Larval Release from the Egg Mass and Settlement of Eupolymnia Nebulosa (Polychaeta, Terebellidae)

The study of distribution and abundance of soft-substrate organisms can be examined by the recruitment mechanisms of the species involved. A study was carried out on Eupolymnia nebulosa (Polychaeta, Terebellidae), starting from the release of larvae from the egg mass through the initial tube formation. The liberation of larvae, extending over 10 days, was counter-balanced by a marked synchrony at the time of settlement which occurred over a 2-day period for nearly 70% of the larvae. Despite the morphological differences present at the time of liberation, settlement took place at the same morphological stage. The duration of the planktonic life varied in relation to the time of release from the egg mass. The larvae were provided with sufficient energy reserves to reach the first benthic stage. At this point, the most essential requirement is the construction of the first tube. Later, two basic requirements arise: food, and material for the prolongation of the tube. Both are satisfied by input from sedimentation. The synchronized settlement period caused a negative inter-individual effect, which tended to distance the individuals from each other, resulting in an even distribution pattern.