MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
https://doi.org/10.47193/mafis.3532022010907
ABSTRACT. Microplastics (MPs) defined as ‘small’ pieces of plastic <5 mm have been found
in almost every marine habitat around the world, and studies have shown that we can find them in
the ocean surface, the water column, the seafloor, the shoreline, in biota and in the atmosphere-
ocean interface. This study aimed to assess both marine and freshwater environments of Cocos
Island, Costa Rica, in the Pacific Ocean, by sampling sediments and biota to determine the presence
and abundance of this pollutant. Sediment samples were superficial and weighed one kilogram each.
For the sampling of freshwater fish and shrimps, nonselective capture with small nets was made in
rivers with access by land, while fishing rods were used for the marine fish sampling, and cage and
scuba diving for lobsters. Plastics were found in all types of samples: 93% of marine sediments,
32% of freshwater sediments, 20% of freshwater fish, 15% of freshwater shrimps, 27% of marine
fish, and 51% of marine lobsters. Like many reports around the world, it was expected to find MPs
at marine samples, and it was concluded that ocean currents, tourism activities, and discarded fish-
ing gear from illegal fishing activities could be the sources of marine pollutants. In contrast, the
amount of MPs found in freshwater environments was not expected. Their possible sources are
unclear at this moment.
Key words: Marine ecosystem, freshwater ecosystem, sediments, oceanic island, fish, lobsters,
shrimps.
Microplásticos encontrados en el Parque Nacional Isla de Cocos, Patrimonio de la Huma-
nidad, Costa Rica
RESUMEN. Los microplásticos (MP), definidos como “pequeñas” piezas de plástico < 5 mm, se
han encontrado en casi todos los hábitats marinos del mundo, y los estudios han demostrado que
podemos encontrarlos en la superficie del océano, en la columna de agua, en el fondo marino, en la
costa, en la biota y en la interfaz atmósfera-océano. Este estudio tuvo como objetivo evaluar los
ambientes marinos y de agua dulce de la Isla de Cocos, Costa Rica, en el Océano Pacífico, mediante
el muestreo de sedimentos y biota para determinar la presencia y abundancia de este contaminante.
Las muestras de sedimento fueron superficiales y pesaron un kilogramo cada una. Para el muestreo
de peces de agua dulce y camarones, se realizó una captura no selectiva con redes pequeñas en ríos
403
*Correspondence:
karol.ulate.naranjo@una.ac.cr
Received: 8 April 2022
Accepted: 10 July 2022
ISSN 2683-7595 (print)
ISSN 2683-7951 (online)
https://ojs.inidep.edu.ar
Journal of the Instituto Nacional de
Investigación y Desarrollo Pesquero
(INIDEP)
This work is licensed under a Creative
Commons Attribution-
NonCommercial-ShareAlike 4.0
International License
Marine and
Fishery Sciences
MAFIS
ORIGINAL RESEARCH
Microplastics found in the World Heritage Site Cocos Island National Park,
Costa Rica
ANGÉLICA ASTORGA1, ANDREA MONTERO-CORDERO2, GEINER GOLFIN-DUARTE3, ANDREA GARCÍA-ROJAS1,
HANNIA VEGA-BOLAÑOS1, FAUSTO ARIAS-ZUMBADO1, DANIELA SOLÍS-ADOLIO1 and KAROL ULATE1, *
1Universidad Nacional, Avenida 1, Calle 9 Heredia 86, 40101 - Heredia, Costa Rica. 2Fundación Amigos de la Isla del Coco (FAICO), Barrio
Escalante, de la Rotonda La Bandera 300 metros oeste Oficentro Casa Holanda oficina 11, 2603-1000 - San José, Costa Rica. 3Sistema
Nacional de Áreas de Conservación (SINAC), Costa Rica; angelica.astorga.perez@gmail.com (AA), amonterocordero@gmail.com (AMC),
geiner.golfin@sinac.go.cr (GGD), andrea.garcia.rojas@una.ac.cr (AGR), hannia.vega.bolanos@una.ac.cr (HVB),
fausto.arias.zumbado@una.cr (FAZ), dsolis.adolio@gmail.com (DSA). ORCID Angélica Astorga https://orcid.org/0000-0003-2373-0455,
Andrea Montero-Cordero https://orcid.org/0000-0003-3537-3045, Andrea García-Rojas https://orcid.org/0000-0003-3451-7094,
Hannia Vega-Bolaños https://orcid.org/0000-0002-9855-9747, Fausto Arias-Zumbado https://orcid.org/0000-0003-0391-592X,
Daniela Solís-Adolio https://orcid.org/0000-0002-5063-1527, Karol Ulate https://orcid.org/0000-0001-5687-555X
INTRODUCTION
Anthropogenic litter on the marine environ-
ment has significantly increased over the recent
decades. Initially described in the marine envi-
ronment in the 1960s, marine litter is nowadays
commonly observed across all oceans (Bergmann
et al. 2015). Plastic, the main component of litter,
has become ubiquitous and sometimes represents
up to 95% of the waste that accumulates on the
shorelines, the sea surface and the seafloor.
