Megan K. La Peyre

The effect of structural complexity, prey density, and "predator-free space" on prey survivorship at created oyster reef mesocosms.

Interactions between predators and their prey are influenced by the habitat they occupy. Using created oyster (Crassostrea virginica) reef mesocosms, we conducted a series of laboratory experiments that created structure and manipulated complexity as well as prey density and “predator-free space” to examine the relationship between structural complexity and prey survivorship. Specifically, volume and spatial arrangement of oysters as well as prey density were manipulated, and the survivorship of prey (grass shrimp, Palaemonetes pugio) in the presence of a predator (wild red drum, Sciaenops ocellatus) was quantified. We found that the presence of structure increased prey survivorship, and that increasing complexity of this structure further increased survivorship, but only to a point. This agrees with the theory that structural complexity may influence predator-prey dynamics, but that a threshold exists with diminishing returns. These results held true even when prey density was scaled to structural complexity, or the amount of “predator-free space” was manipulated within our created reef mesocosms. The presence of structure and its complexity (oyster shell volume) were more important in facilitating prey survivorship than perceived refugia or density-dependent prey effects. A more accurate indicator of refugia might require “predator-free space” measures that also account for the available area within the structure itself (i.e., volume) and not just on the surface of a structure. Creating experiments that better mimic natural conditions and test a wider range of “predator-free space” are suggested to better understand the role of structural complexity in oyster reefs and other complex habitats.

LINKING ACTIONS TO OUTCOMES IN WETLAND MANAGEMENT: AN OVERVIEW OF U.S. STATE WETLAND MANAGEMENT

Despite a national focus on saving wetland systems in the U.S., evaluations of wetland resources and management outcomes have been limited. A fifty-state survey of wetland managers was conducted in order to collect information on (1) wetland resources, (2) management actions taken, and (3) management impact on the resources (wetlands). An overview of the general status of state knowledge of the quantity and quality of their wetland resources is presented. Results indicate that most states have a rough estimate of the resources and most have wetland conservation plans and intend to develop better databases of wetland resources. However, few states track management actions relevant to wetlands and fewer have any idea of the success or impact of past management actions. The ability to assess program effectiveness is key to implementing adaptive management frameworks. A number of lessons learned suggest a basic framework for future wetland management that includes state planning, better quantification (mapping) of wetlands, development of methods to measure wetland quality, and tracking of wetland management actions and outcomes. This framework could also be used as an outline for the development of a more adaptive approach to wetland management.

Comparison of Seed Bank Size and Composition in Fringing, Restored, and Impounded Marsh in Southwest Louisiana

Abstract In coastal Louisiana many restoration projects are approved based on assumed regeneration of submerged aquatic species (SAV) in shallow marsh interior ponds. In this study, we estimated seed bank size and composition of shallow water areas in oligohaline fringing and restored (terraced) marsh, and a freshwater managed (impounded) marsh, located in Sabine NWR, LA, using the sieving method. For the same marshes, we also provided an estimate of the readily germinable fraction of the seed bank using the germination method. Sieving results indicated that restored marsh edges had very low seed densities (5034 seeds/m2) compared to fringing marsh (331,185 seeds/m2), although species composition was similar. Managed freshwater marsh ponds had more diverse seed banks and mid-range seed densities (80,500 seeds/m2). Viability estimates of dominant species in the seed bank reduced seed density estimates at all sites by as much as 10 fold (fringing marsh: 36,185 seeds/m2; restored marsh: 859 seeds/m2; managed marsh 44,388 seeds/m2) suggesting that a correction factor should be applied to future seed density estimates in this region. Seedling emergence was significantly higher in the managed marsh under drawdown conditions (> 2500 seedlings/m2) as compared to flooded conditions (< 500 seedlings/m2; ANOVA, p = 0.0001). Seedling emergence in oligohaline marsh was significantly affected by salinity and management (fringing, restored) (ANOVA, p = 0.0186). Fringing marsh at 0 g/L had the highest seedling emergence (> 500 seedlings/m2). At higher salinities, fringing and restored marsh had similar emergence (< 150 seedlings/m2). Results indicate that recruitment is likely to be more successful under drawdown conditions, and in low salinity conditions. However, both a lack of SAV emergence in the germination experiment and a lack of SAV seeds in the seed banks using the sieving method suggest that reliance on seed banks for the restoration of shallow water areas in southwest Louisiana may prove unsuccessful.

