DENSITY-DEPENDENCE IN POST-RECRUITMENT PROCESSES OF JUVENILE SPARIDS IN THE LITTORAL OF THE MEDITERRANEAN-SEA

While variability in recruitment of young reef fish is now recognised, the question remains how the variation in recruitment will contribute to determining assemblage structure. This has been the basis for an a ctive debate about whether patterns in abundance are determined by the supply of planktonic larvae or whether they result from competition ( for space, food, etc.) between potential recruits leading to density-d ependent recruitment. We tested population regulation of newly recruit ed juveniles of Sparidae in the north-western Mediterranean Sea. Recru itment of three species of Sparidae was followed over a three-month pe riod in each of two years to estimate the peak density of new recruits settling from the ocean, the rate of mortality occurring during the f irst three months after settlement, and the final density after three months. Sites and species were carefully chosen in order to avoid migr ation during the survey. Initial density of recruited larvae of Diplod us spp. varied among species and sites from 0.045 to 3.8 individuals p er metre of coastline. Mortality estimates also varied enormously. Bet ween 24.3% and 99.4% of the initial population disappeared within thre e months. Our survey demonstrated that both post-settlement mortality (r = 0.847; p < 0.0001; n = 18) and final density (r = 0.818; p < 0.00 01; n = 18) were correlated with density of recruitment and consequent ly that both pre-recruitment (larval phase) and post-recruitment proce sses regulated sparid populations of the Mediterranean Sea.