CURRENT ADVANCES AND TRENDS IN POLYCHAETE BIOLOGY AND ECOLOGY FROM PLANKTONIC LARVAL STAGES
Bhaud, M. R.
Observatoire Océanologique de Banyuls, University P. and M. Curie-CNRS, BP 44, 66651 Banyuls-sur-mer Cedex, France.
Numerous fields of research are based upon the study of the planktonic larvae of polychaetes. These include the reproductive activity of adults from the larval calendar, the identification of hydrological and climatic conditions for benthic life, the interannual fluctuations of benthic populations, the transfer of energy between the plankton and the benthos, settlement conditions at the benthic stage, reproduction of high latitudinal benthos, biogeographic implications of larval dispersion, and larvae and evolutionary processes. From this list, it can be clearly seen that in dealing with planktonic larvae, the other part of the life cycle associated with development in the sediment or hard substrates of the benthos must also be studied. Consequently, a study of larvae provides a means to obtain results at the scale of the whole life cycle. Examples of such integration will be provided. Another branch of research concerns the more and more frequently observed links between physical structures and behavioural characteristics of larvae, with the consequential effects on the limitation of space occupation. Along with the paradigm of passive dispersal, must be substituted the idea of the controlled occupation of space. Two consequences arise: a) A difference must be drawn up between the potential for dissemination of larvae and real adult area. Based on Atlantic Ocean results, proof will be provided that larvae, in spite of their ability to cross the ocean, do not bring about the panoceanic presence of adults. b) If species develop a means for the spatial control of larvae, then one consequence of this is that the spreading of the planktonic phase becomes a particularly cumbersome process. Thus, an action of the selective pressure should be the gradual reduction of the planktonic larval stage.