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It’s been said that we know more about the Moon’s behind than the Ocean’s bottom, and we have explored only 5 percent of our ocean’s bottom!
The United Nations Environment Programme (UNEP) defines marine litter as “any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment”. The first intended (as opposed to accidental) disposal of waste in the deep sea predates scientific interest in this environment. The age of sail gave way to the age of steam at the end of the 18th century and, for the next 150 years, one of the main waste products of steam power was a hard residue of burnt coal called clinker. This material was usually dumped over the ship’s side (Ramirez-Llodra et al., 2011). In the past, clinker has been disposed of on abyssal plains, sedimentary slopes and in some canyons. Major occurrences of clinker may be found off large ports where steamships cleaned their boilers. Clinker is no longer dumped into the ocean because steam power is no longer used over the deep ocean and modern regulations would prevent its disposal. The routine dumping of many types of waste from ships was legally banned from 1972 onward (London Convention, 1972).
Before the ban, a large variety of litter was dumped from ships in transit, including from bulk carriers, tankers, fishing boats, ferries and yachts. The amount of litter dumped in the oceans from vessels each year is estimated to exceed 636,000 tonnes (Goldberg, 1975). At present, litter continues to accumulate, through illegal disposal of litter from ships and lost or discarded fishing gear, as well as being adverted from the coast and river discharges (Galil, 2006). Approximately 6.4 million tonnes per year of litter are dumped into the oceans (UNEP, 2009), part of which sinks to bathyal and abyssal depths. Highly erosive deep-sea storms, which may affect 10% of the deep-sea floor, can transport laterally sediment loads along with benthic fauna (Aller, 1989). It is reasonable to assume that these storms may also transport refuse to seafloor depressions, which can serve as debris traps. Litter is observed in almost all scientific seafloor surveys using video (e.g. remote operated vehicles, ROVs) and trawls.
There is an urgent necessity to arouse an accelerated awareness of the environmental and economic importance of every nation’s coastal and offshore marine regions. The vitality of this environment has become a critical issue as society has increasingly applied pressure to our coasts via increased population, recreation, harvesting of fish, transportation, and disposal of waste.
In this context, it is important to realize what benefits oceans provide, marine activities and events that are of grave concern to all, probable solutions to problems that concern us, and major worries and some rays of hopes that rise in the horizon.
- Oxygen, water, food (fisheries products), and nutraceutical & pharmaceutical products
- Regulation of day-night atmospheric temperature and weather on Earth
- Mineral resources (polymetallic nodules and a variety of other minerals), hydrocarbon resources (oil & natural gas; gas hydrates), energy (tidal; wave; offshore wind; water current; ocean temperature gradient), cheapest transportation medium, and recreation facilities
- Marine related goods and services
- Haven for diverse population of phosphorus- and nitrogen-enriched prokaryotes (belonging to the bacteria and archaea) present within hot subseafloor sediments, and at seeps & vents.
Marine Pollution from Plastic Litter
Since the mass production of plastics began about 65 years ago, the use of this long-lasting cheap material has increased and, in parallel, so has its waste. Plastics are found everywhere, from land to the oceans, from the coast to the deep sea (Barnes et al., 2009). Although some types of litter are recognizable, there is accumulating evidence that “mermaids’ tears” (5 mm in diameter) and micro-plastics (microscopic sand grain-sized particles of eroded plastic) are becoming more common in the world oceans, including the deep sea (Thompson et al., 2009; O’Brine and Thompson, 2010).
Impacts of litter on deep-sea habitats and fauna may include suffocation of animals from plastics, release of toxic chemicals, propagation of invasive species, physical damage to sessile fauna such as cold-water corals from discarded fishing gear, and ghost fishing from lost/discarded nets (Barnes et al., 2009; UNEP, 2007), but these impacts are poorly quantified on a large geographical scale. The increasing evidence of continuous accumulation of litter has been recognised by the UNEP-Regional Seas initiative, which identified the need for further research on the impacts of marine litter in coastal areas (UNEP, 2009), and with an increasing interest in deep-sea habitats.
Whereas the coastal waters have already become the dumping ground for all kinds of waste materials, the remoteness of the deep seafloor has promoted the disposal of residues and litter. The deep sea served as a convenient site for disposal of waste, especially where land options were not politically and “ethically” attractive. Those very attributes which are found desirable in plastics—lightness, strength, cost effectiveness, safety, versatility, adaptability and flexibility in manufacturing, durability together with relative inertness and resistance to microbial and other degradational processes, not to mention transparency and prolonged shelf life and benefits in packaging—are also the very reasons that they have become a globally significant contaminant of marine waters (e.g. Gregory, 1978; Gregory, 1987; Gregory, 1990; Pruter, 1987; Andrady, 1988; Johnson, 1988). Fishing floats, fish boxes, milk crates, a diversity of plastic containers and bottles, netting, ropes, hawsers and strapping loops are typical examples (see the below given photographs). Because they float, discarded plastic items are a highly visible, and comprise both a volumetrically and numerically over-represented constituent of beach litter (Pruter, 1987).
