Understanding and Managing Living Resources

The Grand Bay system, located on the coast of Alabama and Mississippi, has been naturally transgressing in response to sea-level but has an uncertain future as sediment is in deficit for the marsh. Dominated by residual ebb tidal currents, the system tends to export more sediment from the tidal creeks and estuaries than it imports onto the marsh. Riverine sediment inputs are limited or non-existent leaving estuarine bed erosion or marsh bank erosion as the dominant sources of suspended sediment. However, published sediment budgets along two shoreline-proximal marsh sites suggest marsh-estuarine shorelines are well balanced with nearly equivalent erosional and depositional mass fluxes across temporal scales (annual to decadal). In the present study, we further examine cored sediments collected along two shore-perpendicular transects at these two sites (i.e., Sites-1 and -3) for environmental proxies to help constrain the source and accumulation of sediment delivered to the marsh surface. Site-1 is located along a high-wave-energy shoreline while Site-3 is located along a low-wave-energy shoreline with more protection from waves. Vertical 1-cm intervals were analyzed for benthic foraminifera, natural and anthropogenic radionuclides (210Pb and 137Cs), and sediment properties. A cluster analysis was used to identify foraminiferal assemblages and subsequently interpret biofacies: estuarine-influenced marsh; middle marsh; marsh-to-upland transition. The geometry and volumetric budgets of the age-correlated biofacies suggest that both estuarine-sourced sediment and bank eroded sediment are inputs to the shoreline-proximal marsh transect.

Louisiana is proposing to develop a large sediment diversion to divert Mississippi River water containing sediment and nutrients into the subsiding estuaries of Breton Sound to mitigate wetland loss. Because of the proposed capacity and location of outflow, the Mid-Breton Large Sediment Diversion (MBLSD) has the potential to affect the ecology of the Mississippi Sound and Bight. In order to evaluate these potential effects, we have built a modeling framework to simulate hydrodynamics, water quality, habitat suitability, and biomass and distribution of living resources. The framework consists of a previously developed Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modeling system, habitat suitability indices calculated for eastern oyster and brown shrimp, and an Ecospace model developed using Ecopath with Ecosim. The Ecospace model was newly developed for this project based on local survey data of seventy-five groups of fish and shellfish species collected by state and federal agencies. The framework was used to simulate the following scenarios: 1) Typical conditions (based on an 11-year average) with and without the MBLSD open under the proposed flow regime; 2) Extremely fresh conditions (based on 2019) with and without the MBLSD open at full capacity. Temperature, salinity, and habitat suitability were used to determine the biomass and distribution of living resources in the MS Sound and Bight. Model output shows that the MBLSD is expected to lower salinities in the MS Sound and Bight when opened in a typical year, affecting the biomass of sessile species (i.e. eastern oyster) and the distribution of nektonic species. The diversion is not expected to affect the ecology of the MS Sound and Bight in an extremely fresh year when salinity is already low. Results of this research provide resource managers with the information needed to anticipate and respond to potential future conditions.

Louisiana is proposing to create the Mid-Breton Sediment Diversion (MBrSD), whose stated design purpose is to reconnect and re-establish the deltaic sediment deposition processes between the Mississippi River and Breton Sound Basin via the diversion of Mississippi River water that will deliver up to 75,000 cfs of sediment-laden freshwater to the estuaries of Breton Sound to mitigate wetland loss. However, the potential addition of a new pathway for freshwater to be introduced into the Mississippi Sound (MSS) requires careful assessment of the potential impacts that may be incurred. Particularly important are the timing and volume of MBrSD freshwater releases that may negatively affect water quality at oyster reef locations, potentially disrupting critical larval recruitment pathways and/or dislocating regions of once-favorable habitat. Thus, a coupled hydrodynamic and habitat suitability index (HSI) modeling framework was employed to evaluate how disparate environmental stressors arising from the proposed operation of the MBrSD might affect the capacity of a given habitat to support the resilience, recovery, and/or sustainability of oysters within the jurisdictional waters of Mississippi. For simulations exploring the potential impacts of MBrSD during a typical climatological year, HSI analyses suggest that the MBrSD would cause a significant degradation of habitat suitability for oyster larvae within Mississippi waters from Jul – Aug. Oyster spat, seed, and sack were more sensitive to MBrSD effects within the western MS Sound (WMSS) and were projected to be negatively affected for a much longer period, from Jan – Jul (diminishing somewhat by Aug). Thus, the only period of negligible MBrSD impacts to all age-classes of oysters found within MS waters is from Sep – Dec.

Coastal ecosystems are undergoing significant changes driven by a range of stressors, many resulting from localized impacts of climate change. Long term environmental changes affect community structure, primarily by shifts in dominant or key species. This study quantified nekton community and species level responses to environmental variation over recent decades. These analyses aim to improve predictions of coastal living resources' response to environmental changes. Trawl sample data from the Alabama Department of Marine Resources Fisheries Assessment and Monitoring Program were used to describe multidecadal patterns in nekton communities across 16 stations in coastal Alabama between 1981 - 2018. Shifts in community structure were assessed through nonmetric multidimensional scaling analysis and post hoc testing. Nekton communities were significantly grouped by station, however there was overlap between stations and a gradient from fresh to saline communities was present. In preliminary analyses, temporal patterns in the multivariate community analysis were convoluted by interacting factors and no significant patterns were identified. Further analyses will assess long-term trends in community structure, and identify relationships between community structure, key species, and key drivers such as freshwater inflow and temperature. This work emphasizes the importance of understanding the relationship between long term environmental changes and biota at a regional scale, and results will be shared with local environmental managers.

