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Marine Litter Distribution and Density in European Seas,
from the Shelves to Deep Basins
Christopher K. Pham 1'2", Eva Ramirez-Llodra3'4, Claudia H. S. Alt5, Teresa Am aro6, M elanie B ergm ann7,
M iquel Canals8, Joan B. C om pany3, Jaim e D avies9, Gerard D u in eveld 10, François G algani11,
Kerry L. H ow eii9, V eerle A. I. H uvenn e12, Eduardo Isidro1'2, Daniel O. B. J o n es12, Galderic Lastras8,
Telm o M orato1'2, José N uno G om es-Pereira1'2, Autun Purser13, H eather Stew art14, Inés Tojeira15,
Xavier Tubau8, David Van Rooij16, Paul A. Tyler5
1 Center of the Institute of Marine Research (IMAR) and Department of Oceanography and Fisheries, University of the Azores, Horta, Portugal, 2 Laboratory of Robotics
and Systems in Engineering and Science (LARSyS), Lisbon, Portugal, 3 Institut de Ciències del Mar (ICM-CSIC), Barcelona, Spain, 4 Norwegian Institute for Water Research
(NIVA), Marine Biology section, Oslo, Norway, 5 Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, United Kingdom,
6 Norwegian Institute for Water Research, Bergen, Norway, 7 Alfred-Wegener-lnstitut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany, 8 GRC
Geociències Marines, Departament d 'Estratigrafía, Paleontología i Geociències Marines, Facultat de Geología, Universität de Barcelona, Campus de Pedralbes, Barcelona,
Spain, 9 Marine Biology & Ecology Research Centre, Marine Institute, Plymouth University, Plymouth, United Kingdom, 10 Netherlands Institute for Sea Research (NIOZ),
Texel, The Netherlands, 11 Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Bastía, France, 12 National Oceanography Centre, University of
Southampton Waterfront Campus, Southampton, United Kingdom, 130ceanLab, Jacobs University Bremen, Bremen, Germany, 1 4 British Geological Survey, Murchison
House, Edinburgh, United Kingdom, 15 Portuguese Task Group for the Extension of the Continental Shelf (EMEPC), Paço de Arcos, Portugal, 16 Renard Centre of Marine
Geology (RCMG), Department of Geology and Soil Science, Ghent University, Gent, Belgium
Abstract
A nthropogenic litte r is present in all marine habitats, from beaches to the m ost rem ote points In the oceans. On the
seafloor, marine litter, particularly plastic, can accum ulate in high densities w ith deleterious consequences for Its
Inhabitants. Yet, because o f the high cost Involved w ith sam pling the seafloor, no large-scale assessment o f d istribu tion
patterns was available to date. Here, we present data on litte r d istribu tion and density collected during 588 video and trawl
surveys across 32 sites In European waters. We found litte r to be present In the deepest areas and at locations as rem ote
from land as the Charlie-Gibbs Fracture Zone across the M id-A tlantic Ridge. The highest litte r density occurs In subm arine
canyons, w hilst the lowest density can be found on continental shelves and on ocean ridges. Plastic was the most prevalent
litte r item found on the seafloor. Litter from fishing activities (derelict fishing lines and nets) was particularly com m on on
seamounts, banks, m ounds and ocean ridges. Our results h igh lig ht the extent o f the problem and the need fo r action to
prevent Increasing accum ulation o f litte r In marine environm ents.
C i t a t i o n : 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
E d i t o r : Andrew Davies, Bangor University, United Kingdom
R e c e i v e d August 23, 2013; A c c e p t e d March 31, 2014; P u b l i s h e d April 30, 2014
C o p y r i g h t : © 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.
F u n d i n g : This research was supported by the European Community's Seventh Framework Programme (FP7/2007A2013) 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 Generalität 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, ARKXX/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/LA0009/2011A2014, 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.
C o m p e t i n g I n t e r e s t s : The authors have declared that no competing interests exist.
* E-mail: phamchristopher@uac.pt
Introduction
M a rin e litter is defined as “ any persistent, m an u factu red or
processed solid m aterial discarded, disposed o f or a b an d o n e d in
ple m ara le ancj coasta] en v iro n m en t” [1]. T h e issue has b een
L itter disposal a n d accum ulation in the m arin e env iro n m en t is
one o f the fastest grow ing threats for the w orld’s oceans health.
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1
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Litter on the Seafloor o f European Waters
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Litter on th e Seafloor o f European Waters
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highlighted b y the U n ite d N ations E n v iro n m en t P ro g ra m [1] a n d
was included in the 11 D escriptors set by E u ro p e ’s M arine
Strategy F ram ew ork directive (2 0 0 8 /5 6 /E C ) (M SFD) [2]. T h e
M S F D requires each D escriptor in all E u ro p ea n m arin e w aters
n ot to deviate from the u n d istu rb ed state a n d re ac h G ood
E n vironm ental Status (GES) b y 2020.
W ith a n estim ated 6.4 m illion tonnes o f litter en terin g the
oceans each y ear [1], the adverse im pacts o f litter o n the m arine
env iro n m en t are not negligible. Besides the unquestionable
aesthetic issue, litter can be m istaken for food item s a n d be
ingested by a w ide variety o f m arin e organism s [3 -8 ], E ntangle­
m en t in derelict fishing gear is also a serious th reat, p articularly for
m am m als [9—11], turtles [12] a n d birds [13] b u t also for benthic
b io ta such as corals [14,15]. Fligh m ortality o f fish th ro u g h “ ghost
fishing” is a n o th e r consequence o f derelict fishing gear in the
m arin e e nvironm ent [16], M oreover, floating litter facilitates the
transfer o f non-native m arin e species (e.g. bryozoans, barnacles) to
new habitats [17,18], B arnes et al. [19] estim ated th a t the dispersal
o f alien species th ro u g h m arin e litter m ore th a n doubles the ra te o f
na tu ra l dispersal processes, especially du rin g a n e ra o f global
change.
A lthough the type o f litter found in the w o rld ’s oceans is highly
diverse, plastics are b y far the m ost a b u n d a n t m aterial recorded
[20-22]. Because o f th eir persistence a n d h ydrophobic natu re,
their im pact o n m arin e ecosystem s is o f g reat concern. Plastics are
a source o f toxic chem icals such as p olychlorinated biphenyls
(PCBs) a n d dioxins th a t can b e lethal to m arin e fauna [23].
