Oyster Reefs of the Past Hold Lessons for Future Coastal Restoration
This is part 2 of a two-part series concerning Richard Condrey and Natalie Peyronnin’s recent paper, “Using Louisiana’s coastal history to innovate its coastal future,” published in Shore & Beach, Fall 2017. See part one here.
It’s hard to imagine the lush and expansive complex of marshes and oyster reefs that early explorers encountered in south Louisiana, as described in Dr. Condrey’s recent blog. It is equally as hard to imagine how Louisiana’s coast will look into the future.
Unfortunately, there will be large areas of marsh that are lost in the next 50 years, even as we start an aggressive restoration program. We can’t save it all. And as the Gulf of Mexico gets closer, we lose the protection from storms that our coast provides.
In a recent paper, Dr. Condrey and I propose that we should explore innovative approaches to transforming the current landscape instead of maintaining the landscape that exists today – and that we should look to the past to rethink our future.
Benefits of oyster reefs
We cannot rebuild the Great Barrier Reef of the Americas or other massive offshore oyster reefs off the coast of Louisiana. This is due to the lack of appropriate salinities and human alterations to the hydrology, as well as the immense cost of such an endeavor. But the coastline of today will become the offshore environment of the future. Within 50 years, and in some areas as soon as 30 years, water depths within the current marsh platform will increase, especially as sea level rises exponentially, and large swaths of marsh will be lost. These realities remind us that we must understand the past if we are to plan for a successful future.
By constructing shallow subtidal oyster reefs in small, open water bodies within areas of degraded marsh, the oyster reefs can establish and grow over the coming decades and centuries, providing biological diversity and storm surge protection to delay the demise of adjacent wetlands (Figure 1). Over time, the marsh slowly subsides or floods while oyster reefs grow and expand in their place (Figure 2).
In the near-term, the oyster reef restoration will increase habitat diversity and provide other key ecosystem services. In the long-term, habitats could transition from a marsh complex to an oyster reef complex, thereby maintaining the coastline, protecting interior wetlands from further erosion and providing storm surge protection to valuable infrastructure and communities.
Figure 1: Conceptual diagram depicting the future of coastal marshes affected by sea level rise and subsidence both without human intervention (a) and with the potential growth of oyster reefs over decades and centuries to replace ill-fated marshes and provide a coastal buffer (b).
Figure 2: Conceptual diagram depicting the (a) current degraded state of coastal wetlands, (b) predicted future wetland loss without human intervention, (c) implementation of shallow oyster reefs among degraded marsh today, and (d) the growth of oyster reefs over decades and centuries to provide a coastal buffer, prevent future wetland loss and protect remnant coastal marshes.
Lessons from the past
Louisiana’s Coastal Master Plan consistently looks toward the past, when the Mississippi River flowed naturally, for ideas on how to restore the delta. Reconnecting the river to adjacent basins through sediment diversions – keystone restoration projects of the plan – will provide some benefits today, but also have long-term benefits that will be seen in future generations.
Oyster reef restoration can be carried out with the same long-term vision. Louisiana’s coastal waters have historically been the site of vast offshore oyster reefs, which played a vital role in the overall health and sustainability of Louisiana’s coastline – but planning efforts have consistently undervalued the benefits of oyster reef restoration.
Shell mining, altered freshwater flows, and changes in hydrodynamics are largely responsible for the historic degradation of this resource, resulting in increased wave energy, erosion and loss of interior wetlands during fair weather events and tropical storms, as well as a loss of biodiversity.
We call on planners, scientists and engineers in Louisiana, and beyond, to explore and research how investing in oyster reef restoration today can be a return on investment for future generations and help to establish a sustainable coast.