COASTAL FORUM: Using Louisiana’s coastal history to innovate its coastal future By Natalie S. Peyronnin Richard Condrey Environmental Defense Fund, [email protected] Louisiana State University (retired), [email protected]

ouisiana’s Comprehensive Mas- LOUISIANA’S COASTAL Plain). This harbor provided an entrance ter Plan for a Sustainable Coast REEF HISTORY into the River of the Holy Spirit (now (Coastal Master Plan or CMP) To envision a more sustainable coastal Vermillion Bay’s Southwest Pass), the isL an evolving coastal planning process future, it might help to look back at our westernmost outlet for the Mississippi that began before 1998. The successive coastal history, back to when the coast River. During the annual flood, the River iterations of the Coastal Master Plan have was functioning as a more natural system of the Holy Spirit sent plumes of fresh never envisioned that its implemented — one that was self-sustaining. Within water out over the face of the reef for 16 projects would restore Louisiana’s coast 45 years of their “discovery of the New km into the GoM (Chaves ca 1537; Evia to historic levels (LCWCRTF and WCRA World,” Spanish sailors had outlined the 1968; Condrey et al. 2014), likely limiting 1998 Table 5-1; Barras et al. 2003 Figure coast of the Americas from the northern the reef’s height. 19; Couvillion et al. 2011; CPRA 2012 Atlantic to the southern Pacific and From the 1500s through the early Figures 5.11 and 5.12; Couvillion et al. documented the extensive reefs which 1800s, the GBRA was a dangerous im- 2013; CPRA 2017). Rather, until 2017, lined the Gulf of Mexico’s (GoM) shore pediment to navigation. Spanish vessels the plan predicted that its implemented (Chaves ca. 1537; Condrey et al. 2014). sailed along its southern face in the open projects would first slow then reverse At least three of the reefs throughout waters of the GoM even though this Louisiana’s current, catastrophic annual the GoM were apparently dominated made the mainland hard to see, appar- rates of land loss if, and only if, at least by the oyster Crassostrea virginica and ently using grounded drifttrees from the two events occurred: the observed rates are hypothesized to have depended on Mississippi River as markers (Barroto of subsidence declined and the rate of sea submarine freshwater discharges of 1687). Narrow channels meant tedious level rise was “moderate” (CPRA 2012 groundwater, as well as periodic surface passage of shallow draft vessels across the Figure 3.3). The science behind the 2017 water inputs during flood periods, from north-south axis of the reef (Evia 1968; Coastal Master Plan suggests that neither the Mississippi, Apalachicola, and Su- Audubon 1837). An east-west channel of these events are likely. Rather the 2017 wanee River basin aquifers to maintain separated the GRBA’s northern face from CMP concluded that the observed rates viable offshore salinities (Chaves ca. 1537; Louisiana’s mainland, and was used as an of subsidence had not declined (Reed Barroto 1667; Evia 1968; Dumain 1807; “inland passage” during the late 1700s and Yuill 2016) and concurred with the Charlevoix 1744; Condrey et al. 2014). and 1800s. Frequent shipwrecks involv- possibility that the rates of sea level rise ing the GBRA and its east-west channel would be “high” (CPRA 2017 Figure 3.6). One of these offshore oyster reefs — as prompted two government-financed As such, the 2017 CMP predicts an even we here name it, the Great Barrier Reef surveys, while international rivalry less optimistic future for the Louisiana of the Americas (GBRA) — was massive. prompted a third. The first was conducted coast than its previous iterations, with It extended along the coast of central under Spanish rule by Evia in 1785, the the predicted loss of between 5,800 and Louisiana for more than 160 km and out second under U.S. President Thomas 10,600 square kilometers of the coast, into the GoM for 8 to 16 km (Figure 1). Jefferson’s orders to Dumain in 1807, over the next 50 years, without further Its surface was normally under ~1 m of and the third by Gauld in 1778 scout- human intervention (CPRA 2017). The water, but was visible to sailors during ing the Spanish coast of Louisiana coast plan lays out $25 billion in projects over periods of low water (Chaves ca. 1537; for Great Britain. Evia (1968) provides 50 years to restore the coastline (and an- Barroto 1667; Evia 1968; Dumain 1807; detailed measurements of the GBRA, other $25 billion in storm risk reduction Condrey et al. 2014). the freshwater outflow of the Mississippi features for