Effects of poecilogony and delayed larval emission on recruitment of Subantarctic population of Boccardia polybranchia (Polychaeta: Spionidae)

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 poecilogonous species exhibited adelphophagy where the females deposited eggs in capsules of which only 3-5% of the eggs undergo a normal development and fed on the remaining eggs. Type I larvae utilized their yolk reserves and fed on nurse eggs. After 8 d a second larval type was visible in the capsules. These Type II larvae presented a well developed and functional gut at the third setiger stage and never ingested any nurse eggs in the capsules. The consequences of this developmental pattern were important for recruitment. The number of hatching larvae was considerably reduced, but the protection in the capsules and the position of the capsules within the tubes ensured good local recruitment. Larval behavior was also modified with the nearly complete lack of a planktonic phase. Dispersal existed for a small number of Type II larvae but the general trend led to the formation of dense populations of up to 50,000 ind m -2 .