Oyster Larval Transport/Hydrodynamic Modeling for the Herring Bay Sanctuary, Maryland

Background: The Chesapeake Bay Agreement 2014 goal of successfully restoring oysters to 10 tributary rivers, 5 in Virginia and 5 in Maryland is on track to be achieved in 2025. This was the initial goal of the Chesapeake Bay Program's Oyster Goal Implementation Team (GIT). In considering future restoration efforts, USACE-Baltimore District and the Maryland Department of Natural Resources (MDNR) are considering selecting Herring Bay, an open water sanctuary for a large-scale restoration project. Herring Bay is in the mainstem of the middle Chesapeake Bay along the western shoreline. The Herring Bay Sanctuary is expansive at 16,792 ac. Within the sanctuary, 7,981 (48%) is historic oyster bottom or Yates Bars that would be evaluated for restoration potential as part of the process to develop a restoration plan for the sanctuary. Historically, this portion of the Bay held abundant oyster habitat, but over harvesting, impaired water quality, loss of habitat, and disease have all contributed to low populations today. Limited sampling by the Maryland Department of Natural Resources (MDNR) have identified populations to be essentially eliminated from the existing sanctuary. Conditions including water quality and bottom substrate support reef restoration, however little information on reproduction and larval transport are available to support developing restoration plans. An understanding of local currents and their ability to transport oyster larvae to and within the sanctuary will play a key role in reestablishing sustainable oyster reef habitat and populations. It is known that most oyster reef systems consist of both source and sink reefs, with the source reefs providing oyster larvae to self-replenish, as well as providing larvae to other hydrodynamically-connected reefs (Lipcius et al. 2015, Theuerkauf et al. 2021). The intent of this investigation is to generate information to identify source and sink dynamics within Herring Bay. That information will be folded into tributary plan development to prioritize sites for restoration sites. Simulations from bio-physical models can be used to identify potential restoration sites based on how they fit into the regional metapopulation. USACE and MDNR intend to use the findings of the proposed modeling to identify a phased restoration plan to restore sustainable oyster populations to Herring Bay.

Lipcius, R.N., Burke, R.P., McCulloch, D.N., Schreiber, S.J., Schulte, D.M., Seitz, R.D., Shen, J., 2015. Overcoming restoration paradigms: Value of the historical record and metapopulation dynamics in native oyster restoration. Frontiers in Marine Science 2, 65.

Theuerkauf, S.J., Puckett, B.J., Eggleston, D.B., 2021. Metapopulation dynamics of oysters: sources, sinks, and implications for conservation and restoration. Ecosphere 12, e03573.

Program Description/Objective: The objective of this investigation is to perform hydrodynamic modeling of the region with a linked oyster larval model in order to assess oyster larval transport and metapopulation dynamics in the region and inform a restoration plan for the Herring Bay Sanctuary. Source and sink reefs should be identified, as well as reefs that auto-recruit sufficiently to be self-sustaining on their own. If possible, indicate, based on oyster biology, how large a particular source area should be to augment regional recruitment to a detectable level. Restoration in Herring Bay has the potential to be very expansive. Understanding the larval connections within and to Herring Bay will enable a multi-phase restoration plan to be developed. An additional objective is to understand from where larvae are transported to Herring Bay, thereby developing connectivity to other oyster restoration efforts as well as adjacent harvest grounds.

Public Benefit: Undertaking a large-scale ecosystem restoration project in the open, mainstem of the Chesapeake Bay is a new approach compared with past efforts that focused on retentive tributary systems. Determining how to implement mainstem restoration efforts could serve as a model for restoration in other regions.

The societal benefits from restoring functioning oyster reef habitat are numerous. Oysters are a keystone species in Chesapeake Bay providing unique hard habitat to reef-dwelling and reef- associated species. Once estimated to able to filter the entire volume of Bay water in approximately three days, the present population, being severely depleted, takes over a year to perform this ecological service. Restored reef are expected to improve water quality by restoring filtering capacity and increasing denitrification rates and water clarity. In addition to providing oyster habitat, the restored reefs will improve local production of commercially and recreationally valuable fished species, such as blue crabs. Further, oyster reefs stabilize sediment to improve water clarity. Understanding larval connections to adjacent areas could provide benefits to wild harvest areas.

The results of this study shall also be published in a peer-review journal in collaboration with Baltimore District personnel, to provide the information gathered in the proposed study to the wider scientific community.