Pelagic Sargassum as a Potential Vector for Microplastics into Coastal Ecosystems

Macroalgal blooms are increasing globally, with those linked to pelagic Sargassum affecting over 30 nations since 2011. As Sargassum mats traverse the Atlantic Ocean and the Caribbean Sea, they entrap and transport plastic to coastal areas, intensifying pollution in diverse ecosystems. This research assessed microplastics (MPs) within Sargassum fluitans III collected from the northern Mexican Caribbean coast (March 2021 to January 2022). The study employed a hydrogen peroxide protocol for macroalgae pretreatment to optimize MP extraction. All samples analyzed contained MPs at monthly mean concentrations that ranged from 3.5 to 15.3 MPs g−1 DW, with fibers constituting ≥90%. Fiber colors, mainly transparent, blue, and black, exhibited diverse sizes and wear stages. The study underscores the pervasive and consistent presence of MPs in pelagic Sargassum reaching the Mexican Caribbean. Considering the documented Sargassum influxes to this coast in recent years (2789–11,297 tons km−1 yr−1), potential annual MP influxes range from 0.1 × 109 to 17.3 × 109 km−1 yr−1. Efficiently removing beach-cast Sargassum and directing it to landfills could serve as a viable strategy for the simultaneous removal of attached MPs from the ocean and coastal waters, offering a promising mitigation strategy to combat plastic pollution in the examined marine environment.