At Belle Island the amounts of radioactivity in specimens of algae from different areas of the intertidal zone (Fig. 4) collected on the same day were compared. Table 4. An example is presented in Table 4. Gross beta activity of four species of algae collected from different areas of Belle Island on May 22, 1954. Values are expressed as thousands of d/m./g of wet tissue at time of collection. Species Area E-1 E-2 F-1 F-2 G Halimeda opuntia 478 375 633 674 621 Caulerpa urvilliana 735 - 704 455 503 Udotea indica - 2040 1320 1170 2060 Microdictyon sp. - 361 208 285 593 This table and similar data from other collection dates showed that the radioactivity of the algae from different areas was essentially the same. The variability in the radioactivity of five to ten specimens of Halimeda sp. from the same area was also determined for eighteen collections. The coefficient of variation, C (C = standard deviation ~ mean), varied from 12 to 65 per cent, the average being 35 per cent, an indication of great variability in the amounts of radioactivity in the samples collected from the same area. Similar conclusions were reached

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