A Long-term Ecological Study On Phytoplankton In A Large-scale Mariculture-Zhelin Bay, Eastern Guangdong

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 two decades, the ecological environment has changed dramatically, e.g., the large-scale of harmful algal blooms (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, especiatly 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. This paper describes the investigated results on phyplanktonic ecology.Samples were monthly collected at least once per month from July of 2000 to December of 2003, but only quarterly in 2004. There were totally 9 sampling stations, including 7 inside the bay and 2 outside the bay. Phytoplankton samples had two types: net samples (fixed quality) and bottle samples (fixed quantity). The net used for sampling was SW-III plankton sampling net (diameter-37cm, area-0.1 square meters and pore size-77μm) according to " Standard of Marine Investigation " (China Standard Press, 1991), and the vertical trawl should be done one to two times from 0.5m above the bottom to the surface. At each station, 1L water samples were collected from 0.5m below the surface and 0.5m above the bottom using a 5-L HQM-1 sampler respectively and put into polythene bottles. Each sample (1L) was fixed with Lugol's iodine solution in situ, and the final concentration was limited to \5‰. The fixed quantitative samples were put into glass measuring cylinders immediately after taken back to laboratory, and concentrated to 30-100ml based on different densities prior to counting on a microscope. The whole process cost at least three days. Species were examined with the inverted microscope (Zeiss Axiovert25, magnification 400x) and a 1-ml Sedgewick-Rafte counting frame was used for cell counting. In order to make the error below 10%, the total phytoplankton cell numbers counted at each time must be more than four hundreds. The net samples were just used for species analysis.Through this investigation, we identified 315 species (including variant and derivative) representing 108 genera. Among these, diatoms (231 species, representing 75 genera) accounted...