An Ecological Study On Marine Microorganisms In A Large-scale Mariculture-Zhelin Bay, Eastern Guangdong

Abstract: Zhelin Bay is one of the most important bays for large-scale mariculture in Guangdong Province, China. Due to the increasing human population and mariculture in the last decades, the ecological environment has changed dramatically, e.g., the large-scale of harmful algal bloom (Phaeocystis) occurred in 1997 and 1999, respectively. Although degenerative and eutrophic environment has brought serious economic loss and made mariculture becoming more and more difficult, especially in caged fish culture, few studies have been performed. To evaluate the environmental condition of Zhelin Bay, from May 2000 our group initiated an ecological investigation around Zhelin Bay. The paper describes the investigated results on nutrients and marine microbial ecology.Samples were monthly collected once per month from May of 2000 to December of 2003, but only once per quarter in 2000 and 2005. There were totally 9 sampling stations, including 7 inside the bay and 2 outside the bay. Five liters of water samples were collected with HQM-1 sampling bottles 0.5 m under the surface and 0.5 m above the bottom at each station, and 100ml water from each sample were aliquoted into sterile polythylene bottles, then transported in ice to the laboratory. Samples of sediment were once collected by HNM_1-2 grab at each station, then 50g were aliquoted from the central surface of sediment without turbulence into sterile dish and transported to laboratory for analyzing. Some water samples were used for assessing the live microorganisms, others were immediately fixed with 5% formaldehyde (final concentration) for direct count of bacteria. After 10g samples of sediment and 90ml sterile sea water (adding 1% Tween 80) filtered through 0.22um polycarbonate filters were mixed completely, supernate were for further analyze. Total bacteria were counted with AODC, heterotrophic and vibrio bacteria were measured with agar plate of Zobell 2216E and TCBS, individually. SRB were enumerated with MPN in liquid medium of sodium lactate. The NH₄-N, NO₃-N, NO₂-N, DIN and PO₄-P were analyzed by the SKALAR Channel Seawater Segmented Flow Nutrient Analyzer. TH SiO₃-Si was analyzed by the SHMADZU UV-2501 PC. Temperature, salinity, dissolved oxygen and pH were determined in situ with a portable instrument for water quality analysis (YSI6600-02, USA).Yearly division was from January to December in a same year. Relations between nutrients, the microorganism abundance and environmental variables were analyzed by means of the linear fit using the software of Origin 7.0The results showed that the concentration of dissolved inorganic nitrogen, dissolved inorganic phosphate and silicate were high greatly, with an average concentration of 33.19, 1.48,...