Intraspecific regulation in the population densities of the intertidal gastropod Planaxis sulcatus(Gastropoda, Planaxidae) in the Suez Canal

Monthly monitoring of the intertidal gastropod (Planaxis sulcatus) population in the Zuez Canal rocky shores revealed a decrease in the adult abundance during recruitment peaks. This produced a periodical imbalance on the adult densities and reflect the regulatory roles of recruits on Planaxis population. Results of experimental manipulation to investigate these role indicated that an increase in the overall densities reduced tha rate of individual growth and declined the adult abundance. The results agreed with the hypothesis that recruits and juveniles have a competitive advantage over adults as they are small and require less energy to survive. It is postulated, therefore that, the rapid decline in the individual numbers during intense competition could be one of the regulatory agents in the Planaxis population dynamics in the Suez Canal.