A new red alga from a ship hull: Stylonema isabui sp. nov . (Stylonematophyceae) with uncertain biogeographic origin

Shipping is one of the most common vectors for marine biological invasions, enabling the dispersal of organisms across large geographic distances. While ballast water was previously considered the primary pathway for species introductions, recent attention has shifted towards hull-fouling communities, prompting tighter international regulations. Macroalgae, with life cycles that include both macroscopic and microscopic stages, may be transported during their inconspicuous early developmental phases. To assess this risk, we investigated potential algal propagules associated with the hull of the research vessel R/V Isabu, which was undergoing maintenance in January 2023. A red algal spore was isolated from biofouling material collected from the submerged hull surface. Morphological observations and molecular analyses of the plastid rbcL and psbA genes, mitochondrial COI-5P and nuclear SSU rDNA revealed that the alga belongs to the genus Stylonema and represents a previously undescribed species. We describe this taxon as Stylonema isabui sp. nov. the first red algal species formally described from a ship hull. Its geographic origin remains uncertain, and further ecological and physiological studies are needed to evaluate its potential to establish in natural coastal habitats. Our findings highlight the need to consider microscopic life stages of macroalgae as potential agents of marine bioinvasions and to expand surveillance efforts accordingly.