This document is a student thesis submitted by Noelle Dunne that examines microplastic ingestion by dab fish (Limanda limanda) off the west coast of Ireland. The study found that 41% of the 87 fish examined contained microplastics in their gastrointestinal tracts, with an average of 2.2 pieces of plastic per fish. Fibres made up 95% of the plastics found. Larger fish and females contained more plastics. The study contributes to understanding of microplastic ingestion in fish and its potential long-term impacts.

1. Ingestion of microplastics by the dab (Limanda
limanda)off the west coast of Ireland: a comparison
between biological traits.
by
Noelle Dunne
Student No: G00251388
Supervisor: Amy Lusher
Submitted in partial fulfilment of the requirements for the B.Sc. Honours Degree in
Applied Freshwater and Marine Biology at the Galway-Mayo Institute of Technology.
Submitted on the 9th of May, 2013.
I confirm that, except where indicated by the proper use of citations and references, this is my
original work.
Signed: ________________________________

2. ABSTRACT1
Plastic pollution in the marine environment has become increasingly dangerous to marine2
biota causing death by entanglement or ingestion throughout the planet. Although many3
studies have documented macroplastic ingestion in sea birds, mammals and sea turtles little is4
known about microplastic ingestion in fish. This study documents microplastic ingestion by5
dab (Limanda limanda) in waters off the west coast of Ireland. Out of the 87 fish examined,6
41% contained plastics in their gastrointestinal tracts. From the fish containing plastics, a7
total of 80 particles were found averaging at 2.2 (± 0.16) pieces per fish. Fibres were the most8
frequently encountered particles, making up 95% of the plastics. 94% of the particles were9
less than 5mm therefore classified as microplastics. Plastic particles were found in 33% of 2710
males and 45% of 60 females. Typically the fish from larger size classes including total fish11
length (cm) and weight (g) contained the most plastics. A dietary analysis showed that12
species from phyla Mollusca and Crustacea were the most frequently occurring food items.13
From the stomachs that were classified as full or empty, there was no significance between14
the numbers of microplastics found. Further investigations are needed to determine the long15
term impacts of microplastic ingestion in fish and if they are capable of passing plastics16
through their digestive system.17
1. Introduction18
The persistent increase in anthropogenic wastes over the last few decades has become a large19
threat to aquatic species, especially with the introduction of plastic litter into the marine20
environment. Mass production of plastics began in the 1950s at around 1.5 million tonnes21
increasing to 280 million tonnes in 2011, with production increasing at an unsustainable rate22
of approximately 10% per year (PlasticsEurope, 2012). Plastic wastes make up approximately23
10% of the world’s waste and represent 50-80% of shoreline debris (Barnes et al., 2009;24
Thompson et al., 2009). Natural forces such as wind and wave action aid in the distribution of25
plastic litter throughout the oceans. During extended periods of sunlight exposure the plastics26
succumb to photo-degradation, where ultraviolet (UV) radiation causes oxidation of the27
polymer matrix, resulting in bond cleavage (Andrady, 2011; Barnes et al., 2009; Moore,28
2008). This process may result in harmful chemical additives leaching out from the plastics29
into the marine environment (Talsness et al., 2009). Two of the most widely used chemicals30
in plastic production are bisphenol A (BPA) and phthalates (plasticizers). These have been31
shown to affect reproduction, behaviour and development in studied aquatic and terrestrial32

3. animal groups (Oehlmann et al., 2009). A laboratory study by von Moos et al. (2012)33
exposed the blue mussel (M. edulis) to high density poly-ethylene, which is an ideal plastic34
free of additives, and found that granulocytomas formed after three hours and then35
destabilization in the lysosomal membrane after six hours which continued to increase with36
longer exposure. These chemicals have been detected not only in aquatic environments, but37
also in dust and air which may have adverse health implications in the human population38
(Rudel et al., 2001).39
Plastics are favourable materials because of their durability, lightweight and low cost,40
however they don’t readily degrade in the environment which has proved to be problematic41
(Andrady, 2011; Sivan, 2011; Thompson et al., 2009). Rather than degrading, plastics42
consistently breakdown into fragments which may then be ingested by organisms (Graham &43
Thompson, 2009). Research has evidenced that over 260 marine species are affected by44
plastic debris worldwide (Moore, 2008), including 86% of sea turtles, 44% of seabirds and45
43% of mammal (Laist, 1997). Plastic ingestion or encounters by marine organisms may lead46
to chemical poisoning, death, strangulation, prevention of feeding, reproductive47
complications and gastrointestinal blockages (Derraik, 2002; Gregory, 2009; Laist, 1997).48
Fisheries often abandon used fishing gear in the ocean which frequently remains buoyant49
causing ghost fishing throughout the planet (Gregory, 2009; Moore, 2008). Plastic debris act50
as an optimal substratum for absorbing and distributing persistent organic pollutants (POPs)51
to new locations throughout the marine ecosystem (Barnes et al., 2010; Mato et al., 2001;52
Rios et al., 2007). It has been found that floating plastic refuse also transport organisms53
leading to the introduction of non-indigenous species into new areas (Barnes, 2002; Gregory,54
2009).55
Over the past few decades small particles of plastics, known as microplastics, have been56
accumulating in the marine environment. Microplastics were first described by Thompson et57
al. (2004) who reported the presence of plastics of around 50µm in size on shorelines and in58
the water column. This term now refers to particles that are less than 5mm in size (Arthur et59
al., 2009). Microplastics have been found as small as 1.6µm in marine environments and at60
this size they could be present virtually anywhere undetected (Thompson et al., 2009). These61
may further be divided into primary and secondary microplastics. Primary microplastics62
comprise of those produced at a microscopic size like microbeads used in facial cleansers63
(Cole et al., 2011; Fendall & Sewell, 2009) and in air blasting technology (Gregory, 1996).64
The wide use of exfoliating cosmetics worldwide contributes greatly to the increase of65

