14 . S.VHTHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 



of C. nereostratttm are not shown in similar detail since full sea- 

 sonal, decalcified, and sectioned material is not available. How- 

 ever, it is clear from preliminary analyses that the patterns are 

 very much the same. 



Reproduction in Clathromorphum compactum 



Adey (1965) demonstrated the seasonally determined de- 

 velopment of sporangial conceptacles in C. compactum in the 

 Gulf of Maine, where conceptacles are initiated in early autumn 

 (September and October), reach maturity in midwinter, and are 



fully overgrown by late spring. The farther north C. compactum 

 plants grow, the later their reproductive maturity is; in northern 

 Labrador, most plants are at the peak of the reproductive cycle in 

 midsummer, the surficial conceptacles being full of ripe sporan- 

 gia (Figure 9; Table 1). Conceptacle initiation is likely controlled 

 by the photoperiod, with light rapidly diminishing in Septem- 

 ber and October; temperature is likely not a significant factor 

 as there is a considerable difference in temperature from south 

 (approximately 10°C ) to north (approximately 5°C) at this time. 



The developmental morphology of a typical sporangial con- 

 ceptacle of C. compactum from southern Labrador is shown in 



FIGURE 9. SEM images of typical C. compactum surfaces from different regions showing reproductive state during midsummer (see 

 Table 1 ). (A) Northeastern Newfoundland, conceptacles mostly grown in, but remain clearly visible. (B) Southern Labrador, conceptacles 

 ranging from immediately postmature to grown in. (C) Northern Labrador, conceptacles mostly fully mature; the low mound in the 

 lower center is a submature conceptacle with a conceptacle cap not fully broken out. (D) Conceptacle roof at larger scale; pores for exit of 

 the spores are mostly free of sporangial cap walls; a few dried pore plugs remain. During summer in the Gulf of Maine, conceptacle roofs 

 with visible pores are not found, and only faint conceptacle "ghosts" appear in 60%-70% of the population. Note the strong chiton 

 grazing marks in A and C and also in B, although somewhat grown out. 



