Silica banding in the deep-sea lithistid sponge Corallistes undulatus:: Investigating the potential influence of diet and environment on growth

We present detailed records of trace metals and carbon isotopes to understand siliceous spicule formation in the deep-sea lithistid sponge Corallistes undulatus Le vi and Levi, 1983 (Demospongiae: Corallistidae). X-ray analysis of two longitudinal sections removed from the lamellae of the cup-shaped sponge revealed 144 and 137 light and dark density band-pairs, respectively, within the siliceous skeleton. Four portions of silica were removed along one of the sections for silicon-32 (Si-32) dating in order to constrain the overall extension rate of the sponge. Although there was some variability in the 32Si data, the overall age established using these data indicated that the sponge was between 135 and 160 yr old. This agreed well with the counts of density band-pairs, indicating that these band-pairs represent an annual deposition of layers of silica in the desma skeleton. Links between silica deposition and growth (food supply) were established using the Delta(14)carbon (C) and delta C-13 signatures of organic material trapped with the spicule matrix and the zinc content of the silica. A carbon budget based on these results indicated that the amount of fresh, labile surface export organic carbon reaching C. undulatus was not sufficient to support its growth. The Delta C-14 results for organic carbon trapped in the silica desmas, deposited after the 1960s, supports this assertion; only a small atmospheric nuclear weapons ' bomb' spike was observed in the D14C data. Taken together, the Delta C-14, delta C-13, and trace-metal results all indicate that the organic carbon source to C. undulatus is likely to be a mixture of fresh, labile, surface-derived material and older, perhaps sediment-derived material, with the latter being dominant.