distribution and also slow down the horizontal distribution, because the plankton would be moving horizontally more slowly than the water. Plankton may carry radioactive materials from the deeper waters of the lagoons to the surface or even up onto the reefs and eventually to the islands by vertical migration. At Bikini it has been observed, for example, that these materials were picked up by the plankton in the deeper waters of the lagoon during the daytime. The concentrated radionuclides in the plankton were then transported to the surface by the diurnal vertical migration of these minute forms. At the surface, their presence at night caused the surface radiation content to increase measurably over the daylight readings. The fouling organisms on the bottoms of the ships and the plankton feeders on the reef became increasingly radioactive at night as the transport of the radioactive products continued. It can be said then that plankton may cause the distribution of radionuclides in the sea to be different from that which would be expected from the distribution by currents alone in the following respects: (1) a delay in the movement from the area of original contamination, (2) a slower down-current movement, (3) a limited dispersion up-current or beyond the currents' boundaries, (4) a greater vertical distribution, and (5) an over-all greater dispersion of relatively lower concentrations. Aquatic plants or algae maybe free-floating (as are the phytoplankton), attached to the reefs, or growing in the shallow water. Just as do land