Stable connections in the deep sea: Temporally consistent larval pathways for the deep-sea coral, Lophelia pertusa (=Desmophyllum pertusum) in the Northwest Atlantic Ocean

Population connectivity facilitates genetic exchange and increases resilience of populations promoting long-term persistence. For sessile benthic invertebrates, larval dispersal provides the main mechanism to achieving population connectivity. Here, we use biophysical modelling of larval dispersal to elucidate potential connections between populations and quantify dispersal pathways, which we combine with network-theoretic analyses to evaluate their potential importance to the stability of the entire network. Because the necessary parameters for these analyses are difficult to quantify for deep-sea species with unresolved life-history traits, we explore multiple scenarios using a range of likely life-history trait values. Focussing on the deep-water coral Lophelia pertusa (=Desmophyllum pertusum) over its North American range in the Northwest Atlantic Ocean, we used a high-resolution ocean circulation model in combination with larval parameters to project larval dispersal for each season over 14 years from 2005 to 2018. We then use the larval dispersal pathways to identify connections between populations, and network theory to uncover network structure and quantify the importance of each population to the overall connectivity within the network. Larval retention was strongest in the northern domain and within the Gulf of Mexico, suggesting these populations could persist without larval influence from other areas. The two dominant transport pathways occurred following the Gulf Stream from Florida north towards the eastern United States and following the Labrador Current travelling southwestwards from the Canadian EEZ with little exchange between northern and southern domains. Our network-theoretic analysis suggested that the populations of L. pertusa in Norfolk Canyon are primarily responsible for exchange between northern and southern populations, with no northward connections. Our community detection analysis based on population connectivity agrees well with previous patterns based on estimates of genetic connectivity in the area. This is the first study to analyse potential connectivity of L. pertusa in the NW Atlantic Ocean, and projects consistency in the dominant connection pathways throughout spawning seasons, years, and for biological parameters. Our results are integral in assessing a populations susceptibility to anthropogenic disturbance and are directly applicable to other deep-sea species in our domain with similar life-history traits to those within the modelled ranges.