Submerged Aquatic Vegetation Habitats Research Articles

A simple approach to estimating the nutrient and carbon storage benefits of restoring submerged aquatic vegetation, applied to Vallisneria americana in the Caloosahatchee Estuary, Florida, USA

Carbon and nutrient storage are important ecosystem services of submerged aquatic vegetation (SAV) and may be enhanced by SAV restoration. This study demonstrates an approach to quantifying the nutrient and carbon storage potential of SAV restoration, focusing on the SAV Vallisneria americana in the oligohaline reaches of Florida's Caloosahatchee River Estuary (CRE). The variables of habitat area, plant size, plant density, and tissue nutrient stoichiometry are considered, and estimates are made both for storage in living tissue and for deposition in sediments. System-specific parameter values are obtained from a combination of abundance surveys, historical accounts of abundance and distribution, and field and mesocosm studies of tissue stoichiometry responses to nutrient addition. These are integrated with literature values for sediment deposition rates of C, N, and P in other SAV systems to estimate carbon and nutrient storage for current conditions and various restoration scenarios. Calculations indicate that under a restoration scenario assuming a return to the abundance documented in 1998–1999, V. americana tissues could act as a substantial sink for macro-elements in the CRE, representing 28.4 mt-C, 2.6 mt-N, and 0.16 mt-P, and depositing 897 mt-C y−1, 68.5 mt-N y−1, and 3.87 mt-P y−1 in meadow sediments. However, at current low shoot densities and small shoot sizes, these benefits are two to three orders of magnitude less. In addition to the large difference between the restoration and current-conditions scenarios, propagation of uncertainty around parameter estimates within each scenario leads to wide ranges of uncertainty around model outputs. More system-specific empirical studies would help constrain parameter estimates and improve the model. Overall, these findings emphasize the sensitivity of C, N, and P storage and deposition rates to SAV habitat conditions, and the importance of reversing declines in SAV density through restoration, and other conservation measures.

Quantifying the Potential Contribution of Submerged Aquatic Vegetation to Coastal Carbon Capture in a Delta System from Field and Landsat 8/9-Operational Land Imager (OLI) Data with Deep Convolutional Neural Network

Submerged aquatic vegetation (SAV) are highly efficient at carbon sequestration and, despite their relatively small distribution globally, are recognized as a potentially valuable component of climate change mitigation. However, SAV mapping in tidal marshes presents a challenge due to optically complex constituents in the water. The emergence and advancement of deep learning-based techniques in the field of habitat mapping with remote sensing imagery provides an opportunity to address this challenge. In this study, an analytical framework was developed to quantify the carbon sequestration of SAV habitats in the Atchafalaya River Delta Estuary from field and remote sensing observations using deep convolutional neural network (DCNN) techniques. A U-Net-based model, Wetland-SAV Network, was trained to identify the SAV percent cover (high, medium, and low) as well as other estuarine habitat types from Landsat 8/9-OLI data. The areal extent of SAV was up to 8% of the total area (47,000 ha). The habitat areas and habitat-specific carbon fluxes were then used to quantify the net greenhouse gas (GHG) flux of the study area for with/without SAV scenarios in a carbon balance model. The total net GHG flux was in the range of −0.13 ± 0.06 to −0.86 ± 0.37 × 105 tonne CO2e y−1 and increased up to 40% (−0.23 ± 0.10 to −0.90 ± 0.39 × 105 tonne CO2e y−1) when SAV was accounted for within the calculation. At the hectare scale, the inclusion of SAV resulted in an increase of ~60% for the net GHG sink in shallow areas adjacent to the emergent marsh where SAV was abundant. This is the first attempt at remotely mapping SAV in coastal Louisiana as well as a first quantification of net GHG flux at the scale of hectares to thousands of hectares, accounting for SAV within these sub-tropical coastal delta marshes. Remote sensing and deep learning models have high potential for mapping and monitoring SAV in turbid sub-tropical coastal deltas as a component of the increasing accuracy of net GHG flux estimates at small (hectare) and large (coastal basin) scales.

