Quantifying Marine Surface Microplastics in La Parguera Natural Reserve, Puerto Rico

Microplastic pollution has become a global concern due to its widespread impacts on organisms and ecosystems. While there have been a few studies quantifying microplastics in inland areas of Puerto Rico, none, to our knowledge, have studied nearshore coastal surface waters. This study, therefore, presents the first assessment of microplastic concentrations and descriptions in the surface waters of La Parguera Natural Reserve, southwestern Puerto Rico. Using 333-micron plankton net trawls, we found low mean ± standard deviation microplastic concentrations of 0.02 ± 0.07 microplastic particles m−3 (95% confidence interval = 0.01 to 0.04 microplastic particles m−3). The most prevalent polymers were high-density polyethylene (48%) and polyethylene (32%), followed by polypropylene (11%) and polystyrene (7%). The most common colors were white (50%), blue (34%), black (8%), red (5%), and colorless (3%). Subsequently, the common structures found were fragments (78%), filaments (12%), films (8%), and fibers (2%). No clear coastal gradient or seasonal patterns were detected (p < 0.05), and mean concentrations were similar to previously surveyed oceanic waters from the Caribbean, suggesting coastal sources of marine microplastics were minimal compared to oceanic sources. This study provides a foundational understanding of microplastics in the coastal waters of La Parguera Natural Reserve and provides critical baseline data for detecting potential future changes in microplastic concentrations.