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. Bamboo corals (Order Gorgonacea: Calcaxonia: Isididae) are sedentary, non-tropical, octocorals with a conspicuously jointed, central skeletal axis comprised of white calcareous segments or internodes alternating with dark gorgonin nodes, often referred to as organic or proteinaceous material. The gorgonin provides a structural framework in the biomineralisation process and is responsible for flexibility of the skeletal axis. The calcite provides skeletal support, facilitating growth in regions with significant current flows. The central axis is covered by a coenenchyme containing calcareous spicules and bearing polyps. Skeletal micro- and ultra-structure of isidid skeletons is described in detail in Noe and Dullo (2006). Genera within the Isididae can be tentatively identified from their mode of branching, and species can be identified based on the microscopic form of the spicules and their arrangement within the polyps and coenenchyme. The lack of a comprehensive systematic description often makes it difficult to differentiate genera and species. Bamboo corals are widely distributed in New Zealand’s Exclusive Economic Zone occurring on seamounts, as well as in areas of comparatively flat slope topography and deep-sea reef (Grant, 1976; Smith et al., 2004). They are found at water depths in excess of 100 m, with many living well below 1000 m. To date, 14 species of subfamily Keratoisidinae have been identified for the New Zealand region (Grant, 1976; Smith et al., 2004; Sanchez, unpubl. data), some are endemic (Sanchez et al., 2004). Together with other gorgonian, stony, and encrusting corals, bamboo corals provide an ideal habitat for small invertebrates and shelter for fish species (Auster and