Lifespans and growth patterns of two deep-sea corals:: Primnoa resedaeformis and Desmophyllum cristagalli

A subfossil fragment of the deep-sea gorgonian coral Primnoa resedaeformis was C-14 AMS dated along a radial growth transect. Dates ranged from 2600+/-50 at the outside, to 2920+/-60 C-14 years BP near the interior, suggesting an age of >300 years. The avergae radial growth was approximately 0.044 mm.yr(-1). Based on comparisons with live-collected specimens, we estimate the entire colony may have been about 0.5-0.75 m tall, with a linear tip extension rate of 1.5-2.5 mm.yr(-1). Towards the centre of the main stem, the coral skeleton is composed of alternating couplets, 200 mum in width, of gorgonin (a horn-like organic skeletal protein) and calcite. We believe these couplets are annual. Within this larger scale of banding are finer couplets of gorgonin and calcite, with frequencies suggesting lunar monthly periodicity. Both scales of banding may reflect fluctuations in food supply from sinking POM, or from tidally-resuspended bottom POM, along with benthic consumers. Outer skeletal growth is predominantly massive calcite with intermittent gorgonin layers. If carbonate precipitation in this zone were continuous, approximately 25 mum radial growth would be deposited every year. The Scleractinian Desmophyllum cristagalli lives to >200 years, and has rates of linear extension of 0.5-1.0 mm.yr(-1). The skeletons show growth bands approximately 10 mum wide, which may be annual. Due to tissue extension and retraction in life, parts of the skeleton may be overgrown, or suffer dissolution. Although we have shown in previous publications that sea water temperatures may be obtained from analysis of this coral, periods of skeletal dissolution, coupled with isotopic disequilibrium, will make obtaining long climatic records extremely difficult.