EFFECTS OF POECILOGONY AND DELAYED LARVAL EMISSION ON RECRUITMENT OF SUBANTARCTIC AND TEMPERATE POLYCHAETE POPULATIONS
Duchêne, J.-C.
Laboratoire Arago, BP 44, F-66651, Banyuls Sur Mer, France
Populations of the spionid polychaete Boccardia polybranchia were monitored for several years in the intertidal sediments of Kerguelen Island in the subantarctic province. This shallow water poecilogonic species presents adelphophagy: the females place eggs into capsules and only 3-5% of the eggs achieve a normal development and feed on the remaining nurse eggs. Type I larvae feed on vitellus reserves and on nurse eggs. After 8 days a second larval type is visible in the capsules. These Type II larvae present a well developed and functional gut at 3 setiger stage. The consequences are important for the recruitment. The number of hatching larvae is considerably reduced, but the protection in the capsules and the position of the capsules within the tubes insure a good local recruitment. Larval behaviour is also modified with a nearly complete lack of planktonic phase. Dispersal exists for a small amount of Type II larvae but the general trend leads to the formation of dense patches of up to 50,000 individuals/m². This type of reproductive adaptation, involving a considerable reduction or a complete disappearance of the planktonic phase, is developed in the archipelago. Comparisons are made with populations of terebellid worms in the same area and in different thermal environments: modalities of retention within egg masses and corresponding early recruitment is analyzed. Initial influence of reproductive pattern and brood protection is discussed for the population dynamics of Boccardia polybranchia (Spionidae), Thelepus extensus (Terebellidae, subantarctic populations) and Eupolymnia nebulosa (Terebellidae, temperate population).