Population genomic and morphological datasets from: An evolutionary mosaic challenges traditional monitoring of a foundation species in a coastal environment - the Baltic Fucus vesiculosus

Genetic diversity in foundation species is critical for ecosystem
functions and resilience under environmental change but remains largely
overlooked in environmental monitoring. In the Baltic Sea, a key
species for monitoring is the brown seaweed Fucus vesiculosus,
which forms sublittoral 3D habitats providing shelter and food
for fish and invertebrates.  Ecological distribution models
predict a significant loss of Baltic F. vesiculosus due to ocean warming
unless populations can adapt. Genetic variation and recombination during
sexual reproduction are essential for adaptation, but studies have
revealed large-scale clonal reproduction within the Baltic Sea. We
analyzed genome-wide SNP data from the east Atlantic, the "Transition
zone", and the Baltic Sea, and found a mosaic of divergent lineages
in the Baltic Sea contrasting an outside dominance of a few genetic
groups. We determined that the previously described endemic species Fucus
radicans is predominantly a large female clone of F. vesiculosus
in its northern Baltic distribution. In two Estonian
sites, however, individuals are sexual but reproductively
isolated from Baltic F. vesiculosus, revealing a separate diverged lineage
that predates the formation of the Baltic Sea. Monitoring Baltic Fucus
without considering this genetic complexity will fail to prioritise
populations with adaptive potential to new climate conditions. From our
genomic data, we can extract informative and diagnostic genetic markers
that differentiate major genetic entities. Such an SNP panel will provide
a straightforward tool for spatial and temporal monitoring and informing
management decisions and actions.