2000～2001年柘林湾浮游植物群落结构及数量变动的周年调查

Annual Dynamics of Phytoplankton in Zhelin Bay: 2000~2001

2 0 0 0年 5月～ 2 0 0 1年 5月对粤东赤潮重灾区柘林湾进行的浮游植物周年调查表明 ,柘林湾共有浮游植物 5 4属1 5 3种。其中硅藻为优势类群 ,共 37属 1 1 4种 ,占总种数的 74 .5 1 % ;甲藻 1 5属 36种 ;其它 2属 3种。浮游植物种数和丰度的平面分布表现为湾内低于湾外 ,东部低于西部的基本格局 ,季节波动模式则为单峰型 ,全年数量最高峰位于盛夏 7月份。中肋骨条藻 ( Skeletonema costatum)为该湾的全年优势种 ,在群落总细胞数中的百分比年平均高达 5 8.7%。通过对水温、营养盐、浮游植物群落的多样性指数和均匀度以及中肋骨条藻的种群密度等相互之间的回归分析 ,并考虑增养殖渔业等因素 ,发现柘林湾因大规模增养殖渔业和高强度的排污排废引起的富营养化已在很大程度上改变了该湾浮游植物的群落结构及时空分布 ,使生物多样性与均匀度明显下降 ,中肋骨条藻等少数种类则大量增殖。硅藻赤潮 ,尤其是中肋骨条藻赤潮的发生机会明显增多 ,但发生甲藻赤潮的可能性较小。

Zhelin Bay is one of the most important bays for marine culture in Guangdong Province of China. Due to the increasing human population and marine culture in the last 10 years, the environment has changed dramatically. Although Phaeocystis blooms had brought tremendous economic loss and ecological damage to this area in 1997 and 1999, few studies followed and there are no previous investigations of phytoplankton. To understand why Phaeocystis blooms frequently hit this area and how the increased marine culture affects this ecosystem, we investigated the temporal and spatial distribution of phytoplankton, zooplankton, nutrients, trace elements, dissolved oxygen, etc. from May 2000. This paper describes the distribution of phytoplankton communities in a 1-year period (2000-05～2001-05).Water samples were collected from eight stations weekly (March to November) or biweekly (December to February). Sampling was scheduled to cover the period around high tide (±1.5h). At each station, water samples were collected from 0.5 m below the surface and 0.5 m above the bottom using a 5-L HQM-1 sampler. Each sample (1 L) was fixed with acid lugol solution in situ, and concentrated to 30~100ml based on different densities. Species were analyzed with the Zeiss microscope and a 1-ml Sedgewick-Rafte counting frame was used for cell counting. Most organisms were identified to species, but a few were clustered into higher classes. Because Zhelin Bay is shallow (mean depth 4.8m) and the water is well-mixed, the data were recorded as the average of samples from surface and bottom unless otherwise indicated. The diversity index (H′), max-diversity index (H′ max ) and evenness (J) were calculated according to Shannon-Weaver (1949) and Pielou(1969). Among 153 taxa recorded, diatoms (114) accounted for 74.5%, followed by dinoflagellates (36), chrysophyta (2) and cyanophyta (1). In terms of cell number, diatoms contributed 99.1% of the total biomass, while dinoflagellates only had 0.78%. Diatoms were present throughout the whole year, but dominant species varied by season: spring was dominated by Leptocylindrus danicus, Pseudonitzschia pungens, Thalassionema nitzschioides and Chaetoceros curvisetus; summer was dominated by Eucampia zoodiacus and C. affinis; autumn was dominated by P. pungens, T. nitzschioides and Melosira sulcata; and winter was dominated by M. sulcata. Skeletonema costatum was abundant and dominated throughout the whole year. Species abundance increased from 51 species at the inner bay (station 1) to 91 at the outer bay (station 7). Temporally, phytoplankton reached the highest abundance of 86 species in June and dropped to the lowest of 26 in January. The density of phytoplankton also increased gradually from 1.6×10 5 cells/L in the inner bay (station 1) to 6.7×10 5 cells/L at the outer bay (station 7). However, the horizontal distribution of nutrient was inversed with phytoplankton abundance. We suggested that the large-scale filter-feeding oyster culture and high turbidity in the inner part of Zhelin Bay could be responsible for the low density of phytoplankton and high nutrients in the inner bay. Phytoplankton density also showed significant seasonal changes. Mean density in the investigated area was low in January (2.1×10 4 cells/L), but increased from February along with water temperature. Its peak reached to 1.1×10 6 cells/L in July. Generally, phytoplankton blooms in spring and autumn in subtropical regions. In Zhelin Bay, however, the highest density was in July and August, ranging from 6.4×10 5 to 1.1×10 6 cells/L, which resulted in a positive correlation (r = 0.594, P < 0.0001) between phytoplankton and water temperature. In fact, the density was not low in spring (March - May, ranging from 1.3 to 5.6×10 5 cells/L), but the vigorous growth of S. costatum in the warm season (July-August) made the total cell number of phytoplankton higher in summer. In Zhelin Bay, S. costatum accounted for 58.7% of the total biomass in cell number, and it positively correlated to the total biomass (r = 0.909, P <