How Does Seagrass Cope with Eutrophication? From Stress Responses to Molecular Adaptive Mechanisms

Purpose of Review

Seagrass meadows, essential yet vulnerable marine ecosystems, display complex dual responses to eutrophication. These impacts are especially concerning in seagrass meadows due to the higher frequency and intensity of eutrophication. This review was aimed at summarizing stress responses and adaptive mechanisms of seagrass from the view of eutrophication.

Recent Findings

Moderate nitrogen and phosphorus inputs initially enhance photosynthesis and biomass accumulation in nutrient-poor environments by increasing chlorophyll synthesis and photosynthetic efficiency. However, prolonged exposure leads to detrimental effects, including light attenuation from algal blooms, ammonium toxicity impairing electron transport rates, and competitive exclusion by fast-growing algae. Species-specific tolerance varies significantly: resilient seagrasses like Halodule wrightii upregulate antioxidant enzymes (e.g., superoxide dismutase and catalase) and accumulate non-enzymatic flavonoids to mitigate oxidative stress, while sensitive species such as Syringodium filiforme suffer metabolic imbalances and biomass loss. Adaptive mechanisms span multiple scales. At the molecular level, stress-responsive transcription factors (e.g., WRKY transcription factor gene and MYB proto-oncogene transcription factor gene) regulate antioxidant and carbon metabolism genes in Posidonia oceanica under nutrient excess. Physiologically, seagrasses reallocate carbon to belowground tissues under shading and suppress algal competitors via allelochemicals. Ecologically, herbivory-mediated algal control indirectly reduces oxidative stress. Despite these adaptations, chronic eutrophication degrades ecosystem services and destabilizes fishery habitats.

Summary

This review summarized the stress responses and adaptive mechanisms of seagrass under eutrophication. Future research must address climate–eutrophication synergies and leverage omics technologies to decode epigenetic resilience mechanisms. Such interdisciplinary efforts are critical to preserving seagrass meadows as blue carbon hubs and biodiversity refuges in rapidly changing coastal ecosystems.