Spatial and temporal variations in the succession patterns of periphytic diatom communities in tidal shrimp ponds (Gei Wais) at the Mai Po Marshes Nature Reserve

Student thesis: Master's Thesis

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  • Heidi LI


Awarding Institution
Award date27 Jan 1999


Periphytic diatom communities developed on different substrates, including reed stems (Phragmites australis), as well as plastic and glass slides were studied in gei wai 13 at the Mai Po Marshes Nature Reserve using USEPA-recommended periphyton samplers. Results indicate that artificial substrates supported communities with a higher species number and density than natural ones. A total of more than 40 species were recorded on various substrata in autumn 1996. Amphora spp. were the most common species, while the genus Nitzschia was represented by the highest number of species. The spatial variations in periphytic diatom communities were also investigated at 3 separate gei wais with different management regimes between April, 1996 and February, 1997. The various operational practices at these gei wais controlled the flow or exchange of water between the gei wai and Deep Bay waters, resulting in significant differences in water quality. Gei wai 13, a semi-open system and actively managed for shrimp and fish culture, had a higher species number as a result of colonization species from incoming water as compared to gei wai 6 (a closed system) and gei wai 21 (an opened system). Periphytic communities were also compared at three locations (seaward, middle and landward station) within gei wai 13. The seaward station always supported a more abundant and diverse community than the middle and landward stations, possibly attributable to the incoming water which brought in diatoms and nutrients from Deep Bay. Two peaks in diatom abundance were observed during spring and autumn, with the former having a higher species number (average 46.5) than the latter. Although wide variations in seasonal pattenls existed in the gei ronis, Cyclotelln comta occurred mainly in the warmer spring period, while Amphora spp. in the cooler months. A total of 85 species of periphytic diatoms were found in the 3 study gei wais. These periphytic diatoms were mainly pennate diatoms. Among these, Nitzschin spp. (relative abundance > 30%) were the dominant taxa, and then followed by Nnviczlla spp. (about 10%) Of the environmental factors examined, silicate, temperature, water velocities and substrate types were the major factors determining the successional patterns and community structure of periphytic diatoms.

    Research areas

  • Spatial analysis (Statistics), China, Mai Po (Hong Kong, China), Diatoms, Hong Kong