Response of the microbial community to environmental change during seagrass transplantation

• We sampled the sediment microbial community during seagrass restoration.
• We examined genes for sulfate reduction (dsrB) and denitrification (nirK).
• Transplanted seagrass cores retained microbial characteristics from the donor site.
• dsrB abundance and porewater sulfides increased over time.
• Increasing porewater sulfide concentrations contributed to seagrass mortality.

Previous studies have shown that interactions between seagrasses and sediment microbial communities can influence the success of seagrass transplantation. How the microbial community responds to transplantation and how that may influence seagrass survival still remains unclear. We sampled the sediment microbial community during a restoration project of shoalgrass (Halodule wrightii) to determine how the abundance and diversity of dsrB (sulfate reduction) and nirK (denitrification) genes change during transplantation. We related these patterns to the health of the restored seagrass bed. Our results show that transplanted seagrass cores act as microhabitats that retain sediment and microbial characteristics from the donor site for at least two months after transplantation. The diversity of dsrB genes remained significantly different between transplanted seagrass cores and native sediment in the restoration site. There was little difference in the abundance of dsrB and nirK genes between donor site, transplants and native sediment, which suggests that the size of these populations was not influenced by the presence of H. wrightii. After transplantation, abundance of dsrB genes and porewater sulfide concentrations increased over time, corresponding with a decrease in health and survival of the transplanted seagrass cores. Increasing sulfide concentrations likely contributed to the mortality of the transplanted seagrass bed. However, the failure of the restoration project was probably due to a combination of factors, including the lack of water movement and the high amplitude of diurnal cycles of dissolved oxygen in the water column of the restoration site.