Figure 1.

Life cycle of Gracilaria gracilis. The individuals are fixed to the rocky substrate via a perennial holdfast. The deciduous erect thalli decay after reproduction in late autumn and grow back from the holdfast in spring. Diploid tetrasporophytes produce haploid spores from meiosis that develop into dioicous male and female haploid gametophytes. Spermatia (non-flagellated male gametes) are released into the water column. After fertilization, the zygote is retained on the female and develops into a complex, macroscopic post-fertilization structure: the cystocarp. One fertilization gives rise to thousands of identical diploid carpospores that, after release and germination, grow into new tetrasporophyte individuals.