F u rth e rm o re , the d eg rad atio n o f plastics generates m icroplastics
w hich, w h en ingested by organism s, c an deliver c o n tam inants
across trophic levels [24-27].
L itter type, com position a n d density vary greatly am o n g
locations a n d litter has b e en found in all m arin e habitats, from
surface w ater convergence in the pelagic realm (fronts) dow n to the
deep sea w here litter d eg rad a tio n is a m u ch slower process [21].
T h e spatial distribution a n d accum ulation o f litter in the ocean is
influenced b y hydrography, geom orphological factors [21,28],
prevailing w inds a n d a nthropogenic activities [29]. Flotspots o f
litter accum ulation include shores close to p o p u late d areas,
particularly beaches [30], b u t also subm arine canyons, w here
litter originating from lan d accum ulates in large quantities [28,31].
In E urope, m u ch has b e en w ritten o n the a b u n d an c e a n d
distribution o f litter o n the coastline a n d in surface w aters [32-41],
As m ore areas o f E u ro p e ’s seafloor are b ein g explored, benthic
litter is progressively b ein g revealed to be m ore w idespread th an
previously assum ed [15,28,29,31,42-52]. T h e sources o f litter
accu m u latin g o n the seafloor are variable, d ep en d in g upon
interactions b etw een distances from shore [31,45], oceanographic
a n d h ydrographic processes [47] a n d h u m a n activities such as
com m ercial shipping [29] a n d leisure craft [43].
E arly studies used traw ling to quantify litter a b u n d an c e o n the
seafloor [53], whilst m ore recent studies have d e m o n stra ted the
poten tial o f rem otely o p e rated vehicles (RO Y ), m an n e d subm ers­
ibles o r tow ed cam eras to study litter in the deep sea
[15,31,43,47,54,55]. H ow ever, u n d erstan d in g spatial p attern s in
litter a b u n d an c e a n d distribution in the deep sea is challenging,
ow ing to the lack o f standardization in the sam pling a n d analytical
m ethodologies used. F u rth erm o re, the high cost o f sam pling in the
deep sea has lim ited o u r ability to perform standardized surveys
across large areas to u n d e rstan d fully the extent o f this pollution
issue.
T h e p ro b lem o f m arin e litter o n the deep seafloor was addressed
by the EET-FP7 p roject H E R M IO N E , recognising the need to use
the surveys cond u cted b y all p a rtn e rs (although designed for o th er
purposes) to g ath er d a ta on litter in the deep sea. T his p a p er
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Litter on the Seafloor o f European Waters
50°W
40°W
30°W
I_________ I_________ I
20°W
10°W
30 E
I_________ I
Sam pling method
Imaging technology
Trawling
Arctic Ocean
;
'
F.C
Atlantic Ocean
m
r
■40°N
30 °N
Figure 1. Locations o f th e study sites sam pled w ith im aging technology (ROVs, m anned subm ersible, tow ed camera systems) and
traw ling . A-B.B = Algero-Balearic Basin (W. Med.), A.S = Anton Dohrn S eam ount, B.C = Blanes Canyon (NW Med.), C.C = Cascais Canyon, C.S =
C ondor S eam o u n t, Calabrian Slope & Basin = C.S&B, Crete-Rhodes Ridge = C.R.R, D&E.C = D angeard & Explorer Canyons, D.M = Darwin M ounds,
G.L.C = Gulf of Lion canyons (NW Med.), G.L = Gulf o f Lion, G.C = Guilvinec Canyon, H.B = H atton Bank, H.IV = HAUSGARTEN, statio n IV, J.S =
Jo sep h in e S eam o u n t, L.C= Lisbon Canyon, N.C = Nazaré Canyon, N.C-G = North Charlie G ibbs Fracture Zone, N-E.F.C = North-East Faroe-Shetland
C hannel, N.F.C = North Faroe-Shetland C hannel, N.W= N orwegian m argin, P.D.M = Pen Duick A lpha/Beta M ound, R.B = Rockall Bank, Ros.B =
Rosemary Bank, S.C = Setúbal Canyon, S.C-G = S outh Charlie G ibbs Fracture Zone, W.C = W hittard Canyon, W.M.S = W estern M editerranean slope,
W-T.R = Wyville-Thomson Ridge.
doi:10.1371/jo u rn al.pone.0095839.g001
presents the results on the distribution a n d densities o f m arine
litter o b tain e d d u rin g these surveys, w ith ad ditional d a ta provided
by the U K ’s M a p p in g the D eep project as well as o th er previous
projects. It provides a unique large-scale analysis o f litter o n the
seafloor across different physiographic settings a n d depths.
M aterials and M ethods
S tu d y a r e a s
D a ta w ere g a th e red from surveys c o n d u cted d u rin g research
cruises led b y various E u ro p ea n institutions b etw een 1999 a n d
2011. A total o f 32 sites in the n o rth ea stern A tlantic O cean , Arctic
O c ea n a n d M e d ite rran e a n Sea w ere surveyed (T able 1; Figure 1).
Surveyed sites w ere located o n co n tinental shelves a n d slopes,
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subm arine canyons, seam ounts, banks, m ounds, ocean ridges a n d
deep basins, a t depths ra nging from 35 to 4500 m eters (T able 1).
S a m p l in g m e t h o d s
Sam pling m ethods included b o th im aging technology (still
p h o to g rap h a n d video) a n d fishing traw ls (Figure 1; T ab le 2). T h e
A tlantic sites w ere surveyed uniquely using im aging technology,
whilst sites located in the M e d ite rran e a n Sea w ere prim arily
investigated by traw ling (except for som e R O V transects in the
Blanes subm arine canyon). V ideo footage was collected by
different R O V s (Genesis, Isis, Liropus, Luso, Lynx, SP a n d Victor
6000), m a n n e d subm ersible (JAGO, G E O M A R ) a n d tow ed
c am era systems (Seatronics a n d the FID -video h o p p e r video
system). Still p h o to g rap h s w ere taken w ith the O c ea n Floor
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Litter on the Seafloor o f European Waters
Table 2.
