Abundance patterns of intertidal caprellids associated with the alga Corallina elongata were studied along the Iberian Peninsula. Nineteen stations were selected. The Mediterranean coast showed higher seawater temperature and conductivity and lower dissolved oxygen and turbidity than the Atlantic coast. Cover of C. elongata was negatively correlated with seawater temperature and decreased towards the Mediterranean sites. Number of caprellid species and abundances were higher in stations in the Strait of Gibraltar, probably related with the currents' dynamic around this area. In general, caprellids associated with C. elongata were more abundant along the Mediterranean than along the Atlantic, in spite of the lower algal cover in Mediterranean stations. Caprella hirsuta and C. liparotensis were restricted to the Mediterranean coast whereas C. penantis was only found in the Atlantic and the Strait of Gibraltar. Although C. grandimana has been reported along the Mediterranean, its presence on Corallina elongata was restricted to the Strait of Gibraltar. Oppositely, Caprella liparotensis, which usually inhabits Atlantic and Mediterranean intertidal ecosystems, was only present in the Mediterranean and did not coexist with C. penantis along the Atlantic. Probably, competence process among C. grandimana, C. hirsuta, C. liparotensis and C. penantis are regulating the distribution patterns on the intertidal alga Corallina elongata. On the other hand, canonical correspondence analysis showed a clear preference of Caprella penantis at sites with high oxygen concentrations, whereas C. hirsuta was mainly influenced by higher temperature and conductivity.