Curved filaments of Aulacoseira complex as ecological indicators in the Pearl River, China

摘要

Morphological traits of diatoms have been paid more and more attention recently, since new ecological indicators are desired under current rapidly changing environments. The shape features (including curved filaments and ending spines) of Aulacoseira filaments have been proved to be good indicators to spatio-temporal patterns of aquatic environments in the downstream of the Pearl River. Furthermore, curved Aulacoseira filaments with a wide variation range in curve degree have attracted our attention. Here, we hypothesized that these curved filaments were also good indicators to water environments. The major difficulties are how to quantify the values of curve degree and define its indicating functions to water environments. To test this hypothesis, morphological traits of these curved Aulacoseira filaments, including traditional traits (cell and filament size) and novel traits (filament ending spines and curve degree), were collected and analyzed. The different curve degrees were quantified and artificially divided into four curve degree ranges, thereby more effective ranges to water environments could be confirmed. Based on ecological modelling, the results showed that clusters mainly exhibited spatially variations based on cell size, and clusters mainly exhibited temporally alternations based on occurrence proportion of filament ending spines. The high curve degree was a potentially good indicator to high eutrophication levels, because the highest curve degree generally occurred in clusters that mainly originated from the city center. The occurrence proportion of filament ending spines was a good indicator to seasonal changes, since it showed lower values in flood seasons and higher values in low flow seasons. A more ideal standard to define the curved filaments might be that curve degree = 0.1, based on the effective indicating function. This is the first study to quantify the different curve degrees of Aulacoseira filaments and use them as ecological indicators, which has been proved based on comparing with traditional morphological traits. This study enhances the role of shape features as bioindicators to environments. The conclusions are more applicable in aquatic environments dominated by filamentous diatoms.