Molecular-assisted revision of red macroalgal diversity and distribution along the Western Antarctic Peninsula and South Shetland Islands

The Antarctic marine flora is well known as a flora composed of relatively few species in comparison with other marine realms. Using molecular taxonomy as complementary tool for traditional taxonomy, we studied red macroalgal diversity and biogeography along the Western Antarctic Peninsula (WAP) and South Shetlands Islands (SShs) coasts and across a bathymetric gradient; in addition, we compared both methods of identification in terms of accuracy and number of observed taxa. Our results show low diversity levels at the regional and local scales, with around 50 taxa registered in total. Molecular tools allowed us to detect putative cryptic species within the genera Callophyllis, Curdiea and Georgiella, and to identify 98% of our specimens at species level. Our results also allowed us to identify significant differences between red macroalgal assemblages of three distinct biogeographic sub-regions: SShs and Northern part of the WAP (at ≈63°S), Central part of the WAP (at ≈64°S) and Central-Southern part of the WAP (at ≈67°S). Our sub-regions do not correspond to the classical separation of SShs/WAP reported in previous studies and suggest that the Bransfield Strait is not a strong biogeographic barrier for red macroalgae. Since our three sub-regions correspond to three latitude levels, we propose that past and present-day dynamics of sea-ice disturbance may have shaped the observed differences in red algal communities. We believe that the construction of accessible genetic dataset associated with voucher specimens in the present work will benefit future studies of macroalgal diversity and distribution in the region.