Together with its breakdown products, mesoplas-
tics (5-25 mm) and microplastics (<5 mm)
(GESAMP 2019) have become more abundant in
the marine environment than any other pollutant
(Bergmann et al. 2015).
The term ‘plastic’ is used in many fields and
has different definitions. For the purpose of this
study, it is defined as a sub-category of the larger
class of materials called polymers, including ther-
moplastics and some thermoset materials such as
polyurethane foams, epoxy resins, and some coat-
ing films that are generally counted within the
category of ‘plastics’ in marine debris (GESAMP
2015). Traditionally, the term microplastic (MP)
has been widely adopted as a generic form for
‘small’ pieces of plastic (<5 mm) (Andrady 2011;
Gewert et al. 2017; Miller et al. 2017; Herrera et
al. 2018; Froese and Pauly 2021).
There are primary and secondary sources of
MPs. The difference relies on whether particles
are originally manufactured to be <5 mm (prima-
ry) or if they are a result from the breakdown of
larger pieces of plastic (secondary) (GESAMP
2015; UNEP and GRID-Arendal 2016). Some
primary MPs include production pellets/powders
and engineered plastic microbeads used in cos-
metic formulations, cleaning products, and indus-
trial abrasives. On the other hand, secondary MPs
are degraded and then fragmented, such as textile
fibers, tire dust, and water bottles, among others
(UNEP and GRID-Arendal 2016).
Visual characterization is the most used
method for the identification of MPs (using size,
type, shape, and color as criteria). The minimum
resolution is allocating into bin sizes of 100 μm
(Hanke et al. 2013). Type categories are usually
defined as fragments, pellets, filaments, films,
foamed plastics, granules and Styrofoam. Colors
are diverse and have been reported as transparent,
crystalline, white, clear-white cream, red, orange,
blue, opaque, black, grey, brown, green, pink, tan,
and yellow (Hanke et al. 2013).
Studies on MP pollution in marine environ-
ments have received significantly greater atten-
tion compared to those of freshwater and terres-
trial environments. Sampling efforts have been
done in the beaches, water column, ocean surface,
subtidal sediments and biota (Zobkov et al. 2018;
Gola et al. 2021; Ugwu et al. 2021). However, in
recent years, studies have expanded to freshwater
and terrestrial ecosystems (mainly surface water
and sediments) (Wong et al. 2020; Baho et al.
2021).
Global effects of MP pollution have even been
documented in remote regions, such as the snow
from mountains (Free et al. 2014; Napper et al.
2020), the Arctic (Bergmann et al. 2019) and arc-
404 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
con acceso por tierra. Para el muestreo de peces marinos se utilizaron cañas de pescar, y para langostas se utilizaron jaula y buceo con
escafandra autónoma. Se encontraron plásticos en todo tipo de muestras: 93% de sedimentos marinos, 32% de sedimentos de agua dulce,
20% de peces de agua dulce, 15% de camarones de agua dulce, 27% de peces marinos y 51% de langostas marinas. Al igual que muchos
informes en todo el mundo, se esperaba encontrar MP en las muestras marinas, y se concluyó que las corrientes oceánicas, las actividades
turísticas y los aparejos de pesca desechados por actividades de pesca ilegal podrían ser fuentes de contaminantes marinos. Por el con-
trario, no se esperaba la cantidad de MP encontrada en ambientes de agua dulce. Sus posibles fuentes no están claras hasta el momento.
Palabras clave: Ecosistema marino, ecosistema de agua dulce, sedimentos, isla oceánica, peces, langostas, camarones.
tic polar waters (Bergmann and Klages 2012;
Lusher et al. 2015), and deep-sea sediments (Van
Cauwenberghe et al. 2013), to mention a few. In
high-altitude remote areas, the presence of MPs is
mostly due to atmospheric transportation (by
wind, storm, or rain); therefore, MPs can easily
reach different isolated ecosystems (Allen et al.