Inform ation on each platform used to collect video and photographs for the collection o f data on litte r densities and
d istribu tion on the seafloor o f European waters.
S am pling p la tform
N am e
Form at
N° o f s a m p l e s
Total area
s u r v e y e d ( m 2)
F ie l d o f v i e w
(m)
R eferences
M anned sub m ersible
Jago
video
13
5561
1.5
[95]
RO V s
Luso
video
8
35587
3.6-4.4
[15]
Sp
video
44
29749
2.3
[15]
Isis
video
64
167308
2.0
[31]
Genesis
video
20
86700
2.6
[96]
Liropus
video
4
19867
3.0
[97]
Lynx
video
19
3750
1.0
[98]
Victor 6000
video
6
421840
10.0
[46]
video
194
158528
1.5
[99]
HD video hopper system
video
6
21490
3.0
[100]
Ocean Floor Observation
System
photographs
2882
8570
0.8-11.6
[43]
T o w e d c a m e r a s y s t e m s Seatronics
Further technical information about each platform can be found in the indicated references.
doi:10.1371 /journal.pone.0095839.t002
O bservation System (O FO S) a t the H A U S G A R T E N observatory,
station IV . T echnical details ab o u t each platform can b e found
elsew here (see T ab le 2). T raw l sam ples w ere collected using two
different gears: a n et (G O C 73) w ith a 20 m m -d ia m o n d stretched
m esh size a t the cod-end [56] a n d a n otter traw l M a ireta System
(O T M S), w ith a c o d-end m esh size o f 40 n in i a n d a n o u ter cover
o f 12 nin i [29,57].
T raw lin g a t the o th er M e d ite rran e a n sites was p erfo rm ed using
an otter traw l M a reita System (O T M S ). All litter item s w ere
separated a n d classified into different categories (see above) a n d
w eighed, after excess w ater a n d m u d h a d b e en rem oved. T h e use
o f w eight ra th e r th a n n u m b e r to quantify litter was based on the
high a b u n d an c e o f bro k en plastics (from w hole plastic bags to very
small (< 0 .5 cm) pieces o f plastics) a n d bro k en glass, w hich
im p ed ed the q uantification o f single item s w ithout overestim ating
abu n d an ces o f certain categories over others [29].
Analysis o f i m a g e d a t a
Protocols for video analysis varied slightly according to the
platform used, b u t follow ed the sam e general outline. T h e entire
footage was visualised a n d the n u m b e r o f litter item s a n d d ep th
recorded. E ac h litter item was classified into six different
categories: plastic (all plastic w ith exception o f fishing line a n d
net), derelict fishing gear (fishing line o r net), m etal, glass, clinker
(residue o f b u rn t coal). B ecause o f the low densities found at all
sites, p a p e r a n d c ard b o a rd , fabric, w ood a n d unidentified item s
w ere gro u p ed in the sam e category (other items). A lthough fishing
lines a n d nets are m ostly m ad e o f plastic, fishing gear was
considered as a separate litter category because o f o u r know ledge
o n its source a n d social im plications a n d the p a rticu la r im pacts o f
this type o f litter, such as ghost fishing a n d entanglem ent.
F o r each dive (sample), the a re a covered was calculated by
m ultiplying the lin ear distance o n the seafloor (off b o tto m footage
w ere excluded from the analysis) b y the average w idth o f view o f
each o f the platform s (T able 2).
F o r d a ta derived from still pho to g rap h s (O FO S), all im ages
along each transect (taken a t 30 s to 50 s-intervals) w ere analysed
for the presence o f litter item s. Parallel laser points o n the im ages
allow ed calculations o f the a rea for each im age; ran g in g betw een
0.8 a n d 11.6 m~. F or O F O S , each im age was considered to b e a
separate sam ple, while for video d ata, each dive was considered a
single sam ple.
D ata analy sis
F o r each sam ple (video a n d still photographs), litter density was
estim ated as item s o f litter hectare 1 (lia; 10,000 m~) o f seafloor
surveyed. F o r traw l d a ta w here litter was m easu red in w eight, litter
density was estim ated as kg o f litter h a - 1. Sites w ere gro u p ed into
6 different groups acco rd in g to physiographic characteristics
(T able 1); (1) co n tinental shelves; (2) co n tinental slopes (excluding
subm arine canyons); (3) subm arine canyons; (4) seam ounts, banks
a n d m ounds; (5) ocean ridges a n d (6) deep basins. T ests for
investigating differences am o n g litter densities across physiograph­
ic settings w ere done separately according to the unit in w hich
litter density was estim ated (num ber h a 1 o r w eight h a *). F or
b o th cases, the d a ta w ere n o t norm ally distributed b u t variances
w ere equal, therefore, the n o n -p a ra m etric K ruskal-W allis rank
sum test follow ed b y a m ultiple com parison test (D u n n ’s pairw ise
com parison) w ere p erfo rm e d using the statistical package R.
V a riatio n in litter com position b etw een physiographic settings
w ere tested for significance using A N O S IM (Analysis o f similarity)
in P R IM E R v6 software [58], B ray-C urtis sim ilarity [59] was
calculated o n log(x+l) tran sfo rm atio n o f the percen tag e c o n trib u ­
tion o f litter type for each o f the physiographic settings, across the
entire d a ta set. A sim ilarity percentage analysis (SIM PE R ) was
applied to identify the discrim inating feature o f the dissim ilarities
a n d sim ilarities b etw een physiographic settings.
Trawl d a t a
Results
H auls in the G u lf o f L ion (shelf a n d subm arine canyons) w ere
p erfo rm ed w ith a b o tto m traw l eq u ip p ed w ith a G O C 73 n et [56],
A fter traw ling, litter item s w ere co u n te d a n d classified into the
different categories (see above).
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U tte r d e n s i ty
L itter was found a t all sites a n d all depths (from 35 m dow n to
4500 m) sam pled. M ost co m m o n litter item s included plastic bags,
5
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Litter on the Seafloor o f European Waters
A
B
C
D
E
F
T h e sites sam pled by traw ling in the M e d ite rran e a n revealed a
relatively even distribution o f litter b u t w ith a h igher density on the
continental slope, south o f P alm a de M allorca (western M e d ite r­
ranean) w ith a m ea n (± S E ) o f 4.0 ± 1 .8 kg o f litter h a 1 as
opposed to densities ran g in g betw een 0.7 a n d 1.8 kg o f litter h a 1
at the o th er sites (Figure 5).
