Not Cryptogenic: Molecular and Historical Evidence Supports Introduction of Asparagopsis taxiformis (Rhodophyta) Into the Galápagos Islands

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Aim Identifying the origins of widespread species is crucial for conservation in isolated biodiversity hotspots, where ‘cryptogenic’ status often hinders effective biosecurity. We investigated the genetic identity and introduction history of the red macroalga Asparagopsis taxiformis in the Galápagos Islands to resolve its cryptogenic status. Location Galápagos Archipelago, Ecuador. Methods We conducted the first molecular survey of A. taxiformis across the archipelago, integrating contemporary collections with archival herbarium specimens spanning 40 years (1985–2024). Three genetic markers ( cox2‐3 spacer, rbcL and LSU) were used to identify lineages and assess genetic uniformity over time. Results All successfully sequenced specimens, including historical samples, belong exclusively to the L2 lineage, a clade associated with the Indo‐West and Central Pacific. The repeated detection of this single, genetically uniform lineage across four decades is consistent with long‐term establishment following introduction. Main Conclusions Our findings indicate that A. taxiformis in the Galápagos is most consistent with an introduction via shipping activity, based on the combination of molecular uniformity and historical absence prior to the mid‐20th century. This study demonstrates the power of archival DNA in resolving invasion histories. These results underscore the urgent need for ecological risk assessments to safeguard the unique marine biodiversity of the Galápagos from non‐native macroalgae.