锦州湾浮游植物群落结构特征及其对环境变化的响应

Abstract

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 of3. 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 andspring 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. 44×103cell /L and the first two dominant species were Thalassiosira spp.and Cerarium furca. In May 2012,the average cell abundance was 13. 80 ×103cell /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.