Life history, reproduction and growth of Gracilaria domingensis (Gracilariales, Rhodophyta) from Brazil.

The life history, reproduction and impact of fertilization on growth rate o f Gracilaria domingensis (Kutzing) Sender ex Dickie were studied in vitro. The life history is of the Polysiphonia-type, and was completed in six mont hs. 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 d eep conceptacles, verrucosa-type, as well as confluent ones, henriquesiana- type. Mature cystocarps have a conspicuous fusion cell and tubular nutritiv e cells formed from the gonimoblast to both pericarp and cystocarps floor. Non-fertilized female gametophytes showed a higher number of new apices dur ing cultivation. Fertilized female branches grew similarly to the unfertili zed branches during the first three weeks, but much slower from that time o n. The reproductive cost, expressed as growth differential was around 55% s maller than the control.