INFESTATION, POPULATION-DYNAMICS, GROWTH AND REPRODUCTIVE-CYCLE OF MYZOSTOMA-CIRRIFERUM (MYZOSTOMIDA), AN OBLIGATE SYMBIONT OF THE COMATULID CRINOID ANTEDON BIFIDA (CRINOIDEA, ECHINODERMATA)

The population dynamics of the symbiont Myzostoma cirriferum and the d ynamics of infestation of its host Antedon bifida were investigated at Morgat (Brittany, France) over a 5-year period. The larger the host, the greater the infestation. The infestation varies according to the s eason: it is maximum in winter, decreases in spring, and becomes stabi lized at a low level from summer to the next winter. The huge infestat ion in winter is due to the recruitment of young individuals into the population of M. cirriferum. That recruitment is independent of myzost ome reproductive activity (ovarian maturity, spermatophoral emissions, and egg layings are steady throughout the year), but may be linked to an increase in the comatulid feeding activity: in feeding more, comat ulids can catch more infestive-stage myzostome larvae. In spring, the infestation falls, which may be due to both the myzostomes' natural mo rtality and the appearance of amphipods on the hosts which may act as predators. From summer to the next winter, infestation stays stable, w hich can be explained by the equilibrium existing between the natural mortality of the myzostomes and their continuous reproduction. The lon gevity of M. cirriferum is estimated to be ca 6 months.