Some aspects of the growth of Gracilaria birdiae (Gracilariales, Rhodophyta) in an estuary in northeast Brazil

The agarophyte Gracilaria birdiae Plastino & Oliveira was cultivated under field conditions in an estuary over a 6-month period. Biomass production varied significantly (p < 0.01) and ranged from 900.0 to 3537.0 g m(-2) with a mean of 2124.4 +/- 1004.36 g m(-2) over the cultivation period. The epiphyte-biomass varied from 64.7 to 313 g m(-2), with maximum values observed in July. Relative growth rate (RGR) of G. birdiae varying from -0.59 to 4.67% day(-1), with a maximum mean observed in July. Correlation analysis showed that RGR was positively correlated with epiphyte-biomass (R-Pearson=0.69; p < 0.01) and negatively correlated with salinity (R-Pearson=-0.41; p < 0.05). These correlations were used in a mathematical regression model to estimate the growth of Gracilaria in an estuary. The regression model explained 61% of RGR variability demonstrating that growth rates of Gracilaria were directly related to the variables salinity and epiphytes. The model was developed to help to predict production at a cultivation site in order to evaluate its suitability for Gracilaria cultivation.