4. microplastics in the marine environment (Browne, 2007). Due to their small size, often less66
than 1mm, the beads used in facial cleansers travel through wastewater systems and often67
escape capture by preliminary treatment screens which have varied mesh sizes (Fendall &68
Sewell, 2009). Secondary microplastics include those established from the breakdown of69
larger materials from natural processes such as weathering both on land and at sea (Ryan et70
al., 2009; Thompson et al., 2004).71
Microplastics have reached high concentrations in the world’s oceans. A survey carried out in72
the North Pacific Central Gyre by the Algalita Marine Research Foundation in 199973
discovered that neustonic plastics outweighed zooplankton by a ratio of 6:1 and averaged74
over 300,000 pieces per km2 (Moore et al., 2001). A similar study carried out in the75
Mediterranean sea found microplastics reached maximum levels of 892,000 particles per km276
(Fossi et al., 2012). Plastics are reaching remote areas with the least human contact, although77
not yet abundant, plastics are present in Antarctica (Barnes et al., 2010). Microplastics are in78
the same size range as plankton and sediments, therefore available to a wide array of marine79
organisms, including invertebrates from the base of the food chain (Browne et al., 2008).80
Various studies have shown microplastics are present in sedimentary habitats, therefore81
deposit and detritus feeding organisms, including crustaceans, polychaetes, molluscs and82
echinoderms are susceptible to ingestion (Claessens et al., 2011; Murray & Cowie, 2011;83
Thompson et al., 2004). Recent studies have also confirmed the presence of microplastics in84
mesopelagic fish species in the NPCG (Boerger et al., 2010; Davison & Asch, 2011),85
commercially important fish species in the English Channel (Lusher et al., 2012) and larger86
mysticete cetaceans in the Mediterranean Sea (Fossi et al., 2012). A study carried out on the87
decapod crustacean, (N. norvegicus) from the Clyde Sea showed that 83% of the sample size88
had microplastics in their stomachs (Murray & Cowie, 2011). Research carried out on the89
mussel, (M. edulis), confirmed their ability to both ingest and retain microplastics for up to 4890
days (Browne et al., 2008). Studies have also evidenced that microplastics are capable of91
trophic level transfer and trans-locating from the stomach to the circulatory system (Browne92
et al., 2008; Farrell & Nelson, 2013).93
The impact of microplastics on marine organisms is not well established and requires more94
extensive research, particularly with fish. Many studies have been carried out on dab95
primarily focusing on dietary composition, however little research has determined if96
microplastics are present in this species. The dab Limanda limanda are found in coastal97
waters and are one of the most abundant flatfish species in the North Sea with an estimated98