2019) and spread into terrestrial systems (Rilling
2012). Also, remote coastal areas, where local
pressures are low or even absent, are expected to
be less affected by environmental pollution (Zhao
et al. 2015; Çomakli et al. 2020). Additionally,
there is increasing evidence of MP pollution in
remote coral reef systems (Imhof et al. 2017;
Ding et al. 2019; Tan et al. 2020). These remote
systems are considered healthy ecosystems now
facing the potential threats of the emerging MP
contaminants as well. Despite this, little is known
about key issues such as the spatial distribution of
MPs within these remote uninhabited areas or the
possible sources and input pathways of MPs into
these regions (Tan et al. 2020).
The research of MPs in Costa Rica is just
beginning, and the information is scarce. Current-
ly, Costa Rica has only two studies of MPs in
marine organisms. The first report of MPs was in
a sample of 30 sardines from the Family Clupei-
dae, with Opisthonema libertate (filter feeders’
fish) from the Pacific coast. Researchers detected
MPs in all individuals with an average of 36.7
pieces per fish, 79.5% were microfibers and
20.5% were other types of plastic particles
(Bermúdez-Guzmán et al. 2020). In another study
a year later from the Pacific coast, 27 individuals
from seven different species of fish from higher
trophic levels were sampled. Eighty-nine percent
of the fish had MPs, with an average of 3.75 MPs
per fish and 93% of these particles were
microfibers. Also, they sampled 29 benthonic car-
nivorous crabs (Callinectes arcuatus), 76% of
which had MPs with 2.64 MPs per crab, and 93%
microfibers (Astorga-Pérez et al. 2022).
Moreover, Cocos Island National Park is the
only oceanic island of Costa Rica, located 535 km
from the Costa Rican Pacific coast, far away from
any populous city. The highest elevation point is
Cerro Iglesias with an altitude of 575.5 m above
sea level. The island is covered by tropical rain-
forest and its average annual precipitation varies
between 4,500 to 6,000 mm (Alfaro 2008). Her-
rera (1985) suggested that the high precipitation
is because the island is strongly influenced by the
north-south movement of the Inter-Tropical Con-
vergence Zone. The island is drained by three
main watersheds: the Genio River, which flows
north and empties into Wafer Bay; the Iglesias
River, which flows from north to south and emp-
ties into Iglesias Bay; and the Lièvre River water-
shed, which flows from east to west and empties
into Chatham Bay. In addition, the hydrographic
network of this island is formed by permanent
rivers and streams, which differentiates it from
other oceanic islands located in the Eastern Trop-
ical Pacific, such as those from the Galapagos
archipelago, which are more arid (Bergoeing
2012; Gutiérrez-Fonseca et al. 2013).
Furthermore, Cocos Island is regarded as one
of the few effective Marine Protected Areas
around the world and it has become famous
because of its large aggregations of pelagic
species (Naranjo-Elizondo and Cortés 2018).
Apart from a few park rangers and some facilities
provided for regular visitors such as researchers
and volunteers, the island is almost inhabited
(Díaz-Bolaños et al. 2012). Because of this, plas-
tic residues in the National Park could be gener-
ated from daily human activities (e.g. cooking,
cleaning, among others), the majority of which
happen at the Wafer base. Besides this local pro-
duction of plastic residues, the confiscation of
illegal fishing gear around the island and marine
debris carried by marine currents to the coasts of
Cocos Island National Park could also be impor-
tant sources of plastic pollution (SINAC 2017).
Because Cocos Island is a remote island with
low anthropogenic influence, the aim of this
research was to assess the presence and abun-
dance of MPs and estimate differences between
405
ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
terrestrial and aquatic ecosystems regarding this
pollutant. This study examined sediments and
biota from both ecosystems.
MATERIALS AND METHODS
Sampling site
Cocos Island is part of the Cocos Marine Con-
servation Area, a site managed by the Costa Rican
National System of Conservation Areas (Sistema
Nacional de Áreas de Conservación, SINAC).
This island with a surface area of 24 km2possess-
es an extensive diversity of ecosystems at both
land and marine levels, where the cloud forest
and coral reefs predominate (Díaz-Bolaños et al.
2012; Alvarado et al. 2016). It has abundant fresh
water with numerous streams that flow along the
coast surrounding the two main rivers of the
island (Genio River and Iglesias River). The legal
category of this protected area only allows diving
activities, while hunting, fishing and any other
activity threatening the different ecosystems’
health are banned (González-Andrés et al. 2020).
