Composition,Photosynthetic Pigments And Activity Of Microphytobenthos In Intertidal Zone Of Xiamen

The temporal variations on microphytobenthos composition, biomass, photosynthetic pigments and photosynthetic activity were studied from January2013to January2014in the intertidal zone of Xiamen. Sampling and measurements were conducted1-2times every month with microscopic technique, high performance liquid chromatography (HPLC) and pulse amplitude modulation chlorophyll fluorescence (PAM) technique. The chlorophyll fluorescence response to temperature and light change was explored, and the likely controlling factors for community succession were investigated in this study. Results are showed as following:1. The intertidal microphytobenthos community were dominated by Bacillariophyta, occasionally Cyanophyta, Dinoflagellates, Euglena and Chrysophyta. For mud sediment, the dominated genera were Gyrosigma, Pleurosigma, Diploneis Coscinodiscus; while they were Navicula, Amphora, Cylindrotheca, Tropidoneis in mud-sandy. The dominant species were Amphora acuta, Cylindrotheca closterrium, Amphiprora alata and Diploneis bombus. Microphytobenthos biomass and diversity reached peak in July and October.2. Fifteen photosynthetic pigments were identified. Chlorophyll c, Fucoxanthin, Diatoxanthin, Zeaxanthin, Chlorophyll a and β-carotene were observed frequently, while Peridinin, Zeaxanthin, Chlorophyll b and Lutein only occurred in some samples. These results showed consistency between different methods (microscopic and chromatographic) to a large extent. Chlorophyll a and Fucoxanthin had a bimodal distribution, and the peak appeared in December and January in mud, while it appeared in July and September in mud-sandy. Zeaxanthin showed a bimodal distribution too, but the peak appeared in February and September both in mud and mud-sandy. Peridinin distributed in unimodal type, and the peak appeared in December. Lutein and Chl b distributed irregularly. Correlation analysis showed that Bacillariophyta was potentially limited by phosphate, and Cyanophyta changed with temperature and N/P ratio. Dinoflagellates was mainly limited by the nutrients, and Chrysophyta were affected by temperature and phosphate.3. The minimal and maximal chlorophyll fluorescence (Fo, Fm) of microphytobenthos varied with time and sediment types. Fo and Fm in mud sediment were higher than those in mud-sandy sediment in spring and winter, but reversely in summer and autumn. It was mainly due to the variation of microphytobenthos biomass. Fv/Fm showed a bimodal distribution in the mud sediment with the two peaks appeared in August and December, while they were August and October in the mud-sandy. Relative electron transport rate (ETR) and light chemical quenching (qP) in the mud sediment were higher than those in the mud-sandy sediment in winter and spring, but reversely in summer and autumn. It was mainly due to the different benthic microalgae composition in sediment.4. The result of controlled experiment showed:the maximum quantum efficiency (Fv/Fm) of the photosynthetic system II in different sediment types was mud (0.33)> mud-sandy (0.28)> sand (0.01) during the sampling period in spring. The short-term (0.5-2h) temperature (15～35℃) and light (0-100%) experiments showed the optimum temperature (about27℃) for microphytobenthos photosynthesis tended to be close to the environmental temperature(about26.5℃) which indicated that the thermal adaption, extreme high temperature (above35℃) was harmful to microphytobenthos. In addition, we found that microphytobenthos may accommodate to the light change with different adaptation strategies emerged from different types of sediment.