monitoring of large ecosystems. The deep sea is the largest ecosystem on the planet, the least accessible, and perhaps the least understood. Nevertheless, deep-sea data collected over the last few decades are now being synthesised with a view to both measuring global change and predicting the future impacts of further rises in atmospheric carbon dioxide concentrations. For many years, it was assumed by many that the deep sea is a stable habitat, buffered from shortterm changes in the atmosphere or upper ocean. However, recent studies suggest that deep-seafloor ecosystems may respond relatively quickly to seasonal, inter-annual and decadal-scale shifts in upperocean variables. In this review, we assess the evidence for these long-term (i.e. inter-annual to decadal-scale) changes both in biologically driven, sedimented, deep-sea ecosystems (e.g. abyssal plains) and in chemosynthetic ecosystems that are partially geologically driven, such as hydrothermal vents and cold seeps. We have identified 11 deep-sea sedimented ecosystems for which published analyses of long-term biological data exist. At three of these, we have found evidence for a progressive trend that could be potentially linked to recent climate change, although the evidence is not conclusive. At the other sites, we have concluded that the changes were either not significant, or Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site 2 were stochastically variable without being clearly linked to climate change or climate variability indices. For chemosynthetic ecosystems, we have identified 14 sites for which there are some published longterm data. Data for temporal changes at chemosynthetic ecosystems are scarce, with few sites being subjected to repeated visits. However, the limited evidence from hydrothermal vents suggests that at fast-spreading centres such as the East Pacific Rise, vent communities are impacted on decadal scales by stochastic events such as volcanic eruptions, with associated fauna showing complex patterns of community succession. For the slow-spreading centres such as the Mid-Atlantic Ridge, vent sites appear to be stable over the time periods measured, with no discernable long-term trend. At cold seeps, inferences based on spatial studies in the Gulf of Mexico, and data on organism longevity, suggest that these sites are stable over many hundreds of years. However, at the Haakon Mosby mud volcano, a large, well-studied seep in the Barents Sea, periodic mud slides associated with gas and fluid venting may disrupt benthic communities, leading to successional sequences over time. For chemosynthetic ecosystems of biogenic origin (e.g. whale-falls), it is likely that the longevity of the habitat depends mainly on the size of the carcass and the ecological setting, with larg...

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