Two field expeditions were conducted to
obtain samples. During the first expedition (June
18th to July 7th 2019 under Permission 2019-I-
ACMC-08) most of the samples of sediments,
freshwater fish, freshwater shrimps and marine
fish were collected (Figure 1). Later, in the sec-
ond expedition (October 3th to October 15th
2020 under Permission 2020-I-ACMC-08) the
majority of the marine lobster samples were col-
lected.
406 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
Figure 1. Collection sites and sample types from Cocos Island (m.a.s.l =meters above the sea level).
Sample collection
Marine and freshwater sediments
All sediment samples were superficial and
weighed one kilogram each. They were sampled
by taking approximately the top 5 cm of the sedi-
ment in a 50 50 cm square with a clean stainless
steel hand trowel and stored in metal containers
previously washed with distilled water. Metal
containers were stored in freezers at 0 °C prior to
processing (Herrera et al. 2018).
Freshwater organisms
All freshwater fish species were indistinctly
caught with small nets in the rivers, which were
accessed by land. Fishing nets were also used at
two more sites, Liévre creek and Genio River, for
freshwater shrimps sampling.
Marine organisms
Fishing rods were used for the marine fish
sampling at the north side of the island due to
unfavorable environmental conditions on the
south side of the island. Captured freshwater and
marine fish were placed in coolers with ice for
transportation to the processing point in the
island. All instruments were sterilized with alco-
hol and quantitatively washed with distilled
water. Tables were covered with bags and cotton
garments to avoid cross-contamination. Collected
organisms were weighed (g) and measured (total
body length in cm) (Table 2). Subsequently, lob-
sters and fish were dissected to remove the entire
gastrointestinal tract (GIT) following the proce-
dures described by Boerger et al. (2010) and
Lusher et al. (2013). Extracted GITs, composed
by stomach, intestine, liver, pancreas, and pyloric
cecum were weighed separately and preserved in
glass containers with 70% alcohol. In the case of
freshwater shrimps, the digestive system could
not be extracted due to their small size, therefore,
the exoskeleton was carefully removed and the
whole animal was preserved in glass containers
with 70% alcohol.
Sample processing
In order to prevent and/or reduce potential con-
tamination from external sources, such as air-
borne fibers, the laboratory workspace was fre-
quently cleaned, and work was performed in a
laminar airflow cabinet, particularly for preparing
solutions, sieving and filtrating, when possible. In
addition, glassware was washed thoroughly,
oven-dried and covered with aluminum foil when
not in use.
Sediments
For sediment samples, a density separation and
filtration method using aqueous solutions was
performed. The aim of this process was to utilize
density differences to separate different types of
polymers from organic and inorganic natural par-
ticles such as the sediment, sand or silt particles
(Kershaw et al. 2019). One kilogram of every
sediment sample was mixed with a NaCl solution
(1.2 g cm-3) and stirred for at least 2 h for sand
samples, and 24 h for silty sediment samples
(Hidalgo-Ruz et al. 2012; Qiu et al. 2016; Martin
et al. 2017; Enders et al. 2020). After agitation,
the sample was allowed to settle (covered with
aluminum foil) for 24 h, allowing denser con-
stituents to sink and less dense particles to float or
to remain in suspension. After 24 h, the super-
natant was filtered with a Büchner funnel and
passed through a 10 μm retention glass fiber filter
paper. In most cases, a triplicate was required
while filtering since the presence of silt made the
process difficult. Filter papers were removed in a
laminar cabin and stored in sealed Petri dishes
prior to examination under a stereo microscope.
Organisms
Freshwater shrimps and GITs of lobsters,
marine and freshwater fish, were chemically
digested to extract MPs. Extraction was carried
out according to the method described by Cole et
al. (2014), Kühn et al. (2017), and Bessa et al.
(2019). A solution of 10% KOH to digest the
407
ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
organic matter was added. The volume of the liq-
uid did not exceed 50% of the total volume of the
Erlenmeyer (250 or 500 ml). To obtain a dis-
solved solution, Erlenmeyers were covered with
aluminum and placed in an oscillating incubator
at 60 °C at 300 rpm for 24 h. Subsequently, the
digested content from the chemical process was
sieved through a 60 µ stainless steel sieve and
transferred to a clean Petri dish. The excess of
water was evaporated in an oven at 45 °C for
30 h. Glass Petri dishes were covered with alu-
minum foil with small holes to allow water to
evaporate and prevent possible airborne plastic
contamination (Enders et al. 2020).
