ABSTRACT. DECAPOD CRU STACEANS FROM ROCKY SHORE AT FAROL ISLAND, MAn-NHOS, PARANÁ , BRAZIL . I. TEMPORAL DISTRIBUTION OF POPULA nON DENSITI ES. A study of the temporal distribution of the decapod populations from a rocky shore at Farol Isle, Matinhos, State ofParaná, Brazil (25°51'S e 48°32'W) was carried out. The rocky shore is 13m wide when the tidal levei is zero meter and about 8° incJination. ln the supralittoral, the rocky basins is mostly covered by a layer of litter com ing from the telTestrial environment. ln the midlittoral and upper infralittoral, the rocky slope is overlayed by boulders and pebbles and they constitllte a hi ghly complex environment ofcrevices, holes and concavities; the underlayer pebb les are embedded in sand, gravei and mudo ln the infralittoral fringe, macrocospic algae grow as a continuous bel!. Eight samples were taken by hand, monthly, from May-90 to April-91: two [rom sllpra littoral, four from midlittoral and two from infralittoral fringe. The density was calculated as number ofindividuals per cubic meterofpebble pi les. The air temperature osci llated from 13.0°C (May-90) to 27.0°C (March-91), the surface water temperature from 16.0°C (J uly-90) to 28.0°C (February-9 1) and salinity fro m 6.7%0 (November-90) to 29.4%0 (Jul y-90). There were registered 27 species ( 14 brachyuran crabs, 5 anomuran crabs and 8 caridean). The total density of decapod varied from 309.28 ind.m-J (June-90) to 1,483.22 ind.m-J (July-90). The density osci llated according to the temperature or salinity fluctuation on ly in three species. High densities were correlated to the breeding months in four species. Pelrolislhes arma/us (Gibbes, 1850) was the most numerous spec ies and its density oscillated from 111.76 ind.m-J (Augllst-90) to 668.25 ind.m-J (March-91). Eleven species occurred constantly (at least in 8 months), among whi ch, tive had a continuous breeding ali year round: Synalpheusfri/=l11l1e/leri Coutiere, 1909, Alpheus bouvieri A. Milne Edwards, 1878, Menippe nodifrons Stimpson, 1860, Pilumnus dmypodus Kingsley, 1879 and Pelrolislhes arma/uso Armases allgus/ipes (Dana, 1852, Pachygrapsus /ransversus (G ibbes, 1850) and Panopeus occiden/alis (Sa ussure, 1857) showed ovigerous females during lhe warm months, when the surface water temperature was equa1 or above 24°C, wh i1 stPanopeus americanlls Saussure, 1857 and Eurypanopeus abbrevialus Stimpson, 1860, eq ual or above 20°C. Despite of the constant occurrence of the porcelain crab Pelrolislhes galalhinus (Bosc, 180 I), it was not possible to infer its breeding period due to lhe absence of ov igerous fema les and the presence of juveni1es only in a few samples.