5. abundance of 2 million tonnes (Daan et al., 1990). They are widely distributed with a99
majority of the population inhabiting shallow waters (30-50m) in the southern North Sea100
although they can be found at depths of up to 100m (Daan et al., 1990; Rijnsdorp et al.,101
1996). Dab typically reach maturity at around 11-12 cm in length (Rijnsdorp et al., 1992).102
Hinz et al. (2005) carried out a study on the feeding strategy of dab and classified them as103
surface oriented feeders based on their stomach contents. Hard bodied animals living towards104
the surface were found more frequently then buried soft bodied prey. Dab are further105
classified as visual feeders based on morphological traits such as their ability for rapid106
movement together with surface facing eyes and mouth (Ortega-Salas, 1988; Piet et al.,107
1998). Dab tend to prey on the species that are most abundant in their environment rather108
than displaying a preference for prey species (Hinz et al., 2005; Ortega-Salas, 1988). In109
temperate waters dab feed largely in the summer months (April-August) with feeding reduced110
in the winter months (Ntiba & Harding, 1993; Ortega-Salas, 1988). Dab commonly consume111
crustaceans, polychaetes, echinoderms, molluscs, chordates and juvenile fish including112
whiting, gobies and dab (Hinz et al., 2005; Ntiba & Harding, 1993; Ortega-Salas, 1988).113
Large abundances of microplastics have been found in the sedimentary habitats where many114
of these prey species reside. Consequently, dab are at a risk of ingesting microplastics form115
trophic transfer and from the sediment while feeding. Examining the feeding ecology of fish116
species is important because stomach contents directly indicates the health of their habitats117
(Hinz et al., 2005).118
The primary aim of this study is to determine if microplastics are present in the119
gastrointestinal tract of dab. If plastics are obtained comparisons will be made to determine if120
there is a difference in the frequency of particles in relation to physical factors of the fish.121
The following specific questions were examined: (1) establish if microplastics are present in122
the gastrointestinal tract of dab, (2) if present determine if there is a relationship between123
frequency of microplastics and sex, length (cm), weight (g), stomach weight (g) and stomach124
content.125
2. Materials and Methods126
Fish were collected from the west coast of Ireland by the research vessel the RV Celtic127
Explorer in early October during the annual Irish West Coast Groundfish Survey and the RV128
Celtic Voyager in November 2012 at 53º 09.15’ N, 9º 12.05’ W. The fish obtained from the129
Explorer were sampled via otter board trawls from ICES division VIIb which reaches depths130

6. from 15-300m. On the Voyager fish were collected via beam trawls with trawl durations of131
approximately 20 minutes at depths ranging from 15-20m. Both research vessels are132
facilitated with wet and dry labs containing standard scientific equipment. The beam trawls133
on both vessels are designed for catching fish; therefore the cod end consists of a fine mesh134
size to retain the samples. Net feeding is a concern but can be prevented by the short trawl135
times as mentioned in Davison & Asch (2011). The net on the RV Celtic Voyager is dark136
green in colour, therefore if fragments of this colour are found in the stomachs it will be137
assumed that net contamination occurred and the results will be disregarded.138
Dab (Limanda limanda) were the most abundant species encountered on the Voyager,139
therefore used for the analysis. After fish were obtained they were placed in bags and frozen140
in the vessels freezers before they were returned to the lab for analysis. Since dab share141
similar biological traits with the other commercially important flatfish species, they may be142
good indicators for microplastic pollution in the order (Pleuronectiformes). The dab collected143
in October ranged in sizes from 20-31cm and those obtained in November were remarkably144
smaller ranging from 11-19cm. Since all fish were greater than 11cm in length they were145
classified as mature, which was defined by Rijnsdorp et al. (1996) as fish from 11-12cm in146
length.147
Contamination is regarded as a large issue when determining plastic ingestion. Airborne148
fibres are of a particular concern as discussed by Davison and Asch (2011), who mention that149
fibres found on petri dishes were similar to those found in the fish stomachs. It was therefore150
recommended that precautionary measures need to be taken to minimize the risk of air borne151
fibres. Precautionary steps were taken to prevent any contamination prior to dissection. All152
equipment including the workbench, dissecting tools and board were thoroughly cleaned with153
alcohol to minimize contamination. Personal precautions were also practiced such as washing154
hands, wearing a lab coat and gloves (nitrile, powder free) throughout the examination155
process.156
Once fish were returned to the lab they were stored in freezers of until ready for processing.157
When required the fish were defrosted at room temperature. Prior to dissection some basic158
measurements were taken including; length (cm) from the tip of the mouth to the end of the159
caudal fin and total body weight (g). Fish were divided into size classes to improve analyses:160
A (10-15cm), B (16-20cm), C (21-25cm) and D (>26cm). The dab were opened from the anal161
cavity by use of a tweezers and a scissors to make the incision. The area was fully opened162

7. with the skin peeled back exposing the internal organs. The entire gastrointestinal tract was163
removed from the oesophagus to the anus opening, placed in a sterile petri-dish, weighed (g)164
and recorded. The gonads were then removed to determine the sex of each individual.165
A review by Hidalgo-Ruz et al. (2012) on methods for the identification and quantification of166
microplastics found visual examination of the samples to be an obligatory step. Upon analysis167
the stomachs were dissected in the petri dishes and viewed under a dissecting microscope,168
following similar methodology of previous studies by (Boerger et al., 2010; Davison & Asch,169
2011; Lusher et al., 2012). To avoid biasing the samples a standardized time was set at 10170
minutes per stomach. Criteria listed by Noren (2007) were followed to confirm the particles171
were plastic: if no cellular or organic structures are visible in the plastic particle or fibre, if172
the particle is a fibre then it should be equally thick throughout its length and have a three173
dimensional bending (not entirely straight which indicates biological origin) and they should174
be clear and homogeneously coloured (blue, red, black and yellow). All particles resembling175
non-biological material were removed, placed carefully on a filter paper and stored in a176
sterile petri dish. These items were then viewed under an Olympus SZX10 microscope and177
photographed by a Q-imaging Retiga 2000R camera. Particles were then measured using178
Image-Pro Plus software under 2.5X magnification. The particles were then classified by179
colour and shape (fragment, fibre, bead or film).180
After analysis for inorganic materials a dietary analysis commenced. Visible food particles181
were removed, rinsed with water and identified to the nearest taxonomic level using an182
identification key for marine fauna in North-West Europe (Hayward & Ryland, 1995). Based183
on content, stomachs were categorized as full or empty because they could be important184
factors in relation to microplastic ingestion. Stomachs were considered empty if they185
contained few food items and those containing many items were classified as full.186
Statistics were carried out in Minitab V16 to determine relationships between the numbers of187
microplastics and morphological traits. The data were not normally distributed; therefore188
non-parametric tests were chosen. The analyses used included the Kruskal Wallis test and the189
Mann Whitney U test.190
3. Results191
Out of the 87 dab examined, 36 (41%) contained items of plastics in their gastrointestinal192
tracts. From the fish containing plastics, a total of 80 particles were found averaging at 2.2 (±193

