Ecological data of Pseudo-nitzschia delicatissima in the Gulf of Naples

We present ecological information regarding the diatom Pseudo-nitzschia allochrona and other P. delicatissima-like  species, collected in surface waters at long term ecological research (LTER) site, LTER-MC, in the Gulf of NAples. Cell density data were obtained for the group including P, allochrona, P. arenysensis, P. delicatissima and P. dolorosa, which are not distinguishable in light microscopy, and are presented along with temperature, salinity and nutrient data collected simultaneously. Based on molecular data from isolated strain and metabarcoding, Pseudo-nitzschia allochrona was shown to occur invariably only in summer and autumn, whereas the other three species were always detected in winter or spring. We arbitrarily attributed autumn-winter density data to P. allochrona and spring-summer ones to the other three species. This way we could investigate the ecological niche of P. allochrona compared to that of the closely related species.

Methods
For the collection and generation of cell abundance data of Pseudo-nitzschia, phytoplankton samples were collected in surface waters at the LTER-Mc sampling site (40°48.5’N, 14°15’E, Gulf of Naples, Mediterranean Sea) with Niskin bottles. Subsamples were placed in 500 ml dark glass bottles and immediately fixed with neutralised formaldehyde (0.8 % final concentration). A variable amount of fixed sample (3-50 ml) was allowed to settle in a cell count chamber. Cells from two transects were counted according to the Utermöhl method (Utermöhl, 1958; Andersen and Throndsen, 2003), using an inverted microscope (Axiovert 200, Zeiss, Germany) equipped with phase contrast at a final magnification of 400X. Records of Pseudo-nitzschia cf. delicatissima (including P. delicatissima, P. arenysensis, and P. dolorosa) were separated arbitrarily from those of P. allochrona based on the period of the year. Based on cultured strain genotyping and metabarcoding data, the former are found in winter-spring and the latter in autumn-winter.

For the ancillary environmental parameters,  collection and processing methods are found in Sabia, L., Costanzo, A., D’Alcalà, M. R., Saggiomo, V., Zingone, A., & Margiotta, F. (2019). Assessing the quality of biogeochemical coastal data: a step-wise procedure. Mediterranean Marine Science, 20(1), 56–73. https://doi.org/10.12681/mms.15935

本研究报道了采自地中海那不勒斯湾长期生态研究（Long Term Ecological Research, LTER）站点LTER-MC表层水体中的异时伪菱形藻（Pseudo-nitzschia allochrona）及其他类似纤细伪菱形藻物种的生态学数据集。
该数据集包含光镜下无法区分的异时伪菱形藻（P. allochrona）、阿雷尼伪菱形藻（P. arenysensis）、纤细伪菱形藻（P. delicatissima）与多痛伪菱形藻（P. dolorosa）的细胞密度数据，并同步配套了同期采集的水温、盐度及营养盐数据。基于分离菌株的分子数据与扩增子测序（metabarcoding）结果，异时伪菱形藻仅稳定出现于夏季与秋季，而其余三个物种则始终在冬季或春季被检出。本研究主观将秋冬季节的细胞密度数据归属于异时伪菱形藻，春夏季节的数据归属于其余三个物种，以此开展异时伪菱形藻与其近缘物种的生态位对比研究。

研究方法
针对伪菱形藻属（Pseudo-nitzschia）细胞丰度数据的采集与生成，研究人员使用尼斯金采水器（Niskin bottles）在LTER-MC采样点（40°48.5′N，14°15′E，地中海那不勒斯湾）的表层水体采集浮游植物样本。将子样本置于500 mL棕色玻璃瓶中，立即使用中和甲醛（终浓度0.8%）进行固定。取3~50 mL适量固定后的样本于细胞计数框内沉降，采用乌特莫尔计数法（Utermöhl, 1958; Andersen and Throndsen, 2003），借助配备相差装置的德国蔡司Axiovert 200型倒置显微镜（最终放大倍数400×）对两个断面的细胞进行计数。研究人员基于采样时段，将疑似纤细伪菱形藻（Pseudo-nitzschia cf. delicatissima，包含纤细伪菱形藻、阿雷尼伪菱形藻与多痛伪菱形藻）的记录与异时伪菱形藻的记录主观区分；结合培养菌株的基因分型数据与扩增子测序结果，前者仅出现于冬春季，后者则见于秋冬季。

辅助环境参数的采集与处理方法详见以下文献：
Sabia, L., Costanzo, A., D’Alcalà, M. R., Saggiomo, V., Zingone, A., & Margiotta, F. (2019). 评估海岸生物地球化学数据质量的分步流程. 地中海海洋科学, 20(1), 56–73. https://doi.org/10.12681/mms.15935