MULTISCALE GENETIC STRUCTURE OF AN ENDANGERED SEAWEED AHNFELTIOPSIS PUSILLA (RHODOPHYTA): IMPLICATIONS FOR ITS CONSERVATION1

Although marine macroalgae have recently entered the lists of endangered species, conservation efforts are still limited by a lack of data, particularly for naturally rare species. One example is the turf‐forming Ahnfeltiopsis pusilla (Mont.) P. C. Silva et DeCew. Albeit cataloged as vulnerable in the Northwest Iberian Peninsula (NWIP), where it occurs only at five enclaves separated by 1,200 km from the closest recorded presence of the species, nothing is known about its genetic diversity and population connectivity. We used amplified fragment length polymorphism (AFLP) and sequences of the intergenic region between the mitochondrial cytochrome oxidase subunit 2 and subunit 3 genes (cox2‐3) to investigate its genetic structure at large (1,200 km), regional (<125 km), fine (<250 m), and patch (<1 m) scales. While cox2‐3 variability was too low for the intraspecific study, AFLP revealed that most of the genetic diversity was due to differences between populations. Locally, genetic diversity was always low, and clones were frequent, suggesting that asexual reproduction may be common; patches of turf, however, often were composites of various genetic individuals. Genetic structure at local, regional, and large scales indicated that A. pusilla is a poor disperser, and an assignment test found no evidence of real‐time dispersal between NWIP sites. Therefore, it is proposed that the five NWIP enclaves are designated independent management units (MUs). Bayesian‐clustering approaches suggested that the three southernmost sites are particularly valuable for conservation since they concentrate most of the genetic heritage of A. pusilla in NWIP. Our study shows that the approaches of conservation genetics may provide useful insights for endangered seaweeds.