Breaking new ground: trophic ecology and microplastic ingestion in threatened juvenile hammerheads and adult sharpnose sharks from a Puerto Rican estuary

Abstract

This study presents an integrative evaluation of microplastic ingestion and trophic ecology in three shark species from an estuary in the north coast of Puerto Rico. A multi-analytical framework combining stomach content analysis, DNA barcoding, and stable isotope analysis (δ¹³C and δ¹⁵N) was employed to characterize dietary composition, trophic positioning, and plastic exposure. Juvenile individuals of two critically endangered hammerhead species (<em>Sphyrna lewini</em> and <em>Sphyrna mokarran</em>), along with mature individuals of the mesopredatory genus <em>Rhizoprionodon</em> (Sharpnose sharks), were analyzed to investigate interspecific variation in foraging strategies and ecological niche use. Results revealed species-specific dietary preferences, isotopic signatures, and different exposure to microplastics, suggesting distinct habitat utilization patterns and trophic pathways among taxa. The occurrence of plastic particles in the digestive tracts, coupled with evidence of resource partitioning, underscores varying degrees of susceptibility to plastic ingestion, particularly in benthic and benthopelagic feeders. These findings provide critical baseline data on diet and pollutant exposure in coastal elasmobranchs of the northeastern Caribbean and emphasize the value of integrating ecological and pollution-based indicators. The study also highlights the urgent need to assess anthropogenic stressors in understudied tropical shark populations to inform species-specific conservation and management strategies.