W h en g rouping all sites into physiographic settings, th ere w ere
significant differences in litter density (items h a *) betw een the
various groups (Kruskal-W allis x ^ = 26.68; p < 0 .0 1 ; D F = 4).
M ultiple com parisons tests indicated th a t litter density in
subm arine canyons was significantly h igher th a n those from all
o th er physiographic settings, reach in g a n average (± SE) o f
9 .3 ± 2 .9 item s h a - (Figure 6a). L itter density o n seam ounts,
m ounds a n d banks was sim ilar to the densities found o n the
continental slopes w ith m ea n (± SE) densities o f 5 .6 ± 1 .0 a n d
4.1 ± 2 .1 item s h a *, respectively (Figure 6a). M e a n (± SE) litter
density for continental shelves a n d ocean ridges was 2 .2 ± 0 .8 a n d
3 .9 ± 1.3 item s h a *, respectively (Figure 6a). F o r M e d ite rran e a n
sites, w here litter density was q u antified by w eight ra th e r th an
n u m b e r o f item s, no significant differences w ere found in litter
density b etw een the th ree different physiographic settings
(Kruskal-W allis x^ = 3.88; p = 0.144; D F = 2). Flow ever, litter
density in deep basins was slightly h igher (1.5 5 ± 0.5 7 kg h a *)
c o m p a red to continental slopes (1 .3 6 ± 0 .3 4 kg h a *) a n d subm a­
rine canyons (0.71 ± 0 .2 5 kg h a *) (Figure 6b).
.'"i-f'V ÿ & ê ÿ
Litter c o m p o s i t i o n
T h e re was a high variability in the com position o f litter across
the different sites (T able 3). A total o f 546 litter item s w ere
e n co u n tere d th ro u g h o u t all sites surveyed w ith im aging technol­
ogy. Plastic a n d derelict fishing gear w ere the m ost a b u n d a n t litter
item s. Plastic rep resen ted 41% o f the litter item s, whilst derelict
fishing gear acco u n ted for 34% o f the total. Clinker, glass a n d
m etal w ere least co m m o n (1, 4 a n d 7% , respectively). Item s
classified as “ o th er item s” a cco u n ted for 13% o f the litter item s
e n co u n tere d in sites surveyed b y im aging technology a n d included
w ood, p a p e r/c a rd b o a rd , clothing, pottery, a n d unidentified
m aterial. Analysis o f litter density from traw l surveys found plastic
to be the m ost co m m o n litter type to be recovered (found in 98%
o f the trawls), follow ed b y clinker (73%), fabric (48%), derelict
fishing gear (33%), m etal (31%) a n d glass (28%).
Results from A N O S IM show ed th a t th ere w ere significant
differences in litter com position b etw een physiographic settings (1w ay A N O S IM ; G lobal R = 0.32; p < 0 .0 0 1 ), the analysis also
show ed som e settings to b e sim ilar (T able SI). T h e re w ere no
significant differences betw een litter com position in subm arine
canyons a n d continental shelves (R = 0.01; p = 0.58). A ccording to
S IM P E R analysis (Table S2), the sim ilarity in com position
betw een subm arine canyons a n d continental shelves was m ostly
driven b y plastic. Plastic was the d o m in a n t litter category for b o th
settings (Figure 7). L itter com position o n ocean ridges a n d on
seam ounts, banks a n d m ounds did n o t show significant differences
in litter com position (R = 0.17; p = 0.06), due to a p red o m in an ce
o f derelict fishing gear (Figure 7). Finally, litter com position found
o n continental slopes was sim ilar to deep basins ( R = —0.11;
p = 0.87). C linker a n d plastic w ere the categories c o ntributing
m ost to the sim ilarities b etw een these two physiographic settings.
Figure 2. Litter items on th e seafloor o f European w aters. A =
Plastic bag e n tra p p e d by a small d ro p sto n e harbouring sp o n g e s
(Cladorhiza gelida, Caulophacus arcticus), shrim ps (Bythocaris sp.) and a
crinoid (Bathycrinus carpenterii) recorded by an OFOS at th e HAUSGARTEN o b servatory (Arctic) at 2500 m; B = Litter recovered w ithin th e n et
o f a trawl in Blanes o p e n slope at 1500 m during th e PROMETO V cruise
on board th e R/V "Garcia del Cid"; C = "H eineken" b eer can in th e
u p p e r W hittard canyon at 950 m w ater d e p th w ith th e ROV Genesis; D
= Plastic bag in Blanes Canyon a t 896 m with th e ROV "Liropus"; E =
"Uncle Benn's Express Rice" packet a t 967 m in Darwin M ound w ith th e
ROV "Lynx" (National O ceanography C entre, UK); F = Cargo n et
en tan g led in a cold-w ater coral colony a t 950 m in Darwin M ound with
th e ROV "Lynx" (National O ceanography Centre, UK).
doi:10.1371/jo u rn al.pone.0095839.g002
glass bottles a n d derelict fishing lines a n d nets (Figure 2). L ocations
w ith highest litter densities (> 2 0 item s h a ) included the L isbon
C anyon, the Blanes C anyon, the G uilvinec C anyon, a n d the
Setúbal C an y o n (T able 1; Figure 3). Sites w ith in term ed iate litter
density (betw een 10 a n d 20 item s h a ’) w ere found o n the C o n d o r
Seam ount, the W yville-T hom son R idge, the continental slope o f
the F1ALTSGARTEN observatory a n d the C ascais C anyon
(Figure 3). Low densities (betw een 2 a n d 10 item s h a - 1 ) w ere
re co rd e d o n the D arw in M ounds, off the N orw egian m argin, in
D a n g ea rd a n d E xplorer C anyons, o n the Jo sep h in e S eam ount, in
the N azaré C anyon, o n the R o sem ary Bank, south o f the C harlieG ibbs F ra c tu re Z o n e a n d on the P e n D uick A lpha a n d B eta
M ounds (Figure 3). T h e lowest litter density (< 2 item s h a ) was
found o n the F latto n Bank, the continental slope o n the n o rth e rn
side o f the F aro e-S h etlan d C hannel, o n the A nton D o h rn
Seam ount, in the W h ittard C anyon, o n the R ockall Bank, n o rth
o f the C harlie-G ibbs F ra c tu re Z one, a n d in the G u lf o f L ion (in
b o th the continental shelf a n d subm arine canyons). Sites w ith
h igher litter density w ere found principally closer to shore
(Figure 4), b u t th ere w ere exceptions, such as the sam ples from
the G u lf o f L ion w here litter densities w ere low (T able 1).
