Seagrass recovery in the Delmarva Coastal Bays, USA

• Published in: Aquatic botany 2006, Vol.84 (1), p.26-36
• Main Authors: Orth, Robert J., Luckenbach, Mark L., Marion, Scott R., Moore, Kenneth A., Wilcox, David J.
• Format: Article
• Language: English
• Subjects: Argopecten irradians; Branta bernicla; Delmarva Coastal Bays, USA; Eelgrass; Marine; Recovery; Restoration; Seagrass; Zostera marina
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/j.aquabot.2005.07.007

Zostera marina (eelgrass) in the coastal bays of the Delmarva Peninsula, USA, declined precipitously in the 1930s due to the pandemic wasting disease and a destructive hurricane in 1933. This resulted in major changes in many of the ecosystem services provided by this seagrass, such as loss of bay scallops ( Argopecten irradians) and disappearance of brant ( Branta bernicla). Natural recovery of Z. marina, possibly deriving from either small remnant stands or undocumented transplant projects after the demise of Z. marina, has been significant in four northern bays, with over 7319 ha reported through 2003 compared to 2129 ha in 1986, an average expansion rate of 305 ha year −1. This rapid spread was likely due to seeds and seed dispersal from recovering beds. However, no recovery had occurred in the southern coastal bays prior to restoration efforts, possibly due to both their distance from potential donor beds, restricted entrances to the bays, and the narrow time period when seeds are available for colonization via rafting reproductive shoots carrying viable seeds. Survival and expansion of small test plots (4 m 2) in these southern coastal bays between 1997 and 2000 demonstrated that propagule supply, rather than water quality, was limiting seagrass recovery in these bays. In 2001, we initiated a large-scale Z. marina restoration effort in the southern coastal bays utilizing seeds, while simultaneously monitoring water quality using spatially and temporally intensive water quality mapping techniques. Between 2001 and 2004, approximately 24 million seeds harvested from natural, dense beds in Chesapeake Bay were broadcast into experimental plots ranging in size from 0.2 to 2 ha in four coastal bays having no seagrass, totaling approximately 46 ha through 2004. Successful germination (estimated at 5–10% of seeds broadcast), growth and expansion of Z. marina in and around these plots over this 3-year test period, as well as water quality data, suggest conditions are appropriate for plant growth. Low-level aerial photographs in 2004 showed 38% of the bottom in 52–0.4 ha plots was covered by vegetation. Increasing Z. marina coverage will have important implications for fisheries and waterfowl but may potentially conflict with aquaculture, which is rapidly expanding in this region. Continued recovery will depend on maintaining good water quality to avoid the macro-algal accumulations and phytoplankton blooms that have characterized other coastal lagoons. The pa