REPRODUCTIVE-CYCLE AND ENERGETIC COST OF REPRODUCTION OF THE NEOGASTROPOD BUCCINUM-UNDATUM IN THE IRISH SEA

The annual reproductive cycle and cost of reproduction of the common w helk, Buccinum undatum L. (Gastropoda: Prosobranchia) were studied off Douglas, south-east of the Isle of Man. Sexual maturity was reached a t 60-70 mm shell length. Two years of laboratory observation and field data indicated an autumn to mid-winter breeding season. Egg-laying oc curred in the laboratory mainly between December and January, and hatc hing ofjuveniles between April and early May, 3-5 months after spawnin g. The cycles of testis and ovary development were very similar, espec ially during the breeding period. The annual energy invested in reprod uction was estimated to be at least 4.1 kJ m-2. The investment by fema les (3.84 kJ m-2 y-1) was much greater than by males (0.26 kJ m-2 y-1) .