Ecological studies for harvesting and culturing Gymnogongrus furcellatus (Rhodophyta,Gigartinales) in Central Chile

Every year, several hundred tonnes of dry Gymnogongrus furcellatus are exported from Chile for carrageenan production. The present study provides ecological information for rational harvesting practices, including an understanding of the effects of environmental factors on growth. Field results indicate that the species is abundant in areas where disturbing factors do not destroy the crustose base of the plants, which can survive sand burial, but is grazing sensitive. In central Chile the erect axes have a clear seasonal pattern of growth which, as extrapolated from laboratory experiments, is most affected by seasonal changes in quantum dosage and photoperiod. Laboratory experiments show that vitamins and CO₂ additions also influence growth rates significantly. Field data indicate that harvesting in central Chile should be done bi-monthly, within the six most productive months of the year and be stopped before March, when the female gametophytes become fertile. Hand picking is the least destructive harvesting method. Even though the daily growth rate of the species could be raised to 7% in laboratory experiments, tank cultivation appears uneconomical. The cost of some of the factors required for the growth of this species, such as daily vitamin additions, aeration and CO₂ supplements, are unlikely to be recovered by the 25% average carrageenan content of this species. In addition, the high light requirements of the species would restrict culture to only 6 months a year at these latitudes. Therefore adequate management of the beds is required for sustained production.