Microplastic exposure and biological correlates in a key intertidal crab (Grapsus grapsus) from the Galápagos Islands

Microplastics (MPs) are pervasive contaminants in marine ecosystems, yet data from remote oceanic islands remain limited. We quantified MP occurrence in gills and gastrointestinal tracts (GIT) of Sally Lightfoot crab (Grapsus grapsus, n = 60) from three sites on San Cristóbal Island, Galápagos Marine Reserve, and assessed relationships with morphometric and physiological indices. MPs were detected in 78% of gills and 52% of GIT samples, with a total of 138 particles identified. Fibers predominated (77%), mostly <1 mm, and cellulose was the most frequent polymer, followed by polyethylene terephthalate (PET) and polyolefin (PO) blends. Gill tissues exhibited higher MP loads and greater polymer diversity than GIT samples, indicating branchial interception as a key exposure pathway. Negative binomial models showed no significant associations between GIT MP abundance and the scaled mass index, heart rate, sex, or site. These findings reveal widespread exposure to MPs in an ecologically important intertidal crustacean and confirm that even protected insular ecosystems are permeated by anthropogenic microdebris.