We analysed data from 29,798 clean-ups around the world to uncover some of the worst litter hotspots


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Lauren Roman, CSIRO; Britta Denise Hardesty, CSIRO, and Chris Wilcox, CSIROCoastal litter is a big environmental problem. But how does this litter differ around the world, and why? In the first global analysis of its kind, we set out to answer those questions using data collected by thousands of citizen scientists.

Our analysis, released today, discovered litter hotspots on every inhabited continent, including Australia. This finding busts two persistent myths: that most of the world’s plastic pollution comes from just a few major rivers, and that countries in the Global South are largely to blame for the marine plastic problem.

Single-use plastics formed the majority of litter in this study. And in general, litter hotspots were associated with socioeconomic factors such as a concentration of built infrastructure, less national wealth, and a high level of lighting at night.

Our insights reveal the complex patterns driving coastal pollution, and suggest there is no “one size fits all” solution to cleaning up the world’s oceans. In fact, the best solution is to stop the waste problem long before it reaches the sea.

This study analyses the data collected by hundreds of thousands of citizen scientists conducting clean-ups worldwide.
Copyright PADI AWARE

A complex picture

We are scientists from the CSIRO’s Marine Debris Research team. Our study involved working closely with Ocean Conservancy and the PADI AWARE Foundation, which together hold the world’s most comprehensive litter data sets gathered by citizen scientists.

We analysed hundreds of thousands of items from 22,508 clean-ups on land (at beaches and the edge of rivers and lakes) as well as 7,290 seafloor clean-ups. The clean-ups spanned 116 and 118 countries, respectively, and involved participants recording counts for each item collected.

The analysis showed a huge diversity in the location and scale of plastic pollution hotspots. They were not limited to single countries or rivers – instead, the hotspots occurred in all inhabited continents and across many countries. In many places, litter patterns between neighbouring locations were vastly different.




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Most litter comprised single-use items: cigarette butts, fishing line, food wrappers, and plastic bottles and bags.

In general, places with more overall litter tended to have:

  • more built infrastructure
  • less national wealth
  • bright lighting at night (which indicated urban density).

Cities and other dense urban areas around the world were linked with hotspots of “convenience” single-use plastic items, such as plastic bags, food wrappers, drink bottles, take-away containers, straws, plastic cutlery and lids. These hotspots are represented in the infographic below.



However, not all litter items followed this pattern. For example, cigarette butts followed a regional pattern and were more common in Southern Europe and North Africa.

Fishing line was most abundant in wealthier countries where recreational fishing is a popular pastime. Hotspots included Australia, the United Kingdom and the United States.

Clusters of hotspots were often associated with partially enclosed bays, seas and lakes. These included areas such as the Mediterranean Sea, the Bay of Bengal, the South China and Philippine seas, the Gulf of Mexico, the Caribbean Sea, Lake Malawi and the Great Lakes of North America.

Plastic accumulation in these areas is likely due to factors such as high local littering combined with relatively contained bodies of water.

Plastic bottle hotspots were more common in tropical countries such as Costa Rica and Jamaica, among others. Plastic food wrappers were abundant in the island nations of Southeast Asia, particularly around Indonesia and the Philippines.




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fishing line and bobber wrapped around twig in water
Australia contained several global hotspots for fishing line waste.
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Cleaning up our coasts

Ultimately, our study reveals the diversity and complexity of the plastic pollution issue. We hope it helps governments make waste policy decisions based on sound scientific evidence.

The findings suggest programs to tackle ocean litter should be rolled out at the grassroots level, or within one part of a country, as well as nationally.

In Australia, for example, Zoos Victoria’s Seal The Loop program aims to tackle localised fishing line waste at locations where the pastime is common. The program includes fishing line bins placed on piers and at boat ramps to encourage responsible waste disposal.

And in Malawi and 15 other countries in southern Africa, national bans on plastic bags target this locally problematic item.

Our analysis shows much non-degradable waste found in the environment comes from pre-packaged food and beverages. So regulations specifically addressing this type of packaging can be useful.

In Australia, for example, Hobart is aiming to become the first Australian city to ban single-use plastic takeaway food packaging, as part of an ambitious goal of zero-waste to landfill by 2030.

Other strategies known to change litter behaviour include recycling incentives such as container deposit schemes, particularly in lower socioeconomic areas where littering is highest, as well as education campaigns. And levies on plastic items could also help stop litter entering the environment.

This Saturday September 18, Ocean Conservancy is holding its annual International Coastal Cleanup – come along if you can and if COVID restrictions allow. You’ll be helping your local environment and collecting data to inform tomorrow’s waste management policies.

