Population biology of the gastropod Olivella minuta (Gastropoda, Olividae) on two sheltered beaches in southeastern Brazil Marcelo Petracco * , Rita Monteiro Camargo, Daniel Teixeira Tardelli, Alexander Turra Depto. Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo (USP), Praça do Oceanográfico, 191, Cidade Universitária, São Paulo CEP 05508-120, SP, Brazil article info Article history: Received 11 December 2012 Accepted 17 October 2013 Available online 25 October 2013 Keywords: benthos beaches gastropod intraspecific relationships population dynamics abstract The structure, dynamics and production of two populations of the olivid gastropod Olivella minuta were analyzed through monthly sampling from November 2009 through October 2011 on two sandy beaches, Pernambuco (very sheltered) and Barequeçaba (sheltered) in São Paulo state (23  48’S), southeastern Brazil. On both beaches, samples were taken along five transects established perpendicular to the waterline. Parameters of the von Bertalanffy growth function were estimated for both populations from monthly length-frequency distributions. The production and turnover ratios were determined using the mass-specific growth rate method. The population on the less-sheltered Barequeçaba Beach was less abundant (120.02  22.60 ind m 1 ) than on Pernambuco Beach (3295.30  504.86 ind m 1 (SE)), which we attribute to the greater environmental stability of the latter. Conversely, the mean length, size of the largest individual, and body mass were higher at Barequeçaba than at Pernambuco. The significant differences in the growth of individuals and the mortality rate (Z) between the beaches suggest that density-dependent processes were operating at Pernambuco Beach. The production and P/B ratio at Pernambuco (12.12 g AFDM m 1 year 1 and 1.91 year 1 ) were higher than at Barequeçaba (0.82 g AFDM m 1 year 1 and 1.06 year 1 ). The difference in production can be attributed to the higher abundance on Pernambuco, while the higher P/B ratio resulted from the scarcity of smaller individuals in the intertidal zone of Barequeçaba. The P/B ratio estimated for the Pernambuco population is the highest found so far for sandy-beach gastropods. This study reinforces the theory that biological interactions are important regulators of sheltered sandy-beach populations. Future studies with multi-beach sampling are needed to better understand the life-history variations of O. minuta along gradients of degree of exposure of sandy beaches. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In the last decade, several studies have examined life-history traits of macrofauna populations in relation to different physical factors of sandy beaches. These studies were conducted mainly with crustaceans that live in the intertidal and supralittoral zones of exposed sandy beaches with different morphodynamic states (Gómez and Defeo, 1999; Defeo et al., 2001; Defeo and Martínez, 2003; Celentano and Defeo, 2006; Celentano et al., 2010; Defeo and McLachlan, 2011). The studies found marked differences in population structure and dynamics according to the beach morphodynamics. In general, the abundance, growth and survival rate of intertidal species increase from beaches with a more rigorous morphodynamic state (reflective) to a more benign state (dissipative), while supralittoral populations follow an inverse pattern (Defeo and Gómez, 2005; Defeo and McLachlan, 2005, 2011). In contrast to the considerable knowledge regarding the popu- lation ecology of the macrofauna of exposed sandy beaches (see Defeo and McLachlan, 2005), the study of the life-history traits of sheltered sandy-beach macrofauna is a historically neglected area of sandy-beach ecology (Cardoso et al., 2011; Mattos and Cardoso, 2012). Recently, a few studies have addressed the population dy- namics of macrofauna species on sheltered sandy beaches, most of them mollusks in southeastern Brazil (e.g., Denadai et al., 2004; Yokoyama, 2010; Mattos and Cardoso, 2012; Cabrini and Cardoso, 2012). However, there is no information on how the population parameters of mollusks respond to different degrees of exposure of the beaches (e.g., very sheltered versus sheltered sandy beaches). Gastropod mollusks are important components of the mac- rofauna of sheltered sandy beaches, generally as predators and/or * Corresponding author. E-mail addresses: mpetracco@uol.com.br, marcelopetracco@gmail.com (M. Petracco). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ecss.2013.10.015 Estuarine, Coastal and Shelf Science 150 (2014) 149e156