Antarctica, the world’s most remote, harsh and pristine continent, is not free from marine pollution. Where human activity goes, plastic debris inevitably follows.
What might the early explorers of this icy wilderness think today, upon discovering a continent transformed by permanent fishing activities, research stations, military presence, tourism, and all their environmental impacts? Among these, plastic pollution stands out, as it has created a unique new ecological niche in the ocean.
Once it gets into the water, plastic debris provides surfaces that can be quickly colonised by microbial communities, forming a biofilm. This plastic-borne community is known as the plastisphere, and it poses a serious threat to marine ecosystems, particularly in the cold, understudied waters of the Southern Ocean.
The plastisphere: an emerging threat
As plastic debris drifts through the ocean, the plastisphere develops through typical ecological succession, eventually becoming a complex and specialised microbial community. Plastics not only provide shelter for these microorganisms but also act as a vector, allowing potentially harmful pathogens like Vibrio spp., Escherichia coli, and bacteria carrying antibiotic resistance genes, to spread across marine environments, even reaching remote, untouched areas.
Beyond being a home for microbes, the plastisphere can disrupt the natural balance of ocean life at the microscopic level. These changes don’t stay in the water, as they can spread outward, potentially affecting how the ocean absorbs carbon and produces greenhouse gases. This has consequences for the air we breathe around the world.
However, it’s not all bad news, as bacteria known for their potential to degrade plastics or hydrocarbons – such as Alcanivorax sp., Aestuariicella sp., Marinobacter sp. and Alteromonas sp. – are frequently identified on plastics.
A hostile research environment
We currently know very little about the plastisphere, especially in the Southern Ocean, where uncovering its dynamics is key to understanding its impacts on one of the planet’s most remote and vulnerable marine environments. For this reason, our recent study sought to investigate the abundance and diversity of microbial communities in the Southern Ocean plastisphere, particularly following the initial colonisation of plastic debris.
Working in Antarctica is not an easy task. Just reaching this continent is a challenge, and once there, scientists have to contend with harsh environmental conditions: freezing temperatures, powerful winds, icebergs, and the constant pressure of limited time to carry out their work. These challenges make every moment in the field both demanding and invaluable.
This is why we approached our study with a controlled and manageable experiment. We set up aquariums filled with seawater collected near the Spanish research station on Livingston Island, South Shetlands. Inside, we placed small, rounded pellets of the three most common types of plastic polluting the sea – polyethylene, polypropylene, and polystyrene. We left them at environmental conditions (around 0 ºC and between 13 – 18 h of sunlight) for 5 weeks, aiming to recreate the most plausible outcomes in the field.
We compared the colonisation of plastics with glass, an inert surface. Samples of plastics and glass were collected periodically to track bacterial colonisation.
Plastisphere dynamics in Antarctica
Studying bacteria means making the invisible visible, so we combined several techniques to get a better picture of the plastisphere. Using scanning electron microscopy, we obtained biofilm images. We combined flow cytometry and bacterial culture to count total cells and colonies, and we sequenced the 16S rRNA gene to identify the succession of bacterial settlers.
This meticulous approach revealed that time was the key driver of change. Microbes quickly colonised the plastic, and within less than two days, bacteria like genus Colwellia were already fixed in the surface, showing a clear progression from initial settlers to a mature diverse biofilm including other genera like Sulfitobacter, Glaciecola or Lewinella.
These species, although also detected in water, show a clear preference for the social life of a biofilm community. Moreover, we did not detect clear differences between the bacterial communities from plastics and glass, suggesting that any stable surface can host these communities.
While similar processes happen in the other oceans, in Antarctica the process seems slower. The region’s lower temperatures slow bacterial development. (The Conversation)