Ashley Jackson
CO 300 Section 4: Journal Article
Abstract
Humans began incorporating plastics into their lives over a century ago. Because plastic
goods are durable, light weight and inexpensive, the trend in manufacturing has been to produce
goods made of or containing plastic in higher and higher quantities. These discarded plastic
goods often end up in the oceans. Due to their durable nature, they take hundreds to thousands
of years to break down. During that time period, they become brittle and break into tiny pieces
of varying shapes and sizes. Marine animals often ingest the particles, mistaking them for prey;
this can result in a variety of health problems and/or death. Other animals become entangled in
larger plastic debris which too can lead to death. Additionally, tiny organisms are able to hitchhike on buoyant plastic debris, traveling great distances where they are considered invasive
species. All of these detrimental effects are impacting the already endangered sea turtles. They
are most often affected by floating plastic bags which resemble jellyfish. Overall, the
biodiversity of the oceans is being impacted by the presence of plastic.
Keywords
polychlorinated biphenyls (PCBs), Chelonia mydas, Caretta caretta, Dermochelys coriacea
Introduction
One of the most detrimental anthropogenic activities affecting marine ecosystems is the
pollution of plastic debris (Derraik, 2002). Although plastics have only been in existence for a
little over a century, today, they are a versatile component of people’s everyday life. Plastic
production is estimated at 225 megatons per year (Barnes; Galgani; Thompson; Barlaz, 2009)
making them the fastest growing component of waste. The modern trend in manufacturing is for
nearly all goods to contain and/or be wrapped in plastic. Many of these goods are considered
one time use only or have little to no options for reuse, leaving nearly 95% of plastic goods
purchased in the United States discarded. Some of this plastic waste reaches landfills and
disposal sites, however much of it escapes and eventually makes its way to the oceans (Moore,
2008). Plastics residing in marine environments negatively affect the species diversity of the
oceans, especially sea turtles. This is partially due to the long life of plastic debris. Plastic is
estimated to remain chemically intact for hundreds to thousands of years; far longer in deep sea
and non-surface polar environments (Barnes et al, 2009). Most plastic does not retain its original
form; large plastic debris breaks down into small plastic pellets, changing shape and size, making
them more ingestible to a variety of marine animals (Ivar do Sul; Spengler; Costa, 2009). This
is not to say that plastics do not break down; a slow deterioration from ultraviolet light weakens
the plastic; however, the cool ocean environment and removal from sunlit areas extends the UV
light degradation process. Because plastics have only been around for nearly a century, it is
believed that any plastic (aside form those incinerated) that has ever been made, still exists
today, either in its natural form or broken down into small fragments (Barnes et al, 2009). The
very properties that make plastic goods desirable to humans are the same reasons they have
become so detrimental to the marine environment. Plastics’ anti-aging characteristics which
make them resistant to UV radiation become brittle when exposed to the oxidative properties of
the atmosphere combined with the high salinity of ocean waters. Once brittle, they continually
break down into smaller and smaller pieces and eventually become individual polymer molecules
(Moore, 2008). These tiny plastic fragments along with larger debris are all detrimental to the
biodiversity of marine ecosystems.
Evidence suggests that plastic debris can be found almost anywhere in marine and coastal
environments (Ivar do Sul et al, 2009). This wide dispersal directly affects at least 267 species
worldwide, including 86% of all sea turtle species, 44% of all seabird species, and 43% of all
marine mammal species; a conservative estimate considering the overall number of species
affected by plastics remains largely unknown due to undiscovered species, and areas where
species affected are never found, either because they sink to the bottom or are eaten by predators
before the data can be collected. Because threatened and endangered species are already at risk,
plastics have an even greater detrimental effect on those species (Derraik, 2002).
Discussion
Marine animals are directly affected by plastics in three main ways: ingestion,
entanglement and the transport of invasive species.
a) Ingestion: Many species often mistake small plastic particles for food; some such as sea
turtles are selective in the shape, size or color of plastic particles they ingest which suggests the
particles resemble organisms in their usual diet (Derraik, 2002). It is probable that because of
the endless ways multi-colored plastic debris can change shape and size, nearly every natural
food source in the marine environment can be mimicked (Moore, 2008). Once swallowed these
plastic particles are indigestible and remain in the stomachs of the organism (Seibert, 2009).
