Seed addition facilitates eelgrass recovery in a coastal bay system

Abstract

Eleven years of eelgrass Zostera marina seed additions conducted in a coastal bay system where Z. marina had not been reported since 1933 have resulted in rapid Z. marina expansion beyond the initially seeded plots. From 1999 through 2010, 37.8 million viable seeds were added to 369 individual plots ranging in size from 0.01 to 2 ha totaling 125.2 ha in 4 coastal bays. Subsequent expansion from these initial plots to approximately 1700 ha of bay bottom populated with Z. marina through 2010 is attributable to seed export from the original plots and subsequent generations of seedlings originating from those exports. Estimates of annual patch vegetative expansion showed mean estimated diameter increasing at varying rates from 10 to 36 cm yr −1 , consistent with rhizome elongation rates reported for Z. marina. Water quality data collected over 7 yr by spatially intensive sampling, as well as fixed-location continuous monitoring, document conditions in all 4 bays that are adequate to support Z. marina growth. In particular, median chlorophyll levels for the entire sampling period were between 5 and 6 µg l −1 for each of the bays, and median turbidity levels, while exhibiting seasonal differences, were between 8 and 9 NTU. The recovery of Z. marina initiated in this coastal bay system may be unique in seagrass recovery studies because of how the recovery was initiated (seeds rather than adult plants), how rapidly it occurred (years rather than decades), and the explicit demonstration of how one meadow modulated water clarity and altered sediments as it developed and expanded. Our results offer a new perspective on the role seeds can play in recovery dynamics at large spatial scales.

Restoration recovers population structure and landscape genetic connectivity in a dispersal‐limited ecosystem

“…Our genetic analyses indicated that those naturally recruited patches had a relatively low genetic diversity and showed signs of genetic drift, probably due to a small founding population and subsequent inbreeding. Through intervention via seed-based restoration, areal coverage (see Orth et al 2012) has increased, and the resulting genetic diversity was similar to donor meadows . In this case, restoration is less likely than natural recovery to result in populations that exhibit issues such as inbreeding, because restoration involves a large pulsed addition of seeds rather than the small and slow addition of seeds as in natural recruitment.…”

Eelgrass survival in two contrasting systems: role of turbidity and summer water temperatures

“…1). One site, South Bay, is lo cated within a large Z. marina restoration site in 1 sub-basin along the Virginia and Maryland (USA) Delmarva peninsula's coastal bay system (see Orth et al 2012 …”

Eelgrass restoration by seed maintains genetic diversity: case study from a coastal bay system

“…The use of seeds harvested from multiple parents, rather than adult plants, could offset this genetic bottleneck. The successful re-establishment of Zostera marina into unvegetated coastal bays in the mid-Atlantic region of the United States using seeds from a number of source beds (Orth et al 2012) offered a unique opportunity to test the hypothesis that genetic diversity is not eroded when seeds are used as in restoration. Here we present results from our analysis of genetic diversity from both natural Z. marina beds in Chesapeake Bay, several of which have served as source beds for restoration, and the restored beds in the Virginia coastal bays.…”