Effects of Ocean Acidification on Seagrass Ecosystems

The ecological effects of ocean acidification are among the central issues in contemporary global change research. As a key component of blue carbon ecosystems, seagrass beds were once simplistically framed as "carbon-limited beneficiaries" of rising CO 2 concentrations. However, evidence accumulated over the past two decades has revealed a far more complex picture.This review synthesizes major advances in seagrass acidification research from 2008 to 2026, organizing core findings and controversies across three levels: individual physiology, interspecific interactions, and ecosystem function.It shows that direct physiological responses of seagrasses to acidification are markedly species-specific, time-dependent, and environmentally contingent, enhanced photosynthesis does not necessarily translate into enhanced growth, and short-term responses are not equivalent to long-term effects. By weakening phenolic chemical defenses and restructuring epibiont communities, acidification may trigger indirect effects across trophic levels that partially offset its direct "carbon fertilization" benefits.Seagrass beds can provide localized acidification buffering during the day, but this capacity declines markedly under multiple co-occurring stressors. This review argues that casting seagrasses simply as climate change "winners" or "losers" is misleading, a more accurate understanding treats them as "conditional responders" whose ecological fate depends on the interaction of species identity, stressor combinations and spatiotemporal scale.