Site and Season Influence the Success of Seagrass Transplantation in Aotearoa New Zealand

Seagrasses are important ecosystem engineers that create nursery habitat for fish, support high biodiversity, enhance water quality and store carbon. However, seagrasses are declining globally, including in many places in New Zealand. One approach to counter these losses is shoot‐based seagrass restoration, which involves transplanting adult seagrass plants together with their surrounding sediment and associated communities. We investigated the feasibility of shoot‐based restoration by transplanting 150 mm plugs of seagrass ( Zostera muelleri ) from donor seagrass meadows to nearby unvegetated soft sediment at two sites in Nelson Haven, New Zealand. Sites differed in donor meadow age (old vs. new) and environmental conditions. We also tested whether transplant season (winter vs. summer) influenced success. Transplant success was monitored over 2 years and determined by an increase in seagrass area, blade number, and blade length. Bayesian modelling showed that both site and season influenced success. The best‐fit model showed greater success when transplants from the ‘older’ donor meadow, which had higher seagrass cover, lower mud content and shorter tidal exposure, performed better than those from the ‘newer’ meadow. Model predictions also indicated greater success in winter than in summer. Empirical observations supported these patterns; for example, we observed 30% survival of transplants at the older site after winter transplantation, whereas zero transplants survived after summer transplantation or at the ‘newer’ meadow. There were no obvious detrimental effects of seagrass removal from donor meadows, and this study shows that transplanting Z. muelleri with an intact sediment community can be an effective restoration method in intertidal habitats, though success is highly context dependent. This study gives practical insights to guide future seagrass‐restoration efforts.