Population structure and species dynamics of Spisula solida, Diogenes pugilator and Branchiostoma lanceolatum along a temporalespatial gradient in the south coast of Portugal M. Dolbeth * , I. Viegas, F. Martinho, J.C. Marques, M.A. Pardal Institute of Marine Research (IMAR), c/o Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal Received 8 March 2005; accepted 1 August 2005 Available online 29 September 2005 Abstract The population structure, dynamics and distribution of Spisula solida, Diogenes pugilator and Branchiostoma lanceolatum, common species in the south coast of Portugal, were studied in a spatialetemporal manner in order to understand the influence of cross-shore sediment transport and anthropogenic activities. Spisula solida is harvested commercially, whereas D. pugilator and B. lanceolatum are non-target species, with little information available on the population dynamics of these species. The study was performed in 2001e2002, and along a gradient of 100e5000 m from the coastline, corresponding to a depth gradient of between 1 and 32 m deep. Spisula solida was distributed preferentially at 3e12 m deep, and its distribution appeared to be influenced seasonally by the cross-shore sediment dynamics. Results suggested benthic re- cruitment in June. Some recruitments had no expression (year 2001) since adults were not present, which seems to be a direct impact of clams’ fisheries. Diogenes pugilator showed preferential distribution at shallow depths, from 1.3 to 8 m. Results suggested recruitments every 4 months, in June, February and October. Branchiostoma lanceolatum showed the widest distribution, from 7 to 26 m deep. Recruitment seemed to start in June until October, when it attained an abundance peak of juveniles. For both non-target species no clear effects of the cross-shore dynamics or the clams’ fisheries impact were visible. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Spisula solida; Diogenes pugilator; Branchiostoma lanceolatum; population dynamics; hydrodynamics; fisheries 1. Introduction Information on species’ spatial and temporal distribution is important for the understanding of organism’s interactions with each other and the environment (Dauvin et al., 2004). In marine soft sediments, physical disturbance seems to be a key factor controlling the spatial and temporal compositions of the populations inhabiting those areas (Dernie et al., 2003). This disturbance may be naturally induced, such as waves and tide impacts (Snelgrove et al., 1998; Hewitt et al., 2003), but may also be due to anthropogenic perturbations, such as fishing (Chı ´charo et al., 2002a,b; Gaspar et al., 2002; Dernie et al., 2003) and dredging activities (Sarda ´ et al., 2000). At a smaller scale, complex biological interactions, which in turn control sediment properties, also play an important role in regulating patterns of the biota (Snelgrove et al., 1998; Reise, 2002; Hewitt et al., 2003). In the south coast of Portugal (Algarve), the mean wave en- ergy in the Algarve is considered low to moderate (Sa ´-Pires et al., 2002). Seasonally this energy may increase, mainly due to stormy episodes in winter (Sa ´-Pires et al., 2002), which may induce cross-shore sediment transport, from which the offshore transport may result in beach erosion (Rey and Bernardes, 2002). In order to understand these hydrodynamic seasonal differences, their impacts on the sediment transport and on the benthic subtidal communities, a survey took place * Corresponding author. E-mail address: mdolbeth@ci.uc.pt (M. Dolbeth). 0272-7714/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2005.08.006 Estuarine, Coastal and Shelf Science 66 (2006) 168e176 www.elsevier.com/locate/ecss