Eelgrass Restoration Trials on Cape Cod

The Nature Conservancy (TNC) and Barnstable County Cooperative Extension Marine Program recently completed eelgrass restoration trials on Cape Cod.  The project was designed to evaluate sites with potential for full-scale restoration in the region.  The work included identification of potential sites, evaluating the sites for suitability, choosing the top 2 to 3 ranked sites, performing transplant trials at these sites, and monitoring for one year post-planting.

Site selection was done using a modification of the Short et al. (2002) method, with modifications based on available site specific data. In addition, consultation with an advisory team including local natural resource officers, representatives from State and Federal agencies, and the research community were consulted for their ideas on site suitability.  Using the site data and comments from the advisory team, sites were ranked and the top three were chosen for transplant trials: Phinney’s Harbor in Bourne, Nauset/Town Cove in Orleans, and Cape Cod Bay in Truro.

Plantings were done in September 2010 using both the clump transplant method and the horizontal rhizome method.  Monitoring was conducted at four different times:

• 2 weeks post-planting in October 2010 to check planting density and evaluate short-term survival,
• 8 months post-planting in May 2011 to evaluate winter survival,
• 10 months post-planting in July 2011 to evaluate survival and growth over the early part of the growing season, and
• 1 year post-planting in September 2011 to evaluate survival over the first full growing season

Donor beds were monitored in August 2010, July 2011, and September 2011 to evaluate any effect of removing plants for transplanting, and to compare donor bed plants with the transplants.

Transplant success at the test sites was variable until the end of the study, when all three

sites had almost no surviving plants. Initially survival was almost 100% at Phinney’s Harbor and Truro, while the Nauset site almost no plants survived.   At 8 months post-transplant the Phinney’s Harbor site was becoming established, with survival at over 100%.  The Truro site lost many plants, and Nauset showed virtually no surviving plants.  At 10 months post-transplant the Phinney’s Harbor site was dramatically reduced, likely due to high turbidity and low light levels.  At the 1-year mark almost no plants were left at any location (Figure 1). 

Figure 1. Eelgrass Transplant % Survival

 

Reasons for the lack of success differed for all three sites.  Nauset appeared to have been overrun by bioturbators; the Truro site was highly dynamic, with evidence of both scour and burial among plants, grid markers and buoy anchors.  Phinney’s Harbor, despite initial success, declined due to a mid-summer water quality decline, characterized by high turbidity and reduced light at the transplant site.

Truro 9-23-2010

Truro 10-13-2010

Truro 5-31-2011

Truro 7-19-2011

Truro 10-7-2011

Lastly, we include a short video clip taken at the Nauset donor bed in early August, 2011, which very nicely illustrates active photosynthesis - showing plants releasing O2 bubbles within the water column.