Comparative Studies On The Ecophysiological Characteristics Of Two Green Tide Macroalgae And Their Different Responds To Typical Environmental Changes Of Yellow Sea Green Tide

Yellow Sea green tide occurred almost every year from2007to2011in coastalChina and Ulva prolifera （Müller） J. Agardh was identified as the causativemacroalgal species. Another species observed in the bloom area was U. intestinalis,which co-occurred with U. prolifera and was recorded as the green tide formingspecies but not the causative one in this bloom area. The free-floating life form andthe ephemeral bloom then diminishing strategy of U. prolifera, and attaching and thepersistence of U. intestinalis can be observed in the highly dynamic offshore area ofQingdao during the Yellow Sea green tide although they have very similar taxonomicstatus. The aim of this thesis is from comparing the differences of ecophysiologicaltraits of these two co-occurring Ulva macroalgae to bring light on the possibleexplanation for these observed phenomena correlating with their different naturalprocesses.The photosynthetic capacities, defense systems and nutrients absorptioncapacities of these two green tide macroalgae were comparatively determined underfield investigation and controlled laboratory conditions. The main methods and resultswere that:1. By selecting relative growth rate, Fv/Fm as photosynthetic capacity parameterand T-AOC as defense system parameter of these two macroalgae, the orthogonaldesign was used to investigate their responds to environmental factors（temperature, irradiance, salinity and pH value）. Results showed that temperature,irradiance, salinity had a significant effect on physiological characteristics ofthese two macoalgae, but not pH value. Fv/Fm as photosynthetic capacityparameter and T-AOC as defense system parameter were sensitive toenvironmental factor changes （temperature, irradiance, salinity）. The most suitable combination after the orthogonal experiment was: temperature （20℃）,salinity （30PSU），irradience (60μmol photons.m^-2.s^-1).2. The photosynthetic capacities in-situ during the Yellow Sea green tide （June,2010） and after lab acclimation of these two macroalgae were comparativelydetermined by chlorophyll fluorescence. Results suggested that higherphotosynthetic capacity in U. prolifera largely contributes to its free-floating lifeform. Compared with co-occurring attached U. intestinalis, free-floating life formprevented U. prolifera from sinking out of euphotic zone. In addition to moreefficacious photoprotection, the favorable oceanographic conditions and highnutrient levels in the Yellow Sea can support the floating U. prolifera growingand aggregating to form a green tide.3. The antioxidant systems in-situ in the late phase of Yellow Sea green tide （earlyAugust,2010） and after lab acclimation of these two macroalgae werecomparatively determined. Results suggested that U. prolifera was moresusceptible than U. intestinalis to the harsh environmental changes in the latephase of Yellow Sea green tide, but insufficient antioxidative activity in U.prolifera u cannot prevent and repair ROS damaging effects. So, the ephemeralbloom then diminishing strategy of U. prolifera and the persistence of U.intestinalis can be explained in the highly dynamic offshore area of Qingdao.4. The environmental changes （irradiance, temperature and salinity） wereinvestigated from November,2009to March,2011. The results showed that SST,PAR and SSS had the regular variability with the green tide developing phases: ithad low SST and PAR but high SSS at the beginning of the bloom （designated aspre-bloom in the present study）, and intermediate SST, PAR and SSS during thebloom while had high SST and PAR but low SSS at the end of it （designated aspost-bloom）. A close relationship was observed between the changes of theenvironmental factors and the bloom developing phases. Furthermore, ourinvestigation found that some meteorological events （such as rainfall, typhoons,etc.） were closely associated with the bloom and diminishing of green tide.5. Basing on the field investigation three culture condions (pre-bloom, at10°C, 30μmol photons.m^-2.s^-1,35practical salinity units （PSU）; bloom, at20°C,60μmolphotons.m^-2.s^-1,30PSU; post-bloom, at26°C,90μmol photons.m^-2.s^-1,25PSU)were set to estimate the physiological responses of these two macroalgae. Theresuilts suggested that differences of the physiological traits in these twoco-occurring species correlates with their different life strategies: U. prolifera ismore sensitive to dynamic environment especially to the harsh changingenvironment conditions, characterizing their purely opportunistic life strategy;while U. intestinalis is more stable, which is due to its stress tolerance capacitygain by antioxidant system; Ecological success of U. prolifera is inextricablylinked with its higher capacity and plasticity of photosynthesis and nutrientabsorption/assimilation. So once when conditions are favourable, U. proliferaseems to be able to successfully compete with U. intestinalis for nutrients andspace when they co-occur. Therefore, from comparison of the ecophysiologicalbasis of these two species in this present study gave a further understand of theirnature ecological processes, and proved the method successful in the laboratory.