Age and growth of two genera of deep-sea bamboo corals (family isididae) in New Zealand waters

We provide a detailed description of growth zone counts at two locations in the skeletal structure of four bamboo coral colonies (Family Isididae, sub-family Keratoisidinae, genera Lepidisis spp. and Keratoisis sp. from New Zealand). Zone counts were made microscopically on skeletal cross-sections of calcareous internodes producing counts of up to 90 for Lepidisis spp. and 160 for Keratoisis sp. Scanning Electron Microscope (SEM) images taken of cross-sections at the junction of the calcareous internode and gorgonin node revealed clear zone resolution and produced counts that were substantially higher (a maximum 490 zones). Lead-210 dating was applied to the skeletal structure of one specimen of Lepidisis sp. to develop an independent estimate of age and growth. Radial micro-sampling of the skeletal carbonate indicated the age of the colony at the largest section (7.4 mm average radius) was 43 yrs old (26–61 yrs 95% CI), with an average radial growth rate of 0.18 mm yr⁻¹ (0.13–0.29 mm yr⁻¹ 95% CI). Comparisons between the three age estimates for Lepidisis sp. were made and it was hypothesized that zones observed by light microscope have a bi-annual periodicity and that SEM-observed zones at the nodal juncture may represent an environmental event, such as lunar periodicity.