Potential harmful impacts of micro- and nanoplastics on the health of a tropical sea cucumber, Holothuria leucospilota, evidenced by changes of gut microflora, histology, immune and oxidative indexes.

Nanoplastics (NPs) and microplastics (MPs) have emerged as pervasive environmental pollutants, and they ubiquitously distribute in ecosystems and accumulate within organisms, thereby posing a substantial threat to global ecology. Though the disruptive effects of NPs and MPs on physiology and behavior in some aquatic species have been extensively documented, the potential impacts of them on a widespread sea cucumber, Holothuria leucospilota, remain unexplored. In this study, we conducted a comprehensive investigation to reveal the effect of polyethylene NPs (200 nm) and MPs (20 μm) on the health of the sea cucumber. The results indicated that the exposure to NPs and MPs deeply altered the gut microbiota, wherein a substantial alternation of core gut microorganisms such as Rhodobacteraceae and Flavobacteriaceae was observed. NPs and MPs induced oxidative stress in the gut of sea cucumbers, which may be linked to intraspecific variations in the abundance of Rhodobacteraceae, Arcobacteraceae, and Spirochaetaceae, as well as an immune imbalance associated with shifts in Rhodobacteraceae and Arcobacteraceae populations within the gut microbiota. Notably, NPs exerting a more pronounced effect on oxidative stress levels compared to MPs. Additionally, obvious transmission and accumulation of plastic particles could be observed in the gut tissues, and therefore it likely contributed to histological damage, immunological dysregulation, and oxidative stress. These findings clearly demonstrated that NPs and MPs exert harmful impacts on the health of the sea cucumber. This study provides valuable and deep insights into the broader ecological hazards caused by the contamination of plastic particles in marine ecosystems.