Abstract. – This study deals with the analysis of the coleopteran assemblages in a beachdune system located on the Galician coast. In particular, we used experimental manipulation of algal wrack, i.e. artificial patches of Saccorhiza polyschides, to test hypotheses about influences on coleopteran assemblages inhabiting the upper shore level along an exposed sandy beach. Specifically, we tested that (1) abundance of colonizing individuals and species vary with the size of wrack patch and time, and (2) as a result, coleopteran assemblages also vary with patch size and time. Furthermore, responses could differ among sites because of their different environmental conditions. A total of 3 980 individuals belonging to 8 families and 18 species were collected. Tenebrionidae was the most abundant family followed by Staphylinidae and Hydrophilidae families, respectively. The tenebrionid Phaleria cadaverina (Fabricius, 1792) was the most abundant species within this family, with a total of 1 064 adults and 1 124 larvae. Phytosus spinifer Curtis, 1838 was the most abundant staphylinid species represented by 736 adults and 3 larvae. This study showed that coleopterans are very common colonizers in wrack patches on sandy beaches. Patterns of succession differed among species and colonization of patches was rapid, i.e. most species colonised patches on day 3. Coleopteran assemblages changed depending on patch size and time. Wrack may act as islands of food and/or habitat for several coleopteran species on sandy beaches. Cleaning activities on beaches used for recreational purposes might alter the diversity of coleopteran assemblages associated to wrack patches. Thus, for managerial and conservational purposes cleaning activities on beaches should be regulated.