Regional-scale genetic differentiation of the stony coral Desmophyllum dianthus in the southwest Pacific Ocean is consistent with regional-scale physico-chemical oceanography

Abstract

Deep-sea corals are diverse and abundant in New Zealand’s EEZ and the southwest Pacific Ocean. We assessed genetic diversity and gene flow of the deep-sea scleractinian (stony cup coral) Desmophyllum dianthus in five areas (Kermadec Ridge, Louisville Seamount Chain, Chatham Rise, Campbell Plateau, Macquarie Ridge), and applied dispersal kernels estimated from drifters observations and seascape genetics to compare with observed connectivity patterns and regional physico-chemical data. We observed pronounced between-region genetic differentiation, high levels of self-recruitment, but also high connectivity between distant sites (e.g., at the Kermadec Ridge inside the New Zealand EEZ, and the Louisville Seamount Chain outside the New Zealand EEZ). Genetic diversity was marginally highest at the Kermadec Ridge, whilst populations on the Chatham Rise showed evidence of unique genetic diversity that may be driven by converging ocean currents. Overall, patterns of genetic connectivity were consistent with oceanographic predictions of dispersal routes. Seascape genetic analyses indicated that environmental variables most often related to physical seafloor habitat characteristics were important predictors of regional-scale genetic differentiation of D. dianthus. Our research shows that current spatial closures within the New Zealand EEZ and surrounding high seas areas do not encompass the extent of genetic diversity and connectivity for D. dianthus, which parallels research for other deep-sea taxa in the region. Future measures implemented to protect deep-sea coral biodiversity require consideration of complex connectivity patterns and migration routes amongst taxa, at various spatial scales. This study demonstrates that a combined gene flow, seascape genetics and dispersal kernel modelling approach can provide a robust evaluation of connectivity in deep-sea environments to inform management decision making at the scale of the southwest Pacific Ocean.