Identification and validation of microplastic
All particles were identified, measured, and
photographed using a stereo microscope OPTI-
KA SZ-ST2 with image analysis system
AMSCOPE MU1000 Camera with AMPSCOPE
software. Plastic particles <5 mm were classified
as MPs; if their size was >5 mm they were
excluded from the analysis (Andrady 2011). They
were also classified by type as fibers (elongated),
fragments (irregular pieces), pellets or films (thin
and transparent) and categorized by their color
(Hidalgo-Ruz et al. 2012; Qiu et al. 2016; Martin
et al. 2017; Enders et al. 2020). Knots (fragments
of fishing nets between 5-25 mm) were pho-
tographed and counted into the frequency of
occurrence but not considered in the calculation
of the average MPs/lobster, since they are not
considered MPs.
Quality control of experiments
Glassware, plastics and dissection tools were
rinsed three times with distilled water to reduce
possible contamination (Li et al. 2015; Lusher et
al. 2015). Tap water, saline water and sodium
hydroxide were filtered with a 1 mm glass fiber
filter before use, and samples were covered with
aluminum foil to prevent any kind of pollution.
To prevent contamination by airborne MPs, sam-
ple handling was performed in a laminar flow
cabinet (Zhang et al. 2017; Mason et al. 2018;
Oßmann et al. 2018; Wang et al. 2018). Negative
controls (Jabeen et al. 2017) were carried out dur-
ing sodium hydroxide treatments, observation,
identification and validation of MPs, resulting in
a total of 22 controls. All particles identified in
these controls were fibers, and any similar parti-
cles found at sediments and tissues samples were
excluded from the analysis.
Statistical analysis
The number of MPs data in different organisms
and ecosystems were not normally distributed
according to the Shapiro normality test at 95% of
confidence. Therefore, a Mann-Whitney Test for
two independent samples were performed to
determine differences of MPs abundance between
marine and freshwater sediments, marine fish and
lobsters, freshwater fish and shrimps, marine and
freshwater fish, and marine lobsters and freshwa-
ter shrimps. Statistical analyses were performed
using R Statistical Software (R Core Team 2020).
RESULTS
All types of samples resulted positive for the
presence of MPs: 93% of marine sediments, 32%
of freshwater sediments, 27% of marine fish,
20% of freshwater fish, 51% of marine lobsters,
and 15% of freshwater shrimps. In addition, two
types of MPs were observed: fibers and frag-
ments (see Supplementary Material for the most
representative images of MPs found). In marine
lobsters, pieces bigger than >5 mm were found,
photographed, classified as fibers and knots but
excluded from statistical analysis (Appendix,
Figure A1).
Contamination from the laboratory was detect-
ed from 22 contamination controls. An average
408 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
2.3 ± 2.0 plastic/control was determined. Parti-
cles found in negative controls were fibers with
sizes >5 mm. These particles could be derived
from the air pollution in the laboratory, although
many sources of contamination were avoided.
Fibers that were consistent in shape and color in
the controls were not considered in any sample.
Sediment samples
Marine sediment samples were collected from
sandy beaches (14 samples) and shallow water (4
samples) at different locations. In addition, 14
freshwater sediment samples were collected from
Genio River, Villa Beatriz creek, and Liévre creek
(Table 1). All sediment samples were taken at
depths less than 10 m. A frequency of occurrence
of 93% was obtained in marine ecosystems with
an average of 3.35 ±4.30 MPs per sample, and
32% in freshwater ecosystems with an average of
1.00 >1.47 MPs per sample (Figure 2). Mann-
Whitney Test showed a significantly higher quan-
tity of MPs in marine ecosystems ( p=0.025)
when comparing it to the freshwater ecosystems.
Organism samples
For marine fishes, a total of 31 Jordan’s snap-
pers (Lutjanus jordani) from the Family Lut-
janidae were caught. For freshwater fishes a total
of 30 organisms from four families (Gobiidae,
409
ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
Table 1. Locations and sediment textures of sampling sites
located in marine and freshwater sediments of Cocos
Island.
Location site Sediment texture Number
of samples
Wafer Bay Sandy beach 10
Liévre creek Bay Sandy beach 4
Montagne Island Shallow water 1
Manuelita Island Shallow water 1
Juan Bautista Island Shallow water 1
Liévre creek Bay Shallow water 1
Genio River Muddy sediments 10
Villa Beatriz creek Muddy sediments 3
Liévre creek Muddy sediments 1
Figure 2. Comparison of microplastics (MPs) in sediment samples between marine and freshwater ecosystems from Cocos
Island, Costa Rica.