communities). Even with this River’s flood into the GoM, and vividly substantial investment, Louisiana is only At its western end, the GBRA was the documents the reef’s first-line-of-defense predicted to stave off between 30%-40% southern face of an important offshore role in coastal protection. Dumain (1807) of the potential loss. In keeping with the harbor, apparently frequented in the provides independent confirmation of spirit of the CMP, we suggest that a bold, 1500s by Spanish vessels catching favor- Evia’s measurements, discusses the neces- new approach will help to restore and able winds from Veracruz to Havana sity of a GBRA-related lighthouse, and rebuild coastal Louisiana and transition and Spain. Once in the harbor, the ves- describes how enemy vessels could attack to a smaller, more sustainable delta — sels were protected from southerly and New Orleans through GBRA-associated one that will embrace the delta-building easterly winds and seas by the GBRA and waterways. Gauld’s observations (1778) properties of the Mississippi River and from northerly winds by the Cape of the independently support those of Evia, coastal-protection properties of vast Cross (now Chenier au Tigre, the most Dumain, and Barroto and explain how offshore oyster reefs. easterly oak ridge of Louisiana’s Chenier

Page 34 Shore & Beach  Vol. 85, No. 4  Fall 2017 islands were forming from grounded drifttrees on the GBRA. When Audubon sailed from the Mis- sissippi’s Southwest Pass to Galveston Bay, Louisiana’s still sparsely settled coast was beginning to erode. Passage between Louisiana’s islands was no longer limited to pirogues. The oysters on at least the northern face of the GBRA were dead, had been dead for some time, and their empty shells were accumulating on the Louisiana shore, bleaching in the sun. As Audubon writes to his “dear friend” William MacGuillivary while “snugly” anchored in Cote Blanche Bay (Audubon 1838): “After visiting ‘Rabbit Island,’… we make our way between it and Friskey Point [possibly Point au Fer], by a narrow and somewhat difficult channel leading to the bay in which I now write. The shores around us are entirely formed of a bank, from twenty to thirty feet [6-9 m] high, and composed of concrete shells of various kinds, among which the Com- mon Oyster, however, predominates. This bank, which at present looks as if bleached by the sunshine and rains Figure 1. Estimated extent of the Great Barrier Reef of the Americas (GBRA, of centuries, is so white that it might gray area) in 1785-1807 based on the surveys conducted by Evia (1968, well form a guiding line to the vessels dashed lines) and Dumain (1807, dotted line) and the consistency of their which navigate this bay even in the measurements with the observations reported in Chaves (ca. 1537), Barroto darkest nights… (1687), Gauld (1778), and Audubon (1838). Coastal points: a) Cheniere au “The crossing of large bays, cum- Tigre; b) Vermilion Bay; c) Cote Blanche Bay; d) Atchafalaya Bay; e) Point au bered with shallow bars and banks of Fer; f) estimated extent of Last Island in 1800; g) Ship Shoal. The reef, while oyster-shells, is always to me extremely a major impediment to navigation, played a vital role in coastal protection and advance until its demise in first half of the 1800s, likely as the result of disagreeable, and more especially human alterations in ground- and surface-water discharges of the Mississippi when all these bars and banks do not River Basin. No pre-1840 surveys have been located which contradict this contain a single living specimen of that interpretation. most delectable shell-fish. Nay, I am assured by our pilot, who is no young- and distributary closure and resulting Remnants of these historic oyster ster, that ever since he first visited this aquifer recharge. reefs along Louisiana’s coast were heavily extensive waste, not an oyster has been mined from the 1940s through the 1990s VAST OYSTER REEFS WERE procured in these parts.” for commercial purposes, including road OUR FIRST LINE OF DEFENSE bed material, until a moratorium and In the year 1853, Lieutenant B. F. Sands As Louisiana focuses on re-establishing later law was passed in 1998 (USACE surveyed the area between Ship Shoal and the natural, land-building processes of the 2004). The shell mining operations of the Last Island for the U.S. government which river in the current CMP, this recently 20th century decimated what was left of was considering the need for and location discovered history of the GBRA suggests the GBRA. The mining of historic oyster of a