8. 0.16) pieces per fish. Fibres were the most prevalent (95%) and the remaining plastics were194
classified as fragments which were clear in colour (Fig. 1). The fibres were black, blue and195
red in colour (Fig. 2). The size of the plastics ranged from 0.5 mm to 12.05 mm with the most196
frequent size class being 1.0 – 2.0mm (Fig. 3). By defining microplastics as particles of less197
than 5mm as stated by Arthur et al. (2009), microplastics made up 94% of the sample size.198
Of the fish 27 were male and 60 were female. Plastic particles were found in 33% of the199
males and in 45% of the females. The Mann-Whitney U test showed that there was no200
significant difference between fish sex and plastic ingestion (W = 2729.0, P = 0.4168). A201
larger abundance of plastics were typically found in fish from lengths greater than 20cm with202
28 particles in size class C (21-25cm) and 38 particles in size class D (>26cm) (Fig. 4).203
Kruskal-Wallis test showed there was a significant difference between size classes and the204
number of microplastics (P <0.001, df = 3, H = 33.47, χ2 = 7.81). In relation to total fish205
weight (g) 84% of plastics were found in dab greater than 160g (Fig. 5). Mann-Whitney U206
test revealed that there is a significant difference between fish weight and microplastic207
ingestion. Stomach weights ranged from 1g to 17g with weight classes from 1-2g making up208
54% of the sample which contained 10 out of 80 plastics particles. A majority of plastics209
were found in heavier stomachs, particularly from 6-10 grams which contained 65% of the210
total plastics found (Fig. 6). There was a decrease in plastics found in stomach weights from211
11-17g because there was only 12 fish in this range. The Mann-Whitney U test showed there212
was a significant difference between stomach weight and microplastic ingestion (W= 10358.5213
and P <0.001). These particles did not resemble the colour of the nets used for trawls, gloves214
used for examination or the possible plastic contamination from the clear sterile petri dishes215
the stomachs were stored in.216
Out of the stomachs analysed for dietary composition and contents 40 out of 87 stomachs217
were full. A small proportion of both full and empty stomachs contained parasitic worms218
wrapped around the gastrointestinal tract. Surpluses of sand and plant materials were also219
found in a majority of the samples. The empty stomachs were often comprised with white220
mucus like fluid and highly decomposed remains from their prey; however these were221
classified as empty as there were no solid particles. The full stomachs contained a variety of222
food items ranging in different stages of digestion. Many shell fragments were found either223
severely broken down or as whole half shells with the hinge area still attached. These food224
items were difficult to fully classify, but were classified from the Phylum Mollusca.225
The most predominant of food items were specimen from the Phylum Crustacea even more226

