Quantification and evaluation of plastics in the Spanish Mediterranean Sea

Abstract

[eng] To determine the seriousness of an environmental threat, and the steps necessary to work towards a solution, it is important to first measure that threat. In the case of marine plastic, that means quantifying and characterising the plastics present in all areas of the ocean. In this study the presence of both microplastic particles and fibres in the marine environment are considered, and both are referred to using the general term “microplastic” (MP). MP abundance was assessed in surface water, subsurface water and four species of fish in the North Western Mediterranean Sea between 27th June and 13th July 2021. A manta trawl (335μm) was used to measure MP abundance in surface water for 6 stations. Mean abundance was 4.90 (± 3.49) MP/m3 , with fragments being the most frequent particle type (44%). The study found MP abundance along the Costa Brava to be slightly higher than the range given by other studies (0.10-3.52 MP/m3 ) that used a similar methodology in other areas of the western Mediterranean (Collignon et al. 2012; Lucia et al. 2014). A continuous underwater fish egg sampler (CUFES) was used to measure MP abundance in subsurface water (3m depth) in 14 stations. Mean abundance was 0.95 (± 0.44) MP/m3 with fibres being the most frequent particle type (85%). Gastrointestinal tracts from 136 individuals from 5 stations were examined for the four fish species; Engraulis encrasicolus, Sardina pilchardus, Boops boops and Trachurus mediterraneus. MP ingestion occurrence for the different species ranged from 25% (E. encrasicolus) to 65% (S. pilchardus). Mean MP ingestion was found to be highest in T. mediterraneus 2.27 (± 6.16) MPs/ind and lowest in E. encrasiculos 0.25 (± 0.44) MPs/ind. Mean MP ingestion for 3 of the 4 species used in this study (E. encrasicolus, S. pilchardus and B. boops) was found to fall within the range of results found in other studies on the same species, while MP ingestion in T. mediterraneus (2.27 (± 6.16) MPs/ind) was found to be slightly higher than the range of results from other studies on the same species (0.40 – 1.77 MPs/ind) (Gökdağ. 2017; Rios-Fuster et al 2019). Overall, fibres were the most frequent particle type ingested (84%), with fibre occurrence for the different species ranging from 20% (E. encrasicolus) to 93% (T. mediterraneus). The relationship between sea surface MP abundance and two socio-geographic factors; distance to the coast and population density, was also assessed as a case study. Increased MP concentrations were found to correlate with proximity to the coast and higher population density.