Abundance of microplastics in the gastrointestinal tracts of the eelpout (Zoacres viviparous L.) collected in Roskilde Fjord, Denmark: Implications for use as a monitoring species under the Marine Strategy Framework Directive

There is an increasing demand for protocols for the monitoring of marine microplastic (MP) pollution following the adoption of Descriptor 10.1.3 of the Marine Strategy Framework Directive (MSFD). Most monitoring efforts have focused on surface water samples but MP content in biota (typically seabirds and various fish species) have been documented and used in monitoring programs. In order to establish more comprehensive monitoring programs it is necessary to identify a suit of methods and species that can be systematically used to assess MP pollution in different environmental compartments. The present study had a two aims: (1) to assess the content of MPs in the viviparous blenny Zoarces viviparus (eelpout) sampled in Roskilde Fjord, Denmark, and (2) evaluate whether the eelpout could serve as a relevant indicator organism for MP pollution in relation to monitoring under the MSFD. MPs were found in eelpout from all three stations sampled demonstrating that MPs are ubiquitously present in Roskilde Fjord. The frequency of occurrence (FO%) of MPs in collected eelpout was relatively low (FO% =10.1%) compared to fish species sampled in other locations, which could indicate that eelpout may not be a favorable species for MP biomonitoring, possibly due to its benthic feeding mode. More data is however needed and it is recommended that samples collected for other monitoring purposes are examined for MPs in the coming years together with water and sediment samples collected simultaneously to determine the environment/biota MP ratio for eelpouts.