Zostera marina among seagrass suffering from global decline is a representative species in temperate regions in the Northern Hemisphere. Given our recent findings, the decline of seagrasses may be associated with the photosensitivity of the oxygen-evolving complex (OEC). Therefore, understanding the mechanism of OEC photosensitivity is key to understanding the continued decline in seagrasses. Herein, we explored the screening-based photoprotection function in Z. marina by examining the inactivation spectrum of OEC and the differences in photoresponse pathways following exposure to different spectrums. The OEC inactivation was spectral-dependent. High-energy light significantly reduced the PSII performance, OEC peripheral protein expression, and photosynthetic O ₂ release capacity. The increased synthesis of carotenoids under blue light with severe OEC damage implied its weak photoprotection property in Z. marina. However, anthocyanins key synthetic genes were lowly expressed with inefficient accumulation under high-energy light. Furthermore, the acylation modifications of anthocyanins, especially aromatic acylation modifications were insufficient, leading to poor stability and light absorption of anthocyanins. Based on the role of blue light receptors in regulating the synthesis of anthocyanins in vascular plant, we hypothesized that the absence of blue light receptor CRY2 in Z. marina causes the insufficient synthesis of anthocyanins and acyl modifications, reducing the shielding against high-energy light, subsequently causing OEC photoinactivation.