象山港春季网采浮游植物的分布特征及其影响因素

根据2010年春季象山港28个站位的网采样品,共鉴定出浮游植物6门55属158种,其中硅藻135种(占总丰度的99.0%),甲藻18种,其余门类(金藻、蓝藻、绿藻和隐藻)5种。浮游植物平均丰度为35.29×10⁴ 个/m³,其分布呈较强的斑块状(3.41×10⁴-142.35×10⁴ 个/m³),高值区位于横山至白石山水域及乌沙山电厂邻近水域。Shannon-Weiner多样性指数和Pielou均匀度指数总体表现为港口和港口外高于港中部和港底。琼氏圆筛藻(Coscinodiscus jonesianus)为绝对优势种,其丰度(284.97×10³ 个/m³)占总丰度的80.8%。典范对应分析结果显示,影响浮游植物群落的主要因子依次为透明度、悬浮物、温度、水深和氮磷比。光照充足、电厂温排水适度温升、营养盐丰富和氮磷比合适 (接近Redfield比值16)导致了港内微藻旺发。受径流、水交换和海洋开发等影响,象山港的理化参数表现了明显的斑块和梯度分布,这为浮游植物的生长提供了不同类型的生境,客观上造成了其分布的空间异质性。聚类、多维尺度和相似性分析结果表明,港底、港中部、港口至港口外区域间的群落组成差异较大。结合历史数据分析表明,象山港浮游植物丰度的升高及群落结构的改变与电厂运行、水产养殖、临港工业发展和滩涂围垦等海洋开发活动有关。

Distribution of net-phytoplankton and its influence factors in spring in Xiangshan Bay

Xiangshan Bay (121°25''-120°00''E, 29°05''-29°46''N), located at the East China Sea, is a long semi-enclosed bay with slow rate of water exchange. As one of the most important marine economic bases in Zhejiang Province, it has confronted a series of ecological challenges due to the coastal power plants (Ninghai and Wushashan Power Plant) running, excessive aquiculture, industrial development, tidal flat reclamation, and sea-crossing bridge construction. These large-scale human activities certainly lead to hydrodynamic alteration, temperature elevation, and eutrophication aggravation in this bay. The phytoplankton, as the basic and essential part of food chain, is very sensitive to such environmental stresses. However, present data about the combined effects of multiple marine exploitations on phytoplankton in the semi-enclosed bay is scarce. In this context, one cruise of phytoplankton and physical-chemical investigation was conducted in Xiangshan Bay in spring, 2010.Based on 28 net-phytoplankton samples, a total of 6 phyla, 55 genera, and 158 species were found, including 135 diatom species (occupied by 85.4% of the total species number and 99.0% of the total abundance), 18 dinoflagellate species and 5 other taxonomic species belong to Chrysophyceae, Cyanophyceae, Chlorophyceae and Cryptophyceae. The phytoplankton abundances (35.29×10⁴ Cells/m³ on average) represented a strong patchy distribution, varying in the range from 3.41×10⁴ Cells/m³ to 142.35×10⁴ Cells/m³, and the high values occurred in the areas around Hengshan Island to Baishishan Island and also around Wushashan Power Plant. Coscinodiscus jonesianus (284.97×10³ Cells/m³) was the absolute dominant species with its cell number accounted for 80.8% of the total abundance, while other dominant species such as Navicula corymbosa, Skeletonema costatum and Coscinodiscus concinnus also had high cell densities (11.93, 6.92 and 4.06×10³ Cells/m³, respectively). Canonical correspondence analysis (CCA) showed that transparency, suspended solids, temperature, N/P and silicate were the main variables which affected phytoplankton community in turn. The ample solar light, moderate temperature increment of the thermal discharge, abundant nutrition and suited N/P (close to the Redfield ratio 16) induced a phytoplankton (especially the diatom) bloom at the inner bay. Due to the catchment input, water exchange and marine exploitation, the patchiness and gradient of physical-chemical parameters were obviously observed, and such complicated environment supplied different habitats for phytoplankton and resulted in spatial heterogeneity. Both the Shannon-Weiner diversity and Pielou evenness index at the mouth and outside were evidently higher than the midst and bottom of Xiangshan Bay. Thus, there was a great discrepancy among the community composition at embayment bottom, midst, mouth and outside, according to the cluster, multidimensional scaling, and similarity analysis results. Besides, comparing with the historical data, we found that the microalgal abundance increment and community structure alteration were tightly related to the various marine exploitations in this bay.