Increase of litter at the Arctic deep-sea observatory HAUSGARTEN

Abstract

Although recent research has shown that marine litter has made it even to the remotest parts of our planet, little information is available about temporal trends on the deep ocean floor. To quantify litter on the deep seafloor over time, we analysed images from the HAUSGARTEN observatory (79°N) taken in 2002, 2004, 2007, 2008 and 2011 (2500 m depth). Our results indicate that litter increased from 3635 to 7710 items km⁻² between 2002 and 2011 and reached densities similar to those reported from a canyon near the Portuguese capital Lisboa. Plastic constituted the majority of litter (59%) followed by a black fabric (11%) and cardboard/paper (7%). Sixty-seven percent of the litter was entangled or colonised by invertebrates such as sponges (41%) or sea anemones (15%). The changes in litter could be an indirect consequence of the receding sea ice, which opens the Arctic Ocean to the impacts of man’s activities.

Introduction

Although the deep sea covers ∼60% of our planet’s surface the deep ocean floor remains the least explored ecosystem on Earth (Smith et al., 2009). Still less is known of deep-sea ecosystems from remote polar regions such as the Arctic. Despite our scarce knowledge, exploitation of its resources is already underway in terms of hydrocarbon exploration, fisheries, shipping and tourism as the sea ice is receding. Although the disposal of solid waste at sea was prohibited in 1988 (Annexe V, MARPOL Convention) more and more reports indicate that even the most secluded environments such as polar regions and the deep ocean floor are no longer exempt from contamination with litter (Barnes, 2002, Galgani et al., 2000). The annual global production of plastic products is estimated at 230 million tons (Weisman, 2007). Because of their chemical composition plastics are durable and degrade very slowly. Since the 1950s one billion tons of plastic have been discarded, which may persist for hundreds of years (O’Brine and Thompson, 2010). In fact, recent studies suggest that the 1982 figure of 8 million litter items entering the oceans every day may need to be multiplied several fold (Barnes, 2005). Marine litter is defined as “any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment” (UNEP, 2009).

Plastic accounts for the large majority of marine litter (Laist, 1987, Spengler and Costa, 2008), which is hardly surprising given an annual global production of 230 million tons in 2009 (Cole et al., 2011), of which >10% end up in the oceans (Thompson, 2006). Plastics are non-biodegradable but can mechanically be broken down into secondary micro-plastics (Cole et al., 2011). Recently, exposure to ever increasing quantities of micro-plastics was identified as a problem of major environmental concern (Cole et al., 2011, Thompson et al., 2004). Micro-plastics are considered vectors for adsorbed pollutants such as endocrine disrupting chemicals, phthalates, polyaromatic hydrocarbons, organochlorine pesticides and polychlorinated biphenyls (Cole et al., 2011, Zarfl and Matthies, 2010). Through ingestion, they reach the tissues of suspension and deposit feeders (Graham and Thompson, 2009) and other biota (Thompson et al., 2004), accumulate through the food web and may enter the human food chain (Murray and Cowie, 2011). Alarmingly, micro-plastics were also found in most sediment samples from UK waters and increased from the 1960s to the 1990s in plankton samples taken between Scotland and Iceland (Thompson et al., 2004).

Macro-litter is not a mere aesthetic problem. In the oceans, it affects marine life in different ways. Most obviously, it causes entanglement, suffocation and disrupts ingestion/food uptake in birds, fish, mammals, turtles and fish (Derraik, 2002). Such deleterious effects have been documented in >267 marine species in the late 1980s (Laist, 1987) and this figure has probably risen since. In addition to suffocation, fisheries-related litter may increase mortality by ghost fishing (Laist, 1987). Plastic bags may smother and damage organisms from soft and hard substrata (Parker, 1990). Litter on the seafloor can cause anoxia to the underlying sediments, which alters biogeochemistry and benthic community structure (Goldberg, 1994). Furthermore, litter may provide substrata for the attachment of sessile biota in sedimentary environments and increase local diversity (Mordecai et al., 2011, Moret-Ferguson et al., 2010, Pace et al., 2007) although this replaces existing species and leads to non-natural alterations of faunal community composition. Attachment to or entanglement in floating debris, opens new routes of transportation, ‘rafting’ (Barnes, 2002, Barnes and Milner, 2005, Issacs et al., 2000) and may enable alien invasion (Gregory, 2009), especially in polar regions during an era of rapid environmental transition due to global warming (Barnes, 2002, Barnes, 2005, Barnes et al., 2010). Long-distance transport may be enhanced by storms/strong winds (Kukulka et al., 2012), projected to become more frequent as a result of climate forcing (IPCC, 2007).

Since plastic litter is light and durable it can travel long distances in the marine realm distributing its pollutants to hitherto unspoiled remote ecosystems (Barnes et al., 2010, Zarfl and Matthies, 2010). As plastics are colonised or loaded with sediments they sink to the seafloor (Thompson, 2006, Ye and Andrady, 1991). However, recent models indicate that wind stress significantly enhances the vertical mixing of buoyant micro-plastic litter into the water column and that, depending on wind speed, surface observations may underestimate the total amount of buoyant plastic distributed in the upper water column by a factor of up to 27 (Kukulka et al., 2012). In the sediments, plastic litter can persist for centuries (Derraik, 2002). In polar deep-sea sediments degradation rates may be even lower due to the absence of sunlight, low ambient temperatures and low energy input.

Despite these implications, little is known about the distribution of litter on the ocean floor as most studies refer to reports of litter floating on the water surface, coastal areas and beached litter (Barnes and Milner, 2005, Thompson et al., 2004). Several studies highlighted a problem with litter pollution in the Mediterranean, e.g. (Galgani et al., 1995a, Galgani et al., 1996, Galil et al., 1995, Katsanevakis and Katsarou, 2004, Stefatos et al., 1999) and other European coasts (Galgani et al., 1995b, Galgani et al., 2000). More studies on litter emerged from the US (June, 1990, Keller et al., 2010, Moore and Allen, 2000, Moret-Ferguson et al., 2010, Watters et al., 2010, Ye and Andrady, 1991) and elsewhere (Lee et al., 2006). Litter was also recorded from remote localities off Antarctica (Barnes, 2005, Barnes et al., 2010), the Arctic (Day and Shaw, 1987, Feder et al., 1978, Fowler, 1987, Hess et al., 1999, Jewett, 1976, June, 1990, Mallory, 2008, Provencher et al., 2010, Shaw, 1977, Zarfl and Matthies, 2010) and the deep seafloor (Galgani and Andral, 1998, Galgani and Lecornu, 2004, Keller et al., 2010, Mordecai et al., 2011, Pace et al., 2007, Ramirez-Llodra et al., in press, Wei et al., 2012).

Despite an increase in the number of papers on marine debris in recent years, most of these studies deal with litter from specific areas or map its distribution. While such information is crucial to estimate the scope and spread of the problem, information about the amount of oceanic macro-litter over time is scarce (but see (Galgani et al., 2000, Hess et al., 1999, Watters et al., 2010, Wei et al., 2012). Here we analyse photographs taken at a set camera transect at the HAUSGARTEN observatory in 2002, 2004, 2007, 2008 and 2011 to assess if the quality and quantity of litter in the deep Arctic sea has changed over the past decade.