INTRODUCTION
Over the last several decades, the world’s ocean and inland waters have been experiencing enormous blooms of various kinds of micro- and macro-algae and zooplankton, which have caused severe environmental and economic losses. The most reported blooms in scientific papers and media include cyanobacteria (e.g., Shi et al., 2017; Huisman et al., 2018), dinoflagellates (e.g., Glibert et al., 2008, 2009; Zhou et al., 2008), Sargassum (e.g., Schell et al., 2015; Wang et al., 2019), Ulva (e.g., Smetacek and Zingone 2013; Wang et al., 2015), jellyfish (e.g., Richardson et al., 2009; Jackson et al., 2001; Sun et al., 2015), andAcetes chinesis (Zeng et al., 2019). These blooms are widespread and recurrent and have been attributed to eutrophication as well as altered environmental conditions due to climate change and anthropogenic activities (e.g., Anderson et al., 2002; Edwards et al., 2006; Heisler et al., 2008).
Creseis acicula (Rang 1828) is a pteropod species, which widespread in the world oceans and prefers warm waters, particularly in the upper layers of the ocean ranging from 50°N-40°S (Albergoni, 1975). Outbreaks of C. acicula were found in Indian seas (Krishna Murthy, 1967; Sakthivel and Haridas, 1974; Peter and Paulinose, 1978; Pillai and Rodrigo, 1984; Naomi, 1988), Mediterranean sea (Burgi et al., 1962; Albergoni, 1975; Kokelj et al., 1994), Japan sea (Nishimura, 1965; Morioka, 1980), and Gulf of Mexico (Hutton, 1960), occurring during the 1960s to 1990s. The last report of C. acicula bloom was in 1990 in the Mediterranean sea (Kokelj et al., 1994). Since the 1990s, for thirty years, there has not been a single record of its outbreak worldwide, until mid-June 2020, when a sudden outbreak happened in Daya Bay, South China Sea (Fig. 1, 3). This bloom of C. acicula was first observed on June 12, 2020, and persisted into July 2020. It has caused losses to local industry and tourism, particularly the Daya Bay Nuclear Power Plant (DNPP) built on the southwest shore, with highly concentrated C. acicula disrupting the cooling system. Both government and public attached great importance to this bloom, since it has poses a potential threat to the normal operation and safety of DNPP.
Here we present a briefing of this unusual outbreak by summarizing our observations of the bloom and its associated environmental conditions to provide a big picture of this rare zooplankton bloom. This report would facilitate further investigations and advocate attention to possible recurrent aggregation of C. acicula and other organisms in the ocean, particularly in the context of global warming.