Physiological energetics of the ascidian Styela clava in relation to body size and temperature

The ascidian Styela clava is widely distributed in northern China and is thought to be important in the functioning of estuarine systems. This ascidian may experience highly variable physiological conditions, and its physiological responses to these are of interest considering its ecological role. This study presents data on the physiological parameters in relation to body size and temperature (12–28 °C) of S. clava. Respiration, excretion, feces, ingestion and absorption energy were positive related to size and its mass exponents (b-values) varied from 0.2930 to 0.7488. Respiration energy increased with increasing, but critical values were found at 20 °C for energy of ingestion and absorption, while 24 °C for energy in feces and excretion. At the range of 16–24 °C, the scope for growth, gross and net growth efficiencies of ascidians increased with increasing temperature. The energy budget equations of different sized ascidians were obtained at different temperatures. Excretion energy shared a minimal fraction in ingestion energy (1.30–2.47%), the ratios of feces energy and respiration energy to ingestion energy were 46.53–64.27% and 10.26–80.75%, respectively. The physiological data obtained in the present study indicated that S. clava could adjust its energy budget according to the environment and its physiological conditions to meet their nutritional and energetic demands. In the range of experimental temperature (12–28 °C), 16–20 °C was suitable for the rearing of S. clava to achieve optimum development, while deficient metabolic adjustment induced a negative scope for growth of S. clava at 28 °C.