Eelgrass populations have been declining on a global scale, even faster than the rate of deforestation in tropical rainforests. These aquatic plants provide a number of important ecosystem services as food sources and habitat for marine species and offer important benefits in shoreline resilience for addressing climate change. Eelgrass beds can help reduce the effects of sea-level rise and coastal erosion and sequester atmospheric carbon.
As restoration efforts have begun throughout California, some locations such as the Upper Newport Bay, have begun testing efforts to restore eelgrass in conjunction with native oysters. Eelgrass can help boost oyster productivity by reducing the acidity of surrounding waters, allowing oysters to invest more energy in reproduction rather than shell growth. Meanwhile, oysters can help eelgrass by filtering excess nutrients from the water, providing organic nitrogen through waste and increasing water clarity for better photosynthesis.
Prior studies have shown that nitrogen enrichment can benefit eelgrass growth, however, this was the first study to test the Olympia oyster as a source of fertilization. This project measured the nitrogen concentrations around the oyster and eelgrass beds in the Upper Newport Bay State Marine Conservation Area. The researchers also measured the growth and productivity of eelgrass beds, both with and without oyster presence, to assess any correlation with oyster fertilization.
The results of this project indicated that sediment porewater nitrogen is affected by oyster bed density and location within the bay. Porewater nitrogen, however, was not distinct between treatments; therefore, the total impact of oysters on local nitrogen levels is still unclear. In summary, oyster beds appear to elevate local nitrogen and potentially positively impact the below-ground growth, however, how this occurs and the directness of this relationship is still in need of investigation.
Coastal ecosystem restoration will play an important role in mitigating our risks from climate change and sea-level rise in the coming years. These results will help inform practices that can increase the efficiency and effectiveness of such programs through multihabitat restoration.