A juvenile recruitment prediction model for Ruditapes decussatus L.) Bivalvia: Mollusca) Luis Chõ Âcharo, M. Alexandra Chõ Âcharo * Universidade do Algarve, UCTRA/CCMAR, Campus de Gambelas, P-8000 810 Faro, Portugal Received 18 May 2000; received in revised form 7 September 2000; accepted 16 October 2000 Abstract Despite the importance of larval abundance in determining the recruitment of benthic marine invertebrates and as a major factor in marine benthic community structure, relating planktonic larval abundance with post-settlement post-larvae and juveniles in the benthos is dif®cult. It is hampered by several methodological dif®culties, including sampling frequency, ability to follow larval and post-larval or juvenile cohorts, and ability to calculate growth and mortality rates. In our work, an intensive sampling strategy was used. Larvae in the plankton were collected at weekly intervals, while post-larvae that settled into collectors were analysed fortnightly. Planktonic larval and benthic post-larval/juvenile cohorts were determined, and growth and mortality rates calculated. Integration of all equations allowed the development of a theoretical formulation that, based on the abundance and planktonic larval duration, permits an estimation of the future abundance of post-larvae/juveniles during the ®rst year of benthic life. The model can be applied to a sample in which it was necessary only to measure larval length. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Ruditapes decussatus; Bivalve; Larval recruitment; Growth; Mortality; Recruitment model; Coastal system 1. Introduction In recent decades, the importance of the transition of larvae from planktonic to post-larval stages in the benthos has received increased attention. A benthic animal with a planktonic larval stage must survive and prosper in two different realms, making a transition to the plankton and back to the benthos Jackson, 1986). Thus, the transition of larvae from planktonic to benthic habitats exposes them to entirely new envir- onmental conditions within very short time period Gosselin and Qian, 1996). The early recruitment period, which includes settlement plus post-settlement survival, is often considered deterministic for overall recruitment success Roegner and Mann, 1995). In fact, while mortality factors may change during onto- geny, overall vulnerability decreases with increasing age and size Vermeij, 1972) and, therefore, is more intense for newly settled post-larvae. The importance of larval abundance in determining the recruitment of benthic marine invertebrates and as a determining factor in structuring marine benthic communities has been emphasised by several authors Gaines and Roughgarden, 1985; Minchinton and Scheibling, 1991; Miron et al., 1995). However, most of them monitored recruitment patterns with a coarse temporal resolution often months, as discussed by Grassle and Grassle, 1974; Maurer et al., 1979), and were unable to identify periods when structuring Fisheries Research 53 2001) 219±233 * Corresponding author. Tel.: 351-289-800-900; fax: 351-289-818-353. E-mail addresses: lchichar@ualg.pt L. Chõ Âcharo), mchichar@ualg.pt M. Alexandra Chõ Âcharo). 0165-7836/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0165-783600)00300-3