Seafloor currents sweep microplastics into deep-sea hotspots of ocean life



A rockfish hides in a red tree coral in the deep sea.
Geofflos

Ian Kane, University of Manchester and Michael Clare, National Oceanography Centre

What if the “great ocean garbage patches” were just the tip of the iceberg? While more than ten million tonnes of plastic waste enters the sea each year, we actually see just 1% of it – the portion that floats on the ocean surface. What happens to the missing 99% has been unclear for a while.

Plastic debris is gradually broken down into smaller and smaller fragments in the ocean, until it forms particles smaller than 5mm, known as microplastics. Our new research shows that powerful currents sweep these microplastics along the seafloor into large “drifts”, which concentrate them in astounding quantities. We found up to 1.9 million pieces of microplastic in a 5cm-thick layer covering just one square metre – the highest levels of microplastics yet recorded on the ocean floor.

While microplastics have been found on the seafloor worldwide, scientists weren’t sure how they got there and how they spread. We thought that microplastics would separate out according to how big or dense they were, in a similar manner to natural sediment. But plastics are different – some float, but more than half of them sink.




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Plastics which once floated can sink as they become coated in algae, or if bound up with other sticky minerals and organic matter. Recent research has shown that rivers transport microplastics to the ocean too, and laboratory experiments revealed that giant underwater avalanches of sediment can transport these tiny particles along deep-sea canyons to greater depths.

We’ve now discovered how a global network of deep-sea currents transports microplastics, creating plastic hotspots within vast sediment drifts. By catching a ride on these currents, microplastics may be accumulating where deep-sea life is abundant.

Once plastic debris has broken down and sinks to the ocean floor, currents sweep the particles into vast drifts.
Ian Kane, Author provided

From bedroom floors to the seafloor

We surveyed an area of the Mediterranean off the western coast of Italy, known as the Tyrrhenian Sea, and studied the bottom currents that flow near the seafloor. These currents are driven by differences in water salinity and temperature as part of a system of ocean circulation that spans the globe. Seafloor drifts of sediment can be many kilometres across and hundreds of metres high, forming where these currents lose their strength.

We analysed sediment samples from the seafloor taken at depths of several hundred metres. To avoid disturbing the surface layer of sediment, we used samples taken with box-cores, which are like big cookie cutters. In the laboratory, we separated microplastics from the sediment and counted them under microscopes, analysing them using infra-red spectroscopy to find out what kinds of plastic polymer types were there.

A microplastic fibre seen under a microscope.
Ian Kane, Author provided

Most microplastics found on the seafloor are fibres from clothes and textiles. These are particularly insidious, as they can be eaten and absorbed by organisms. Although microplastics on their own are often non-toxic, studies show the build-up of toxins on their surfaces can harm organisms if ingested.

These deep ocean currents also carry oxygenated water and nutrients, meaning that the seafloor hotspots where microplastics accumulate may also be home to important ecosystems such as deep-sea coral reefs that have evolved to depend on these flows, but are now receiving huge quantities of microplastics instead.

What was once a hidden problem has now been uncovered – natural currents and the flow of plastic waste into the ocean are turning parts of the seafloor into repositories for microplastics. The cheap plastic goods we take for granted eventually end up somewhere. The clothes that may only last weeks in your wardrobe linger for decades to centuries on the seafloor, potentially harming the unique and poorly understood creatures that live there.The Conversation

Ian Kane, Reader in Geology, University of Manchester and Michael Clare, Principal Researcher in Marine Geoscience, National Oceanography Centre

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Guns, snares and bulldozers: new map reveals hotspots for harm to wildlife


File 20190312 86699 k7wj98.jpg?ixlib=rb 1.1
Human activity threatens many species across Africa’s savannahs.
Paul Mulondo/WCS, Author provided

James Allan, The University of Queensland; Christopher O’Bryan, The University of Queensland, and James Watson, The University of Queensland

The biggest killers of wildlife globally are unsustainable hunting and harvesting, and the conversion of huge swathes of natural habitat into farms, housing estates, roads and other industrial activities. There is little doubt that these threats are driving the current mass extinction crisis.

