Microplastics (MPs) are ubiquitous contaminants of the marine environment and the deep seafloor is its ultimate sink compartment. Manipulative and field experiments provided evidence of the ingestion of MPs by deep-sea fauna, but knowledge of MPs’ fate once ingested remains still scant. We provide evidence of MPs partial retention and fragmentation mediated by digestion activity of Norwegian langoustine, a good bioindicator for MPs contamination of the deep sea. We report here that MPs in the intestines were more abundant and significantly smaller (up to 1 order of magnitude in surface) than those in the stomachs. Our results show that stomach can act as a size-bottleneck for ingested MPs, enhancing the retention of larger particles within the stomach and promoting fragmentation into smaller plastic debris, which is then released in the intestine. Our results provide evidence that langoustine is responsible for the fragmentation of MPs already accumulated in sediments through its scavenging activity and digestion. These findings highlight the existence of a new peculiar kind of ‘secondary’ MPs, introduced in the environment by biological activities, which could represent a significant pathway of plastic degradation in secluded and stable environment such as the deep sea.

Leiopathes glaberrima is a tall arborescent black coral species structuring important facies of the deep-sea rocky bottoms of the Mediterranean Sea that are severely stifled by fishing activities. At present, however, no morphological in vivo description, ecological characterization, age dating and evaluation of the possible conservation actions have ever been made for any population of this species in the basin. A dense coral population was reported during two Remotely Operated Vehicle (ROV) surveys conducted on a rocky bank off the SW coasts of Sardinia (Western Mediterranean Sea). L. glaberrima forms up to 2 m-tall colonies with a maximal observed basal diameter of nearly 7 cm. The radiocarbon dating carried out on a colony from this site with a 4 cm basal diameter revealed an approximately age of 2000 years. Considering the size-frequency distribution of the colonies in the area it is possible to hypothesize the existence of other millennial specimens occupying a supposedly very stable ecosystem. The persistence of this ecosystem is likely guaranteed by the heterogeneous rocky substrate hosting the black coral population that represents a physical barrier against the mechanical impacts acted on the surrounding muddy areas, heavily exploited as trawling fishing grounds. This favorable condition, together with the existence of a nursery area for catsharks within the coral ramifications and the occurrence of a meadow of the now rare soft bottom alcyonacean Isidella elongata in small surviving muddy enclaves, indicates that this ecosystem have to be considered a pristine Mediterranean deep-sea coral sanctuary that would deserve special protection.