Marine litter and microplastics have become a huge global issue and their negative impact on marine animals causes great concern. A study led by marine scientists from the Ryan Institute at NUI Galway in collaboration with UCC and Villefranche sur Mer Laboratory has found that microplastics may also impact on important ecosystem processes which facilitate the uptake of carbon dioxide from our atmosphere. The research was published in the international peer-reviewed journal 'Environmental Science and Technology'.

Long-term storage of atmospheric carbon dioxide in our oceans

The study’s findings suggest that the uptake and the long-term storage of atmospheric carbon dioxide in our oceans that is fuelled by key organisms may be negatively impacted by microplastics. Carbon dioxide (CO2) is a greenhouse gas released during the burning of fossil fuels and its atmospheric levels have continually risen over the past couple of centuries. It is naturally absorbed by our oceans through biological, chemical, and physical processes. The research team from NUI Galway, the Villefranche Ocean Observatoire, France and UCC studied how microplastics interact with marine animals called salps. [caption id="attachment_49840" align="alignright" width="300"] Alina Wieczorek, Ryan Institute, NUI Galway. Photo: Dawid Piotr Szlaga[/caption] Salps are jellyfish-like animals and they play a very important role in this uptake of carbon dioxide from the atmosphere and its downward transport to the sea floor where the carbon gets stored. Lead author of the study, Alina Wieczorek, Ryan Institute, NUI Galway, said: “Our oceans are estimated to have captured one quarter to one half of all human-derived carbon dioxide from the atmosphere in the last two centuries and this downward transport of carbon by salps and other zooplankton animals accounts for a major portion of this.”

Microscopic algae turn dissolved CO2 into fuel (organic carbon)

At the sea surface, microscopic algae turn dissolved CO2 into fuel (organic carbon). These algae are consumed by many different animals and form the basis of the marine foodweb. As this organic carbon is passed up through the food chain much of it is respired and converted back into CO2 which is then released into the ocean and the atmosphere. However, some of the captured carbon is transported to the sea floor in the form of sinking particles. This is where salps play an important role. They ingest algae at the sea surface and produce dense faecal pellets, which rapidly sink to the deep sea, carrying with them some of this captured carbon. However, during laboratory experiments carried out at the Villefranche Ocean Observatory the researchers found that when salps ingest microplastics and incorporated them into their faecal pellets they did not sink as fast anymore. “Our study suggests that salp faecal pellets will remain at the sea surface for longer when they contain microplastics and while there, they may get broken down causing the carbon dioxide to be re-released back into the ocean and atmosphere," said Wieczorek. "These findings show that microplastics have the potential to lower the efficiency of one of the most important natural processes occurring within our oceans, that is, the biologically driven transport of CO2 to the seafloor.” The researchers also noted that while alterations in the density of the salp faecal pellets may cause some of them to be recycled in the upper waters, some may still reach the sea floor and transport the microplastics within them to the deep sea. Recent findings of microplastics in the Mariana Trench, the deepest point on Earth located in the western Pacific Ocean, support this theory. Dr Fabien Lombard, a co-author of this study, Villefranche sur Mer Laboratory (Sorbonne Université), said: “Most studies focus on the quantity of plastic in the oceans, but when looking at these quantities, it appears that a large quantity of the smaller plastic is 'missing' and disappears from the sea surface without a clear explanation. Such transport mediated by zooplankton faecal pellets may explain why plastics are even found in deep sediments.” Dr Tom Doyle, senior author of the study from UCC, (formerly NUI Galway), said: “Our study highlights that marine litter and microplastics may impact on animals and even ecosystems in ways we just haven’t considered yet.

'Carried out in a laboratory under controlled conditions'

"However, it is very important to point out that our study was carried out in a laboratory and under controlled conditions. We now need to go out into the field to further test our hypothesis by quantifying the abundance of microplastics found in salps and their faecal pellets in different areas of our oceans.” The study was funded by an NUI Galway postgraduate scholarship and by the PLASTOX Project under the Marine Institute’s Marine Research Programme run by the government via framework of JPI Oceans. The research was also supported by the European Marine Biological Research Centre-France, whose French state funds are managed by the ANR within the Investments of the Future program. This research was further supported by a research grant from Science Foundation Ireland’s (SFI) Irish Centre for Research in Applied Geoscience (iCRAG), co-funded under the European Research Development Fund and by PIPCO RSG and its member companies. To read the full study in Environmental Science and Technology, see: http://dx.doi.org/10.1021/acs.est.8b07174 Video of the Salp study: [embed]https://www.youtube.com/watch?v=8mCLaj9cy9g&feature=youtu.be[/embed]