PRIMARY RESEARCH PAPER Do the crabs Goniopsis cruentata and Ucides cordatus compete for mangrove propagules? A field-based experimental approach Siel Wellens • Leonardo Sandrini-Neto • Mercedes Gonza ´lez-Wangu ¨ emert • Paulo Lana Received: 1 December 2014 / Revised: 2 March 2015 / Accepted: 3 March 2015 Ó Springer International Publishing Switzerland 2015 Abstract Mangroves are under threat worldwide by deforestation, overexploitation and climate change. The availability and consumption rates of propagules influence mangrove recruitment and can play a major role in their viability and restoration potential. We assess the potential trophic competition between Goniopsis cruentata and Ucides cordatus, two domi- nant crab species in the New World, by experimentally comparing herbivory levels between forest stands with varying crab abundance. We hypothesize that her- bivory rates (HR) of G. cruentata will be lower in mangroves where it coexists with U. cordatus than in mangroves where U. cordatus is absent. The removal of Rhizophora mangle propagules was very rapid, and HR were overall high and increased through time. However, HR did not differ significantly between mangroves with and without the potential trophic competitor U. cordatus. Our study did not support previous literature indications of food competition between these two crab species, which seem to have developed strategies for competition avoidance. Keywords Propagule predation  Trophic competition  Mangroves  Crabs  Rhizophora mangle Introduction Mangroves are highly productive coastal ecosystems that protect land against coastal erosion, provide forest products and act as major carbon sinks (Manson et al., 2005; Dittmar et al., 2006; Alongi, 2007; Walters et al., 2008). Tree litter, made up mainly of leaves and propagules, provides a high proportion of local production. Herbivores and detritivores which con- sume and burrow plant litter promote nutrient recy- cling in mangrove soils (Robertson, 1986; Robertson & Daniel, 1989; Camilleri, 1992; Skov & Hartnoll, 2002; Alongi et al., 2005). The main consumers of fallen leaves and propagules are crabs, which are often considered ecosystem engineers because of their role in nutrient dynamics and habitat modification (Schories et al., 2003; Cannicci et al., 2008; Lindquist et al., 2009). The grapsid Goniopsis cruentata (Latreille, 1803) and the ucidid Ucides cordatus (Linnaeus, 1763), hereafter referred to by genus, are dominant crab species in the lower intertidal of New World Atlantic mangroves (Wiedemeyer, 1997). Their distribution Handling editor: K. W. Krauss S. Wellens (&)  L. Sandrini-Neto  P. Lana Laboratory of Benthic Ecology, Centre for Marine Studies (CEM), Universidade Federal do Parana ´, Av. Beira Mar s/n, Pontal do Parana ´, Parana ´ 83255-976, Brazil e-mail: siel.wellens@gmail.com M. Gonza ´lez-Wangu ¨emert Centro de Cie ˆncias do Mar (CCMAR), CIMAR- Laborato ´rio Associado, Universidade do Algarve, Gambelas, 8005-139 Faro, Portugal 123 Hydrobiologia DOI 10.1007/s10750-015-2245-x