Meta-analysis of oyster impacts on coastal biogeochemistry

Overfishing, nutrient-fuelled hypoxia and habitat destruction have reduced oyster populations to a fraction of their former abundance. Over the past two decades there has been a widespread effort to restore oyster reefs and develop oyster aquaculture. Yet it remains unclear how re-introduction of large oyster populations will change coastal biogeochemistry. Of particular interest is whether oysters may help offset excess nitrogen loading, which is responsible for widespread coastal water quality degradation, low oxygen conditions and biodiversity declines. Here we used a meta-analysis approach to assess how oysters alter inorganic nutrient cycling, with a focus on nitrogen removal. Additionally, we examined how oysters alter greenhouse gas emissions. We demonstrate that oysters enhance removal of excess nitrogen by stimulating denitrification, promote efficient nutrient recycling and may have a negligible greenhouse gas footprint. Further, oyster reefs and oyster aquaculture appear to have similar biogeochemical function, suggesting the potential for sustainable production of animal protein alongside environmental restoration. Oysters clean nutrient-polluted waters, but their populations have crashed. This study synthesizes research on oyster impacts and finds that they help remove excess nitrogen and promote nutrient recycling without contributing greatly to greenhouse gas emissions.