ORIGINAL ARTICLE Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil Maikon Di Domenico 1,2 , Paulo da Cunha Lana 2 & Andre ´ R. S. Garraffoni 3 1 Post-graduate Programme in Biological Sciences, Zoology, Universidade Federal do Parana ´ , Parana ´ , Brazil 2 Benthic Laboratory, Centre for Marine Studies, Universidade Federal do Parana ´ , Parana ´ , Brazil 3 Biological Sciences Department, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Minas Gerais, Brazil Problem Beaches are highly dynamic environments that have their structure and topography determined by granulometric characteristics and hydrodynamic processes, such as wave regime, tides and currents. Beaches were classified by Ko- mar (1998) and Short (1999), according to their morpho- dynamic features, as ‘reflective’ (with larger grain diameter, absence of surf zone, and ascending and frontal waves); ‘dissipative’ (with fine sediments, extensive surf zone, spilling breaker waves and circulation currents) and ‘intermediate’, beaches in the midst of these two extremes, presenting plunging and spilling breaking waves (Komar 1998; Short 1999). The occurrence and distribution of dominant meiofa- unal groups in sandy beaches, such as nematodes and co- pepods, are clearly correlated to beach morphodynamics, but also depend on biological interactions and environ- mental alterations generated by processes of urbanization and tourism (Moellmann & Corbisier 2003; Rodrı´guez et al. 2003; Gheskiere et al. 2005, 2006; Kotwick et al. 2005; Moreno et al. 2006). As a rule, interstitial fauna is more representative in reflective beaches than are macro- fauna and bacteria. The environmental optimum for Keywords Beach morphodynamics; Brazil; density; dissipative; distribution patterns; diversity; exposed beach; interstitial polychaetes; meiofauna; reflective; sandy beach. Correspondence Maikon Di Domenico, Laborato ´ rio de Bentos, Centro de Estudos do Mar, Universidade Federal do Parana ´ , Avenida Beira Mar s/n, Balnea ´ rio Pontal do Sul, CEP 83255-000, CP 50002, Pontal do Parana ´ , Parana ´ , Brazil. E-mail: maikondidomenico@terra.com.br Accepted: 27 May 2008 doi:10.1111/j.1439-0485.2008.00255.x Abstract This study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Parana ´ (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and sum- mer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sedi- ment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO 3 , chlorophyll a, omega indexes, tempera- ture and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon’s diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that poly- chaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P < 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal var- iability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes. Marine Ecology. ISSN 0173-9565 Marine Ecology 30 (2009) 47–62 ª 2008 The Authors. Journal compilation ª 2008 Blackwell Publishing Ltd 47