Larval biology and benthic recruitment: New ideas on the role of egg-masses and modelling life-cycle regulation

The present study deals with the life-cycle strategies of Eupolymnia nebulosa (Annelida, Polychaeta, Terebellidae) which shows a characteristic geographical differentiation having free-spawning Atlantic populations and direct developing Mediterranean populations. The main questions of interest can be summarized as follows: How is the selection of larvae 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 point; (3) the development of laboratory experiments and (4) the use of comparative biology based on latitudinal transects. The control of dissemination and return to the area inhabited by adults was achieved by Mediterranean E. nebulosa by means of egg-masses. These structures per mit the coexistence of selective requirements in terms of size and shape 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 adjustment of biological and hydroclimatic events. To conclude, we propose a hypothesis to explain the year to year variability of benthic recruitment, 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 of larvae per egg-mass, and patterns of larval release from the egg-masses.