<p>Microplastics are an emerging contaminant in marine ecosystems worldwide. This study evaluated the abundance of microplastics, their relationship with sediment type, and their ingestion by macroinvertebrates in the Eastern South Pacific Ocean and the Southern Caribbean Sea during the rainy and dry seasons. A granulometric analysis was performed applying a Pearson correlation matrix, and microplastics were extracted using the density flotation method and analyzed by type, color, and size. There was an average of 165 ± 22 microplastics/kg in the Eastern South Pacific Ocean and 296 ± 167 microplastics/kg in the Southern Caribbean Sea, however, there were no significant differences among regions or seasons. A negative relationship was found between microplastic abundance and coarser sediment, indicating that they retain fewer microplastics than finer sediments. Blue and red fibers smaller than 2&#xa0;mm were the most common microplastic types in both regions. There was a higher ingestion of microplastics in the Southern Caribbean Sea (22%) compared to the Eastern South Pacific Ocean (3%), and polychaetes were the main microplastic eaters. Our findings highlight the usefulness of marine polychaetes as bioindicators of microplastic pollution and suggest a relationship between the abundance of microplastics and the ingestion of microplastic by benthic organisms.</p>