Schapira Mathilde, Buscot Marie-Jeanne, Pollet Thomas, Leterme Sophie C, Seuront Laurent
School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001, Australia.
Saline Syst. 2010 Feb 24;6:2. doi: 10.1186/1746-1448-6-2.
Picophytoplankton (i.e. cyanobacteria and pico-eukaryotes) are abundant and ecologically critical components of the autotrophic communities in the pelagic realm. These micro-organisms colonized a variety of extreme environments including high salinity waters. However, the distribution of these organisms along strong salinity gradient has barely been investigated. The abundance and community structure of cyanobacteria and pico-eukaryotes were investigated along a natural continuous salinity gradient (1.8% to 15.5%) using flow cytometry.
Highest picophytoplankton abundances were recorded under salinity conditions ranging between 8.0% and 11.0% (1.3 x 106 to 1.4 x 106 cells ml-1). Two populations of picocyanobacteria (likely Synechococcus and Prochlorococcus) and 5 distinct populations of pico-eukaryotes were identified along the salinity gradient. The picophytoplankton cytometric-richness decreased with salinity and the most cytometrically diversified community (4 to 7 populations) was observed in the brackish-marine part of the lagoon (i.e. salinity below 3.5%). One population of pico-eukaryote dominated the community throughout the salinity gradient and was responsible for the bloom observed between 8.0% and 11.0%. Finally only this halotolerant population and Prochlorococcus-like picocyanobacteria were identified in hypersaline waters (i.e. above 14.0%). Salinity was identified as the main factor structuring the distribution of picophytoplankton along the lagoon. However, nutritive conditions, viral lysis and microzooplankton grazing are also suggested as potentially important players in controlling the abundance and diversity of picophytoplankton along the lagoon.
The complex patterns described here represent the first observation of picophytoplankton dynamics along a continuous gradient where salinity increases from 1.8% to 15.5%. This result provides new insight into the distribution of pico-autotrophic organisms along strong salinity gradients and allows for a better understanding of the overall pelagic functioning in saline systems which is critical for the management of these precious and climatically-stress ecosystems.
微微型浮游植物（即蓝细菌和微微型真核生物）是远洋水域自养群落中数量丰富且在生态上至关重要的组成部分。这些微生物在包括高盐度水域在内的各种极端环境中定殖。然而，这些生物沿强盐度梯度的分布几乎未被研究过。利用流式细胞术，沿着自然连续的盐度梯度（1.8%至15.5%）对蓝细菌和微微型真核生物的丰度及群落结构进行了研究。
在盐度介于8.0%至11.0%（1.3×10⁶至1.4×10⁶个细胞/毫升）的条件下记录到了最高的微微型浮游植物丰度。沿着盐度梯度鉴定出了两个微微型蓝细菌种群（可能是聚球藻属和原绿球藻属）以及5个不同的微微型真核生物种群。微微型浮游植物的流式细胞术丰富度随盐度降低，并且在泻湖的咸淡水 - 海洋区域（即盐度低于3.5%）观察到了流式细胞术上最多样化的群落（4至7个种群）。一个微微型真核生物种群在整个盐度梯度上主导着群落，并导致了在8.0%至11.0%之间观察到的水华现象。最后，在高盐度水域（即高于14.0%）仅鉴定出了这个耐盐种群和类似原绿球藻的微微型蓝细菌。盐度被确定为构建泻湖沿线微微型浮游植物分布的主要因素。然而，营养条件、病毒裂解和微型浮游动物摄食也被认为是控制泻湖沿线微微型浮游植物丰度和多样性的潜在重要因素。
这里描述的复杂模式代表了对微微型浮游植物在盐度从1.8%增加到15.5%的连续梯度上动态变化的首次观察。这一结果为微微型自养生物沿强盐度梯度的分布提供了新的见解，并有助于更好地理解盐度系统中整体的远洋功能，这对于管理这些珍贵且受气候压力影响的生态系统至关重要。
