Microplastic ingestion by the farmed sea cucumber is undocumented. Microplastics were isolated from the sea cucumber Apostichopus japonicus that was collected from eight farms along the Bohai Sea and the Yellow Sea in China. To examine microplastic ingestion, the intestines were isolated, digested and then subjected to the floatation test. The microplastic abundance in the sediment ranged from 20 to 1040 particles kg À1 of dry sediment, while the ingested microplastics ranged from 0 to 30 particles intestine À1. After filtering the coelomic fluid, the extracted microplastics from the coelomic fluid ranged from 0 to 19 particles animal À1. Thus, we speculated that microplastics may transfer to the coelomic fluid of sea cucumber. The ingested microplastics did not correlate with the animal body weight but was site dependent, suggesting that sea cucumber may serve as sentinel for microplastic pollution monitoring in the sediment. The microplastics were identified by Fourier transform infrared micro spectroscopy, and the polymer types were mainly cellophane, polyester, and polyethylene terephthalate. This study revealed that, microplastics widely existed in sea cucumber farms, and that sea cucumbers ingest microplastics as suitable with their mouth open. Moreover, the microplastics might transfer to the coelomic fluid of the sea cucumber. Further investigations are needed to assess the chronic effect of the microplastics on the growth and physiological status of the sea cucumber.

The concentrations of eight heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) were measured in the sediment, the isolated microplastics from the sediment and the body wall of sea cucumbers from farms in China. Accordingly, the heavy metal concentrations in the sediment were below the class I upper limit of Chinese sediment quality guidelines. Among heavy metals, the median concentrations of Cd and As were higher in the body wall than in the corresponding sediment. Additionally, the median concentrations of Cd, Pb, and Zn were higher on the microplastics than in the corresponding sediment. Furthermore, there was no significant correlation among heavy metals in sediment, sea cucumber and microplastics. This study contributes to the understanding of the heavy metal accumulation in the sediment, the microplastics and the body wall of the sea cucumber.

Microplastics (MPs) are small plastic particles less than 5 mm in diameter. MPs in the form of microfibers (MFs) are widely detected in aquatic habitats and are of high environmental concern. Despite many reports on the effects of MFs on marine animals, their effect on sea cucumbers is still unclear. In addition, our previous filed study has shown that MFs may transfer to the coelomic fluid of the sea cucumber Apostichopus japonicus (A. japonicus). Here, we show how MFs transfer to the coelomic fluid of the sea cucumber. We captured the MFs during their transfer from the water to the coelomic fluid through the respiratory tree. A. japonicus ingested in the MFs along with the water during respiration; the MFs got stuck in the respiratory tree or transferred to the coelomic fluid. The transferred MFs increased during 72 h of exposure and persisted for 72 h after the transfer to clean water. Among the immunity indices, lysozyme (LZM) levels increased in response to the transferred MFs, which confirms the defensive role of LZMs against strange substances. Additionally, non-significantly decreased levels of total antioxidant capacity (T-AOC), malondialdehyde (MDA), peroxidase (POD) and phenol oxidase (PPO) were observed at 24 h and 48 h post-exposure, suggesting minimal oxidative imbalance. Furthermore, there were no significant changes in the speed and the total distance moved by A. japonicus post MFs transfer. This study revealed that MFs transfer and accumulate in the coelomic fluid of A. japonicus.

Although the sea cucumber Apostichopus japonicus has been characterised as a deposit feeder, nutrients sourced from the water column have been recorded in the intestines of this species. However, the mechanisms whereby nutrients in the water enter the intestinal tract of A. japonicus, and whether other suspended particles can be ingested via the mouth of A. japonicus adults, remain unknown. Here, we reveal how A. japonicus ingests suspended particles through the mouth. We used synthetic particles and video recording to confirm the suspension uptake by the sea cucumber. A. japonicus continued to ingest suspended particles (if present) over time, and the particle-ingestion rate was positively correlated with the concentration of suspended particles (Pearson correlation: r=0.808). Additionally, clearance rates of the suspended particles ranged from 0.3–0.9 L−1 h−1. The findings of this study thus provide evidence of a previously undescribed particle uptake mechanism in a commercially i...