Significant spatial shifting of the eukaryotic plankton community in a small-scale fish-killing harmful algal bloom of Prorocentrum and Karenia near Huangqi Peninsula, Lianjiang, Fujian, China

Abstract

A fish-killing harmful algal bloom (HAB) involving multiple causative genera (Prorocentrum and Karenia) occurred in late May 2024 in the coastal waters near Huangqi Peninsula, Lianjiang, Fujian, China. In this study, a field survey was conducted to collect seawater samples of different bloom phases, and the toxicity, pigment composition, toxin contamination, and eukaryotic plankton community were investigated. HAB-affected seawater exhibited significant lethality to the rotifer Brachionus plicatilis and juvenile marine medaka Oryzias melastigma, and eukaryotic diversities were also significantly declined. Peridinin was detected as the main pigment in the HAB-affected area, which was consistent with the high relative abundance of dinoflagellata. Further species-level analysis suggested a significant shift from Prorocentrum dentatum-dominant at the peak phase site to Karenia mikimotoi-Karenia papilionacea-dominant at the early dissipation phase sites. Additionally, Dinophysis spp. were the primary cause of the pectenotoxin-2 contamination in this region. Environmental parameters showed weak correlations with the causative algae, while complex biological interactions were detected in this area. High relative abundances of the ciliate Tintinnopsis lobiancoi and the parasitic dinoflagellate Amoebophrya were detected in early dissipation phase sites, which significantly correlated with K. papilionacea and Karodinium spp., respectively. This pattern suggested that biological interactions, particularly top-down control, might play crucial roles in the HAB dissipation.

Keywords: Dissipation mechanism; Eukaryotic plankton community; Harmful algal blooms; Multiple causative species; Top-down control.