Studies on spore release and sporeling growth from carpospores of gracilaria foliifera (Forsskål) Børgesen var. Angustissima (Harvey) Taylor. I. Growth responses

Abstract

Optimal conditions for carpospore release in Gracilaria foliifera (Forsskål) Børgesen var. angustissima (Harvey) Taylor were found to be approximately 20°C in the dark or under low light. The highest sporeling growth rates observed, 0.22 doublings per day, occurred at 25.3°C at maximum light available (80 μE m −2 s −1) and at a salinity of 30 p.p.t. on a cross-gradient table. Maximal available light intensity approached saturation at the higher temperatures (22.1–27.9°C). Average growth rates of 0.16 doublings per day were observed at low light intensities (9 and 17 μE m −2 s −1). Phycoerythrin and chlorophyll a concentrations showed an inverse relationship to light intensity and to growth rate. Sporelings showed relatively wide tolerances to salinity, with a minimum of 0.03 doublings per day even in 5 p.p.t. A wide range of N:P ratios (8–28) supported maximum growth rates of 0.16 to 0.18 doublings per day. A short exposure of sporelings to water-saturated air increased growth rates, showing modest tolerance to the intertidal fringe habitat of the species.