LARVAL BIOLOGY AND BENTHIC RECRUITMENT - NEW IDEAS ON THE ROLE OF EGG-MASSES AND MODELING LIFE-CYCLE REGULATION

The present study deals with the life-cycle strategies of Eupolymnia n ebulosa (Annelida, Polychaeta, Terebellidae) which shows a characteris tic geographical differentiation having free-spawning Atlantic populat ions and direct developing Mediterranean populations. The main questio ns of interest can be summarized as follows: How is the selection of l arvae achieved in their respective communities ? What are the origins of year to year fluctuations? How can the structure and functioning of a life-cycle be understood? In this paper, we propose a comprehensive approach to the above questions based on several global strategies: ( 1) the analysis of the physical features of water masses: currents and hydroclimatic parameters:, (2) the use of an autoecological view poin t; (3) the development of laboratory experiments and (4) the use of co mparative biology based on latitudinal transects. The control of disse mination and return to the area inhabited by adults was achieved by Me diterranean E. nebulosa by means of egg-masses. These structures per m it the coexistence of selective requirements in terms of size and shap e of sediment grains - which define a large potential zone for larval settlement - with a spatially limited area of adult distribution. Some important consequences, like the homogeneization of size range of E. nebulosa juveniles during the first benthic stages, emerged from the a djustment of biological and hydroclimatic events. To conclude, we prop ose a hypothesis to explain the year to year variability of benthic re cruitment, together with a diagram of the processes involved using the following parameters: temperature patterns during the spawning period , distribution of egg-masses (number and date of appearance), number o f larvae per egg-mass, and patterns of larval release from the egg-mas ses.