Plastic litter and debris of all kinds is conspicuous on many contemporary shorelines, most frequently near populated and industrial centres, but also on remote and seldom-visited or uninhabited islands, including Raoul, Campbell and Auckland Islands (Ryan, 1987; Ryan and Watkins, 1988, Gregory, 1991). Pollution by plastics is aesthetically distasteful, and also creates a number of environmental problems: e.g. death and/or debilitation of marine wildlife (both large and small, including seabirds, mammals, fish, turtles and invertebrates) through entanglement; blockages to the intestinal tract through ingestion leading to starvation and death, or ulceration of delicate tissues by jagged fragments; reduction in quality of life and reproductive performance (Cawthorn, 1985; Laist, 1987). An encrusting pseudo-planktic biota, similar to that found on floating Sargassum and other seaweeds has been recognised on drift plastics. Alien species, rafted on drifting plastic, could endanger the flora and fauna of protected and conservation island ecosystems.
There has been some speculation on the chemical toxicity of plastics and/or their degradational products, as well as their propensity to adsorb and concentrate quantities of trace toxic compounds from sea water (e.g. PCB’s: Colton et al., 1974; Gregory, 1978); in this the finer particles are the more efficient (Andrady, 1987).
The most common litter types found on the deep–sea floor in the Mediterranean and north-eastern Atlantic are soft plastic (e.g. bags), hard plastic (e.g. bottles, containers), glass and metal (e.g. tins, cans) (Ramirez Llodra et al., 2010; Galil et al., 1995; Galgani et al, 2000; Watters et al., 2010; Miyake et al., 2011).
Plastic debris is now ubiquitous in the marine environment affecting a wide range of taxa, from microscopic zooplankton to large vertebrates. Its persistence and dispersal throughout marine ecosystems has meant that sensitivity toward the scale of threat is growing, particularly for species of conservation concern, such as marine turtles. Their use of a variety of habitats, migratory behaviour, and complex life histories leave them subject to a host of anthropogenic stressors, including exposure to marine plastic pollution.
Nelms et al. (2016) found that, of the seven species of marine turtles all are known to ingest or become entangled in marine debris. Ingestion can cause intestinal blockage and internal injury, dietary dilution, malnutrition, and increased buoyancy which in turn can result in poor health, reduced growth rates and reproductive output, or death. Entanglement in plastic debris (including ghost fishing gear) is known to cause lacerations, increased drag—which reduces the ability to forage effectively or escape threats—and may lead to drowning or death by starvation. In addition, plastic pollution may impact key turtle habitats. In particular, its presence on nesting beaches may alter nest properties by affecting temperature and sediment permeability. This could influence hatchling sex ratios and reproductive success, resulting in population level implications. Additionally, beach litter may entangle nesting females or emerging hatchlings. Lastly, as an omnipresent and widespread pollutant, plastic debris may cause wider ecosystem effects which result in loss of productivity and implications for trophic interactions.
One solution to the problem of plastic litter is the use of enhanced degradable plastics for control of plastic debris in the marine environment (see Andrady, 1988). In recent years, the use of biodegradable materials was proposed as a solution to the accumulation of plastics in the environment, but in some cases, the degradable material merely disintegrated into smaller pieces that are not degradable (Sumida et al., 2008). Little is known, however, of the true effect of these particles on the environment and the fauna (Thompson et al., 2004). Several studies have shown that effects such as ingestion by invertebrates could facilitate the transport of hydrophobic contaminants (Teuten et al., 2007) and the release of potentially toxic bisphenol A and PS oligomers during plastic breakdown, which can disrupt hormonal functioning and reproductive systems in the fauna (Saido et al., 2009). Studies in the deep sea are practically non-existent and an urgent assessment of the impact of micro-plastics on deep-sea fauna is needed along with the development of methods to quantify and monitor their abundance and to identify potential sources and sinks of this debris.
There is need to educate the public about the environmental problems arising from the indiscriminate disposal of plastics and other persistent synthetic compounds. It is unlikely that these problems can ever be solved by regulation, although, along with technological advances, that could alleviate them.
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