Assessing Shoreline Exposure and Oyster Habitat Suitability Maximizes Potential Success for Sustainable Shoreline Protection Using Restored Oyster Reefs

Oyster reefs provide valuable ecosystem services that contribute to coastal resilience. Unfortunately, many reefs have been degraded or removed completely, and there are increased efforts to restore oysters in many coastal areas. In particular, much attention has recently been given to the restoration of shellfish reefs along eroding shorelines to reduce erosion. Such fringing reef approaches, however, often lack empirical data to identify locations where reefs are most effective in reducing marsh erosion, or fully take into account habitat suitability. Using monitoring data from 5 separate fringing reef projects across coastal Louisiana, we quantify shoreline exposure (fetch + wind direction + wind speed) and reef impacts on shoreline retreat. Our results indicate that fringing oyster reefs have a higher impact on shoreline retreat at higher exposure shorelines. At higher exposures, fringing reefs reduced marsh edge erosion an average of 1.0 m y−1. Using these data, we identify ranges of shoreline exposure values where oyster reefs are most effective at reducing marsh edge erosion and apply this knowledge to a case study within one Louisiana estuary. In Breton Sound estuary, we calculate shoreline exposure at 500 random points and then overlay a habitat suitability index for oysters. This method and the resulting visualization show areas most likely to support sustainable oyster populations as well as significantly reduce shoreline erosion. Our results demonstrate how site selection criteria, which include shoreline exposure and habitat suitability, are critical to ensuring greater positive impacts and longevity of oyster reef restoration projects.

State Wetland Protection: A Matter of Context?

Models of integrated management emphasize the role of the surrounding socioeconomic and political environment in influencing management choices for natural resources. In this study, we explore a model that examines the influence of socioeconomic and political variables on the wetland management programs of U.S. states. Logistic regression was used to identify environmental, socioeconomic, and political variables that explained variation in state wetland programs. The likelihood of strong planning, nonregulatory, regulatory, and overall programs increases as the importance of fisheries in the state increases (p < 0.05), but decreases as population density increases (p < 0.15). Furthermore, there is an increasing likelihood of stronger regulatory and overall programs as environmental group activity and industry importance increases (p < 0.05). These findings provide empirical evidence to support the contention that management approaches used in one state often must be adapted to fit the realities of another given state.Models of integrated management emphasize the role of the surrounding socioeconomic and political environment in influencing management choices for natural resources. In this study, we explore a model that examines the influence of socioeconomic and political variables on the wetland management programs of U.S. states. Logistic regression was used to identify environmental, socioeconomic, and political variables that explained variation in state wetland programs. The likelihood of strong planning, nonregulatory, regulatory, and overall programs increases as the importance of fisheries in the state increases (p < 0.05), but decreases as population density increases (p < 0.15). Furthermore, there is an increasing likelihood of stronger regulatory and overall programs as environmental group activity and industry importance increases (p < 0.05). These findings provide empirical evidence to support the contention that management approaches used in one state often must be adapted to fit the realities o...

Oyster reef restoration supports increased nekton biomass and potential commercial fishery value

Across the globe, discussions centered on the value of nature drive many conservation and restoration decisions. As a result, justification for management activities increasingly asks for two lines of evidence: (1) biological proof of augmented ecosystem function or service, and (2) monetary valuation of these services. For oyster reefs, which have seen significant global declines and increasing restoration work, the need to provide both biological and monetary evidence of reef services on a local-level has become more critical in a time of declining resources. Here, we quantified species biomass and potential commercial value of nekton collected from restored oyster (Crassostrea virginica) reefs in coastal Louisiana over a 3-year period, providing multiple snapshots of biomass support over time. Overall, and with little change over time, fish and invertebrate biomass is 212% greater at restored oyster reefs than mud-bottom, or 0.12 kg m−2. The additional biomass of commercial species is equivalent to an increase of local fisheries value by 226%, or

A Modeling Study of the Impacts of Mississippi River Diversion and Sea-Level Rise on Water Quality of a Deltaic Estuary

0.09 m−2. Understanding the ecosystem value of restoration projects, and how they interact with regional management priorities, is critical to inform local decision-making and provide testable predictions. Quantitative estimates of potential commercial fisheries enhancement by oyster reef restoration such as this one can be used directly by local managers to determine the expected return on investment.

Environmental significance of freshets in reducing Perkinsus marinus infection in eastern oysters Crassostrea virginica: potential management applications

Freshwater and sediment management in estuaries affects water quality, particularly in deltaic estuaries. Furthermore, climate change-induced sea-level rise (SLR) and land subsidence also affect estuarine water quality by changing salinity, circulation, stratification, sedimentation, erosion, residence time, and other physical and ecological processes. However, little is known about how the magnitudes and spatial and temporal patterns in estuarine water quality variables will change in response to freshwater and sediment management in the context of future SLR. In this study, we applied the Delft3D model that couples hydrodynamics and water quality processes to examine the spatial and temporal variations of salinity, total suspended solids, and chlorophyll-α concentration in response to small (142xa0m3xa0s−1) and large (7080xa0m3xa0s−1) Mississippi River (MR) diversions under low (0.38xa0m) and high (1.44xa0m) relative SLR (RSLR = eustatic SLR + subsidence) scenarios in the Breton Sound Estuary, Louisiana, USA. The hydrodynamics and water quality model were calibrated and validated via field observations at multiple stations across the estuary. Model results indicate that the large MR diversion would significantly affect the magnitude and spatial and temporal patterns of the studied water quality variables across the entire estuary, whereas the small diversion tends to influence water quality only in small areas near the diversion. RSLR would also play a significant role on the spatial heterogeneity in estuary water quality by acting as an opposite force to river diversions; however, RSLR plays a greater role than the small-scale diversion on the magnitude and spatial pattern of the water quality parameters in this deltaic estuary.