In estuarine ecosystems, salinity and temperature are forecasted to increase in variability concurrent with wide-spread atmospheric change which may alter the phenology of estuarine-dependent fishes and invertebrates. Here, we compiled a dataset of the phenological timing and recruitment for 21 species of fish, crabs, and shrimp collected during the Alabama Marine Resource Division (ALMRD) fishery-independent trawl survey which visited fixed stations in Mobile Bay for 36-years 1982 – 2018. The seasonality of recruitment timing was species-specific with ten species in the spring, seven species in the summer, and four in the fall. Recruitment duration was longest for species whose recruitment peak was in the spring (average recruitment IQR 54 ± 56 days) and shortest in the fall (IQR 44 ± 31 days). Several species had noticeable shifts in recruitment peak timing from their historic baseline in the 1980's including bay anchovy (Anchoa mitchilli; 51 days later), southern flounder (Paralichthys lethostigma; 27 days earlier), and white shrimp (Litopenaeus setiferus; 31 days later). Additionally, several species had substantially longer recruitment periods spotted seatrout (Cynoscion nebulosus; increased 33 days) and brown shrimp (Farfantepenaeus aztecus; increased 26 days), and one had a shorter recruitment period, striped mullet (Mugil cephalus; decreased 26 days). Using generalized additive models with recruitment peak and recruitment range as dependent variables, and annual temperature (average, minimum, maximum), annual river discharge, and annual drought index as independent variables, we saw significant species-specific correlations – ranging from 16% to 97.4% deviance explained. These results suggest a strong correlative link between environmental conditions, recruitment timing, and recruitment duration. Understanding how recruitment dynamics will shift in response to changing environmental conditions is crucial for projecting the consequences of climate change in critical and essential habitats, i.e. estuaries.

Salt marsh and submerged aquatic vegetation (SAV) ecosystems provide habitat for ecologically and economically important species, such as penaeid shrimp, blue crabs, and speckled sea trout. These ecosystems are under anthropogenic pressure, and significant investments are being made in their conservation and restoration. Estimates of fisheries production are an important metric to help quantify the benefits of salt marsh and SAV conservation and restoration. In this study, we used a drop sampler to quantify the densities of nekton (fish and mobile crustaceans) in salt marsh edge and adjacent open water habitat with and without SAV across 10 sites through coastal Alabama over two summers and one autumn (early and late in the recruitment season), amounting to a total of 180 samples. Overall nekton densities were higher in salt marsh edge and SAV than in unvegetated open water habitat. For example, summer densities of blue crabs were 4.8 ± 0.5 individuals m-2 (± 1SE) in salt marsh edge, 3.2 ± 0.7 m-2 in SAV, and 0.6 ± 0.2 m-2 in unvegetated bottom. By applying published growth and mortality estimates we can calculate production enhancement for species that occur in higher densities in marsh edge and SAV, which is the amount of additional production derived from the presence of marsh or SAV in the seascape, above that derived from seascapes of unvegetated bottom habitat. Results will illustrate fisheries production benefits of conserving and restoring salt marsh and SAV habitat.

This presentation shows the results of a nation-wide analysis of the economic impacts of the 2019 openings of the Bonnet Carre Spillway on the commercial fishing industry in the Northern Gulf of Mexico states. Commercial landings of all commercial species landed in Louisiana, Mississippi and Alabama were compiled from the NOAA Fisheries website. Fisheries data are reported in pounds annually valued in dollars. 
The commercial fishery impacts consist of losses of wild harvests by commercial fishers due to the prolonged freshwater intrusion. The direct losses to the commercial fisheries are equal to the actual landing values at time t less the expected landing values at time t. Using 2014-18 as a benchmark period, the dockside values of the major fisheries in the Northern Gulf of Mexico in 2019 declined by more than $81 million. These direct losses are the foregone landing values of the major fisheries in the Northern Gulf of Mexico in 2019. 


Figure 1. Direct fishing losses in the Northern Gulf of Mexico by major species in 2019, in dollars and percent.



A regional IMPLAN economic model of the three northern Gulf of Mexico states was created in the IMPLAN cloud. Individual events on the direct fishing losses in each of the three states were created in the regional IMPLAN model. To track down the impacts of the regional fishing losses to the rest of the United States, a multi-regional input-output (MIRO) link was added to the regional IMPLAN economic model. The MIRO analysis illustrates how the regional impact in the Northern Gulf of Mexico spread out into other regions and how these effects in nearby areas created additional local effects. More than fifty percent more economic impacts were created in states beyond the Northern Gulf of Mexico region.