Can the algicidal material Ca-aminoclay be harmful when applied to a natural ecosystem? An assessment using microcosms

Abstract

The effects of Harmful algal blooms (HABs) are increasingly being felt by natural ecosystems in coastal environments, affecting human health and causing significant economic losses in fisheries. We assessed the ability of an artificial clay (Ca-aminoclay) to act as an algicide and suppress HABs (of Cochlodinium polykrikoides and Chattonella marina) and investigated the ecological responses to this suppression by performing experiments in realistic natural conditions in microcosms. The Ca-aminoclay induced cell lysis in the HAB organisms within several minutes but had negligible impacts on the non-harmful phytoplankton. However, applying Ca-aminoclay could cause adverse impacts in terms of biological and environmental changes. The bacterioplankton abundance and composition increased and changed from being dominated by alpha-proteobacteria to being dominated by gamma-proteobacteria. The abundances of heterotrophic flagellates and ciliates increased rapidly with the increase in bacterioplankton. These changes caused nutrient and dissolved organic carbon concentrations to increase and anoxic conditions to occur. Extremely poor environmental conditions were sustained for long periods in a closed system, while the environmental conditions in open systems (slow inflow and fast inflow systems) deteriorated before recovering to the initial conditions. Therefore, caution should be taken when considering the direct application (Ca-aminoclay) to act as an algicide and suppress HABs (of Cochlodinium polykrikoides and Chattonella marina) and investigated the ecological responses to this suppression by performing experiments in realistic natural conditions in microcosms. The Ca-aminoclay induced cell lysis in the HAB organisms within several minutes but had negligible impacts on the non-harmful phytoplankton. However, applying Ca-aminoclay could cause adverse impacts in terms of biological and environmental changes. The bacterioplankton abundance and composition increased and changed from being dominated by alpha-proteobacteria to being dominated by gamma-proteobacteria. The abundances of heterotrophic flagellates and ciliates increased rapidly with the increase in bacterioplankton. These changes caused nutrient and dissolved organic carbon concentrations to increase and anoxic conditions to occur. Extremely poor environmental conditions were sustained for long periods in a closed system, while the environmental conditions in open systems (slow inflow and fast inflow systems) deteriorated before recovering to the initial conditions. Therefore, caution should be taken when considering the direct application