Nanoplastics affect moulting and faecal pellet sinking in Antarctic krill (Euphausia superba) juveniles

Plastic debris has been identified as a potential threat to Antarctic marine ecosystems, however, the impact of
nanoplastics (< 1 μm) is currently unexplored. Antarctic krill (Euphausia superba) is a keystone species of
Southern Ocean pelagic ecosystems, which plays a central role in the Antarctic food webs and carbon (C) cycle.
Krill has been shown to rapidly fragment microplastic beads through the digestive system, releasing nanoplastics
with unknown toxicological effects. Here we exposed krill juveniles to carboxylic (eCOOH, anionic) and amino-
(eNH2, cationic) polystyrene nanoparticles (PS NPs) and we investigated lethal and sub-lethal endpoints after
48 h. The analysis of PS NP suspensions in Antarctic sea water (SW) media showed that PS-COOH formed large
agglomerates (1043 ± 121 nm), while PS-NH2 kept their nominal size (56.8 ± 3 nm) during the exposure
time. After 48 h, no mortality was found but increase in exuviae production (12.6 ± 1.3%) and reduced
swimming activity were observed in juveniles exposed to PS-NH2. The microbial community composition in SW
supports the release of krill moults upon PS NP exposure and stimulates further research on the pivotal role of
krill in shaping Southern Ocean bacterial assemblages. The presence of fluorescent signal in krill faecal pellets
(FPs) confirmed the waterborne ingestion and egestion of PS-COOH at 48 h of exposure. Changes in FP structure
and properties were also associated to the incorporation of PS NPs regardless of their surface charge. The effects
of PS NPs on krill FP properties were compared to Control 0 h as a reference for full FPs (plastic vs food) and
Control 48 h as a reference for more empty-like FPs (plastic vs lack of food). Exposure to PS NPs led to a FP
sinking rate comparable to Control 48 h, but significantly lower than Control 0 h (58.40 ± 23.60 m/d and
51.23 ± 28.60 m/d for PS-COOH and PS-NH2; 168.80 ± 74.58 m/d for Control 0 h). Considering the important
role played by krill in the food web and C export in the Southern Ocean, the present study provides cues
about the potential impact of nanoplastics on Antarctic pelagic ecosystems and their biogeochemical cycles.