Environmental and compositional correlates of growth rate in deep-water bamboo corals (Gorgonacea; Isididae)

Abstract

Little is known about the factors that affect the growth rates of deep-water corals. Analysis of 23 specimens of bamboo corals, a ubiquitous deep-water group, that were reliably aged using radiometric techniques or validated increment counts indicates that the radial growth rate of the coral's calcite internode declines with depth and increases logistically with ambient temperature. Temperature alone accounts for about half of the variance among specimens in lifetime mean growth rates. Growth rates plateau below 2°C and above 5°C, which likely reflects physiological constraints on growth and calcification. Thus far, the only other effect on growth rate identified is a tendency for colonies from the NE Pacific to grow faster relative to ambient temperature than colonies in other regions. Analysis of elemental composition of the calcite internode, based on data available for 16 of the 23 specimens, shows that, contrary to suggestions in the literature, growth rate does not correlate with Sr/Ca ratios, neither among or within colonies. Rather, within-colony ontogenetic variability in increment width, an index of short-term growth rate, correlates positively with calcium weight-fractions and negatively with the ratio between P and S, an index of organic content. The underlying mechanism is likely to be a link between crystal ultrastructure, which varies with growth rate, and the ratio between CaCO 3 and organic matrix in different crystal types. Between colonies, composition correlates poorly with growth rate. This could reflect spatial and temporal heterogeneity in other environmental factors that determine internode composition, as well as difficulties in standardising P measurements across specimens.

Optical Observations and Geochemical Data in Deep-Sea Hexa- and Octo-Coralla Specimens

“…The mean growth rate is in between 45 µm and 75 µm per year, in agreement with others estimates [43][44][45]. However, the first 10 mm of the specimen exhibited faster growth compared to that of the next 20 mm.…”

“…A focused O − ion beam of about 10 nA was used to analyze the samples. Ions of 7 Li + , 23 Na + , 24 Mg + , 44 Ca + and 88 Sr + were measured using a −70 eV energy filtering after a presputtering time of 2 min, in monocollection mode on an electron multiplier. The possible isobaric interference of 88 Sr 2+ on 44 Ca + was checked by measuring the mass 43.5 ( 87 Sr 2+ ) and was observed as negligible.…”

“…Ions of 7 Li + , 23 Na + , 24 Mg + , 44 Ca + and 88 Sr + were measured using a −70 eV energy filtering after a presputtering time of 2 min, in monocollection mode on an electron multiplier. The possible isobaric interference of 88 Sr 2+ on 44 Ca + was checked by measuring the mass 43.5 ( 87 Sr 2+ ) and was observed as negligible. The calcite in-house reference OKA-C was used to determine the Na/Ca and Mg/Ca ion yields (Na/Ca = 1.94 mmol/mol, Mg/Ca = 4.55 mmol/mol, Sr/Ca = 19.3 mmol/mol, [52]), and CAL-HTP [53] was used to calibrate the Li/Ca.…”

“…The coral powders were dissolved in ultraclean HNO 3 solution (0.5 N). The isotopes of 23 Na, 24 Mg, 43 Ca, 44 Ca and 88 Sr were measured to determine the TE/Ca ratios. The carbonate standard JCp-1 was analyzed before and after the 22 coral samples to ensure of the stability and the accuracy of the measurements.…”

Long-term growth rates of four Mediterranean cold-water coral species maintained in aquaria

“…Several recent studies, such as those performed on Gerardia sp. and bamboo corals, have assessed the growth of CWC from the Atlantic and Pacific oceans, as well as the Caribbean Sea (Matsumoto 2007, Andrews et al 2009, Parrish & Roark 2009, Thresher 2009) and found very slow growth rates of a few micrometres in radial growth per year. However, a higher axial growth rate of 0.5 to 1 cm yr -1 was estimated for large and old bamboo coral colonies.…”