Rising temperature contributed to the outbreak of a macrozooplankton Creseis acicula by enhancing its feeding and assimilation for algal food nearby the coastal Daya Bay Nuclear Power Plant

An outbreak of a macrozooplankton Creseis acicula occurred in the summer of 2020 nearby the Daya Bay Nuclear Power Plant located on the coast of the Daya Bay in the South China Sea. The outbreaks of C. acicula often threaten human health, the marine environment, and other human activities including the safe operation of coastal nuclear power plants. Seawater temperature has been suggested as an important factor influencing such outbreaks. However, the underlying mechanisms through which temperature influences C. acicula remains unknown. Here, we studied the effects of temperature on the ingestion and assimilation of algal food by feeding radiocarbon-labeled algae Chlorella sp. at simulated field temperatures (19–31 °C) to C. acicula collected during the outbreak in the Daya Bay. We also quantified the allocation of the food carbon to dissolved organic carbon (DOC), CO2, and fecal pellets. The results showed that the zooplankton during the same feeding time ingested doubled or tripled algal food at higher temperatures, and it produced and released significantly more DOC, CO2, and fecal pellets with more ingested food carbon. Meanwhile, the assimilation efficiency for the ingested food carbon slightly increased from 48% to 54% with rising temperature. As a result, higher assimilation rates indicating faster growth of C. acicula were observed at higher temperatures. In addition, the high activation energy of 0.908 eV indicated that the assimilation rate was very sensitive to temperature rising. Our results show that relatively rising temperature can enhance C. acicula’s ingestion and assimilation rates for algal food, benefit its growth and metabolism, and contribute to its outbreak. This study provides a mechanistic interpretation for the relationship between rising temperature and the outbreaks of C. acicula and suggests that such outbreaks may occur more frequently and widely in the warming ocean.