Microplastics (MPs) are emerging contaminants in marine environments. This study quantified, chemically identified, and described MPs in reefs of Brachidontes exustus and Petaloconchus spp. on the tropical coast of Brazil. Samples were collected in reefs of northeastern Brazil in the dry (February) and rainy (July) seasons of 2023. MPs were classified (shape and color), measured, and counted. MPs were present in all samples. Most MPs were transparent fibers, with more particles in Brachidontes reefs and during the rainy season. MPs were mainly polystyrene, polypropylene, polyester, and polyamide. The characteristics of reefs and seasonal changes in rainfall are the main drivers of the accumulation of MPs, and the shape and chemical composition of particles reveal that their principal source is probably the textile and apparel industry. The trapping of MPs in Petaloconhus spp. and Brachidontes exustus reefs reveals that biogenic reefs may be a sink for microplastics in tropical coastal areas.