A survey of iodine contents in Laminaria digitata

Laminaria digitata sporophytes sampled from eight European populations (five in Brittany, one in Helgoland, two in the Shetland Islands) were measured for their iodine levels. The average iodine contents were highest in late autumn and in winter (in the range 0.751.20% dw) and were lowest in summer (0.250.60%). Younger plants were richer in iodine, with maxima close to 5% of dry weight for plantlets. Tissuespecific differences in the rates of uptake of iodine correlated with haloperoxidase activity, but not with the iodine contents.