Biogenic debris from the pelagic tunicate, Oikopleura dioica, and its role in the vertical transport of a transuranium element |
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| Authors: | Gabriel Gorsky Nicholas S Fisher Scott W Fowler |
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| Institution: | International Laboratory of Marine Radioactivity, Musée Océanographique, MC 98000 Monaco |
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| Abstract: | The accumulation and retention of 241Am by the pelagic tunicate Oikopleura dioica were examined using laboratory cultures and radiotracer methodology. Animals (i.e., trunks and tails) and discarded empty houses accumulated Am from seawater, giving volume/volume concentration factors of 59±8 and 10±1, respectively. The half-time for retention of Am in empty labelled houses transferred to non-contaminated seawater was 29 h; the retention half-time of Am in houses discarded by larvaceans feeding on Am-labelled diatoms was 219 h; the half-time of Am in fecal pellets produced by animals feeding on a monospecific diet of diatoms was 134 h, and 247 h for fecal pellets from animals fed a mixed diet. Approximately 30% of filtered cells remained in houses after the houses were discarded. Sinking rates of discarded houses and fecal pellets were found to vary with temperature and size, ranging from 26–157 m day?1 (house) and from 25–166 m day?1 (fecal pellets). The ubiquity and abundance of appendicularians, together with their prodigious production of houses (e.g., 10±2 houses day?1 at 17°C for each experimental animal) point to their potential significance in the vertical transport of Am, and probably other reactive metals, to intermediate depths in the ocean. |
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| Keywords: | tunicates biogeochemistry fecal pellets sinking americium Mediterranean Sea |
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