Combined effects of biomass density and low-nighttime temperature on the competition for growth and physiological performance of Gracilariopsis lemaneiformis and Ulva prolifera

Abstract

In order to study combined effects of the biomass densities and low-nighttime temperature on the competition for growth and physiological performance of Gracilariopsis lemaneiformis (GL) and Ulva prolifera (UP), we mono- and co-cultured them with 1:1 and 1:2 biomass density for GL and UP (noted as CC1 and CC2 treatment, respectively) under three temperature conditions (16 °C: 16 °C for day and night period; 22 °C: 22 °C for day and night; 22–16 °C: 22 °C for day period while 16 °C for night period). Then the filtrate of G. lemaneiformis or U. prolifera addition experiments also was performed. Our results showed that: 1) When they were mono-cultured under three temperature conditions, the growth rate of G. lemaneiformis was inhibited at 16 °C while U. prolifera grown at 16 °C and 22–16 °C showed higher growth rate; 2) The growth rate of G. lemaneiformis was inhibited in the presence of U. prolifera while the growth of U. prolifera was promoted in the presence of G. lemaneiformis, but this increase was offset by the higher biomass density; 3) The addition of the pre-culture medium enhanced the growth of each other; 4) For mono-culture and CC1 treatment, the both the superoxide dismutase (SOD) activity of G. lemaneiformis and U. prolifera were enhanced at 16 °C, while both higher the soluble protein contents were observed at 22 °C. Further analysis indicated that low temperature, even only at dark period, was probably a more beneficial to U. prolifera than to G. lemaneiformis, U. prolifera has a strong inhibited influence on G. lemaneiformis mariculture, and the biomass density effects should not be ignored.