The photo-physiologica inhibited mechanism on typical HABs,Scrippsiella trochoidea, by seawater extraction of macroalga, Gracilaria Lemaniformis

Abstract

Macroalga, due to its high-harvesting yield, easily available, low-cost, and eco-friendly, become more and more favored tool-like alga for researchers. The method of control harmful algal blooms (HABs) by macroalga is an international study issue, and the water extract of seaweed have the advantage of full-time and all-location. While the most study were focused on the level of apparent growth, little was known about the photo-physiological inhibited mechanism in HABs by macroalga. In this study, the thecate dinoflagellate bloom microalga, Scrippsiella trochoidea, was co-cultured with different grams seawater extraction from fresh macroalga Gracilaria lemaneiformis under laboratory conditions photosynthetic oxygen evolution and Chlorophyll fluorescence techniques are used, to study the effects of the seawater extract of Gracilaria lemaneiformis on the photosystem II (PSⅡ) of red tide algae. The results are as follows: Compared with control, the biomass of S. trochoideain 0.6g/L treatment was higher, while the biomass in 1.2g/L, 2.4g/L and 4.8g/L treatment are lower, which shows the pattern of hormesis effect. Photosynthetic oxygen evolution rates (P max) were decreased with the increase of extract concentration, while the dark respiration rates (Rd) were converse. The J, I, P points in 0.6g/L treatment were higher than the control one, while J, I, P points in 1.2g/L treatment is lower. OJIP curve in 2.4g/L and 4.8g/L tend to be a straight line. The value of Wk, ABC/RC, TRo/RC, DIo/RC, Vj, φDo and Mo in 2.4g/L and 4.8g/L treatments was increased, while the value of fraction of OEC,φPo, Fv/Fo, ETo/RC, ψ0, and φEo was decreased. The inhibitory effects of the macroalga's sea water extraction on the microalga, according to the JIP-test and pigments contents, include a decrease in the number of active reaction centers, the blocking-up of the electron transport chain. This study suggests that water extraction of G. lemaneiformis is effective in inhibiting photophysiological activity of S. trochoidea, and thus be a potential 'tool alga' for controlling S. trochoidea blooms.