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D iscussion
T h e o ccurrence o f litter o n the seafloor has b e en far less
investigated th a n in surface w aters o r o n beaches, principally
because o f the high cost a n d the technical difficulties involved in
sam pling the seafloor a t bathya! a n d abyssal depths [21,60],
6
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Litter on the Seafloor o f European Waters
40°W
30°W
20°W
10"W
Litter density (n item s h a 1)
Figure 3. L itter densities (nu m b er o f item s ha ') in d iffe re n t locations across European waters o b tain ed w ith ROVs, tow ed camera
systems, m anned subm ersible and trawls.
doi:10.1371/jo u rn al.pone.0095839.g003
C onsidering such lim itations a n d p o o r know ledge o n litter
accum ulation in deep w aters, every survey is o f g reat value for
ob tain in g in form ation o n litter density a n d distribution. In the
presen t study, we in te g rate d d a ta collected d u rin g n um erous
cruises over a large regional scale into a single analysis, providing
insight o n the density a n d com position o f litter across a wide
variety o f seafloor settings a n d over a large geographical a rea in
E u ro p ea n w aters. A lthough standardisation o f the d a ta p e rm itte d
com parisons b etw een sites, dissim ilarities in the sam pling eq u ip ­
m en t implies th a t the results should be tre a te d w ith caution.
F u rth e rm o re , differences in the areas o f the seafloor surveyed
betw een locations m ay lead to overestim ations o r underestim ations o f the litter density. Also, studying litter from traw ls
introduces the issue o f quantification units (num ber vs. weight),
w ith no correct solution. W h en using n u m b e r o f item s, certain
litter categories m ay be overestim ated such as plastic or glass th at
can b re ak into m an y small pieces. As a c o u n te rp art, if w eight is
used, the a b u n d an c e o f litter type w ith different weights (e.g. heavy
clinker vs. light plastic) c an n o t b e com pared. Ideally, b o th units for
litter quantification will help to u n d e rstan d b e tte r trends, b u t the
EFT M a rin e Strategy Fram ew ork D irective stresses th a t for
m on ito rin g litter in the m arin e environm ent, n u m b e r is m a n d a ­
tory whilst w eight is only reco m m en d ed [2].
L itter was found a t all the locations surveyed, from sites close to
pop u latio n centres such as the G u lf o f L ion o r the L isbon C anyon
to as far as the S o u th C harlie-G ibbs F ractu re Z o n e o n the M idA tlantic R idge, located at ab o u t 2000 km from land. L itter was
PLOS ONE I w w w .plosone.org
found from shallow w aters (35 m eters in G u lf o f Lion) dow n to
4500 m eters (Cascais C anyon). Such records w ere n o t surprising,
as litter is know n to b e presen t in all seas a n d oceans o f the planet,
as rem ote as the S o u th ern O c ea n [21] a n d at depths as deep as
7216 m in the R yuku trench, south o f J a p a n [61], T h e range o f
litter densities found o n o u r study sites was w ithin the sam e ord er
o f m agnitude to the ones found on the seabed in o th er p a rts o f the
globe (N orth A m erica [55,62,63], C h in a [54], J a p a n [64,65]) a n d
for o th er locations in E u ro p e [28,44,45,47,48], O n the o th er han d ,
m acro litter densities o n the seabed w ere h igher th a n re p o rte d for
surface w aters [32,66-69], A t the surface, floating litter tends to
accum ulate in frontal areas b u t eventually reaches the seabed
w hen heavily covered b y fouling organism s [70] o r lo ad ed w ith
sedim ents. C o n trary to a co m m o n n otion th a t m ost plastic item s
float a t the sea surface it has b e en estim ated th a t 7 0 % o f the plastic
sinks to the seafloor [23]. T his results in m acro litter accum ulation
o n the seabed ra th e r th a n in the o p en sea [21]. F or exam ple, on
the seafloor o f the M e d ite rran e a n Sea, o u r d a ta show ed m uch
h igher litter densities (0.4 to 48 litter item s h a - 1 ) th a n th at
estim ated to float at the surface (0.021 item s h a - ; [1]).
A lternatively, floating litter m ay be tran sp o rte d for considerable
distances a n d get w ashed ashore [71,72]. L itter density o n the
coastline is typically h igher th a n on the seafloor given th a t th ere is
an ad ditional in p u t o f w aste com ing from inland sources (e.g. m anm ad e drain ag e systems, recreational usage, rivers, w inds, etc.)
[71,73]. O n E u ro p ea n coasts, litter densities can exceed 30,000
litter item s p e r lin ear km [1,41,74], while m u ch h igher densities
7
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Litter on th e Seafloor o f European Waters
70
L .C
•
o
•
60 -
•
•
•
O cean ridges
Seam ounts, banks and m ounds
S ubm arine canyons
Continental shelves
Continental slopes
50 -
40
BC
•
30
m
S .C
m
CD
“O
CD
G C
20
C .S
•
H.IV
10
D & E .C
PÔ M
G .L ^
10
N .C
•
G .L .C ^
R o s .B
N -E .F .C
S . C -G
m
ä H .B
AS vTc^ r-b
® n .F .C
n
r
C -G
o
°
1000
100
D istance from land (km )
Figure 4. Litter densities (num ber o f items h a 1) in d iffe re n t locations across European w aters according to th e ir closest distances
from land, x axis is in a Logq0 scale. A.S = Anton Dohrn S eam ount, B.C = Blanes Canyon (NW Med.), C.C = Cascais Canyon, C.S = C ondor
S eam ount, D&E.C = D angeard & Explorer Canyons, D.M = Darwin M ounds, G.L.C = Gulf of Lion canyons (NW Med.), G.L = Gulf of Lion, G.C =
Guilvinec Canyon, H.B = H atton Bank, H.IV = HAUSGARTEN, station IV, J.S = Jo sep h in e S eam ount, L.C= Lisbon Canyon, N.C = Nazaré Canyon, N.CG = North Charlie Gibbs Fracture Zone, N-E.F.C = North-East Faroe-Shetland C hannel, N.F.C = North Faroe-Shetland Channel, N.W= N orwegian
m argin, P.D.M = Pen Duick Alpha/Beta M ound, R.B = Rockall Bank, Ros.B = Rosem ary Bank, S.C = Setúbal Canyon, S.C-G = South Charlie Gibbs
Fracture Zone, W.C = W hittard Canyon, W-T.R = Wyville-Thomson Ridge.
