Density‐Dependent Interactions Between Hydrilla verticillata (L.F.) Royle and Phytoplankton: A Mesocosm Experiment

Abstract

The management of submerged macrophytes is regarded as a potential method to control algal blooms. However, cell densities in algal blooms often have a wide range. Understanding interactions between varying phytoplankton cell densities and submerged macrophytes may help to develop conservation strategies. In this study, we investigated the density‐dependent interactions between the submerged macrophyte Hydrilla verticillata (L.F.) Royle and the varying concentrations of phytoplankton in an enclosed environment. Our results showed that H. verticillata controlled the density of phytoplankton in the system that maintained it at approximately 30% of the initial level, promoted high phytoplankton diversity, and attained greater biomass and plant length in the low initial phytoplankton density treatment (7.5 × 106 cells/L). In the systems without H. verticillata, phytoplankton multiplied to a density by approximately ninefolds of the initial level during the experiment period, and a number of Bacillariophyta and Chlorophyta species disappeared, which indicated decreased phytoplankton diversity. When the initial phytoplankton density was high (1.9 × 108 cells/L), H. verticillata did not effectively control phytoplankton cell density and the presence of H. verticillata did not significantly influence the final phytoplankton cell density or species composition, while the proportion of Microcystis spp. was increased. High cell density phytoplankton conditions had a negative effect on the biomass and length of H. verticillata. Initial phytoplankton cell density is an important factor that needs to be considered for predicting whether submerged macrophyte planting could inhibit the algal bloom.