Effect of oyster aquaculture on elemental cycling and nitrous oxide fluxes: Insights from ionomics and gene expressions

Background/Question/Methods:

Oyster Aquaculture plays an important role in the growing demand of worldwide seafood market, especially with the decline of marine catches. The United States (US) leads the world in shellfish imports as domestic production contributes to less than 1% of the global production. One primary reason, limiting US productivity is the lack of long - term sustainable aquaculture practices. Oyster Aquaculture can significantly alter the ecology of surrounding ecosystems by modifying the culture habitat. For example, it can improve water quality by filtering phytoplankton, act as “hotspot” of nitrogen removal via denitrification and can lead to low oxygen events by increasing organic matter deposition. Therefore, sustainable practices are needed to promote healthy ecosystems, maximize ecological services (e.g. N removal), and limit negative consequences (e.g. low O₂conditions).

In this study, I am interested to see how N cycling communities (i.e. N₂0 production/consumption), change under different ages of aquaculture farms and how such changes influence sediment fluxes of other biogenic elements. To test the above objectives, I measured gaseos fluxes (e.g. N₂, N₂O, NO₂), gene expressions for 10 N-cycling genes (i.e., nifH, nirS, nirK, nosZ, amoA, napA, narG and nrfA) (using RT-QPCR)and mineral and trace element concentrations (using integrated plasma mass spectrometry (ICP-MS))  on sediments collected from 4 different aquaculture farms in Ninigret Pond, RI that varied in age.

Results/Conclusions

I hypothesized that with increase in age of farms, there will be differences in the fluxes and the expression of genes involved in nitrogen cycling especially denitrification and second, the age of the farms will significantly impact the concentrations and correlations of different elements in the sediments below the oyster racks and bags. Preliminary results suggests that age of the farm significantly impacts the rate of denitrification and nitrous oxide production, where the former decreases and the latter increases with the age of the farms. However, genes involved in denitrification (e.g. nifH) showed no differential expression with increase of the farm age. Additionally, several elements including both mineral and trace elements showed greater accumulation in sediment of older farms.

Data generated from this study will provide information to managers and policy makers about how aquaculture alters N cycling in coastal systems. Further, understanding the underlying genetic processes of N cycling in different aged oyster farms will provide information for proper management of coastal ecosystems, especially in the light of pressing global issues such as green house emissions and eutrophication.