Sclerochronology of deep-sea bamboo corals from the northwest Atlantic: Acanella arbuscula and Keratoisis spp.

Deep-sea corals provide habitat for invertebrates and fish, have high longevities, and slow growth rates, making them vulnerable to anthropogenic disturbances. The bamboo corals Acanella arbuscula and Keratoisis flexibilis have been observed in the NW Atlantic, but growth rates and ages have not been heavily studied. Growth ring counts at the proteinaceous nodes of the coral skeletons were used for aging. Both species exhibited major and minor growth rings, but major rings represent annual growth in A. arbuscula and minor rings represent annual growth in K. flexibilis, determined by comparing age estimates from ring counts to radiometrically validated specimens of each species. Ages, radial, and axial growth rates ranged from 8-29 years, 0.025 – 0.160 mm/yr, and 1.87 – 16.1 mm/yr for A. arbuscula, and 89-168 years, 0.007-0.027 mm/yr, and 1.5-5.3 mm/yr for K. flexibilis. Geographic variations in A. arbuscula growth rates were observed, with the SE Baffin Shelf specimens growing the fastest because these specimens were youngest, and ontogenetic influence on growth rates was observed, causing younger colonies to grow faster. K. flexibilis growth rates were slower than K. grayi, and this inter-specific difference can be attributed to temperature, as the K. flexibilis samples were collected in colder waters