Evaluating impacts of non‐native submerged aquatic vegetation on native nekton

AbstractThe introduction and spread of non‐native species restructure native ecosystems and can be particularly impactful when invaders are ecosystem engineers or habitat‐forming species. In coastal, estuarine, and marine systems, submerged aquatic vegetation (SAV), like macroalgae and seagrasses, form key habitats for nekton, serving as nurseries, foraging grounds, and reproduction sites. If non‐native ecosystem engineers can provide sufficient structure and/or resources, they may exert a neutral or positive effect on organisms occupying higher trophic positions. As such, we hypothesized that nekton response to non‐native SAV species may be neutral or positive. We performed a quantitative meta‐analysis to quantify impacts of non‐native SAV on native crabs, fishes, and shrimps. We extracted data from 35 studies and evaluated 11 response metrics related to facilitation (e.g., habitat use and foraging), restricting our analysis to studies that compared at least one of these metrics in nekton from co‐occurring native and non‐native SAV habitats in marine, coastal, or estuarine systems. We found that nekton abundance, species richness, and biomass were the most assessed metrics of nekton performance. Our pooled data revealed differential results among response metrics, with nekton growth and reproduction enhanced in non‐native habitats and species richness enhanced in a native setting. The mean effect sizes for all other nekton response metrics, including abundance, had 95% CIs that overlapped zero, indicating no difference in response between native and non‐native SAV. For many endpoints, limited sample sizes prevented robust inferences, but they also highlighted areas where more research is needed in future studies. Non‐native species have the potential to restructure the systems they invade. Our results lend support to the relative trophic position hypothesis, indicating that non‐native habitat formers may facilitate native organisms in higher trophic levels. We identify research gaps that may guide future studies and allow for a more comprehensive understanding of responses to non‐native ecosystem engineers.

Clarifying water clarity: A call to use metrics best suited to corresponding research and management goals in aquatic ecosystems

Clarifying water clarity: A call to use metrics best suited to corresponding research and management goals in aquatic ecosystems

Mechanisms of sediment transport around finite patches of submerged aquatic vegetation

Feedback between flow transformation by submerged aquatic vegetation (SAV) and bed morphodynamics influences the long-term survivability of SAV habitats and the engineering services that SAV provides. We conducted a full-scale wave flume experiment to investigate the mechanisms through which finite patches of mimic SAV produce shoreward depositional features. Hydrodynamic observations indicate that a depositional mound is built in two phases, depending on the strength of nearshore seaward mean currents (undertow). During milder wave conditions when undertow is weak, the patches enhance TKE, wave velocity skewness, and within-canopy shoreward currents that together suspend and transport sediment shoreward to form near-symmetrical depositional mounds. Although patch-induced transport mechanisms are greater with higher within-patch stem density, the size and volume of the depositional mound are shown to depend more on patch diameter (i.e., form drag) rather than stem density for the range of patch geometries tested; the small dense patch produced a smaller depositional mound than the larger sparser patch. When waves are more energetic and undertow strengthens, the convergence of undertow with canopy-induced shoreward currents and wave velocity skewness enhances deposition and skews the depositional mound’s shape. As such, the convergence of canopy-induced shoreward currents and undertow-induced seaward currents causes the volume of the depositional mound to nearly triple shoreward of the largest tested patch of SAV.

Influence of seascape spatial pattern on the trophic niche of an omnivorous fish

AbstractHabitat fragmentation of submerged aquatic vegetation (SAV) transforms the spatial pattern of seascapes by changing both the total area and spatial configuration of the habitat patches. The ecological effects of SAV seascapes are most often assessed using metrics of biological community composition (e.g., species and assemblage changes). We know considerably less about the effects of seascape structure on ecological processes such as food web function and energy flow. Here, we assess the difference in the trophic niche of Pinfish (Lagodon rhomboides, a generalist omnivore) across a spatial gradient of SAV from continuous to highly fragmented seascapes in Biscayne Bay (Miami, Florida, USA). The Bay seascapes are influenced by freshwater management practices that alter the distribution of SAV habitat and fish species abundance, diversity, and community assemblage. We combined SAV seascape maps with stable isotope and hypervolume analyses to determine how trophic niche size and overlap varied with changes in the seascape. We observed similar resource use across the seascape, but trophic niche size increased in more fragmented SAV seascapes, suggesting diversification of trophic roles and energy flow pathways. Pinfish collected from more continuous SAV habitats had smaller trophic niche size and higher trophic levels. Both trophic response metrics manifested a threshold response that depended on distinct SAV spatial characteristics (amount vs. spatial configuration) and environmental conditions. Our results suggest that habitat fragmentation of SAV seascape structure has ecological implications that could affect energy flow with cascading consequences for food web stability and ecosystem functioning.

