The relationship between inorganic nutrients and diversity of dinoflagellate cysts: An evaluation from the perspective of species abundance distribution

The relationships between the inorganic nutrients and diversity of dinoflagellate cysts (the N-Dc relationships) are one of the most central issues in coastal ecology. It is not only an important pathway to explore the ecological processes of plankton, but also a key element for assessing eutrophication in marine ecosystems. Although the N-Dc relationships have been studied for many years, they have remained controversial, which may be attributed to (1) using samples collected from a single source (2) considering an insufficient range of nutrient concentrations (3) rarely taking into account species abundance distributions (SAD) that could better represent diversity. In this study, the N-Dc relationships are evaluated according to a compiled dataset, which cover the wide range of nutrient concentrations. Species diversity of cysts are estimated by four common diversity metrics and a new SAD parameter. Results show that all diversity metrics are negative with nutrients, which supports that low diversity of cysts could be considered as a signal of eutrophication. Additionally, this study finds a new pattern that SAD of cysts (N-r/N-1, N-r and N-1 is the abundance of the r-th and the first species in descending order) with decreasing nutrients appears to gradually approach 1: 1/2: 1/3 horizontal ellipsis . In the future, if this pattern can be verified by more investigations, understanding the negative N-Dc relationships is more likely to provide new direction for assessing and managing eutrophication in coastal ecosystem, and even for exploring the general mechanisms determining diversity.

Automated summary

The relationships between inorganic nutrients and the diversity of dinoflagellate cysts have long been studied, but remained controversial due to limitations in sampling sources, nutrient concentrations, and consideration of species abundance distributions (SAD). In this study, a compiled dataset covering a wide range of nutrients is used to evaluate the N-Dc relationships. The results indicate that low cyst diversity may be a signal of eutrophication and a new pattern in the SAD of cysts with decreasing nutrients is observed. Further investigations could provide new insights into assessing and managing eutrophication and understanding diversity mechanisms.