Yet our understanding of where these threats overlap with the locations of sensitive species has been poor. This limits our ability to target conservation efforts to the most important places.




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In our new study, published today in Plos Biology, we mapped 15 of the most harmful human threats – including hunting and land clearing – within the locations of 5,457 threatened mammals, birds and amphibians globally.

We found that 1,237 species – a quarter of those assessed – are impacted by threats that cover more than 90% of their distributions. These species include many large, charismatic mammals such as lions and elephants. Most concerningly of all, we identified 395 species that are impacted by threats across 100% of their range.

Mapping the risks

We only mapped threats within a species location if those threats are known to specifically endanger that species. For example, the African lion is threatened by urbanisation, hunting and trapping, so we only quantified the overlap of those specific hazards for this species.

This allowed us to determine the parts of a species’ home range that are impacted by threats and, conversely, the parts that are free of threats and therefore serve as refuges.

We could then identify global hotspots of human impacts on threatened species, as well as “coolspots” where species are largely threat-free.

The fact that so many species face threats across almost all of their range has grave consequences. These species are likely to continue to decline and possibly die out in the impacted parts of their ranges. Completely impacted species certainly face extinction without targeted conservation action.

Conversely, we found more than 1,000 species that were not impacted by human threats at all. Although this is positive news, it is important to note that we have not mapped every possible threat, so our results likely underestimate the true impact. For example, we didn’t account for diseases, which are a major threat to amphibians, or climate change, which is a major threat to virtually all species.

Hotspots and coolspots

We produced the first global map of human impacts on threatened species by combining the parts of each species range that are exposed to threats.
The overwhelmingly dominant global hotspot for human impacts on threatened species is Southeast Asia.

This region contains the top five countries with the most threats to species.
These include Malaysia, Brunei, Singapore, Indonesia and Myanmar.

The most impacted ecosystems include mangroves and tropical forests, which concerningly are home to the greatest diversity of life on Earth.

Hotspots of threats and threatened species richness.
Allan et al. Plos Biol., Author provided

We also created a global map of coolspots by combining the parts of species ranges that are free from human threats. This map identifies the last vestiges of wild places where threatened species have shelter from the ravages of guns, snares and bulldozers. As such, these are crucial conservation strongholds.

Coolspots include parts of the Amazon rainforest, the Andes, the eastern Himalayas, and the forests of Liberia in West Africa.

In many places, coolspots are located near hotspots. This makes sense because in species-rich areas it is likely that many animals are impacted whereas many others are not, due to their varying sensitivity to different threats.

Coolspots of unimpacted species richness.
Allan et al. Plos Biol., Author provided

What next?

There is room for optimism because all the threats we map can be stopped by conservation action. But we need to make sure this action is directed to priority areas, and that it has enough financial and political support.

An obvious first step is to secure threat-free refuges for particular species, via actions such as protected areas, which are paramount for their survival.




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To ensure the survival of highly impacted species with little or no access to refuges, “active threat management” is needed to open enough viable habitat for them to survive. For example, tiger numbers in Nepal have doubled since 2009, mainly as a result of targeted anti-poaching efforts.

Tackling threats and protecting refuges are complementary approaches that will be most effective if carried out simultaneously. Our study provides information that can help guide these efforts and help to make national and global conservation plans as successful as possible.


The authors acknowledge the contributions of Hugh Possingham, Oscar Venter, Moreno Di Marco and Scott Consaul Atkinson to the research on which this article is based.The Conversation

James Allan, Postdoctoral research fellow, School of Biological Sciences, The University of Queensland; Christopher O’Bryan, PhD Candidate, School of Earth and Environmental Sciences, The University of Queensland, and James Watson, Professor, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.