Insights into the molecular and morphological diversity of Asparagopsis taxiformis in north-eastern Australia

The red seaweed, Asparagopsis taxiformis, consists of multiple genetic lineages that have spread globally through natural and human-mediated dispersal. Endemic to Australia and the Indo-Pacific, A. taxiformis has become an invasive pest in regions such as the Mediterranean Sea. Despite the commercial and ecological importance of this species, the genetic and morphological diversity of Australian populations remains understudied. Understanding this diversity, particularly within biodiversity hotspots like the Great Barrier Reef (GBR), is essential for advancing ecological knowledge and improving conservation and commercial management. This study investigated the genetic and morphological diversity of A. taxiformis within north-eastern Australia, by collecting tetrasporophyte specimens from 13 near and offshore locations in Queensland, including the GBR Marine Park. DNA was extracted from specimens and the chloroplast RuBisCO spacer and mitochondrial cox2-3 intergenic spacer (cox2-3) were sequenced to assess genetic diversity. Nine morphological characteristics of the tetrasporophyte were also measured. While little genetic variation was found using the RuBisCO spacer, cox2-3 analysis revealed that lineage 5 (L5) was present at two locations, lineage 6 (L6) dominated southern Queensland and lineage 4 (L4) was prevalent in the northern GBR, marking its first record in Australian coastal waters. Morphometric analyses identified significant differences in axial cell width and filament width among L4 and L5, with these traits modelled to be most useful for differentiating between lineages. The findings highlight substantial genetic and morphological diversity within A. taxiformis populations of Australia and the need for further systematic sampling in underrepresented locations.