锦州湾浮游植物群落结构特征及其对环境变化的响应

锦州湾是我国北方污染严重的海湾,以水体的富营养化和重金属污染为特征。基于2011年8月(夏季)和2012年5月(春季)在锦州湾进行的航次调查,研究了该湾水采浮游植物的群落结构、时空分布及其对生态环境变化的响应。研究结果表明:锦州湾海域浮游植物群落主要由硅、甲藻组成,其生态类型主要为温带近岸型。春季和夏季共鉴定出浮游植物4门41属62种,硅藻在两个季节的物种数和细胞丰度上均占绝对优势,且底栖硅藻比例较高。夏季浮游植物细胞丰度平均值为41.44×103个/L,主要优势种为海链藻Thalassiosira spp.和叉角藻Cerarium furca;春季浮游植物细胞丰度平均值为13.80×103个/L,主要优势种为新月柱鞘藻Cylindrotheca closterium和中肋骨条藻Skeletonema costatum。锦州湾春季和夏季浮游植物群落组成差异明显,冗余分析(Redundancy analysis,RDA)表明硝酸盐浓度和水温分别是夏季和春季影响浮游植物群落结构的最重要环境因子。与历史资料相比,锦州湾优势种发生了显著变化,适于富营养化环境的微型浮游植物和部分耐污种在群落中占优势,表明人类活动引起的水体富营养化以及其它污染物,可能对浮游植物种类组成及分布产生了一定影响。

Phytoplankton community structure and its ecological responses to environmental changes in Jinzhou Bay, China

Phytoplankton plays a vital role in marine ecosystem functioning. It generates roughly 50% of the global primary production, affects the climate process and biogeochemical cycles and sets the upper limits to fishery yield. In addition, due to its fast population responses to water quality and environment stressors, phytoplankton is usually employed as an indicator for assessing eutrophication caused by excess nutrient input and ecosystem health. Jinzhou Bay (120°55'-121°14'E,40°42'-40°52'N)is a small and shallow semi-enclosed bay in north China with a area of 151.5 km² and an averaged depth of 3.5 m. It has a long history of heavy pollution featured by water column eutrophication and heavy metals contamination. Two cruises were carried out during August 2011 and May 2012 respectively to study the spatial distribution and assemblage structure of phytoplankton as well as their ecological responses to the environment changes. Surface water phytoplankton samples were collected at 26 stations and the relevant environmental parameters, i.e. water temperature, salinity, pH, DO, SPM, and nutrient (nitrate, phosphate, silicate) concentrations were measured or sampled simultaneously. The phytoplankton assemblages in Jinzhou Bay were mainly composed by diatom and dinoflagellates groups, and most of them were temperate coastal types. A total of 62 species belong to 4 phylum and 41 genera were identified in the summer and spring cruises. Diatoms were dominant both in species number and cell abundance, with a relatively higher proportion of benthic species. The phytoplankton community structures were significantly different between the two sampling periods. In August 2011, the average cell abundance was 41.44×10³ cell/L and the first two dominant species were Thalassiosira spp. and Cerarium furca. In May 2012, the average cell abundance was 13.80×10³ cell/L and the first two dominant species were Cylindrotheca closterium and Skeletonema costatum. The species diversity was relatively higher in spring (mean 2.46) than in summer (mean 1.98). Multivariate ordination techniques were employed to explore the relationships between phytoplankton species and environmental parameters by CANOCO 4.5. Detrended correspondence analysis (DCA) for the species data showed the maximum gradient length was lower than 3, therefore linear model was applied. Furthermore, the results of redundancy analysis (RDA) indicated that nitrate concentrations and water temperature was the most important influencing factor in summer and spring respectively. Compared with the historic data, the dominant phytoplankton species significantly changed during the last 30 years. Smaller-sized phytoplankton and the species typically found in the eutrophicated environment tended to dominant in Jinzhou Bay. In contrast, the Chaetoceros sp. and Coscinodiscus sp. which were common and important in coastal areas, were both low in species number and cell abundance. This variation trend suggested that the culture eutrophication together with other contaminants might produce certain impacts to the species composition of phytoplankton community in Jinzhou Bay. Systematic and long-term monitoring and study is needed to reveal the ecological responses of phytoplankton assemblage to environment changes and to identify the species capable of indicating the water column eutrophication and heavy metal pollution status of Jinzhou Bay.