doi:10.1371/journal.pone.0095839.g004
litter density (kg ha1),
’
;
0.6 - 1.0
§
1.1-1.5
1 . 6 - 2.0
Figure 5. Litter densities (kg ha n) in d iffe re n t locations across th e M ed iterran ean Sea obtain ed from traw l surveys.
doi:10.1371/journal.pone.0095839.g005
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Litter on the Seafloor o f European Waters
continental shelf dow n into M o n terey C an y o n [78], Such
p h e n o m e n a m ay explain w hy continental shelves w ere the settings
w ith overall lowest litter density, whilst subm arine canyons h a d the
highest litter concentration. L itter levels o n seam ounts, banks,
m ounds a n d ocean ridges w ere c haracterised by interm ediate
levels w hen c o m p a red to o th er physiographic settings. T h ey are
typically located far aw ay from coastal areas w here the m ain
anthropogenic activities include fishing [79] a n d seabed m ining
[80,81], T h e presence o f litter o n these settings is o f concern
because they h a rb o r V ulnerable M a rin e Ecosystem s (VMEs) (such
as cold-w ater corals a n d h y d ro th erm al vents) th a t have reduced
capacity to recover from d isturbance events a n d for w hich
conservation is a global prio rity [82].
T h e types o f accu m u lated litter can provide a n indication on the
h u m a n activities im pacting a p a rticu la r location. H ow ever, one
m ust b e cautious a n d consider the differences in the b uoyancy a n d
longevity o f the different types o f litter. F or exam ple, w hile some
plastics sink to the seafloor, others float on the surface a n d are able
to travel g reat distances before eventually sinking far from their
initial d u m p in g locations, follow ing biofouling a n d d e gradation
[23]. O n the o th er h a n d , glass, m etal a n d clinker will sink rapidly
a n d are expected to be recovered from the seafloor close to sites
w here they w ere initially released. C a rd b o a rd a n d fabrics (of
organic origin) will b re ak dow n quickly, im plying th a t such item s
will not re ac h the deep ocean w ith the frequency o f m ore resistant
m aterials such as plastic a n d negatively b u o y a n t item s such as
glass, m etal a n d clinker. A lthough it is difficult to d eterm ine the
exact source o f the litter observed o n the seafloor, the dom in an t
litter category can b e used as a n indicator to separate ocean a n d
terrestrial sources [15,29,31,78], Plastic (other th a n derelict fishing
gear) was the m ost a b u n d a n t litter category in subm arine canyons,
continental shelves a n d continental slopes. T h e p red o m in an ce o f
plastics in subm arine canyons reaffirm s th a t litter accu m ulation in
these habitats com es from coastal a n d lan d sources a n d th at
subm arine canyons act as conduits for litter tran sp o rt from
continental shelves into deep er w aters [21,28,29,31,47,78],
T h erefo re, subm arine canyons can b e considered to be a cc u m u ­
lation zones o f land-based m arin e litter in the deep sea. In fact,
subm arine canyons are areas w here m acrophyte detritus th at
originates from coastal areas accum ulates in high quantities. T his
results in a localised increase o f organic m atter a n d high
abu n d an ces o f associated fauna, d o m in a ted by deposit a n d
suspension-feeding invertebrates [83-85]. Since som e depositfeeders (e.g. holothurians) have b e en show n to select plastic
fragm ents over sedim ent grains u n d e r lab o ra to ry conditions [7],
the accum ulation o f plastics in subm arine canyons could have
d etrim en tal effects for these ecologically im p o rta n t deep-sea
organism s. F u rth e rm o re , plastic fragm ents c o n ta in a w ide variety
o f persistent organic pollutants (POPs) th a t m ay accum ulate in the
co n su m er’s tissues a n d can be tran sferred upw ards in the trophic
w ebs to pred ato rs, including h u m an s [86],
D erelict fishing g ear was the m ain litter item found on
seam ounts, banks, m ounds a n d ocean ridges im plying th at, unlike
subm arine canyons, fishing activities are the m ajo r source o f litter
at those settings. Seam ounts a n d banks are targ eted b y com m ercial
fishing activities as they are often highly productive areas
supporting dense aggregations o f com m ercially valuable fish a n d
shellfish [87]. A t o th er locations w here recreational [55,88] a n d
com m ercial [28,54,62,89] fishing activities are intense, derelict
fishing g ear d o m in a ted the litter on the seabed. It was b e y o n d the
scope o f this study to evaluate the im pacts caused by derelict
fishing gear, b u t n um erous studies have show n diverse im pacts
including ghost fishing [16,90] a n d entan g lem en t b y sessile
invertebrates such as corals [15], as well as causing d am age to
E
<D
> : >
X
s’
B
<n
■a
Figure 6. M ean litte r d ensity ( ± standard error) in A = num ber
o f item s ha 1 and B = in kg o f item s ha
across d iffe re n t
physiographic settings in European waters.
doi:10.1371/jo u rn al.pone.0095839.g006
have b e en re p o rte d for beaches in In d o n esia [75] or on the
beaches along A rm açao dos Buzios, R io de Ja n e iro , B razil [76],
H ow ever, com parisons b etw een studies are challenging consider­
ing differences in the size o f the litter item s sam pled a n d the
sam pling m ethodology used [77].