Space use of juvenile and subadult yellow perch (Perca flavescens) in the Detroit River using acoustic telemetry: incorporating variable detection ranges in vegetated areas

Understanding the space use of fishes in early life stages provides information that can contribute to effective fisheries management; however, it can be difficult to track fish in shallow, densely vegetated areas. Using acoustic telemetry, 60 subadult yellow perch (Perca flavescens) were tagged and monitored in a vegetated area of the Detroit River (May–November 2018). Variable detection range from submerged aquatic vegetation (SAV) was incorporated in estimates by applying a spatiotemporal correction to aid with interpretation of seasonal changes in activity space. Although subadult yellow perch were commonly detected in the array, demonstrating the importance of SAV habitat (mean detection residency index: 0.85), 60% of individuals were not detected following August, the period with highest activity space estimates, likely due to seasonal movements and predation. Individuals were more commonly detected during the daylight hours compared to night, but activity peaked at crepuscular periods. This study provided spatial information about the often-overlooked early life history of yellow perch, increasing the ecological information available for a species of management and conservation interest in the Great Lakes.

Modelling the resilience of seagrass communities exposed to pulsed freshwater discharges: A seascape approach.

Submerged aquatic vegetation (SAV) communities display complex patch dynamics at seascape scales that are presently poorly understood as most studies of disturbance on SAV habitats have focused on changes in biomass at small, quadrat-level scales. In this study, analyses of remote sensing imagery and population modelling were applied to understand SAV patch dynamics and forecast the fate of these important communities in Biscayne Bay, Miami, Florida, US. We evaluated how the proximity of freshwater canals influences seagrass-dominated SAV patch dynamics and, in turn, how patch-size structure influences the stability of seagrass seascapes under different salinity scenarios. Seagrass fragmentation rates were higher in sites adjacent to freshwater canals compared to sites distant from the influences of freshwater deliveries. Furthermore, we documented a clear trend in patch mortality rates with respect to patch size, with the smallest patches (50 m2) undergoing 57% annual mortality on average. The combination of higher fragmentation rates and the higher mortality of smaller seagrass patches in habitats exposed to pulses of low salinity raises concern for the long-term persistence of seagrass meadows in nearshore urban habitats of Biscayne Bay that are presently targets of Everglades restoration. Our model scenarios that simulated high fragmentation rates resulted in SAV population collapses, regardless of SAV recruitment rates. The combined remote sensing and population modelling approach used here provides evaluation and predictive tools that can be used by managers to track seagrass status and stress-response at seascape levels not available previously for the seagrasses of South Florida.

Estuarine submerged aquatic vegetation habitat provides organic carbon storage across a shifting landscape

Submerged aquatic vegetation (SAV) thrives across the estuarine salinity gradient providing valuable ecosystem services. Within the saline portion of estuaries, seagrass areas are frequently cited as hotspots for their role in capturing and retaining organic carbon (Corg). Non-seagrass SAV, located in the fresh to brackish estuarine areas, may also retain significant soil Corg, yet their role remains unquantified. Given rapidly occurring landscape and salinity changes due to human and natural disturbances, landscape level carbon pool estimates from estuarine SAV habitat blue carbon estimates are needed. We assessed Corg stocks in SAV habitat soils from estuarine freshwater to saline habitats (interior deltaic) to saline barrier islands (Chandeleur Island) within the Mississippi River Delta Plain (MRDP), Louisiana, USA. SAV habitats contain Corg stocks equivalent to those reported for other estuarine vegetation types (seagrass, salt marsh, mangrove). Interior deltaic SAV Corg stocks (231.6 ± 19.5 Mg Corg ha−1) were similar across the salinity gradient, and significantly higher than at barrier island sites (56.6 ± 10.4 Mg Corg ha−1). Within the MRDP, shallow water SAV habitat covers up to an estimated 28,000 ha, indicating that soil Corg storage is potentially 6.4 ± 0.1 Tg representing an unaccounted Corg pool. Extrapolated across Louisiana, and the Gulf of Mexico, this represents a major unaccounted pool of soil Corg. As marshes continue to erode, the ability of coastal SAV habitat to offset some of the lost carbon sequestration may be valuable. Our estimates of Corg sequestration rates indicated that conversion of eroding marsh to potential SAV habitat may help to offset the reduction of Corg sequestration rates. Across Louisiana, we estimated SAV to offset this loss by as much as 79,000 Mg C yr−1 between the 1960s and 2000s.

