In this paper, we provide the first evidence of a bloom formation of coccolithophore Syracosphaera halldalii in a salt‐wedge estuary of Krka River (Mediterranean Sea), during stratified conditions. The increase of coccolithophore abundance was firstly noticed in August 2017 and occurred again in October 2017. The increased abundance appeared over wide salinity (16.9–35.3) and temperature ranges (16.4–23.3ºC). On these two occasions, the highest abundance of S. halldalii confirmed by SEM counts reached 2.51 × 10⁶ cells L⁻¹ at halocline in October. The contribution of S. halldalii to total coccolithophore assemblage was more than 97%. Vertical distribution of total coccolithophores abundance varied over time and followed the temperature curve, with the highest abundances co‐occurring with maximum temperature in the water column. A positive association of coccolithophore abundances with nitrates was found, but pulses of both organic nitrogen and nitrites seem to be important for sustaining the bloom after the initial proliferation. During the entire study period, S. halldalii was found only in the heterococcolith‐bearing phase, and the absence of the holococcolith‐bearing phase could be related to increased turbulence in the estuary. SEM analysis of cell morphology was in concordance with earlier descriptions, with apical coccoliths and body coccoliths of approximately equal size and both having distinct protruding teeth along the inner rim. A single exothecal coccolith was found in association with two S. halldalii cells indicating possible dithecatism of this species.

中文翻译：

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在高度变化的河口环境（克尔卡河，亚得里亚海）中，球石藻Syracosphaera halldalii大量开花的第一个证据。

在本文中，我们提供了分层条件下克尔卡河（地中海）盐楔河口藻类藻类Syracosphaera halldalii的水华形成的第一个证据。最早在2017年8月发现球石藻富集度的增加，并于2017年10月再次出现。在宽盐度（16.9–35.3）和温度范围（16.4–23.3ºC）中出现了丰度增加。在这两种情况下，通过SEM计数确认的哈氏链球菌最高丰度在10月的卤代上达到2.51×10 ⁶细胞L ^-1。哈氏链球菌的贡献球石总组装体的比例超过97％。总球藻丰度的垂直分布随时间变化，并随温度变化，在水柱中最高丰度与最高温度同时出现。发现球藻石藻的丰度与硝酸盐呈正相关，但是有机氮和亚硝酸盐的脉冲似乎对于在初始增殖后维持花开很重要。在整个研究期间，哈德氏链球菌仅在含异球藻的阶段被发现，而不含全球藻的阶段可能与河口湍流的增加有关。扫描电镜细胞形态的分析与先前的描述是一致的，顶端的球囊和体球囊的大小大致相等，并且都沿内缘具有明显的突出齿。发现与两个哈氏链球菌细胞相关的单个鞘外结石，表明该物种可能具有双生能力。