Lessons Learned from Efforts to Restore Oyster Populations in Maryland and Virginia, 1990 to 2007

Abstract

A century-long decline of the fishery for the Eastern oyster Crassostrea virginica (Gmelin, 1791) in Maryland and Virginia stimulated numerous efforts by federal, state, and nongovernmental agencies to restore oyster populations, with limited success. To learn from recent efforts, we analyzed records of restoration and monitoring activities undertaken between 1990 and 2007 by 12 such agencies. Of the 1,037 oyster bars (reefs, beds, or grounds) for which we obtained data, 43% experienced both restoration and monitoring, with the remaining experiencing either restoration or monitoring only. Restoration activities involved adding substrate (shell), transplanting hatchery or wild seed (juvenile oysters), bar cleaning, and bagless dredging. Of these, substrate addition and transplanting seed were common actions, with bar cleaning and bagless dredging relatively uncommon. Limited monitoring efforts, a lack of replicated postrestoration sampling, and the effects of harvest on some restored bars hinders evaluations of the effectiveness of restoration activities. Future restoration activities should have clearly articulated objectives and be coordinated among agencies and across bars, which should also be off limits to fishing. To evaluate restoration efforts, experimental designs should include replication, quantitative sampling, and robust sample sizes, supplemented by pre-and postrestoration monitoring.

Reef height drives threshold dynamics of restored oyster reefs

“…The threshold dynamics observed in this study are a likely explanation for both the initial loss of reef habitats along the Atlantic coast (Scheffer et al 2001, Kirby 2004) and for the failure of many repletion and restoration efforts that utilized low-relief reefs (Schulte et al 2009, Kennedy et al 2011, Wilberg et al 2013. Destructive harvesting techniques like dredging and hydraulic tonging reduce the height of reefs by disaggregating the reef structure and removing accreted oyster shells along with live oysters (Lenihan & Peterson 1998).…”

“…Concern over these declines and losses of attendant oyster ecosystem services, such as nutrient cycling, water filtration and habitat structure (Grabowski & Peterson 2007), have spurred efforts to restore oyster populations globally (Airoldi & Beck 2007), but these efforts have seen limited success (Airoldi & Beck 2007, Beck et al 2011, Kennedy et al 2011, Zu Ermgassen et al 2012.…”

“…We designed a large-scale field experiment to (1) determine if the threshold of initial reef height suggested in previous studies is realized in the field under identical environmental conditions, and (2) identify the mechanism(s) by which height influences reef trajectory. The identification of threshold responses to reef height would provide insights on the systemic collapse of oyster ecosystems worldwide and provide context for reef ecosystems that have failed to recover despite restoration efforts (Suding et al 2004, Kennedy et al 2011. It would also provide a means by which restoration managers can better understand the mechanistic drivers of restoration and utilize these dynamics to optimize limited resources.…”

Addition of juvenile oysters fails to enhance oyster reef development in Pamlico Sound

“…Eastern oyster Crassostrea virginica populations have been a target of decades of restoration efforts (Brumbaugh & Coen 2009, Kennedy et al 2011 because only 15% of historic oyster populations persist worldwide (Beck et al 2011). Unlike other marine biogenic habitats such as seagrass meadows or coral reefs, oysters are harvested for human consumption, thus increasing risk of degradation and decline.…”

Denitrification and nutrient assimilation on a restored oyster reef

“…taken at 594 locations within Chesapeake Bay and the Maryland and Virginia Coastal Bays (Kennedy et al 2011). Al though many restoration efforts focused on increasing substrate available for settlement of oyster larvae, a substantial number also targeted areas where natural larval supply was a limiting factor.…”