O u r d a ta show ed a general increase in litter density in locations
closer to the shore, a p a tte rn previously re p o rte d for the F rench
M e d ite rran e a n coast [47] a n d off C alifornia [55]. N evertheless,
low litter densities in som e n ear-shore sites (e.g. G u lf o f L ion or
F aro e-S h etlan d channel) suggest th a t m an y o th er factors (such as
geom orphology, h y d ro g rap h y a n d h u m a n activity) affect litter
distribution a n d accum ulation rates [29]. In the G u lf o f L ion,
G algani et al. [47] suggested th a t low litter density on the shelf was
caused b y strong w ater flow from the R h o n e R iver, tran sp o rtin g
litter dow n south to d eep er w aters. A sim ilar situation occurs in
M o n terey B ay w here sedim ent a n d litter are bein g sw ept off the
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Litter on the Seafloor o f European Waters
Table 3.
Com position o f litte r (%) in different locations on the seafloor o f European waters.
Location
D erelict fish in g g e a r
G lass
M etal
Plastic
O th e r item s
Clinker
North Faroe-Shetland Channel
100.0
0.0
0.0
0.0
0.0
0.0
North-East Faroe-Shetland Channel
100.0
0.0
0.0
0.0
0.0
0.0
80.0
0.0
0.0
20.0
0.0
0.0
Dangeard & Explorer Canyons
72.2
0.0
0.0
16.7
11.1
0.0
ATLANTIC
C o n tin e ntal slopes
C o n tin e ntal s h e lf
Norwegian Margin
Subm arine canyons
Nazaré Canyon
37.1
0.0
17.1
25.7
20.0
0.0
Lisbon Canyon
9.2
0.0
1.5
86.2
3.1
0.0
Setúbal Canyon
8.7
4.3
4.3
30.4
52.2
0.0
Cascais Canyon
9.1
0.0
0.0
54.5
36.4
0.0
Guilvinec Canyon
43.8
0.0
0.0
43.8
6.3
6.3
Whittard Canyon
28.6
7.1
14.3
42.9
0.0
7.1
Anton Dohrn Seamount
0.0
0.0
100.0
0.0
0.0
0.0
Condor Seamount
85.5
14.5
0.0
0.0
0.0
0.0
Josephine Seamount
42.9
28.6
14.3
0.0
14.3
0.0
Hatton Bank
87.5
0.0
12.5
0.0
0.0
0.0
Rockall Bank
33.3
0.0
66.7
0.0
0.0
0.0
Rosemary Bank
66.7
0.0
33.3
0.0
0.0
0.0
Pen Duick Alpha/Beta Mound
75.0
0.0
25.0
0.0
0.0
0.0
Darwin Mounds
10.0
0.0
15.0
60.0
15.0
0.0
Seamounts, banks a n d m ounds
Ocean ridges
North Charlie Gibbs Fracture Zone
0.0
0.0
100.0
0.0
0.0
0.0
South Charlie Gibbs Fracture Zone
0.0
28.6
28.6
28.6
14.3
0.0
Wyville-Thomson Ridge
85.7
0.0
14.3
0.0
0.0
0.0
Calabrian Slope (Central Med.)
13.2
0.0
8.4
36.2
26.6
15.5
Western Mediterranean Slope
21.6
0.6
0.2
12.1
0.6
64.9
Crete-Rhodes Ridge (E. Med.)
1.6
9.3
6.0
17.0
20.5
45.5
Blanes slope (NW Med.)
2.3
7.9
8.4
12.6
11.6
57.1
0.0
0.0
0.0
88.9
11.1
0.0
Blanes Canyon (NW Med.)
3 (0.2)
3 (4.9)
6 (2.2)
78 (76.3)
9 (1.7)
0 (14.7)
Gulf of Lion Canyons (NW Med.)
0.0
0.0
0.0
67.3
32.7
0.0
Algero-Balearic Basin (W. Med.)
16.5
0.8
29.6
14.0
2.1
37.0
Crete-Rhodes Ridge (E. Med.)
0.0
9.7
25.0
19.5
7.2
38.5
Calabrian Basin (Central Med.)
0.5
6.7
0.7
5.9
36.1
50.1
2.5
2.5
2.5
60
32.5
0
MEDITERA NEA N
C o n tin e ntal slopes
C o n tin e ntal s h e lf
Gulf of Lion (NW Med.)
Subm arine canyons
Deep basins
ARCTIC
C o n tin e ntal slope
HAUSGARTEN, station IV
^Numbers in parentheses refer to trawl surveys.
doi:10.1371 /journal.pone.0095839.t003
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Litter on the Seafloor o f European Waters
Continental shelves
som e areas o f the seafloor investigated here a n d elsew here
[28,44,45,54,78] h a rb o u r significant quantities o f n on-b u o y an t
litter such as glass, m etal a n d clinker, directly d u m p ed from ships
b u t th a t are seldom found in surface w aters [41,68] o r on the
coasts [41,72]. T h e coasts a n d surface w aters are a source o f litter
item s for the o p en seas a n d all this litter, sooner o r later, will sink
to the seafloor w here it accum ulates.
T h e m ost co m m o n m eth o d used to provide d a ta o n benthic
m arin e litter has b e en traw ling, typically as a parallel objective to
surveys directed to fish o r benthic organism sam pling [53]. W ith
the recent developm ent o f optical m ethods fitted to platform s such
as subm ersibles, R O V a n d d rop-dow n systems, the use o f
u n d e rw ate r im aging technology has greatly increased o u r ability
to quantify deep-sea litter. B oth m ethods (im aging technology a n d
traw ling) have distinct assets for studying benthic litter th a t should
be used in conjunction to best u n d e rstan d the dynam ics o f
pollution o n the seafloor. V ideo surveys c an provide d a ta for areas
w here to p o g rap h y is com plex (e.g seam ounts o r canyon walls),
habitats m ad e b y structure-building organism s (e.g. cold-w ater
corals), or dynam ic systems (e.g. h y d ro th erm al vents a n d cold
seeps), th a t c an n o t be accessed w ith a traw l [53]. F u rth erm o re,
im aging is a non-intrusive m eth o d th a t does not rem ove benthic
organism s o r dam age the environm ent. O n the o th er han d , a traw l
has the advantages o f recovering litter item s o f very small size (e.g.
small plastic fragm ents) o r th a t are b u rie d in the sedim ents (e.g.
clinker), w hich otherw ise w ould n o t b e d etected th ro u g h im aging
technology. In addition, litter item s collected w ith a traw l c an be
analysed in the lab o ra to ry to o b tain fu rth er im p o rta n t inform a­
tion, such as state o f d eg rad atio n or colonisation by fouling
organism s [92]. Such d a ta will help u n d e rstan d sinking processes
o f plastic , facilitate the identification o f th eir location o f arrival into
the ocean a n d provide in form ation o n the im pacts o f litter on
m arin e organism s.
