Genetic assessment of connectivity in the temperate octocorals Eunicella verrucosa and Alcyonium digitatum in the NE Atlantic

Abstract

Elucidating patterns of connectivity for species of conservation concern is crucial in the design of networks of ecologically coherent marine protected areas, and therefore is considered in the design of such a network recently proposed to the UK Government. However, data concerning connectivity are deficient for most invertebrate sessile taxa. Therefore, this study used microsatellite panels developed de novo to assess the population genetic structure and genetic connectivity of two temperate octocorals in the North East Atlantic. Microsatellite panels for both species show evidence of cross-species transferability, and therefore in future may prove to be useful monitoring tools for the target species but also for congenerics further afield in Europe. Eunicella verrucosa (O. Alcyonacea: S.O.Holaxonia: F. Gorgoniidae), a threatened and IUCN red-listed sea fan, was sampled in the northerly extremes of its eastern Atlantic range in southern Portugal, Brittany, the South West UK and western Ireland. In this vicinity, connectivity appears to be defined at regional scales and localised cases of inbreeding and differentiation suggest that the population structure of this species is best described as a metapopulation. Alcyonium digitatum (O. Alcyonacea: S.O. Alcyoniina: F. Alcyoniidae), a soft coral, was sampled in the central portion of its range in Brittany, western Ireland, south west UK and the North Sea. This species exhibited very little population structure and apparent panmixia across the sampled range. However, high levels of heterozygote deficiencies and inbreeding in the majority of populations implies that the genetic structure of some populations of this species may be defined by self-seeding and rarer dispersal events that occur sufficiently often to offset divergence via genetic drift. Coalescent analyses indicate that in both species, migration between regions occurs asymmetrically. The presence of few duplicate genotypes in both datasets implies that sexual reproduction predominates in both species in the sampled area. Eunicella verrucosa is a charismatic species that is often used to promote marine conservation efforts in the UK and A. digitatum is a ubiquitous animal around western European coasts; the two species often occur together and both may suffer the damaging effects of mobile fishing gears. This research represents the first population genetic assessment of both species and the first time microsatellites have been used to assess population structure of octocorals in the North East Atlantic.