Once an animal has ingested a plastic particle, it can be harmful in many ways. Firstly, a reduced
intake of food partially because the plastic particles have reduced the amount of space available
in the animal’s stomach, and partly because the plastic residing in the stomach gives a false sense
of satiation, therefore reducing the natural feeding stimulus. Secondly, a blockage of the
intestinal tract and a disruption with the secretion of gastric enzymes which can interfere with
normal digestion. Lastly, a reduction in steroid hormone levels which can lead to reproductive
failure and delayed ovulation. All of the effects from ingesting plastic debris can lead to death.
Even after the animal has died the plastic particle remains in the carcass and therefore the food
web, available for another organism to ingest and follow the same cycle. Not only is the physical
presence of the plastic particle detrimental to the organisms, but the chemicals emitted from the
plastics which are absorbed by the animal are harmful as well. Chemicals contained in most
plastics called polychlorinated biphenyls or PCBs, can even in small quantities lead to
reproductive disorders, increased susceptibility to disease and/or death, and artificially alter
hormone levels (Derraik, 2002). In addition to PCBs, some manufactures also use a variety of
additives when producing plastic goods which increase the functionality of the plastic.
Unfortunately, these additives such as phthalate plasticizers and brominated flame retardants are
harmful to animals and have been associated with carcinogenic disorders and health problems
associated with the endocrine system (Barnes et al, 2009). Whether the ingested plastic debris
kills the animal directly or merely impedes its ability to fully function, it is clear that ingesting
plastic is detrimental to the overall survival of all marine organisms.
b) Entanglement: Over the last four decades, the accumulation of both macro (>20 mm
diameter) and micro-plastics (<5 mm) has consistently increased in marine ecosystems (Barnes
et al, 2009). These plastics encroach on breeding and feeding grounds, nurseries, migratory
routes and areas to hide from predators. One of the most common effects of the presence of
macro-plastic debris in marine ecosystems is animal entanglement. Discarded fishing equipment
is the largest contributor to entanglement, but is not the sole contributor. Plastic six-pack soda
can holders and other plastic rings often end up around the necks of juvenile marine mammals,
particularly seal pups. As the animal grows, the ring begins to cut off blood flow and eventually
strangles the animal to death (Derraik, 2002). If an entangled animal is able to survive, it suffers
in many aspects of it life: food acquisition, locomotion, wounds can developed from abrasive
rubbing or cutting from the debris, or it may drown. The presence of plastic debris in a marine
animal’s habitat can negatively affect its overall livelihood and ultimately its survival.
c) Transport of Invasive Species: Some plastic debris in the marine environment has become a
sole contributor to the expansion of invasive species in oceans around the world. Evidence has
shown that because of the great abundance of plastic debris, its durability, buoyancy and ability
to travel with the current and by wind, it has become an excellent vehicle to transport tiny
organisms (Barnes et al, 2009). Plastic debris has allowed for species such as bacteria, algae and
barnacles, unable to travel great distances, the ability to colonize parts of the marine ecosystem
previously uninhabited by those same species. Because of this, invasive marine species are
increasing as a direct result of plastic debris. These invasive species are harmful to other species
and therefore decrease the biodiversity in the oceans (Derraik, 2002).
Sea turtles are one of the most affected species by plastic pollution; the green turtle
Chelonia mydas, loggerhead turtle Caretta caretta and leatherback turtle Dermochelys coriacea
are all endangered species (Bugoni; Krause; Petry, 2001). Case studies have shown that sea
turtles are particularly prone to eating floating plastic debris (Bugoni et al, 2001). One of the
most common and most frequently ingested objects is plastic bags; this is because of their
similarity in shape and movement to jellyfish, common prey for sea turtles (Bjorndal; Bolten;
Lagueux, 2003). As previously discussed, the ingestion of plastic debris of any kind is
detrimental to the overall livelihood of an animal; several case studies were used to examine the
frequency sea turtles ingest plastic debris.