9. so from the Order Decapoda (Fig. 7). Although many of these items were in perfect condition227
in the stomach full identification was challenging because there was often several body parts228
including thorax with legs, claws, arms, heads, antennae or tails. Many of the samples229
contained several body pieces in one stomach. In relation to microplastic content and stomach230
fullness, 50% of full stomachs contained plastics in comparison to 34% of empty stomachs231
(Fig. 8). A total of 35 particles were found in the empty stomachs and 45 in the full stomachs.232
Mann-Whitney U test results revealed that there was no significant difference between233
stomach content and the number of microplastics (W= 1885.0 and P= 0.2890).234
4. Discussions235
The present study investigates and confirms that dab are ingesting relatively low abundances236
of plastics in coastal waters off the west coast of Ireland. A total of 41.5% of fish from the237
sample had plastic particles present in their gastrointestinal tract which is a much higher238
proportion than reported by Lusher et al. (2012) who found flatfish ingested the lowest level239
of plastics from the eight species sampled. Lusher et al. (2012) examined two species of240
flatfish including a total of 50 solenettes (B. luteum) and 51 thick back sole (M. variegatus);241
the results established that 22% of thick back sole and 28% of solenettes contained plastics in242
their gastrointestinal tracts. Juvenile species of winter flounder (P. americanus)243
approximately 5mm in length collected from southern New England contained polystyrene244
spherules of 0.5mm in diameter in their stomachs (Carpenter et al., 1972). Plastic ingestion in245
juvenile fish may have serious implications for successful growth in flatfish populations.246
Research carried out in the Severn Estuary found large abundances of polystyrene spherules247
(as many as 30 spherules in fish from 2-5cm) in the intestines of young flounders (P. flesus)248
which reached a peak in June 1973 where 20.7% of 530 fish had ingested plastics (Kartar et249
al., 1976; 1973). These results indicate that flatfish are particularly susceptible to ingesting250
small spherules.251
In the study by Lusher et al. (2012) an average of 1.90 (± 0.10) plastics were found per fish252
which is comparable to the 2.2 (± 0.16) particles found in this study. Of the plastic pieces253
collected, fibres made up 95% of the sample which is considerably higher than the 36%254
found by Davison & Asch (2011) but similar to the 94% found in the study by Boerger et al.255
(2010). In the study by Boerger et al. (2010) the fish were sampled from the neustonic water256
column in comparison to the mid-water trawls at depths of 200m and greater carried out by257
Davison & Asch (2011) which may indicate that fibres are more prevalent in surface waters.258

10. Considering flatfish are susceptible to ingesting polystyrene spherules, the high abundance of259
fibres may indicate that plastic beads are in low abundances around the west coast of Ireland.260
Various studies have found that fibres are the most frequently encountered plastics in the261
marine environment. Previous studies on the occurrence of microplastics in marine sediment262
by Claessens et al. (2011) and Thompson et al. (2004) found plastic particles of a fibrous263
form to be the most prevalent in the oceanic environment. A similar study by Browne et al.264
(2011) found that microplastics on coastlines from six continents tended to be fibrous in265
shape and describes that an important source of microplastic appears to be through sewage266
contaminated by fibres from washing clothes, one garment can release over 100 fibres per267
litre of effluent. The large abundance of fibres found in this study could indicate that waste268
water systems off the west coast of Ireland aren’t effectively eliminating fibrous plastics from269
the marine environment but further research is required.270
Most of the plastics found in this study (94%) are less than 5mm in length which provides271
evidence that demersal flatfish species are more susceptible to ingesting microplastics than272
macroplastics. Although this sample consisted predominantly of females, the sex of the fish273
did not have a significant effect on the number of microplastics ingested. The amount of274
plastics found in the sample increased with fish size with 83% found in fish greater than275
21cm in length and 84% were found in dab weighing more than 160g. Dab were not aged in276
this study however; assuming that larger fish are typically older than smaller ones, aging the277
fish would be beneficial for understanding feeding ecology and distribution throughout the278
lifecycle. This may give insight to a better understanding of the relationship between age279
classes and microplastic ingestion. Fish with greater stomach weights, especially from 6-10g,280
consumed the most plastics; however there were different numbers of fish for each weight281
class. Stomach weights from 11-17g had very few fish, therefore a larger sample size would282
be recommended for future studies.283
During stomach content analysis, fuller stomachs often consumed parts of animals from284
Phylum’s Mollusca and Crustacea. Species from these phyla occupy sedimentary habitats285
which are known to contain microplastics. Stomach contents found in dab in waters off the286
Isle of Man included mollusc feet, small crustaceans, seaweeds, pebbles, sand, thorax with287
legs, siphons of bivalves and parts of annelids (Ortega-Salas, 1988) which is similar to the288
prey items found in this study. These results confirm the surface oriented feeding strategy289
mentioned by Hinz et al. (2005). Species of crustaceans have been shown to ingest290
microplastics both in the wild and in laboratory tests (Murray & Cowie, 2011) which291

