Providing evidence to improve practice

Individual study: A compararison of mechanized versus manual transplanting success of eelgrass Zostera marina in Chesapeake Bay, Virginia, USA

Published source details

Fishman J.R., Orth R.J., Marion S. & Bieri J. (2004) A comparative test of mechanized and manual transplanting of eelgrass, Zostera marina, in Chesapeake Bay. Restoration Ecology, 12, 214-219

Summary

Restoration of seagrass communities damaged due to anthropogenic activities has led to attempts to develop efficient methods for transplanting seagrass as the laborious process of manual transplanting has often limited the size of restoration efforts. This study tested the efficiency of a mechanized planting boat relative to manual transplanting methods for establishing ellgrass Zostera marina in Chesapeake Bay.

Sites: Sites for the comparison of manual versus mechanical planting of eelgrass Zostera marina were chosen based on previous manual transplanting eelgrass success. The first site was in the Rappahannock River and the second in the James River. Sediments at both are predominantly sand (sand/silt/clay content of 97.4/0.8/1.9 and 97.1/2.0/0.9% for the Rappahannock and James rivers, respectively). Both have a southerly exposure, while the James River site also has an easterly exposure component.

Eelgrass collection: Adult Zostera shoots were collected from a seagrass bed in the York River, Virginia that had served as a successful donor site in previous transplantings. Plants with intact rhizomes were dug up using shovels and sieved to remove sediment. At the transplant sites, plants were sorted into bundles of approximately three to four shoots. These bundles were used as planting units (Pus) for both the machine and manual planting methods.

Eelgrass planting: Planting took place in October 2001. Eelgrass was planted four 60 m rows at each site using the mechanized transplanting boat (owned by Seagrass Recovery Inc.) which was initially designed to transplant tropical seagrasses (particularly Halodule wrightii). Rows were 10 m apart and parallel to shore. Each row consisted of two lines (one from each planting wheel) of approximately 65 bundles/line planted every 0.91 m. Two snorkelers or SCUBA divers then manually transplanted four rows (two lines per row) next to each of the machine rows using approximately the same size bundles at the same spacing as the machine.

The two methods were evaluated by three criteria:

1) initial planting success (i.e. proportion of PUs initially established, number confirmed by diver surveys)

2) survival (proportion of the initially established PUs persisting over 1, 4 and 24 weeks)

3) efficiency (labour, in person•seconds, invested in each surviving PU)

Initial PU planting success was significantly lower for the planting boat (24% at Rappahannock and 56% at the James site) than for manual transplanting (100% at both sites).

In the Rappahannock River, survival of initially established PUs declined over time for both methods, but while average survival was always higher for manually planted rows, differences in survival between methods were not statistically significant.

In the James River, survival to 1 and 4 weeks was significantly lower for the mechanical compared to the manual method, but survival to 24 weeks was not significantly different. Whilst the mechanised method was able to attempt planting faster (2.2 s/PU) than the manual method (5.8 s/PU) this faster speed was negated by poorer planting success, resulting in a much greater total labour investment for each machine-planted PU that persisted to 24 weeks (40.6 person/seconds/PU, averaged across sites) than for each similarly persisting manually planted PU (22.4 person/seconds/PU).

Conclusions: Those PUs successfully planted by the machine survived similarly to PUs planted by hand, but as a result of poorer initial planting success, the machine required a greater investment of labor and plant donor stock for each PU surviving to 24 weeks. Therefore, in its tested configuration this planting boat is not a significant improvement over the manual method for transplanting eelgrass.


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