100
90
80
70
60
50
40
30
20
10
0
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Frecuency of ocurrance (%)
Average of MPs
Marine cosystem Ne18=Freshwater ecosystem N 14=
Fibers Fragments Average
Mugilidae, Eleotridae and Gobiesocidae) were
captured. Species from each family were respec-
tively: eleven organisms Sicydium cocoensis,
nine organisms Dajaus monticola, six organisms
Eleotris picta and four organisms Gobiesox ful-
vus. During the first expedition, 14 green spiny
lobsters of the species Panulirus gracilis (Family
Palinuridae) were captured with traps. Because of
high predation by whitetip reef sharks in the
traps, in the second expedition the lobsters were
captured directly through scuba diving, resulting
in 39 lobsters from the same Family Palinuridae:
11 Panulirus gracilis and 28 Panulirus penicilla-
tus. Also, a total of 32 shrimps of the Genus Mac-
robrachium sp. were captured. Table 2 describes
the characteristics of the captured organisms.
A frequency of MPs occurrence of 27% was
obtained in marine fishes, with an average of 1.37
±0.51 MPs per organism (Figure 3). A total of 11
MPs were found, 82% of them were fibers, while
only 18% were fragments (Table 3). Ninety per-
cent of the MPs had a mean size <3 mm and the
main color was black, followed by red and blue.
In the case of freshwater fishes, a frequency of
occurrence of 20% was obtained with an average
of 1.16 ±0.40 MPs per organism. A total of 7
MPs were found, 57% of them were fibers, while
43% were fragments. All sizes of the MPs were
<3 mm and the main color was blue, followed by
black and red.
In marine lobsters, a frequency of occurrence
of 51% was obtained with an average of 1.42 ±
0.75 MPs per organism. A total of 18 MPs were
found, 56% of them were fibers, while 44% were
fragments. Eighty-three percent of the MPs found
in marine lobsters had mean size <3 mm, but
they were the only organism with three pieces
bigger than >5 mm (11.25 mm, 10.22 mm, and
9.85 mm), identified as knots but excluded from
the analysis, since they are not considered MPs
410 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
Table 2. Morphometric characteristics of the organisms collected in the Cocos Island National Park to determine the presence
of microplastics (MPs) in their tissues.
Characteristics
Fish species N Average of body weight (g) Average of total length (cm)
Marine fishes
Lutjanus jordani 30 567 ±109 35 ±2 (31.6-81.5)
Freshwater fishes
Dajaus monticola 9 5.9 ±3 13 ±6 (7.5-23.5)
Eleotris picta 6 205 ±168 25 ±6 (19.5-34.1)
Gobiesox fulvus 4 14 ±3 11 ±4 (8.4-17)
Sicydium cocoensis 11 13 ±9 9 ±2 (5.3-11.5)
Marine lobsters
Panulirus gracilis 23 302 ±87 10 ±1 (7.8-12)
Panulirus penicillatus 11 650 ±340 11 ±3 (7.3-19)
Freshwater shrimps
Macrobrachium sp. 39 4 ±6 5 ±2 (3.5-13.3)
(Appendix, Figure A1). The main color of MPs in
marine lobsters was red. In freshwater shrimps,
the frequency of occurrence was 15% with an
average of 1.16 ±0.40 MPs per organism. A total
of 6 MPs were found, 100% of them were fibers.
Mean size of the MPs were all <3 mm and the
main color was blue and red, followed by black.
Microplastics were observed in all organisms.
The number of MPs between marine and fresh-
water fish was not statistically significant (Mann-
Whitney Test, p =0.4895). The abundance of
plastics by items/individual was significantly
higher in marine lobsters than in freshwater
shrimps (Mann-Whitney Test, p =0.0056).
411
ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
Figure 3. Microplastics (MPs) found in marine and freshwater organisms at Cocos Island National Park, Costa Rica.
Table 3. Types, sizes, and colors of microplastics found in the biota of Cocos Island National Park, Costa Rica.
