BROUSSEAU: REPRODUCTION OF MYTILUS EDUL1S 



RESULTS 

 Reproductive Cycle 



Reproductively active individuals were encoun- 

 tered throughout the 2-yr study period with the 

 largest numbers occurring in December 1980; 

 January, April, May, and December 1981; and March, 

 April, and May 1982 (Fig. 2). In September 1980, 

 gametogenesis had begun in both sexes. Ripe 

 mussels were observed in the February samples and 

 by mid-April about 96% were gravid (Fig. 3). Spawn- 

 ing began in May and continued through the summer 

 with most of the gametes released in June. 



A similar spawning pattern was observed in 1981- 

 82, except that gametogenesis began 1 mo later, and 

 individuals with ripe gametes appeared in Decem- 



ber. Presence of a sizable number of ripe individuals 

 in the population during winter months suggests that 

 the spawning period in 1981-82 was earlier and less 

 defined than in the previous year. Although com- 

 pletely spent individuals were not present in any of 

 the samples until June 1982, the presence of partially 

 spawned mussels indicates that during the second 

 year of this study, "dribble spawning" may have 

 occurred during the winter and early spring. 

 Although no direct information is available on the 

 environmental factors, such as temperature and food 

 availability, it seems reasonable to assume that 

 annual variation in one or a combination of such fac- 

 tors was responsible for this difference in the timing 

 of gametogenic events. 



The GVF values for male and female M. edulis from 

 this population are given in Figure 4. During both 



INDIFFERENT 

 DEVELOPING 



Figure 3. — Proportions of Mytilus edulis with gonads in each developmental phase during 1980-82. Values for males and females are 



combined. 



o N 



1980 



MONTHS 



FIGURE 4. — Mean gamete volume frac- 

 tions ( solid line) and variance ( dotted line) 

 for Mytilus edulis. Values for males and 

 females are combined. 



735 



