Data from: Contrasting patterns of population structure and gene flow facilitate exploration of connectivity in two widely distributed temperate octocorals

Connectivity is an important component of metapopulation dynamics in
marine systems and can influence population persistence, migration rates
and conservation decisions associated with Marine Protected Areas (MPAs).
In this study, we compared the genetic diversity, gene flow and population
structure of two octocoral species, Eunicella verrucosa and Alcyonium
digitatum, in the northeast Atlantic (ranging from the northwest of
Ireland and the southern North Sea, to southern Portugal), using two
panels of 13 and 8 microsatellite loci, respectively. Our results
identified regional genetic structure in E. verrucosa partitioned between
populations from southern Portugal, northwest Ireland and Britain/France;
subsequent hierarchical analysis of population structure also indicated
reduced gene flow between southwest Britain and northwest France. However,
over a similar geographical area, A. digitatum showed little evidence of
population structure, suggesting high gene flow and/or a large effective
population size; indeed, the only significant genetic differentiation
detected in A. digitatum occurred between North Sea samples and those from
the English Channel/northeast Atlantic. In both species the vast majority
of gene flow originated from sample sites within regions, with populations
in southwest Britain being the predominant source of contemporary
exogenous genetic variants for the populations studied. Overall,
historical patterns of gene flow appeared more complex, though again
southwest Britain appeared to be an important source of genetic variation
for both species. Our findings have major conservation implications,
particularly for E. verrucosa, a protected species in UK waters and listed
by the IUCN as ‘Vulnerable’, and for the designation and management of
European MPAs.