Time-associated physiological responses and transcriptomic changes in the bivalve Cyclina sinensis under ELF-EMF exposure.

The rapid expansion of coastal wind farms raises concerns about extremely low-frequency electromagnetic fields (ELF-EMF) affecting marine organisms. Using Cyclina sinensis as a model, this study examined effects of short-term (24-h intermittent exposure, 2-h on/off, then field-free recovery to day 14) and long-term (14-d intermittent exposure, 2-h on/off) ELF-EMF exposure (15 ± 1 μT, 50 Hz) versus geomagnetic control. Physiological indices were measured at 0, 1, 14 days post exposure (dpe) with time-matched controls, transcriptomic controls existed only at 0 dpe. Survival was 100 ± 0% (Control), 95.56 ± 1.92% (Short-term), and 90.00 ± 3.33% (Long-term). Short-term exposure elevated hepatopancreatic SOD, CAT activities and reduced MDA levels, returning to baseline by 14 days after exposure ceased. Long-term exposure reduced SOD, CAT and increased MDA. Transcriptomic profiling versus 0 dpe baseline identified 5479 and 4985 differentially expressed unigenes in Short- and Long-term groups, respectively. Because no time-matched transcriptomic controls at 1 and 14 dpe were included, these comparisons are confounded by experimental time and cannot be attributed solely to ELF-EMF. Short-term enrichment of endoplasmic reticulum stress and oxidative phosphorylation agrees with a parallel study using the same exposure conditions and 14-d time-matched controls, supporting an ELF-EMF-associated early response. Other long-term transcriptomic changes including amino acid metabolism, translational changes remain exploratory. These results suggest time-associated physiological responses and provide preliminary molecular insights for ecological risk assessment of offshore wind farms and sustainable coastal management. Future studies with time-matched controls at both 1 and 14 dpe are required to validate the molecular findings.