Institute of Oceanography and Fisheries, 21000 Split, Croatia.
Mar Environ Res. 2010 Aug;70(2):239-49. doi: 10.1016/j.marenvres.2010.05.007. Epub 2010 May 21.
Vranjic Basin, in the eastern part of KastelaBay (middle Adriatic Sea), received municipal wastewater until offshore submarine outfalls were finished in November 2004. To identify the responses of the microbial community to changes in the trophic status of the marine environment, two 4-year periods were compared: a eutrophic period (2001-2004) when the sewage waters entered the Basin and an oligotrophic period (2005-2008) after the outfalls were completed. The switch from eutrophic to oligotrophic conditions was accompanied by decreases in bacterial abundance, bacterial production and chlorophyll a, and increase in heterotrophic nanoflagellate (HNF) abundance and bacterial specific growth rate. Qualitative changes in the phytoplankton community manifested through dramatically decreased abundance of the diatom species Skeletonema costatum and Euglenophyta Eutreptiella spp. during the oligotrophic period. Furthermore, the percent contribution of pico-nano phytoplankton chlorophyll to total chlorophyll increased from less than 40% during the eutrophic period to more than 60% during the oligotrophic period. Changes in seasonal patterns of phytoplankton, bacteria and HNF abundance were also observed, with summer maxima during the eutrophic period and spring and autumn maxima during the oligotrophic period. Significant changes in the microbial food web were also identified. During eutrophic conditions, bacteria were dominantly under the phytoplankton-mediated bottom-up control whereas HNF were dominantly controlled by ciliate grazing (top-down control). In contrast, during the oligotrophic period, predominantly top-down control of bacteria by strong HNF grazing was observed. At the same time, HNF were spared from strong ciliate predation pressure because the ciliates apparently switched their dominant prey from HNF to the pico-nano phytoplankton fraction during that period.
弗拉尼奇盆地位于卡斯特尔湾（亚得里亚海中部）的东部，在 2004 年 11 月完成近海海底排污口之前，一直接收城市污水。为了确定微生物群落对海洋环境营养状态变化的响应，对两个为期 4 年的时期进行了比较：富营养期（2001-2004 年），污水进入盆地；贫营养期（2005-2008 年），排污口完成后。从富营养化到贫营养化的转变伴随着细菌丰度、细菌生产力和叶绿素 a 的减少，以及异养微型浮游动物（HNF）丰度和细菌比生长率的增加。浮游植物群落的定性变化表现为在贫营养期硅藻种类 Skeletonema costatum 和 Euglenophyta Eutreptiella spp. 的丰度显著下降。此外，pico-nano 浮游植物叶绿素在总叶绿素中的百分比贡献从富营养期的不到 40%增加到贫营养期的 60%以上。还观察到浮游植物、细菌和 HNF 丰度季节性模式的变化，富营养期夏季达到最大值，贫营养期春季和秋季达到最大值。微生物食物网也发生了显著变化。在富营养条件下，细菌主要受到浮游植物介导的自上而下的控制，而 HNF 主要受到纤毛虫摄食的自上而下的控制（自上而下的控制）。相反，在贫营养期，观察到主要由强烈的 HNF 摄食对细菌的自上而下控制。与此同时，由于纤毛虫显然在那段时间将其主要猎物从 HNF 切换到 pico-nano 浮游植物部分，HNF 免受强烈的纤毛虫捕食压力的影响。
