Trick or treat? Ingestion of biofouled plastic fibres by sea urchins

Life is full of surprises. Sea urchins may find that some of what they eat is nutrient-free plastic. Australian exchange students may find that sun-deprived Tromsø is a great place to live. And if you read on, you may find that the paths of sea urchins and exchange students sometimes intersect.

By: Claudia Halsband // Akvaplan-niva, Alex Abrahams* and Sophie Bourgeon // UiT The Arctic University of Norway,  Dorte Herzke // NILU – Norwegian Institute for Air Research 

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The green sea urchin (Strongylocentrotus droebachiensis). Photo: Claudia Halsband / Akvaplan-niva

Microplastics, fragments of plastic less than 5 mm long, are known to be abundant and persistent in the world’s oceans; thus it is important to research their behaviour in the marine environment and how they interact with the organisms living in the water column and the seafloor.

This can help us understand the risks microplastics pose to ecosystems. Microfibres are common constituents of microplastics in marine habitats, originating from synthetic clothing such as fleece sweaters, but also from fishing gear and other items made of fibrous polymers.

Due to their elongated shape, microfibres may have different effects on marine organisms than microplastic fragments or spheres, but how marine animals respond to encounters with microfibres is poorly known. Photo: Fibres egested in faecal pellets are counted under a microscope.

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Photo: Alex Abrahams / UiT and Akvaplan-niva

The project Arctic Fibre, within the Fram Centre research programme Plastic in the Arctic, is a collaboration between SINTEF Ocean, Akvaplan-niva, and NILU, and investigates the effects UV degradation and biofilm formation have on the behaviour of microplastic fibres.

As part of this endeavour, Australian Alex Abrahams is doing a thesis project where she examines the interactions between microfibres and the green sea urchin.

Although named after the Norwegian town of Drøbak, the green sea urchin (Strongylocentrotus droebachiensis) is a common component of the benthos throughout northern seas, both on the Atlantic and the Pacific side. Alex investigates whether biofilm formation on microfibres has an effect on their ingestion or egestion by the sea urchins. In the summer of 2020, she collected sea urchins near the shore on Kvaløya, and conducted an experimental study, exposing the sea urchins to both microplastic fibres (blue acrylic) and a natural control fibre (wool) to see if the fibres were ingested, egested, and for how long they remain in the intestinal tract. Some fibres were incubated (“aged”) in natural seawater for two weeks to allow a biofilm to form on their surface.

Then, Alex ran experiments where five groups of sea urchins were exposed to  clean or aged acrylic fibres, clean or aged wool, or a control condition without fibres.

The urchins were measured and put into individual beakers of seawater, along with fibres (except the controls) and a piece of seaweed as food source. After 48 hours, Alex dissected half of the urchins and placed the other half in clean (fibre-free) water for depuration.
Faecal pellets from these urchins were collected after 2, 3 and 5 days of incubation. Because of the nice weather and the Kvaløya summer heat, lab activities were moved to the jetty outside the Akvaplan-niva lab at Kraknes. Later, the ethanol-preserved faecal pellets were analysed under the microscope at the Fram Centre to count and measure the fibres the urchins had egested with their faeces.

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Collecting sea urchins on Kvaløya. Photo: Kristine Hopland Sperre / Akvaplan-niva.

Alex found the highest numbers of fibres in pellets from the wool exposures after two days of incubation. In the faecal pellets from urchins exposed to acrylic fibres, the number of fibres per pellet was higher for aged fibres than for clean ones.

After three and five days, no acrylic fibres were found in the faeces and only very few wool fibres were present. This seems to suggest that the acrylic fibres are egested quickly, within two days.

They may also be more durable, and the high number of wool fibres in the faecal material may point to degradation during the digestion process, such that wool fibres break into several pieces.

In a next step, Alex will analyse the urchin gut contents for fibres. If there is retention of fibres in the intestines, this may increase the possibility of ecotoxicological effects on the urchins and/or trophic transfer of fibres from the urchins to their predators, such as sea stars, crabs, large fish, mammals, birds – and humans.

The year 2020 has been full of surprises, characterised by continuous readjustment and change. The difficulties of the pandemic have been felt by everyone, not least by our students, who had cruises, fieldwork, conferences, and travel scheduled this year. We were lucky to be able to offer Alex field and lab facilities during this period and prevent delays in completing her degree. We look forward to more exciting results from the Arctic Fibre project in 2021.

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The diameter of a sea urchin is measured. Photo: Claudia Halsband / Akvaplan-niva.
Diagram: Claudia Halsband / Akvaplan-niva

Sea urchins were incubated under five different treatment conditions, after which half were dissected. The other half were placed in clean, fibre-free water, and faecal pellets were collected at 2, 3 and 5 days.

Alex Abrahams places sea urchins into individual beakers with or without fibres, along with pieces of seaweed for food.

Alex, a master’s student in Sophie Bourgeon’s Arctic Marine System Ecology group at UiT, grew up in Adelaide, South Australia. She first came to Tromsø in the darkness of January 2017 and stayed for a one-year exchange as a part of her bachelor studies in Environmental Science.

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Photo: Kristine Hopland Sperre / Akvaplan-niva.

She quickly fell in love with the mountains, the seasons, the people, and the atmosphere in Tromsø. After going back to Australia to complete her studies, she decided to return to Tromsø and start a master’s in biology at UiT in August 2019. Now, she is working at the Fram Centre on her MSc dissertation under the supervision of Drs Sophie Bourgeon (UiT), Claudia Halsband (Akvaplan-niva) and Dorte Herzke (NILU) in the Fram Centre project Effects of degradation and biofilm formation on the fate and ingestion of microplastic fibres in the Arctic.

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Photo: Jonas Thoresen.