Culture and field studies on the growth and reproduction of Gracilaria species in the Maritime provinces of Canada

Gracilaria sp, in the Maritime Provinces demonstrated a Polysiphonia - type of life history in culture. A 1:1 ratio of males to females was found for plants originating from tetraspores. Reproductive maturation of plants occurred in 8-10 wks following spore germination, Detached plants showed the greatest reproductive potential, A salinity of 25-30 °/oo, was favorable for growth, Temperature range for optimum growth of sporelings (24°-28°C) was above that for mature plants (20°~25°C) although the lower and upper temperature limits for growth were similar (15°-16°C and above 30°C, respectively). Mature plants and month-old sporelings were cold temperature (5°C) tolerant. Saturating light levels for growth of sporelings and their total light energy tolerance range were lower than those found for mature plants. Growth of mature plants in aerated culture medium followed the standard microbial growth curve where k=0.24 during the exponential phase. An attached Gracilaria sp. population was present at Barrachois, N. S. in a narrow, sharply defined zone at 2 m depths. Growth was maximum during July and ' August, the period of maximum population reproductivity. Growth declined as the population senesced in late August, Acutal fertility ratios indicated that fertile tetrasporophytes and carposporophytes were abundant in July and August, respectively. A potential fertility ratio of 1:1 was found for males and females at the end of July. Reproductive maturation of sporelings transplanted in the field was similar to that found in culture.