Large numbers of invertebrates were collected from the lower layer of seasonal ice in the nearshore Beaufort Sea, off the northern Beaufort Sea, off the northern coast of Alaska in spring 1980. Over 90% of the individuals found belonged to meiofaunal taxa. Although density within the ice was low compared to that typically found in sediments, it was comparable to the highest previous estimate from ... sea ice. Densities were lowest in samples taken in April and reached a maximum of around 50000 individuals m-2 in June. Nematodes were numerically dominant, but copepods and turbellarians were also abundant. Population structures of the 2 most numerous copepod species were examined and found to differ greatly. Cyclopina gracilis appeared to reproduce continuously during the study; both adults and young copepodites were always present. The population of Harpacticus sp. initially consisted of only juveniles; the growth fo a single cohort was observed. Harpacticus sp. mated in the ice, but gravid females did not appear during the sampling period. Although the ephemeral seasonal sea ice habitat would seem to be very different from typical habitats of benthic copepods, these two species did not appear to posses any special strategies for living there.