A study about composition, relative abundance and densities of peracarid populations associated to worm reefs of P. caudata (Kröyer, 1856) from Caiobá Beach, Matinhos, State of Paraná (25º51'S and 48º 32'W) was carried out. Monthly samples were obtained from August/1997 to July/1998. The density was calculated as the number of individuais per liter of worm reef. Three amphipod and three isopod species were obtained. The total density of the amphipod populations varied from 3.85 ind./l (July) to 70.56 ind./l (December) and that of the isopod from 0.25 ind./l (May) to 11.73 ind./l (March), The annual fluctuation of the amphipod densities was closely related to the weight fluctuation of the associated algae. The most numerous amphipod species was Elasmopus pectenicrus (Bate, 1862) followed by Hyale media (Dana, 1853) and Ericthonius brasiliensis (Dana, 1853). The isopod Paradynoides brasiliensis Loyola e Silva, 1960 was the most numerous followed by Excirolana armata (Dana, 1852) and Dynoides castroi Loyola e Silva, 1960. All amphipods and two isopod species were considered as constant species and they showed continuous breeding all year round. The occurrence of males, females (including ovigerous ones) and juveniles in the most amphipod and isopod populations in the present study indicates that these peracarids perform a complete life cycle within the Phragmatopoma caudata reefs. These constitute an alternative substrate to peracarids living on phytal and sandy habitats.
Peracarids; composition; Phragmatopoma caudata; Matinhos; Paraná