Microplastic ingestion and Phthalate ester levels as plastic tracers in the Mediterranean Velella velella: a candidate plastic indicator for the pelagic neustonic environment

Bioindicator species can help assess plastic pollution's impact on biodiversity by integrating spatial distribution and temporal trends, highlighting associated ecological risks. To investigate a potential indicator for pelagic neustonic environments, the holoplanktonic hydrozoan V. velella was collected in the Pelagos Sanctuary (SPAMI, NW Mediterranean Sea). A total of 460 individuals from 27 stations were collected alongside manta net trawls. Isolated organisms were digested through an alkaline solution and examined for the presence of microplastics (MPs). The correlation among the abundance of floating microplastics in the area, microplastic ingestion and levels of 11 Phthalate Acid Esters (PAEs) in V. velella have been investigated to provide a comprehensive assessment of the multiple stressors impacting this species. Over 200 MPs were isolated, with an occurrence of 93 % in the sampling stations (0.6 ± 0.7 items/individual). Polyester filamentous-shape particles (including fibres and filaments; 81 %) and polyamide, polyolefin and polystyrene fragments (17 %) were the predominant particle types. PAEs concentration averaged 313 ± 66 ng/g w.w. with Dibutyl-phthalate, Diisobutyl-phthalate, and Diethylhexyl-phthalate, listed as reprotoxic by EU regulation, comprising 95 % of total compounds. Despite no statistical correlation, a slightly positive trend between ingested plastic and total PAEs load was found shedding light on the potential direct release from particles. With its wide distribution, key trophic role, ability to capture smaller MPs fractions (<300 μm) and fibres and to accumulate the chemicals from the surrounding environment, V. velella emerges as a promising bioindicator of MPs pollution in the pelagic areas of the Mediterranean Sea and the other seas and oceans worldwide.