Growth and defense mechanism of Phaeocystis globosa exposed to extremely low frequency electromagnetic fields

Marine power cables are increasingly exposing marine ecosystems to artificial extremely low-frequency electromagnetic fields (ELF-EMF). The harmful and periodic outbreaks of Phaeocystis globosa blooms in the Beibu Gulf, though driven by complex factors, raise questions about potential links to ELF-EMF. While existing studies suggest that ELF-EMF promote microalgal proliferation, and electromagnetic conditions in the Beibu Gulf have undergone changes, research exploring their connection remains scarce. To assess the impacts of ELF-EMF on the microalga P. globosa, we expose it to ELF-EMF at three electromagnetic strengths (0, 0.2, 1 millitesla (mT)) over a 24 h period. Analysis of growth indicators, physiology, biochemistry, and the metabolome is performed to identify how this alga responds to ELF-EMF. Exposure to 0.2 mT 24 h^-1 and 1 mT 24 h^-1 increased cultured P. globosa cell density, enhanced photosynthesis, and increased chlorophyll a content, but decreased protein and carbohydrate accumulation. Metabolome analysis revealed, 916 differently expressed metabolites, of which cyclic adenosine monophosphate (cAMP) and linoleic acid are significantly down-regulated, while γ-aminobutyric acid is significantly up-regulated. Pathway analysis reveals cAMP signaling pathway and linoleic acid metabolism to be inhibited following ELF-EMF exposure. We demonstrate that P. globosa growth was promoted with exposure to ELF-EMF. Under the influence of electromagnetic fields, P. globosa exhibits enhanced growth, reproduction, and photosynthesis, along with stronger stress resistance. Therefore, under changing electromagnetic conditions in the Beibu Gulf, the threat of P. globosa algal blooms may increase. This study sheds light on potential drivers of harmful algal blooms (HABs), suggesting that ELF-EMF may play a role in bloom initiation. However, the exact mechanisms underlying this relationship warrant further investigation to establish causality and ecological relevance.