First report on microplastics ingestion in the Critically Endangered spiny butterfly ray Gymnura altavela (Elasmobranchii, Gymnuridae) from a Southwestern Atlantic estuary

Microplastics (MPs) are ubiquitous in aquatic ecosystems and can trigger various harmful effects on key species. Studies regarding sharks and rays (elasmobranchs) in this sense, however, are still scarce. Thus, this study assessed MP ingestion in the endangered spiny butterfly ray (Gymnura altavela) from a Southwestern Atlantic estuary to provide the first particle quantification and characterization for this species. Ten specimens were samples and stomachs were processed employing a adapted HO 15 % digestion, NaCl 1.2 g cm separation and dual filtration (8 and 0.45 μm pore diameters) protocol. The adapted method was found to be more effective than the original in decomposing organic matter. A total of 389 MP particles were recorded, with fibres and lines overwhelmingly dominant (89.2 %), followed by fragments (8.0 %) and pellets (2.8 %). Transparent (57.5 %) and blue (25.7 %) particles were most frequent, while other colours (black, red, yellow, pink, orange, green) were detected at lower amounts. Particle sizes ranged from 0.025 to 8.75 mm, spanning micro-to mesoplastic scales and females showed higher intra-group MP heterogeneity compared to males. A negative binomial GLM detected an inverse relationship between gastric fullness index and MP loads, indicating longer residence or slower evacuation of non-digestible particles in emptier stomachs. The findings indicate that MPs ingestion may potentially compromise individual health and facilitate trophic transfer to higher predators. This study contributes novel insights into elasmobranch exposure to plastic pollution in the Southwest Atlantic and highlights that morphology provides robust indicators of MPs sources and biological interactions, reducing the need for advanced spectroscopic identification in certain contexts.