Growth in cold-water octocorals: rates, morphology and environmental controls

De Moura Neves, Bárbara (2016) Growth in cold-water octocorals: rates, morphology and environmental controls. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Deep-water corals can have high longevities and slow growth rates. While most studies have been focusing on growth rates of gorgonians, few studies have examined rates and patterns in other octocorals, such as sea pens. Here I studied growth rates and patterns in the sea pens Halipteris finmarchica, Umbellula encrinus, and Pennatula grandis, and in the gorgonians Primnoa pacifica, Primnoa resedaeformis, and Keratoisis sp. Longevity and growth rates were estimated by examining growth rings in their skeletons (axes), whose morphology and composition were also explored. Growth patterns were investigated by examining relationships between colony and axis characteristics. Relationships between colony growth rates and environmental factors were also assessed. The morphology of the axis in sea pens varies among taxa and within colonies, and their carbonate portion is composed in average of 65-85% of magnesian calcite (Ca, Mg)CO₃. Sea pens can have longevities reaching ~70 years in U. encrinus. Diametric growth rates in H. finmarchica, U. encrinus, and P. grandis were comparable in magnitude, ranging between 0.13-0.14 mm∙yr⁻¹. Using new and published data, diametric growth rates in P. pacifica and P. resedaeformis averaged 0.43 mm∙yr⁻¹ and were not statistically different. In the Arctic populations of Keratoisis sp. studied here radial growth rates ranged between 0.010-0.018 mm∙yr⁻¹, much slower than in most other populations of this coral. Relationships between growth rates and environmental variables were statistically significant for bottom temperature (U. encrinus), chlorophyll a (P. grandis and Primnoa spp.), and depth (Primnoa spp.). Geochemical analyses yielded a number of trace element peaks comparable to the number of growth rings in sea pens. The ¹⁴C curves for the studied sea pens follow the same patterns seen in the calcite of other octocorals in the region, in which rings are formed annually. Growth rate and longevity data can support conservation efforts for these vulnerable species.

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