Plastisphere dynamics in Mediterranean aquaculture: Microbial colonization and pollution in fish farm cages

Herein, we describe the characterization of plastisphere communities colonizing fish farm cages in Monastir Bay (Tunisia) to evaluate their potential as bioindicators of plastic pollution. The collected plastispheres were predominantly composed of Bacillariophyceae, exhibiting the highest relative abundance among microalgal taxa, followed by Cyanobacteria and Dinophyceae. Among phytoplankton, the diatom Licmophora sp. And the filamentous cyanobacterium Oscillatoria sp. were identified as the most dominant species. Across all sampling substrates, potentially harmful microalgae were primarily represented by the diatom Pseudo-nitzschia sp. And Oscillatoria sp. In addition to microalgae, protozoans and metazoans were also sheltered within the plastisphere, with foraminifera showing the highest relative abundance among zooplankton. The foraminiferal assemblages were dominated by stress-tolerant species, including Rosalina bradyi, Ammonia beccari, and Elphidium crispum. Based on the Shannon-Wiener diversity index and the interpretative framework of, the breeding net exhibited heavy pollution (H' = 0.83), whereas the floating tube and anchor ropes were classified as lightly polluted. These findings underscore the plastisphere's utility as an integrative bioindicator for assessing plastic pollution in aquaculture environments.