Land-based clean-ups were conducted across 116 countries. Please join us for the next one.
Rafeed Hussain Ocean Conservancy

The authors would like to acknowledge the tireless volunteers from the International Coastal Cleanup and Dive Against Debris, and collaborators; Ocean Conservancy’s Dr George H. Leonard and Nicholas Mallos, and PADI AWARE Foundation’s Hannah Pragnell-Raasch and Ian Campbell.The Conversation

Lauren Roman, Postdoctoral Researcher, Oceans and Atmosphere, CSIRO; Britta Denise Hardesty, Senior Principal Research Scientist, Oceans and Atmosphere, CSIRO, and Chris Wilcox, Senior Principal Research Scientist, CSIRO

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

Smoke from the Black Summer fires created an algal bloom bigger than Australia in the Southern Ocean


Himawari-8, Author provided

Christina Schallenberg, University of Tasmania; Jakob Weis, University of Tasmania; Joan Llort, Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS); Peter Strutton, University of Tasmania, and Weiyi Tang, Princeton UniversityIn 2019 and 2020, bushfires razed more than 18 million hectares of land in Australia. For weeks, smoke choked major cities, leading to almost 450 deaths, and even circumnavigated the southern hemisphere.

As the aerosols billowed across the oceans many thousands of kilometres away from the fires, microscopic marine algae called phytoplankton had an unexpected windfall: they received a boost of iron.

Our research, published today in Nature, found this caused phytoplankton concentrations to double between New Zealand and South America, until the bloom area became bigger than Australia. And it lasted for four months.

This enormous, unprecedented algal bloom could have profound implications for carbon dioxide levels in the atmosphere and for the marine ecosystem. But so far, the impact is still unclear.

Meanwhile, in another paper published alongside ours in Nature today, researchers from The Netherlands found the amount of carbon dioxide emitted by the fires that summer was more than double previous estimates.

Absorbing 680 million tonnes of carbon dioxide

Iron fertilises phytoplankton and helps them grow, in the same way nutrients added in soil help vegetables grow. And like plants on land, phytoplankton photosynthesise — they absorb CO₂ as they grow and produce oxygen for fish and other marine creatures.

Bushfire smoke is an aerosol made up of many different chemicals, including iron.
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We used satellite data to estimate that for phytoplankton to grow as much as they did in the Southern Ocean, they would have absorbed 680 million tonnes of CO₂. This means the phytoplankton absorbed roughly the same amount of CO₂ as released by the bushfires, according to the latest estimates released today.

The Dutch researchers found the bushfires released 715 million tonnes of CO₂ (or ranging 517–867 million tonnes) between November 2019 and January 2020. This surpasses Australia’s normal annual fire and fossil fuel emissions by 80%.

To put this into perspective, Australia’s anthropogenic CO₂ emissions in 2019 were much less, at 520 million tonnes.

Phytoplankton can have dramatic effects on climate

But that doesn’t mean the phytoplankton growth absorbed the bushfire’s CO₂ emissions permanently. Whether phytoplankton growth extracts and keeps CO₂ from the atmosphere depends on their fate.

If they sink to the deep ocean, then this represents a carbon sink for decades or even centuries — or even longer if phytoplankton are stored in ocean sediments.

But if they’re mostly eaten and decomposed near the ocean’s surface, then all that CO₂ they consumed comes straight back out, with no net effect on the carbon balance in the atmosphere.

Himawari satellite image showing the January aerosol plume stretching over the South Pacific.
Himawari-8, Author provided

In fact, phytoplankton have very likely played a role on millennial time scales in keeping atmospheric CO₂ concentrations down, and can affect the global climate in the long term.

For example, a 2014 study suggests iron-containing dust billowing over the Southern Ocean caused increased phytoplankton productivity, which contributed to reducing atmospheric CO₂ by about 100 parts per million. And this helped transition the planet to ice ages.




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Inside the world of tiny phytoplankton – microscopic algae that provide most of our oxygen


Phytoplankton blooms can also have a big impact on the marine ecosystem as they make excellent food for some marine creatures.

For example, more phytoplankton means more food for zooplankton that feed on phytoplankton, with effects up the food chain. It’s also worth noting this huge bloom occurred at a time of year when phytoplankton are usually in decline in this part of the ocean.

But whether there were any long-lasting effects from the bushfire-fuelled phytoplankton on the climate or ecosystem is unclear, because we still don’t know where they ended up.

Using revolutionary data

The link between fire aerosols and the increase in phytoplankton demonstrated in our study is particularly relevant given the intense fire activity around the globe.

Droughts and warming under global climate change are expected to increase the frequency and intensity of wildfires, and the impacts to land-based ecosystems, such as habitat loss and air pollution, will be dramatic. But as we now know, wildfires can also affect marine life thousands of kilometres away from land.

A robotic float being deployed on board the CSIRO RV Investigator.
Jakob Weiss, Author provided

Previous models have predicted the iron-fertilising effect of bushfire aerosols, but this is the first time we’ve observed and demonstrated the connection at a large-scale.

Our study is mainly based on satellite data and observations from robotic floats that roam the oceans and collect data autonomously. These robotic floats are revolutionising our understanding of chemical cycling, oxygen variability and ocean acidification.

During the bushfire period, our smoke tracers reached concentrations at least 300% higher than what had ever been observed in the 22-year satellite record for the region.

Interestingly, you wouldn’t be able to observe the resulting phytoplankton growth in a true-colour satellite image. We instead used more sensitive ocean colour sensors on satellites to estimate phytoplankton concentrations.




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Tiny plankton drive processes in the ocean that capture twice as much carbon as scientists thought


So what’s next?