lighthouse. Despite a detailed survey it had reached a size substantial enough reefs in the East Cote Blanche Bay (which which included 35,000 lead casts, Sands’ to provide key ecosystem services to the Audubon had visited in 1837) has re- report and accompanying map show no coast. These vast oyster reefs, or “living sulted in drastic changes to the hydrody- indication of this portion of the GBRA shorelines,” played an essential role in namics of the Atchafalaya and Vermilion (Sands 1853; Gerdes 1853), suggesting attenuating wave energies from storms or Bay systems and a substantial increase in that at least this portion of the reef which regular tidal cycles and stabilizing sedi- the freshwater influence on the western Audubon had found dead in 1837 had ments, subsequently protecting sandy bar- portion of this system. Modeling indi- not recovered, but disintegrated, likely rier islands and headlands, as well as in- cates that wave heights in Atchafalaya due to human-induced reductions in terior wetlands from erosion (Evia 1968), Bay have increased by nearly 2.5 feet in the amount of Mississippi River water allowing the wetlands in turn to provide fair-weather conditions due to the loss of flowing to the basins as a result of levees additional storm protection benefits.

Shore & Beach  Vol. 85, No. 4  Fall 2017 Page 35 Figure 2. Coastal land change over 50 years without human intervention under the medium environmental scenario (CPRA 2017). these reef structures (Stone et al. 2004). environment for many species (Scyphers n.d.). Similar to coral, oysters are referred The increase in storm surge energy and et al. 2011). The more quiescent environ- to as “ecosystem engineers” because they waves during tropical events can also be ment created behind the reef increases change the physical environment and attributed in part to the removal of the sediment deposition and trapping from provide spatial habitat for a multitude historic shoal reefs. The loss of this pro- river flood events, sustaining and build- of other marine organisms (Stokes et al. tective coastal feature resulted in much ing interior marshes. Older, established 2012). Recent studies of natural, restored, of the Louisiana coast being transformed reefs can also contribute shell bits to the and artificial reefs indicate that oyster reef from a low-energy, protected environ- marsh surface that help maintain marsh communities in many areas are highly di- ment to an open, wave-dominated, high- surface elevation, which is particularly verse and include many species not found energy marine environment (Stone and important in areas of high subsidence and in adjacent soft-bottom habitats. Plunket McBride 1998; Sheremet and Stone 2003; low sediment input, such as Terrebonne and La Peyre (2005) found that the oyster Stone et al. 2004). The loss of shoreline Bay and the Chenier Plain. structures provide important habitat for oyster reefs has also allowed increased benthic fish and decapod crustaceans Oyster reefs provide a diversity of water exchange between the gulf and the and provided valuable foraging sites for microhabitats that support complex interior water bodies of the Chenier Plain transient species. ecological communities including fish (USACE 2004), allowing more saltwater and invertebrate species. The oyster reef Oysters greatly influence nutrient intrusion into interior freshwater and ecosystem function is linked to the reef’s cycling in estuarine systems and help intermediate marshes. unique shell structure, as the reefs are to maintain ecosystem stability. Oysters These reefs can provide a wide ar- created by the constant adhesion of new filter large amounts of phytoplankton and ray of other ecosystem services. Their larva to existing shells. As new oysters detritus in the water column, as well as three-dimensional structure can reduce grow, available space accretes above the metabolize nutrients and cycling carbon water velocities, increase sedimentation substrate, which forms a matrix of inter- which benefits the entire ecosystem. In rates, and enhance propagule settlement stitial spaces that are critical to habitation this cycling process, oysters consume and retention, creating a more suitable by oysters and other organisms (NOAA suspended particles and utilize the or-

Figure 3. Conceptual diagram depicting the future of coastal marshes affected by sea level rise and subsidence both (a) without human intervention and (b) with the potential growth of oyster reefs over decades and centuries to replace ill-fated marshes and provide a coastal buffer.