11. increases the risk of dab consuming plastics from possible trophic level transfer. Farrell &292
Nelson (2013) found that blue mussels (M. edulis) were capable of transferring microplastics293
to the crab (C. maenas). Studies have also confirmed the ability of microplastics to trans294
locate from the stomach to the circulatory system in mussels and crabs (Browne et al., 2008;295
Farrell & Nelson, 2013). Although trophic level transfer and trans location of microplastics296
has not yet been explored for flatfish, this may pose a potential threat, however this study297
showed no significant difference between the number of plastics ingested and stomach298
content (full or empty).299
It is not yet established if dab are consuming plastics from their prey or from the environment300
or both. The sample size in this study was limited therefore results may not have shown301
sufficient relationships between morphological traits and microplastic ingestion. It is302
unknown if the plastics had been recently consumed. Almost half of the fish examined had303
plastic particles present in their stomachs; however it is unknown if the fish are capable of304
passing the plastics through their guts and how long the plastics remain in their system.305
Plastic retention could cause internal blockages and chemical poisoning in fish leading to306
death by starvation or suffocation and potential decreases in fish populations. Plastics are307
known to absorb POPs in the marine ecosystem and leach harmful chemicals. If fish are308
capable of transferring plastics to other trophic levels then this could pose a large threat to309
larger species and work its way up the food chain. Plastics were not identified in this study310
therefore; to fully confirm the items were of plastic composition FT-IR spectroscopy is311
recommended.312
The objective of this study was to determine if plastics were present in the dab, Limanda313
limanda, and compare quantitative data among different morphological traits. The results314
from this study promote future research on the long term effects of microplastic ingestion in315
demersal flatfish. The fish were not aged in this study which may prove beneficial for future316
work to determine ecological characteristics. A larger sample size with various species would317
give a better understanding about plastic ingestion by marine fish around the west coast of318
Ireland. This study focused on mature flatfish; however future research on microplastic319
ingestion by juvenile flatfish would be beneficial to determining possible impacts throughout320
the life cycle. Although dab aren’t commercially harvested in Ireland for human321
consumption, the presence of plastics in their guts could indicate that other commercially322
important species of flatfish in the NE Atlantic such as the European plaice (P. platessa) are323
also consuming microplastics. Further study is needed to understand if plastics are capable of324

12. trans locating from the gastrointestinal tract in fish to other areas in the body such as the gills,325
gonads and circulatory system.326
ACKNOWLEDGEMENTS327
I would like to thank my supervisor Amy Lusher for assisting me with this study as well as328
Dr. Ian O’Connor. I would like to thank the crew from the Celtic Voyager and Explorer for329
assisting with sample collection. I would also like to thank GMIT for the facilities provided330
in the Marine and Freshwater Research Centre which made this study possible. Furthermore I331
would like to thank John Boyd for assisting with fish collection.332
333

13. References334
Andrady, A.L. (2011). Microplastics in the marine environment. Marine Pollution Bulletin335
62, 1596-1605.336
Arthur, C., Baker, J., & Bramford, H. (2009). Proceedings of the International Research337
Workshop on the Occurence, Effects and Fate of Microplastic Marine Debris, 9-11338
September 2008. NOAA Technical, Memorandum NOS-OR&R30.339
Barnes, D.K.A. (2002). Biodiversity: Invasions by marine life on plastic debris. Nature 416,340
808-809.341
Barnes, D.K.A., Galgani, F., Thompson, R.C., & Barlaz, M. (2009). Accumulation and342
fragmentation of plastic debris in global environments. Philosophical Transactions of the343
Royal Society 364.344
Barnes, D.K.A., Walters, A., & Goncalves, L. (2010). Microplastics at sea around Antarctica.345
Marine Environmental Research 70, 250-252.346
Boerger, C.M., Lattin, G., L, Moore, S.L., & Moore, C.J. (2010). Plastic ingestion by347
planktivorous fishes in the North Pacific Central Gyre. Marine Pollution Bulletin 60, 2275-348
2278.349
Browne, M.A. (2007). Microplastic - an emerging contaminant of potential concern?350
Integrated Environmental Assessment and Management 3(4), 559-566.351
Browne, M.A., Crump, P., Niven, S.J., Tueten, E.L., Tonkin, A., Galloway, T., & Thompson,352
R.C. (2011). Accumulations of microplastic on shorelines worldwide: sources and sinks.353
Environmental Science and Technology.354
Browne, M.A., Dissanayake, A., Galloway, T.S., Lowe, D.M., & Thompson, R.C. (2008).355
Ingested microscopic plastic translocates to the circulatory system of the mussel, Mytilus356
edulis (L). Environmental Journal of Toxicology 42, 5026-5031.357
Carpenter, E.J., Anderson, S.J., Harvey, G.R., Miklas, H.P., & Peck, B.B. (1972). Polystyrene358
spherules in coastal waters. Science 178, 749-750.359
Claessens, M., De Meester, S., Van Landuyt, L., De Clerck, K., & Janssen, C.R. (2011).360
Occurrence and distribution of microplastics in marine sediments along the Belgian coast.361
Marine Pollution Bulletin 62, 2199-2204.362
Cole, M., Lindeque, P., Halsband, C., & Galloway, T.S. (2011). Microplastics as363
contaminants in the marine environment: A review. Marine Pollution Bulletin 62, 2588-2597.364
Daan, N., Bromley, P.J., Hislop, J.R.G., & Nielsen, N.A. (1990). Ecology of North Sea fish.365
Netherlands Journal of Sea Research 26(2–4), 343-386.366

