The biology of the host-specific epiphytic red alga Ceramium codicola and some other epiphytes of Codium spp. in British Columbia

Field and culture studies have been carried out with the epiphytic red alga, Ceramium codicola J. Agardh, with the objective of determining what factors in its biology cause it to be limited to growth on one host plant, Codium fragile (Suringar) Hariot. A survey of epiphytes of C. fragile and C. setcheIIii confirm the absence of C. codicoIa on C. setcheIIii and shows that C. codicola is the most abundant epiphyte on C. fragiIe. More species of epiphytes were present in wave sheltered areas. C. codicoIa was not present in samples from the Strait of Georgia. In culture, C. codicoIa grew to reproductive maturity apart from C. fragiIe from spores, but the life history was not completed. The presence of living or extracted C. fragiIe or C. setcheIIii did not promote germination, growth or reproduction of C. codicola, and typically inhibited it. C. codicoIa did not grow well at temperatures above 15°C in culture; C. fragiIe, Ceramium pacificum and C. gardner i grew weII at 10-18°C. Rhizoids of C. codicola have bulbous tips, which appears to be genetically determined. Substratum can affect later development of these rhizoids, which may obscure the bulbous nature of the rhizoid tips. C. codicoIa is unable to produce digitate holdfasts on its rhizoid tips, as was observed in other Ceramium spp. , and may only be able to attach by entangling its rhizoids in loosely constructed substrata such as Codium spp. C. setcheIIii is not suitable because it is too compact, and penetration of rhizoids is inhibited. Field studies show that C. codicoIa is reproductive throughout the year, although reduced in the winter. Thallus length was also reduced in the winter. In addition, thalIi were longer in wave sheltered sites, and longer in the upper regions of their intertidal distribution. Male and female gametophytes and tetrasporophytes of C. codicola exhibit a hetermorphism in branching pattern. Gametophytes differ from tetrasporophytes by having more primary branches and larger angles of branching. Females differ from males by having a higher degree of proliferous branching, resulting in a higher number of primary branches and a higher branching ratio. Branching pattern in females may be the result of continued growth of involucral ramuli, and it may optimize reproductive potential.Science, Faculty ofBotany, Department ofGraduat