The effects of different stocking densities and some abiotic factors on cage culture of Gracilaria sp. (Rhodophyta, Gigartinales)

Abstract

Specific growth rates (% day^-1) and production rates (g m^-2 day^-1) of Gracilaria sp. reared in net cages on a bamboo floating raft from March 1989 to February 1990 were determined at different stocking densities (200, 250, 300 and 350 g 0.5 m^-2/net cage). Mean specific growth rates for the whole culture period were highest at stocking densities of 200 and 250 g 0.5 m^-2 (P < 0.05). Highest mean net production rate was obtained at a stocking of 250 g 0.5 m^-2, but was not significantly different from stocking densities of 300 and 350 g 0.5 m² (P < 0.05). Highest monthly mean specific growth rates and monthly mean net production rates for all treatments were obtained during March and November 1989 and February 1990. There were no significant differences (P > 0.05) in monthly mean specific growth rates and mean net production rates between the three peak months, although they were significantly different from the rest of the months (P < 0.05). Production was higher during the dry season. Correlation analysis showed that total rainfall was negatively correlated with specific growth rate and production rate. Salinity, temperature and pH were not correlated with specific growth rate and production rate.