14. Davison, P., & Asch, R.G. (2011). Plastic ingestion by mesopelagic fishes in the North367
Pacific Subtropical Gyre. Marine Ecology Progress Series 432, 173-180.368
Derraik, J.G.B. (2002). The pollution of the marine environment by plastic debris: a review.369
Marine Pollution Bulletin 44, 842-852.370
Farrell, P., & Nelson, K. (2013). Trophic level transfer of microplastic: Mytilus edulis (L.) to371
Carcinus maenas (L.). Environmental Pollution 177(0), 1-3.372
Fendall, L.S., & Sewell, M.A. (2009). Contributing to marine pollution by washing your face:373
Microplastics in facial cleansers. Marine Pollution Bulletin 58, 1225-1228.374
Fossi, M.C., Panti, C., Guerranti, C., Coppola, D., Giannetti, M., Marsili, L., & Minutoli, R.375
(2012). Are baleen whales exposed to the threat of microplastics? A case study of the376
Mediterranean fin whale (Balaenoptera physalus). Marine Pollution Bulletin 64, 2374-2379.377
Graham, E.R., & Thompson, J.T. (2009). Deposit and suspension feeding sea cucumbers378
(Echinodermata) ingest plastic fragments. Journal of Experimental Marine Biology and379
Ecology 368(1), 22-29.380
Gregory, M.R. (1996). Plastic ‘Scrubbers’ in Hand Cleansers: a Further (and Minor) Source381
for Marine Pollution Identified. Marine Pollution Bulletin 32(12), 867-871.382
Gregory, M.R. (2009). Environmental implications of plastic debris in marine settings -383
entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien384
invasions Philosophical Transactions of the Royal Society 364.385
Hayward, P.J., & Ryland, J.S. (1995). Handbook of the Marine Fauna of North-West Europe.386
University of Wales, Swansea: Oxford University Press.387
Hidalgo-Ruz, V., Gutlow, L., Thompson, R.C., & Thiel, M. (2012). Microplastics in the388
Marine Environment: A review of the methods used for identification and quantification.389
Environmental Science and Technology 46, 3060-3075.390
Hinz, H., Kroncke, I., & Ehrich, S. (2005). The feeding strategy of dab Limanda limanda in391
the southern North Sea: linking stomach contents to prey availability in the environment.392
Journal of Fish Biology 67, 125-145.393
Kartar, S., Abou-seedo, F., & Sainsbury, M. (1976). Polystyrene spherules in the Severn394
Estuary - A progress report. Marine Pollution Bulletin 7, 52.395
Kartar, S., Milne, R.A., & Sainsbury, M. (1973). Polystyrene waste in the Severn Estuary.396
Marine Pollution Bulletin 4, 144.397

15. Laist, D.W. (1997). Impacts of Marine Debris: Entanglement of Marine Life in Marine398
Debris Including a Comprehensive List of Species with Entanglement and Ingestion Records.399
Marine Debris, 99-139.400
Lusher, A.L., McHugh, M., & Thompson, R.C. (2012). Occurrence of microplastics in the401
gastrointestinal tract of pelagic and demersal fish from the English Channel. Marine402
Pollution Bulletin.403
Mato, Y., Isobe, T., Takada, H., Kanehiro, H., Ohtake, C., & Kaminuma, T. (2001). Plastic404
resin pellets as a transport medium for toxic chemicals in the marine environment.405
Environmental Science and Technology 35, 318-324.406
Moore, C.J. (2008). Synthetic polymers in the marine environment: A rapidly increasing,407
long-term threat. Environmental Research 108(2), 131-139.408
Moore, C.J., Moore, S.L., Leecaster, M.K., & Weisberg, S.B. (2001). A Comparison of409
Plastic and Plankton in the North Pacific Central Gyre. Marine Pollution Bulletin 42(12),410
1297-1300.411
Murray, F., & Cowie, P.R. (2011). Plastic contamination in the decapod crustacean Nephrops412
norvegicus (Linnaeus, 1758). Marine Pollution Bulletin 62, 1207-1217.413
Noren, F. (2007). Small plastic particles in Coastal Swedish waters. KIMO report.414
Ntiba, M.J., & Harding, D. (1993). The food and the feeding habits of the long rough dab,415
Hippoglossoides platessoides (fabricius 1780) in the north sea. Netherlands Journal of Sea416
Research 31(2), 189-199.417
Oehlmann, J., Schulte-Oehlmann, U., Kloas, W., Jagnytsch, O., Lutz, I., Kusk, K.O.,418
WOllenberger, L., Santos, E.M., Paull, G.C., Van Look, K.J.W., & Tyler, C.R. (2009). A419
critical analysis of the biological impacts of plasticizers on wildlife. Philosophical420
Transactions of the Royal Society 364, 2047-2062.421
Ortega-Salas, A.A. (1988). Diet, food consumption and growth of the dab Limanda limanda422
(Linnaeus) in Isle of Man Waters, UK. Anales del Instituto de Ciencias del Mar Y423
Limnologia, Universidad Nacional Autonoma De Mexico 15(1), 31-40.424
Piet, G.J., Pfisterer, A.B., & Rijnsdorp, A.D. (1998). On factors structuring the flatfish425
assemblage in the southern North Sea. Journal of Sea Research 40(1–2), 143-152.426
PlasticsEurope. (2012). Plastics - the Facts 2012 An analysis of European Plastics427
Production, Demand and Waste Data for 2011. In.428
Rijnsdorp, A.D., van Leeuwen, P.I., Daan, N., & Heessen, H.J.L. (1996). Changes in429
abundance of demersal fish species in the North Sea between 1906-1909 and 1990-1995.430
ICES Journal of Marine Science 53, 1054-1062.431

