Memorization of nuclear atmospheric tests by rhizomes and scales of the mediteranean seagrass Posidonia oceanica (Linnaeus) Delile

Determination of the age of rhizome sections of Posidonia oceanica (Linnaeus) Delile (Potamogetonaceae) by the examination of their dead leaf scales (lepidochronology), makes it possible to cut out the rhizomes in precisely dated 1- or 5-year sections. With increasing age of the section, the annual section length and the C:N ratio increase, while the dry weight per unit length and the ratio of dry weight:ash weight decrease. At a site where the only significant ¹³⁷Cs contamination can be ascribed to global nuclear fallout bombs, the activity of ¹³⁷Cs was measured i n 5-year age groups of rhizomes and scales separately. The maximum activity of ¹³⁷Cs in scales occurred in groups produced between 1960 and 1964, a period during which a peak of activity occurred in fallout. The distribution of ¹³⁷Cs activity in rhizome age groups indicates an apparent lag, perhaps owing to transport of material in the rhizome. In situ dead rhizome scales of P. oceanica thus constitute a memory, at least 30-years long, of an environmental chemical pulse. Posidonia oceanica could prove a valuable tool for marine-pollution surveys.