THE EMISSION OF PRECOCIOUS LARVAL STAGES OF EUPOLYMNIA-NEBULOSA (POLYCHAETA, TEREBELLIDAE)

Numerous egg masses of Eupolymnia nebulosa were often found in breedin g grounds outside the Laboratoire Arago, in 1991, during the reproduct ive period, presenting 4 peaks from mid-March to the beginning of June . Cocoons were counted in a 30 m2 working area. Larval emergence from cocoons placed in aquariums was monitored by regular countings every 4 hours until complete depletion. Results emphasize the importance of t emperature, light and particularly the larval density within the cocoo ns, on larval output. Emission from cocoons occurs mostly in the diurn al phase. Temperature acts on the larval development speed and thus co ntrols the larval stage as the larvae leave the cocoon. These variatio ns lead to a first emissive spawning, with numerous free swimming stag es, followed by 3 retention spawnings showing limited numbers of eggs with increased brooding within the egg masses.