Biophysical Modelling of Lophelia pertusa Larval Dispersal in the Skagerrak – An Area Isolated by Distance?

Poster presentation at ATLAS 3rd General Assembly.

The Skagerrak basin in northeastern North Sea constitutes an outpost in terms of the geographical distribution of the reef-forming cold-water coral Lophelia pertusa. Colonies of L. pertusa are currently known to occur in a restricted region comprised by the Hvaler-Koster area located in the northeast corner of the basin. Within this area, living corals are found at six locations while remains of extinct reefs have been found at a number of additional sites. Bottom trawling has historically constituted the main threat to the coral reefs and marine protected areas have been established in both Swedish and Norwegian waters to reduce further damage. Previous transport modelling and genetic studies indicate that the Skagerrak population of L. pertusa is considerably isolated, likely due to a restricted exchange of larvae with other populations. Genetics have also revealed a varying degree of isolation for individual reef sites within the Skagerrak. Young L. pertusa colonies of unknown origin were recently discovered on the remains of a dead reef in the Koster area, demonstrating the possibility of re-colonization of extinct reef sites. The objective of this project is to use biophysical modelling of L. pertusa larval drift as a tool to study population connectivity within the Skagerrak and to investigate possible connections with populations outside of this region. A high resolution regional ocean circulation model will be run to generate current velocity fields, which will in turn be used to drive a larval drift model. Biological traits such as planktonic larval duration and vertical migration patterns of L. pertusa larvae, observed during previous and planned laboratory experiments, will be incorporated into the drift model to optimize the reliability of the simulations. The resulting larval drift data will be used for connectivity analyzes which may aid in further developing interventions to protect and restore L. pertusa sites within the Skagerrak basin.