Seagrass recovery in the Delmarva Coastal Bays, USA § Robert J. Orth * , Mark L. Luckenbach, Scott R. Marion, Kenneth A. Moore, David J. Wilcox Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, Gloucester Point, VA 23062, USA Received 27 July 2004; received in revised form 15 July 2005; accepted 18 July 2005 Abstract 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 patterns of natural seagrass recovery and the results of restoration efforts we describe here, as well as seagrass recoveries from wasting disease outbreaks, anoxic events, hurricanes, and propeller scarring reported elsewhere, suggest that seeds and seed dispersal play an important role in the recovery and expansion of these beds. # 2005 Elsevier B.V. All rights reserved. Keywords: Seagrass; Zostera marina; Eelgrass; Recovery; Restoration; Delmarva Coastal Bays, USA 1. Introduction One of the most dramatic but least understood events in seagrass population biology was the pandemic decline of Zostera marina L., eelgrass, in the 1930s (Cottam, 1934; Milne and Milne, 1951; Hemminga and Duarte, 2000). Populations of Z. marina in the western Atlantic were almost completely eliminated in the span of just a few years. Speculation on the cause of this decline centered on climatic changes and a disease organism, the marine slime mold, Labyrinthula zosterae (Renn, 1936; Rasmussen, 1977; Short et al., 1988), but the exact cause was never conclusively proven. Recent work has shown that L. zosterae is capable of causing death to Z. marina on a local scale (Muehlstein et al., 1991; Muehlstein, 1992; Short et al., 1986, 1987, 1988; Ralph and Short, 2002) but its role in the pandemic decline remains unclear. This pandemic decline had significant consequences for the many ecosystem services (Costanza et al., 1997) associated with seagrasses. Most notable were reductions in animal populations (Rasmussen, 1973), including commercially and recreationally important organisms, e.g. brant (Branta bernicla) and bay scallops (Argopecten irradians)(Milne and Milne, 1951), but the decline also completely eliminated one www.elsevier.com/locate/aquabot Aquatic Botany 84 (2006) 26–36 § Contribution No. 2686 from the Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA, USA. * Corresponding author. Tel.: +1 804 684 7392; fax: +1 804 684 7293. E-mail address: jjorth@vims.edu (R.J. Orth). 0304-3770/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquabot.2005.07.007