Abstract

The life history, reproduction and impact of fertilization on growth rate of Gracilaria domingensis (Kützing) Sonder ex Dickie were studied in vitro. The life history is of the Polysiphonia-type, and was completed in six months. Carpospores developed into plants which produced tetraspores in 60 days. The gametophytes originated from the released tetraspores became fertile after 101 days with a sex ratio of 1:1. Spermatangia were found in single deep conceptacles, verrucosa-type, as well as confluent ones, henriquesiana-type. Mature cystocarps have a conspicuous fusion cell and tubular nutritive cells formed from the gonimoblast to both pericarp and cystocarps floor. Non-fertilized female gametophytes showed a higher number of new apices during cultivation. Fertilized female branches grew similarly to the unfertilized branches during the first three weeks, but much slower from that time on. The reproductive cost, expressed as growth differential was around 55% smaller than the control.