T h e large quantities o f litter reach in g the deep ocean floor is a
m ajo r issue w orldw ide, yet little is know n ab o u t its sources,
p attern s o f distribution, a b u n d an c e and, particularly, im pacts on
the habitats a n d associated fauna [1], A t present, density o f litter in
the deep sea is low er th a n found o n som e heavily p o lluted beaches
[33,93], b u t unlike the coastal zone, only a tiny fraction o f the
(deep) seafloor has b e en surveyed to date. F u rth e rm o re , m icroplastic accum ulation m ay becom e a n im p o rta n t c o m p o n e n t o f
pollution in deep-sea ecosystem s [94] th a t urgently needs to be
evaluated. O u r results for E u ro p ea n w aters show th a t litter sources
are distinct across different physiographic settings a n d th a t their
ab u n d an c e is variable, m ost p ro b ab ly guided b y a com plex set o f
interactions b etw een physiography, a nthropogenic activities a n d
hydrography. It is im p o rta n t th a t in the future, large-scale
assessments are done in a standardised m an n e r to u n d e rstan d
fully the scale o f the pro b lem a n d set the necessary actions to
p re v en t the accum ulation o f litter in the m arin e environm ent.
Continental slopes
*
Submarine canyons
*
Seamounts, banks & mounds
•
Ocean ridges
•
Deep basins
*
□
■
■
■
Plastic
Fishing gear
Metal
Glass
Other
Clinker
Figure 7. L itter com position in d iffe re n t physiographic settings
across European waters.
doi:10.1371/jo u rn al.pone.0095839.g007
fishing eq u ip m en t [91]. D iscarded traw l gear can also have a
co m p o u n d in g effect by trap p in g m o re m obile litter resulting in a
litter ‘d e p o t’ th a t has a greater im pact th a n single pieces o f litter
[31]. Since m ost fishing eq u ip m en t (lines a n d nets) is m ad e m ostly
o f highly resistant plastics, such negative effects will likely persist
for a long tim e. Sites located in deep basins a n d continental slopes
w ere d o m in a ted by clinker. Clinker, the residue o f b u rn t coal, was
com m only d u m p ed from steam ships from the late 18th century
a n d well into the 20th century. In the M e d ite rran e a n Sea, its
occurrence on the deep seafloor has b e en show n to coincide w ith
such shipping routes [29]. H ow ever, it is im p o rta n t to acknow l­
edge th a t in this study, deep basins a n d co n tinental slopes w ere
principally sam pled b y traw ling a n d it is difficult to d eterm ine if
the differences in litter com position w ith o th er physiographic
settings are the results o f differences in the sam pling m ethodology,
p articularly since clinker is difficult to identify from un d erw ater
footage. Indeed, clinker was present in n o n -quantitative traw ls
u n d e rta k en at H A U S G A R T E N (B ergm ann, u n p ublished data),
b u t could n o t b e detected on im ages from the seafloor. Sim ilarly, a
high a b u n d an c e o f clinker was recovered from traw l surveys in
Blanes C an y o n th a t could not b e identified in analysis o f R O V
footage from the sam e a rea (T able 3). G iven th a t m ost o f the
clinker presen t on the seafloor was d u m p ed over 100 years ago,
sedim entation will have b u ried it, w hich w ould explain the
differences in clinker quantification betw een im ages a n d traw l
d ata. T h e deep seafloor is a passive accum ulation a rea for litter,
integrating in form ation over long-tim e periods. If traw ls are able
to recover heavy clinker deposited o n the seafloor over a century
ago, these gears m ust be retrieving at the sam e tim e all o f the
lighter a n d m ost recent litter item s, such as plastic for exam ple,
th a t have b e en accu m u latin g only in the last 50 years. O verall, the
com position o f litter found o n the seafloor show ed some
dissim ilarity w ith the com position fo und o n the coasts or in
surface w aters. A lthough plastics are d o m in a n t in all settings [70],
PLOS ONE I w w w .plosone.org
Supporting Information
T a b le S I R esults o f analyses o f sim ilarity (A N O SIM ) evaluating
variatio n in the com position o f litter am o n g physiographic settings.
R ID G E : ocean ridges; CAN Y: subm arine canyons; SH E L F:
continental shelves; S L O P E : co n tinental slopes; SBM : seam ounts,
banks a n d m ounds; BASIN: deep basins.
(D O C X )
T a b le S2 Sim ilarity percen tag e analysis (SIM PER) o f litter
com position for each pooled physiographic settings (based on
sim ilarities revealed b y A N O S IM ) a n d the con trib u tio n o f litter
category to group sim ilarity.
(D O C X )
11
A pril 2014 I V olum e 9 | Issue 4 | e95839
Litter on the Seafloor o f European Waters
A ck n ow led gm en ts
Author C ontributions
T he authors would like to thank the captains, crews and scientific parties of
all cruises for their help and support during the data collection. P T would
like to thank G ideon M ordecai for analytical work and D oug Masson.
Finally, the authors would like to thank M artin T hiel and two other
anonym ous reviewers, whose suggestions and com m ents greatly improved
the m anuscript. This is publication num ber 33575 o f the Alfred-W egenerInstitut H elm holtz-Zentrum für Polar- und Meeresforschung.
Conceived and designed the experiments: C K P E R L C H SA T A MB M C
JB C J D G D F G K L H V A IH E I D O B J GL T M JN G P AP HS IT X T
D V R PT. Perform ed the experiments: C K P E R L C H SA T A MB M C JB C
J D GD F G K L H V A IH EI D O B J GL T M JN G P AP H S IT X T D V R PT.
Analyzed the data: C K P. W rote the paper: C K P.
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