New Zealand deep-sea black coral (Antipatharia) age and growth rates: Insights into early life growth patterns

Black corals (Order Antipatharia) are a diverse group found worldwide and in high abundance around Aotearoa New Zealand where their spatial distribution extends from coastal regions to the deep sea. They provide biologically important habitats and host various benthic invertebrate organisms. There is concern however, that black corals are under threat from anthropogenic activities such as mining and bottom fishing as well as from environmental changes in temperature and dissolved oxygen concentrations. Understanding the potential for black corals to recover after disturbance requires knowledge of their longevity and growth rates. Fortunately, the proteinaceous skeletons of black corals can be radiometrically dated to high precision providing age and growth data to help inform impacts. Ten black corals from two genera (Antipathella and Leiopathes) were selected from the invertebrate collection at the National Institute of Water and Atmospheric Research and radiometrically dated using radiocarbon and uranium-thorium disequilibrium (U-Th) techniques. Coral lifespans ranged from 71 years (Antipathella fiordensis) up to 2221 years (Antipatharia), and skeletons show radial growth rates ranging from 2.6 (Leiopathes sp.) – 126.7 μm/yr (A. fiordensis). High-resolution age-depth models (1.7–42.7 years/sample) were generated from U-Th age measurements leading to observations of an early life radial growth rate pattern that could provide further insights for black coral physiology. This pattern is comprised of a large growth slump after colony birth followed by a triple peak pattern which contained the maximum growth rate. These data advance our knowledge of longevity for these corals, the variability in ages and growth rates between species and regions, and their vulnerability to physical disturbances due to slow recovery rates.