Page 36 Shore & Beach  Vol. 85, No. 4  Fall 2017 ganic matter for growth, and the excess inorganic nutrients (dissolved carbon, nitrogen, phosphorous) are excreted by the bivalves for use to support the trophic system (NOAA n.d.). Encrusting organ- isms on oyster reefs, such as tunicates and barnacles, can contribute to the overall filter capacity of a reef, and thrive where the structure of reefs is three-dimensional (e.g. pyramid-shaped) rather than shal- low (NOAA n.d.). In addition to nutrient cycling, the denitrification of coastal wa- ters and filtering of suspended sediment facilitates the growth of marine grasses which helps to hold wetlands in place (Stokes et al. 2012). Since these oyster reefs provide con- centrated and abundant food sources for gamefish, they also enhance the value of recreational fisheries and help sup- port other trophic levels of the estuarine ecosystem. Their potential to increase marine fisheries production supports over 200,000 jobs in a $2.4 billion fishing industry (Stokes et al. 2012). LOUISIANA’S COASTAL REEF FUTURE The 2017 Coastal Master Plan clearly suggests that a loss of marsh habitat will occur across the coast over the next Figure 4. Conceptual diagram depicting the: a) current degraded state of coastal wetlands; b) predicted future wetland loss without human 50 years (Figure 2), even with planned intervention; c) implementation of shallow oyster reefs among degraded wetland restoration efforts. Instead of marsh today; and d) the growth of oyster reefs over decades and centuries considering success in terms of restor- to provide a coastal buffer, prevent future wetland loss, and protect remnant ing the “status quo,” we may be better coastal marshes. served to start envisioning a smaller, more sustainable coastline of the future ter reefs until the marsh is already gone. The predicted future without human that could be restored and maintained Instead, we propose to utilize the natural intervention (Figure 2) can be used to with the limited natural resources, such growing features of an oyster reef over define areas where oyster reefs could as sediment and fresh water, and limited the next few decades to transform areas be established to provide protection to societal resources, such as time and fund- of brackish or intermediate marsh today coastal communities and remnant marsh- ing. We propose that we should explore into extensive oyster reefs in the future. es that would otherwise be lost. Proper innovative approaches to transforming By constructing shallow subtidal oyster siting would be necessary to ensure that the current landscape instead of main- reefs in small, open-water bodies within the oyster reefs could be established and taining the landscape that exists today. areas of degraded marsh, the oyster reefs prosper. However, the location does not can establish and grow over the coming need to be constrained by the narrower We cannot rebuild the GBRA or other decades and centuries, provide diversity, range of the harvestable oyster, as growth massive offshore oyster reefs, due to the and provide protection to delay the de- will occur over many decades. Sediment lack of appropriate salinities and human mise of the adjacent wetlands (Figure 3). diversions, hydrologic restoration and the alterations to the hydrology, as well as Over time, the marsh slowly subsides or maintenance of existing freshwater flows the immense cost of such an endeavor. floods while oyster reefs grow and expand would be essential to the establishment But the coastline of today will become in their place (Figure 4). In the near-term, and long-term viability of these oyster the offshore environment of the future. the oyster reef restoration will increase reefs. Under the right salinity conditions, Within 50 years, and in some areas as habitat diversity and provide other key oyster reefs can adapt to other environ- soon as 30 years, water depths within ecosystem services. In the long-term, mental shifts, such as sea level rise, grow- the current marsh platform will increase, habitats could transition from a marsh ing fast enough to outpace even the most especially as sea level rises exponentially, complex to an oyster reef complex, there- extreme predictions of future sea level rise and large swaths of marsh will be lost. by maintaining the coastline, protecting (Rodriguez et al. 2014). Land loss and increasing water depths interior wetlands from further erosion will challenge the cost-effectiveness of One example of where this could be and providing storm surge protection to putting off establishing large-scale oys- implemented in is the Chenier Plain of valuable infrastructure and communities.

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