16. Rijnsdorp, A.D., Vethaak, A.D., & van Leeuwen, P.I. (1992). Population biology of dab432
Limanda limanda in the southeastern North Sea. Marine Ecology Progress Series 91, 19-35.433
Rios, L.M., Moore, C., & Jones, P.R. (2007). Persistent organic pollutants carried by434
synthetic polymers in the ocean environment. Marine Pollution Bulletin 54, 1230-1237.435
Rudel, R.A., Brody, J.G., Spengler, J.D., Vallarino, J., Geno, P.W., Sun, G., & Yau, A.436
(2001). Identification of selected hormonally active agents and animal mammary carcinogens437
in commercial and residential air and dust samples. Journal of the Air and Waste438
Management Association 51(4), 499-513.439
Ryan, P.G., Moore, C.J., van Franeker, J.A., & Monoley, C.L. (2009). Monitoring the440
abundance of plastic debris in the marine environment. Philosophical Transactions of the441
Royal Society 364.442
Sivan, A. (2011). New perspectives in plastic biodegradation. Current Opinion in443
Biotechnology 22, 422-426.444
Talsness, C.E., Andrade, A.J.M., Kuriyama, S.N., Taylor, J.A., & vom Saal, F.S. (2009).445
Components of plastic: experimental studies in animals and relevance for human health.446
Philosophical Transactions of the Royal Society 364.447
Thompson, R.C., Moore, C.J., vom Saal, F.S., & Swan, S.H. (2009). Plastics the environment448
and human health: current consensus and future trends. Philosophical Transactions of the449
Royal Society 364, 2153-2166.450
Thompson, R.C., Olsen, Y., Mitchell, R.P., Davis, A., Rowland, S., John, A.W.G.,451
McGonigle, D., & Russell, A.E. (2004). Lost at sea: Where is all the plastic? Science 304.452
von Moos, N., Burkhardt-Holm, P., & Kohler, A. (2012). Uptake and effects of microplastics453
on cells and tissue of the blue mussel Mytilus edulis L. after an experimental exposure.454
Environmental Science and Technology 46, 11327-11335.455
456
457

17. APPENDICES458
a) b)459
460
461
462
463
464
c) d)465
466
467
468
469
470
Fig. 1. Photographs of microplastics, scale bar represents 2mm. a). Classified as a fragment471
measuring 4705µm at X0.63 magnification. The rest of the fibres were measured at X0.25472
magnification. b). Fibre measured at 6mm. c). Microplastic measured at 2mm. d). Fibre473
measured at 8mm.474
475
476
477
Fig. 2. Pie chart displays the per cent of colours found in the plastics.478
76%
13%
6%
5%
Black
Blue
Red
Clear

18. 479
Fig. 3. Frequency of plastics sorted by size.480
481
a)482
Size Classes Length (cm) Number in sample Number of plastics
A 10-15 39 11
B 16-20 18 3
C 21-25 14 28
D >26 16 38
483
b)484
485
Fig. 4. Summary of the data showing the number of fish and microplastics in each of the size486
classes. Bar graph shows the mean number of plastics ingested per size class (𝑋̅ ± se).487
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5 6 7 8 9 10 11 12
Frequency
Size of plastics (mm)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
A B C D
Meannumberofplastics
Size class

19. 488
Fig. 5. The number of microplastics per weight class. Values show the number of fish (n) per489
weight size class.490
491
492
493
Fig. 6. Mean number of plastics found in each stomach weight class per fish (x̅ ± se). Values494
show number of fish per weight class (n).495
496
(49)
(7)
(5)
(14)
(7)
(3)
(1)
(1)
0
5
10
15
20
25
30
0-50 51-100 101-150 151-200 201-250 251-300 301-350 351-400
Numberofmicroplastics
Weight class (g)
(24) (23)
(6)
(2) (1)
(6)
(0)
(6)
(4)
(3)
(2)
(3)
(3)
(2)
(1)
(0) (1)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
MeanPlastics
Weight classes (g)

20. 497
a). b).498
499
500
501
3mm 4mm502
c). d).503
504
505
5mm506
507
508
Fig. 7. a). Head of a crustacean. b). Claw from a crustacean. c). Shell fragment from mollusc.509
d).Part from a crustacean.510
511
Fig. 8. Displays the mean number of plastics found in full and empty stomachs (x̅ ± se).512
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
A B C D
Meannumberofmicroplastics
Size class
Mean Full
Mean
Empty
2mm