The influence of seagrass donor source on small‐scale transplant resilience

Abstract

1. Concern for conservation of seagrass habitat has prompted international transplantation-style restoration efforts. A recent review of these restoration efforts has highlighted the low success associated with small-scale restorations, yet scaling up transplantation effort may be too costly for underfunded regions. Small-scale transplant survival can be enhanced with alleviation of two underlying issues: restoration site selection and donor site selection. 2. To investigate appropriate donor source selection, donor site environmental influence on seagrass (Halodule wrightii) transplant survival was examined by transplanting donor cores from two environmentally disparate sites to a transplantation site with limited environmental uncertainties. Donor sites were chosen to represent either end of a benthic light gradient (high versus low) to elucidate seagrass resilience to transplantation stress, with respect to donor site conditions. 3. After total loss of the first trial, a second trial was conducted with stabilizing mesh placed over transplants to reduce stingray bioturbation. The second trial resulted in 100% survival of high light transplants after 12 months and moderate survival (30-60%) of low light transplants for the first six months. 4. At 18 months, the second trial ended after sediment burial from a hurricane. One year post-burial, a patch of H. wrightii recovered at the high light transplant site; after six years the patch expanded to approximately 74 m 2 , an area 37-fold larger than originally planted. 5. Results from this transplant experiment provide evidence that donor environment plays a role in transplant resilience. The transplants sourced from high light had 47% greater leaf area per shoot, were more resistant to transplantation stress, and recovered following an extreme event relative to low light transplants. Therefore, selection of donor plants with more resilience features, a transplantation site with limited environmental uncertainties, and adaptive intervention can enhance seagrass resilience at a small planting scale.

Rewilding the Sea with Domesticated Seagrass

“…Third, a global analysis has shown that large-scale restoration trials are on average more successful than small-scale trials (van Katwijk et al 2016 ). Finally, in multisite, multiyear restoration programs, it is often observed that only a few trials within the program expand vigorously, whereas the remaining trials fail (Suykerbuyk et al 2016 , Paulo et al 2019 , McDonald et al 2020 ). These failures can often be explained in hindsight (McDonald et al 2020 ) or, at least, alluded to (Suykerbuyk et al 2016 , Paulo et al 2019 ), but they cannot be predicted, suggesting the operation of chance dynamics in the recovery process.…”

Macrophyte species richness improves resilience to grazing

“…Additionally, when genotypes or species have different and asynchronous responses to disturbances and stress, this can lead to increased stability and is termed the ‘insurance hypothesis’ (Yachi & Loreau, 1999). Seagrass rhizomes store non–structural carbohydrates that can be mobilized to facilitate re‐growth following disturbances or stress (Sanmartí et al, 2014), and variation in rhizome carbohydrate storage as well as variation in plant growth rates among seagrass species and genotypes can drive delayed and asynchronous responses to disturbances (Barry et al, 2018; Dawes & Lawrence, 1980; Evans et al, 2018; Hughes et al, 2009; Maxwell et al, 2014; McDonald et al, 2020; Ralph et al, 2007; Reynolds et al, 2016; Touchette & Burkholder, 2000).…”

Recovery of a Halodule wrightii donor meadow

“…The fourth method can damage the donor meadow and, in addition, generate changes in local sediment dynamics with erosive impacts, which may impair or delay the recolonization (Maxwell et al 2017; Githaiga et al 2019). Plants can be extracted from a donor meadow with or without sediments, but the introduction of transplants with the original sediments preserves the rooting environment and provides better anchorage, resulting in successful transplant establishment (Paling et al 2001; Hall et al 2006; McDonald et al 2020). Paulo et al (2019) comment that the failure rate of using sediment‐free methods has been high (e.g., 100% failure for Zostera marina , Zostera noltei , and Cymodocea nodosa in Portugal) and recommend using seagrass harvesting methods with their natural sediment.…”

“…Paulo et al (2019) comment that the failure rate of using sediment‐free methods has been high (e.g., 100% failure for Zostera marina , Zostera noltei , and Cymodocea nodosa in Portugal) and recommend using seagrass harvesting methods with their natural sediment. Sods and cores/plugs are the most common and effective extraction methods with sediments, but small‐sized cores are preferred if the damage to the donor meadow should be minimized (Verduin et al 2012; Paulo et al 2019; McDonald et al 2020).…”

“…H. wrightii is the second most used seagrass species in restoration efforts (58 trials) after Z. marina (202) (van Katwijk et al 2016). H. wrightii is a faster‐growing species (horizontal rhizome extension rate of 80–365 cm/year; Marbá & Duarte 1998) and is tolerant to low light conditions due to water turbidity (14–33% surface irradiance) and variable salinity conditions (15–30) and can persist in unstable and disturbed environments (Larkin et al 2008; McDonald et al 2020).…”