From 1995-1999 the diet of Chelonia mydas off the Gulf of California in Mexico were
studied by the examination of the esophagus, stomach and fecal matter. Both live specimens and
stranded carcasses were used. Anthropogenic debris such as plastic bags and nylon cord were
commonly found in the specimens (Seminoff; Resendiz; Nichols, 2002).
In 2001 the esophagus and stomach contents were examined from 38 endangered juvenile
Chelonia mydas off the coast of Brazil. Anthropogenic debris was ingested by 60.5 percent of
the specimens analyzed, plastic bags and plastic ropes constituted the majority of the debris, the
main colors were transparent, white, and black; this evidence coincides with the turtles mistaking
the plastic bags for jellyfish (Bugoni et al, 2001).
In 2003, The Center for Sea Turtle Research conducted their own case study on the
digestive tract of 51 sea turtle carcasses found on the east and west coast of Florida; 49 percent
of the turtles were found to have anthropogenic debris in their digestive tract including plastic
and fishing line (Bjorndal et al, 2003).
A study in 2009 reviewed 408 autopsy reports on Dermochelys coriacea that lived
between 1885-2007, the analysis of these reports revealed 33.8 percent of the specimens
contained some form of plastic debris. An increase in the ingestion of plastic was seen between
1960-1980; however, the exact reason for this increase cannot be precisely determined. What
can be concluded by looking at the records decade by decade over the past century is that the
ingestion of plastic has remained common, and it can be assessed that at least one third of adult
sea turtles have ingested some form of plastic (Mrosovsky; Ryan; James, 2009).
Although it cannot be directly stated that the deaths of these sea turtles were caused by
plastic, it is safe to conclude there is direct correlation between the presence of plastic debris and
a degradation in the overall fitness of marine animals. Because sea turtle have a slow life
history, it takes longer for turtle populations to recover form the harmful human footprint.
Because of their slow recovery, a higher then usual number of deaths can abruptly reduce the
gene pool and cause an array of genetic problems; this too will reduce the fitness of sea turtles
and therefore the biodiversity of the oceans. It is apparent that the use of plastics by humans is
negatively affecting the marine ecosystems and species diversity, especially sea turtles.
References
Barnes, D; Galgani, F; Thompson, R; Barlaz, M (2009) Accumulation and Fragmentation of
Plastic Debris in Global Environments. Philosophical Transactions of The Royal Society
364 (1526): 1985-1998
Bjorndal, K; Bolten, A; Lagueux, C (2004) Ingestion of marine debris by juvenile sea turtles in
coastal Florida habitats. Marine Pollution Bulletin 28 (3): 154-158
Bugoni, L; Krause, L; Petry, M (2001) Marine Debris and Human Impacts on Sea Turtles in
Southern Brazil. Marine Pollution Bulletin 42 (12): 1330-1334
Derraik, J (2002) The pollution of the marine environment by plastic debris: a review. Marine
Pollution Bulletin 44 (9):842-852
Gregory, M (2009) Environmental implications of plastic debris in marine settings –
entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions.
Philosophical Transactions of The Royal Society 364 (1526): 2013-2025
Ivar do Sul, J; Spengler, A; Costa, M (2009) Here, there and everywhere. Small plastic
fragments and pellets on beaches of Fernando de Noronha (Equatorial Western Atlantic).
Marine Pollution Bulletin 58(8): 1236-1238
Moore, C (2008) Synthetic polymers in the marine environment: A rapidly increasing, long-term
threat. Environmental Research 108 (2): 131-139
Mrosovsky, R; Ryan, G; James, M (2009) Leatherback Turtles: The Menace of Plastic. Marine
Pollution Bulletin 58 (2): 287-289
Seminoff, J; Resendiz, A; Nichols, W (2002) Diet of East Pacific Green Turtles (Chelonia
mydas) in the Central Gulf of California, Mexico. Journal of Herpetology 36 (3): 447-453
Siebert, T (2009, November). Plastic in the Environment. [Lecture notes]. Presented to the class
FW104: Wildlife Ecology and Conservation, Fort Collins, CO.