Characteristic Classification Marine fish (%) Freshwater fish (%) Marine lobster (%) Freshwater shrimp (%)
Form* Fibers 82 57 56 100
Fragments 18 43 44 0
Size <1mm 45 57 83 67
1-3 mm 45 43 17 33
3-5 mm 9 0 0 0
Color Red 36 14 28 33
Black 45 29 22 17
Blue 18 43 22 33
Others 0 14 28 17*
*Even though other categories of forms were considered in this research, such as fiber, fragment, films and pellet, only two types
of MPs were found (fibers and fragments). Predominant colors were blue, black and red. Category ‘other’ included green, trans-
parent and white.
60
50
40
30
20
10
0
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Frecuency of ocurrance (%)
Average of MPs
Freshwater
shrimp N = 39
Marine lobster
N = 34
Freshwater fish
N = 30
Marine fish
N = 30
Ocurrence MPs indv-1
DISCUSSION
Cocos Island National Park is sparsely popu-
lated and far away from the continent and big
cities; despite that, MPs were found at both fresh-
water and marine ecosystems. Furthermore, high-
er frequency and quantity of MPs were found in
marine sediments compared to freshwater sedi-
ments. In the marine environment, the presence
of MPs has been demonstrated in a wide diversity
of regions and concentrations because of their
persistence and long-range transportation by
wind, rainfall and/or currents. Particularly, beach-
es and subtidal sediments appear to function as
sinks for MPs (Duis and Coors 2016; Katare et al.
2021; Nammalwar 2021).
Studies of the surface circulation in the South
Pacific Ocean have shown an accumulation of
debris in the eastern-center region of the South
Pacific Gyre (Martinez et al. 2009). Also, large
debris concentrations were found just north of the
North Pacific Transition Zone within the North
Pacific Subtropical Convergence Zone (Pichel et
al. 2007). Cocos Island is located between these
two giant gyres (North Pacific and South Pacific),
which could be important sources of MPs. In fact,
the California Current, which can carry materials
from the North Pacific Gyre, is the possible
source of MPs of the north coast of Costa Rica
(Johnson et al. 2018).
A lower abundance of MPs was expected in
samples from terrestrial ecosystems, but an
occurrence of 32% was determined in sediments,
20% in freshwater fish, and 15% in shrimps.
According to Lwanga et al. (2016), the majority
of MPs particles entering the freshwater are pri-
marily from i) secondary plastics generated by
the breakdown of larger plastic items (single-use
packing, tires, fibers from synthetics fabrics and
road paint particles); and ii) effluent discharges
from wastewater and sewage. Additionally, it was
determined that population density and quality of
waste management can be established as the key
anthropogenic factors affecting the presence and
abundance of MPs in the freshwater environment
(Free et al. 2014; Lwanga et al. 2016). Neverthe-
less, due to the low density of people that inhabit
the island (SINAC 2017) and the pristine origin
of the island's rivers, the sources of plastic con-
tamination in freshwater ecosystems remain
unclear.
One possible source are MPs from atmospheric
transportation by wind and/or storms. The tropi-
cal area where the island is located receives large
volumes of annual rainfall, and its humidity
comes from the Pacific Ocean (Alfaro 2008).
Recently, it has been demonstrated that MPs can
travel within the air as ‘urban dust’ (Dehghani et
al. 2017; Dris et al. 2017), which usually origi-
nates from road dust from tires, paint particles, or
fibers from synthetic textiles (GESAMP 2015;
Dris et al. 2017; Horton et al. 2017). Also, studies
on atmospheric fallout in Paris, France (Dris et al.
2016) and Dongguan, China (Liqi et al. 2017)
suggest an atmospheric MPs conveyance and
subsequent deposition. Remote and pristine areas
are also affected. Research in a remote area of the
Pyrenees mountains provided evidence of direct
atmospheric fallout of MPs deposition (Allen et
al. 2019). Additionally, the detection of MPs in
glacier surface snow collected from an isolated
area from human impact on the Tibetan Plateau,
indicated that MPs can be transported over long
distances (Zhang et al. 2021).
The majority (63%) of the MPs found in organ-
isms were classified as microfibers, this result is
consistent with those of Celik (2021), Makhdou-
mi et al. (2021) and Pan et al. (2021). According
to the literature, microfibers are considered as the
major marine pollutant throughout the world.
Some authors estimate a million tons of coastal
synthetic fabric waste entering the ocean each
year, affecting different marine ecosystems. They
also point out that there is an urgent need for
development of cost-effective and efficient reme-
diation technologies, legislative action towards
412 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
the source and public awareness (Mishra et al.
2019; Singh et al. 2020).
