Overcoming restoration paradigms: value of the historical record and metapopulation dynamics in native oyster restoration

Abstract

Restoration strategies for native oyster populations rely on multiple sources of information, which often conflict due to time-and space-varying patterns in abundance and distribution. For instance, strategies based on population connectivity and disease resistance can differ, and extant and historical records of abundance and distribution are often at odds, such that the optimal strategy is unclear and valuable restoration sites may be excluded from consideration. This was the case for the Lynnhaven River subestuary of lower Chesapeake Bay, which was deemed unsuitable for Eastern Oyster (Crassostrea virginica) restoration based on physical conditions, disease challenge, and extant oyster abundance. Consequently, we (i) evaluated previously unknown historical data from the 1800s, (ii) quantified extant oyster recruitment and abundance, physical conditions, and disease presence on constructed restoration reefs and alternative substrates, and (iii) assessed simulations from biophysical models to identify potential restoration sites in the metapopulation. The collective data distinguished numerous restoration sites (i) in the polyhaline zone (salinity 18.4-22.2) where disease resistance is evolving, (ii) where oysters were abundant in the late 1800s-early 1900s, (iii) of recent high recruitment, abundance and survival, despite consistent and elevated disease challenge, and (iv) interconnected as a metapopulation via larval dispersal. Moreover, a network of constructed restoration reefs met size structure, abundance and biomass standards of restoration success. These findings demonstrate that assumptions about the suitability of sites for oyster restoration based on individual processes can be severely flawed, and that in-depth examination of multiple processes and sources of information are required for oyster reef restoration plans to maximize success. We use these findings and previous information to recommend a strategy for successful restoration of subtidal oyster reefs throughout the range of the Eastern Oyster.

Millennial-scale sustainability of the Chesapeake Bay Native American oyster fishery

“…Although the effectiveness of the modern restoration strategy of Chesapeake oysters is debated (5,15), our Pleistocene-toAnthropocene size and archaeological relative abundance data provide some support for recent Chesapeake Bay oyster restoration efforts, including reduction of modern harvest levels and creation of increased no-take zones (13,43) that would mimic the more mobile and flexible Native American fishery. Current restoration plans (44) include enhancement of oyster density using hatchery seed, addition of new hard substrate where needed, and no-take reserves that are conceptually similar to deep-water areas where harvest was unlikely before the introduction of oyster tongs and dredges.…”

“…Following decades or more of overfishing, pollution, and other perturbations, estuaries and bays around the world are in a dramatic state of decline (1,2). Oysters (Ostreidae) are ecosystem engineers in many estuaries, providing a variety of ecosystem services including water filtration and habitat construction for other organisms (3)(4)(5)(6). Oysters have also long been an attractive food source for people, including those living near North America's Chesapeake Bay (7)(8)(9)(10).…”

“…A key element missing from discussions of past oyster abundance and population structure is a comprehensive understanding of the fishery before historical overfishing (5,6,8,11). Native Americans have lived in the Chesapeake region since the late Pleistocene (>13,000 y ago), when it was part of the Susquehanna River valley, throughout the Holocene submergence of the valley…”

Quantitative Validation of a Habitat Suitability Index for Oyster Restoration

“…For low-relief reefs, reef persistence depends greatly on whether live oyster shell accretion outpaces subsidence and sedimentation (Schulte et al, 2009;Jordan-Cooley et al, 2011;Colden and Lipcius, 2015;Lipcius et al, 2015). In several cases, low-relief reefs in the GWR with HSI ≥ 0.3 exhibited low live adult oyster densities.…”

Reef height drives threshold dynamics of restored oyster reefs

“…These differences were driven mainly by flow speed, which varied with reef height and influenced sedimentation patterns. Schulte et al (2009) and Lipcius et al (2015) determined that high-relief reefs (0.25 to 0.45 m) had higher oyster abundances and tended to persist while low-relief reefs (0.08 to 0.12 m) had lower abundances and were variable in their success. Similarly, Powers et al (2009) determined that sedimentation was a major factor influencing the success of restored oyster reefs and that a minimum of 0.2 m relief was required for restoration success.…”