The plastisphere consists of ecosystems that have evolved to live in human-made plastic environments. All plastic accumulated in marine ecosystems serves as a habitat for various types of microorganisms, with the most notable contaminant being microplastics. There are an estimate of about 51 trillion microplastics floating in the oceans. Relating to the plastisphere, over 1,000 different species of microbes are able to inhabit just one of these 5mm pieces of plastic.
Plastic pollution acts as a more durable "ship" than biodegradable material for carrying the organisms over long distances. This long-distance transportation can move microbes to different ecosystems and potentially introduce invasive species as well as harmful algae. The microorganisms found on the plastic debris comprise an entire ecosystem of autotrophs, heterotrophs and symbionts. The microbial species found within plastisphere differ from other floating materials that naturally occur (i.e., feathers and algae) due to plastic's unique chemical nature and slow speed of biodegradation. In addition to microbes, insects have come to flourish in areas of the ocean that were previously uninhabitable. The sea skater, for example, has been able to reproduce on the hard surface provided by the floating plastic.
History
Discovery
The plastisphere was first described by a team of three scientists, Dr. Linda Amaral-Zettler from the Marine Biological Laboratory, Dr. Tracy Mincer from Woods Hole Oceanographic Institution and Dr. Erik Zettler from Sea Education Association. They collected plastic samples during research trips to study how the microorganisms function and alter the ecosystem. They analyzed plastic fragments collected in nets from multiple locations within the Atlantic Ocean. The researchers used a combination of scanning electron microscopy and DNA sequencing to identify the distinct microbial community composition of the plastisphere. Among the most notable findings were "pit formers," crack and pit forming organisms that provide evidence of biodegradation. Moreover, pit formers may also have the potential to break down hydrocarbons. In their analysis, the researchers also found members of the genus Vibrio, a genus which includes the bacteria that cause cholera and other gastrointestinal ailments. Some species of Vibrio can glow, and it is hypothesized that this attracts fish that eat the organisms colonizing the plastic, which then feed from the stomachs of the fish.
Anthropogenic sources
Plastic itself was invented in 1907 by Leo Baekeland using formaldehyde and phenol. Since then, the material has been used in anything from clothes to artificial heart valves. As a result, the use of plastic has increased twenty-fold since 1964, and it is expected to double by 2035. Despite efforts to implement recycling programs, recycling rates tend to be quite low. For instance, in the EU, only 29% of the plastic consumed is recycled. The plastic that does not reach a recycling facility or landfill, will most likely end up in our oceans due to accidental dumping of the waste, losses during transport, or direct disposal from boats. In 2010, it was estimated that 4 to 12 million metric tons (Mt) of plastic waste entered into marine ecosystems.
The smaller, more inconspicuous microplastic particles have been aggregating in the oceans since the 1960s. A more recent worry in the pollution of microplastics comes from the use of plastic films in agriculture. 7.4 million tons of plastic films are used each year to increase food production. Scientists have found that microbial biofilms are able to form within 7–14 days on plastic film surfaces, and have the ability to alter the chemical properties of the soil and plants that we are ingesting. Microplastics have been recorded everywhere, even the Arctic due to atmospheric circulation.
Research
Diversity
Large scale sequencing studies have found alpha diversities to be lower in the plastisphere relative to surrounding soil samples due to a decrease in species richness in the plastisphere. Polymer film fragments affect microbes in different ways, leading to mixed effects on microbial growth rates in the plastisphere. Certain polymer degrading bacteria release toxic byproducts as a result of the degradation of the plant fragment, serving as a deterrent to the colonization of the plastisphere by susceptible species. Phylogenetic diversity is also decreased in the plastisphere relative to nearby soil samples.