The present study analyzed two groups of
organisms in marine and freshwater ecosystems:
fish and crustaceans, whose different feeding
habits, behaviors and habitats, play important
roles in the ingestion of debris. Indeed, an
increase in the abundance of plastics will also
increase the bioavailability of this pollutant to
other organisms (Boada et al. 2015; Jabeen et al.
2017). The marine fish analyzed (Lutjanus jor-
dani) are usually found over hard bottoms in the
inshore reef areas and are carnivorous, feeding
mainly on invertebrates and smaller fish (Fischer
et al. 1995; Bussing and López 2005). The fresh-
water fish were caught in shallow and turbulent
rivers, and the different genus of the species
found are reported to feed on zooplankton, algae,
and small benthic invertebrates (Bussing 1998).
Freshwater fish caught are considered ‘benthonic
fish’ and the MPs found in these organisms could
be related to heavy plastics in the benthic zone,
unlike marine fish that consume plastics floating
in the water column. Marine lobsters and fresh-
water shrimps are both benthic macroinverte-
brates associated to rocky bottoms, hence they are
more exposed to the debris deposited on the sea
bottom or stream bed (Naranjo 2011; Figueroa
and Mero 2013; García-Guerrero et al. 2013).
It could be predicted that marine lobsters will
have a higher exposure to debris than freshwater
shrimps. Naranjo-Elizondo and Cortés (2018)
found anthropogenic debris at Cocos Island,
between 200 and 350 m depth, from which 60%
of the items were plastics from local boats and
fishing gears. Fishing gears comprised lost lines
and most of fishing debris observed in contact
with fish or crabs (Naranjo-Elizondo and Cortés
2018). These authors’ concern about the possible
plastic ingestion by different organisms eventual-
ly confirmed it with the present study. Nylon fish-
ing knots found inside marine lobsters’ digestive
system were >5 mm (11.25 mm, 10.22 mm, and
9.85 mm), and were in the process of conversion
to MPs. Only a higher number of items per indi-
viduals was determined in marine lobsters versus
freshwater shrimps. This coincides with the result
of a higher number of MPs in marine sediments
versus freshwater sediments. This last could be
influenced by the feeding mode of each organism
and the abundance of MPs in the habitat in which
they are found.
Statistical analyzes did not detect differences
in the type of plastic particles ingested by marine
and freshwater organisms. Therefore, investiga-
tion regarding types and abundance of debris in
both ecosystems should continue. However,
strategies that involve behavioral change, remov-
ing/cleaning-up and mitigation measures to
reduce the inputs of plastics from land or sea bot-
tom sources are being taken to tackle this com-
plex problem (Ogunola et al. 2018).
CONCLUSIONS
It was conclusive that both marine and fresh-
water ecosystems are being affected by MP parti-
cles. It is important to continue investigating the
sources and impacts of MPs in both ecosystems
to find solutions that can be effectively imple-
mented. Although the sources of MPs in the
freshwater ecosystem are so far unclear, trans-
portation of MPs from seabirds or by wind are
possible hypothesis that should be investigated in
future assessments.
ACKNOWLEDGEMENTS
This work was funded by FAICO (Fundación
Amigos Isla del Cocos), supported by ACMC-
SINAC (Área de Conservación Marina Coco-Sis-
tema Nacional de Áreas de Conservación) of the
Costa Rican government and implemented by
LEMACO (Laboratorio de Estudios Marino Cos-
413
ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
teros) from the School of Biological Sciences of
the Universidad Nacional de Costa Rica. We
thank the rangers and volunteers from Cocos
Island National Park, particularly to: Eduardo
Alvarado-García, Moíses Gómez-Vargas, Manuel
Ruíz-García, Filander Ávila-Calderón, Keylor
Morales-Paniagua, and Guillermo Blanco. None
of the authors have any conflict of interests to
declare. FAICO donors were not involved and
had no influence on the survey design, sampling
process, data analysis, or results interpretation
process, nor in the submission for publication.
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ASTORGA ET AL.: MICROPLASTICS FOUND IN COCOS ISLAND NATIONAL PARK
APPENDIX
Pieces between 5-25 mm were found in three
of the marine lobster’s digestive systems. Figure
A1 shows the particles identified as fishing knots
made from nylon fibers. Besides the knots, a con-
siderable amount of nylon fibers was also extract-
ed and counted. Lobsters had 81, 14, and 37
nylon fibers resulting from the fragmentation of
the knots, respectively.
420 MARINE AND FISHERY SCIENCES 35 (3): 403-420 (2022)
Figure A1. Mesoplastic extracted from a marine lobster digestive system.