Of course, we need more research to determine the fate of the phytoplankton. But we also need more research to better predict when and where aerosol deposition (such as bushfire smoke) will boost phytoplankton growth.

For example, the Tasman Sea — between Australia and New Zealand — showed only mildly higher phytoplankton concentrations during the bushfire period, even though the smoke cloud was strongest there.

Was this because nutrients other than iron were lacking, or because there was less deposition? Or perhaps because the smoke didn’t stick around for as long?

Whatever the reason, it’s clear this is only the beginning of exciting new lines of research that link forests, wildfires, phytoplankton growth and Earth’s climate.




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The Conversation


Christina Schallenberg, Research Fellow, University of Tasmania; Jakob Weis, Ph.D. student, University of Tasmania; Joan Llort, Oceanógrafo , Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS); Peter Strutton, Professor, Institute for Marine and Antarctic Studies, University of Tasmania, and Weiyi Tang, Postdoc in Biogeochemistry, Princeton University

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

Pregnant male seahorses support up to 1,000 growing babies by forming a placenta


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Jessica Suzanne Dudley, Macquarie University and Camilla Whittington, University of SydneySupplying oxygen to their growing offspring and removing carbon dioxide is a major challenge for every pregnant animal. Humans deal with this problem by developing a placenta, but in seahorses — where the male, not the female, gestates and gives birth to the young — exactly how it worked hasn’t always been so clear.

Male seahorses incubate their embryos inside a pouch, and until now it was unclear how the embryos “breathe” inside this closed structure. Our new study, published in the journal Placenta, examines how pregnant male seahorses (Hippocampus abdominalis) provide oxygen supply and carbon dioxide removal to their embryos.

We examined male seahorse pouches under the microscope at different stages of pregnancy, and found they develop complex placental structures over time — in similar ways to human pregnancy.

Male pot-bellied seahorses have large fleshy pouches where embryos develop during pregnancy.
by Aaron Gustafson



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A pregnant dad gestating up to 1,000 babies

Male pregnancy is rare, only occurring in a group of fish that includes seahorses, seadragons, pipehorses and pipefishes.

Pot-bellied seahorse males have a specialised enclosed structure on their tail. This organ is called the brood pouch, in which the embryos develop.

The female deposits eggs into the male’s pouch after a mating dance and pregnancy lasts about 30 days.

While inside the pouch, the male supplies nutrients to his developing embryos, before giving birth to up to 1,000 babies.

Male pot-bellied seahorse filling his pouch with water in a mating display.
by Kymberlie R. McGuire

Embryonic development requires oxygen, and the oxygen demand increases as the embryo grows. So too does the need to get rid of the resulting carbon dioxide efficiently. This presents a problem for the pregnant male seahorse.

Enter the placenta

In egg-laying animals — such as birds, monotremes, certain reptiles and fishes — the growing embryo accesses oxygen and gets rid of carbon dioxide through pores in the egg shell.

For animals that give birth to live young, a different solution is required. Pregnant humans develop a placenta, a complex organ connecting the mother to her developing baby, which allows an efficient exchange of oxygen and carbon dioxide (it also gets nutrients to the baby, and removes waste, via the bloodstream).

Placentae are filled with many small blood vessels and often there is a thinning of the tissue layers that separate the parent’s and baby’s blood circulations. This improves the efficiency of oxygen and nutrient delivery to the fetus.

Surprisingly, the placenta is not unique to mammals.

Some sharks, like the Australian sharpnose shark (Rhizoprionodon taylori) develop a placenta with an umbilical cord joining the mother to her babies during pregnancy. Many live-bearing lizards form a placenta (including very complex ones) to provide respiratory gases and some nutrients to their developing embryos.

Our previous research identified genes that allow the seahorse father to provide for the developing embryos while inside his pouch.

Our new study shows that during pregnancy the pouch undergoes many changes similar to those seen in mammalian pregnancy. We focused on examining the brood pouch of male seahorses during pregnancy to determine exactly how they provide oxygen to their developing embryos.

A Pot-belly seahorse (Hippocampus abdominalis) floats in water
By viewing the seahorse pouch under the microscope at various stages of pregnancy, we found that small blood vessels grow within the pouch.
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What we found

By viewing the seahorse pouch under the microscope at various stages of pregnancy, we found that small blood vessels grow within the pouch, particularly towards the end of pregnancy. This is when the baby seahorses (called fry) require the most oxygen.

The distance between the father’s blood supply and the embryos also decreases dramatically as the pregnancy goes on. These changes improve the efficiency of transport between the father and the embryos.

Interestingly, many of the changes that occur in the seahorse pouch during pregnancy are similar to those that occur in the uterus during mammalian pregnancy.

We have only scratched the surface of understanding the function of the seahorse placenta during pregnancy.

There is still much to learn about how these fathers protect and nourish their babies during pregnancy — but our work shows the morphological changes to seahorse brood pouches have a lot in common with the development of mammalian placentae.




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The Conversation


Jessica Suzanne Dudley, Postdoctoral Fellow, Macquarie University and Camilla Whittington, Senior lecturer, University of Sydney

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