We studied fauna and species composition dynamics of Cladocera in 54 rock pools of Kandalaksha gulf islands (White sea) in the first ten days of August 2003-2005. We can distinguish two groups of Cladocera on the basis of their coexistence (Daphnia magna group and Polyphemus pediculus group). The first group used to inhabit high, acid and poor-mineralized pools, the second one used to inhabit more mineralized and alkaline pools. Cladocera species quickly disappear from one pools and appear in other ones. We observed two events which can cause species extinction: flow over of marine water during storms and appearance of vertebrate predator (three-spined stickleback) in the pool. Our data don’t let us distinguish cases of appearance of Cladocera species from resting studies and cases of species immigration in the pool.