Editors’ Introduction

Editors’ Introduction Hilda E. Kurtz and Deepak R. Mishra Four years ago this month (as we write this in July), we were new to the helm of Southeastern Geographer and working hard to develop our own templates and processes. Our pitch to the Executive Board of SEDAAG had been that as a regional journal for arguably the most dynamic region in the United States, Southeastern Geographer was poised to publish geographic scholarship considered broadly relevant to diverse audiences. As we wrote to SEDAAG’s then president Skeeter Dixon in a Letter of Intent, The region’s social, cultural, economic, and political diversity and broad climate and ecosystem variability from southern Appalachian Mountains to vast Gulf Coast wetlands make it a fascinating and important object of study. In that sense, the southeastern United States is arguably a bellwether for myriad human and geophysical processes shaping our collective present and future. At the same time, the region is intricately linked to processes, flows, and conditions that extend across the country, continent, and globe. We aim to focus one or two special issues per year on scholarship that explores such relational themes. Then, just as we stepped in to run Southeastern Geographer, a White supremacist murdered nine Black members of Mother Emanuel Church in Charleston, South Carolina. The words in our Letter of Intent to SEDAAG took on much heavier and more sober meaning. The murders, in the sanctuary of their own church, of Depayne Middleton Doctor, Cynthia Hurd, Susie Jackson, Ethel Jackson, Reverend Clementa Pinckney, Tywanza Sanders, Reverend Dr. Daniel Simmons, Sr., Shoronda Coleman-Singleton, and Myra Thomson, were a terrible display of the racial hatred that has poisoned this region and the country as a whole for centuries. People across the country struggled to make any kind of sense out of such a heinous act. We turned to geographers from across the country and from across this wide discipline, asking them to draw on geographic thought to offer insight into the origins or implications of the massacre at Mother Emanuel or the aftermath in which Confederate flags and memorials were debated and in some cases, taken down. By late 2018, papers from the issue (56-1) in which the Special Forum on the Charleston Massacre of 2015 was published, have been downloaded through Project Muse 4,162 times. We could see the promise of the model almost immediately. The essays, by Kate Derickson, Priscilla McCutcheon, LaTonya Eaves, Derek Alderman and Josh Inwood, and Jonathan Leib and Gerald Webster, helped a wide [End Page 332] audience grapple with a complex issue. They demonstrated the relevance of geographic thought in a complex world. We followed up with a Special Forum on the Paris COP21 Climate Conference: What Does It Mean for the Southeast? in 56-2 and a Special Forum on Geographies of the 2016 Presidential Election in 56-3. Papers from that issue of Southeastern Geographer were downloaded 6,862 times by late 2018. In addition to the occasional Special Forum, we are proud to have worked with several guest editors to shepherd the production of Special Issues which offer an opportunity to showcase thematically integrated papers. The first of these was Black Geographies In and Of the United States South. Guest editors and emerging scholars Adam Bledsoe, LaToya Eaves, and Brian Williams, edited a generative set of papers (in issue 57-1) which with 1,892 downloads, was the ranked first in Project Muse downloads by issues for the 2017–2018 year. The second of these was Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico, by guest editors Patrick Biber and Hyun Cho. This issue too was well-read, with 825 downloads. The third of these—published earlier this year—explored Wild Foods (59-1), guest edited by Nancy O’Hare. We do not yet have download data. The last four years in the life of Southeastern Geographer has brought several more changes to how the journal operates. The biggest change was the conversion from email submissions to Manuscript Central’s ScholarOne Interface. We extend our thanks to the SEDAAG Executive Committee for the foresight to invest resources in updating the journal in this and other ways...

Submerged aquatic vegetation mapping in coastal Louisiana through development of a spatial likelihood occurrence (SLOO) model

Determining the spatial distribution of coastal foundation species is essential to accurately determine restoration goals, predict the ecological effects of climate change, and develop habitat management strategies. Mapping the distribution of submerged aquatic vegetation (SAV) species assemblages, which provide important habitat resource and ecological services in Louisiana, has been difficult due to the dynamic nature of SAV occurrence and the limited water clarity across much of the coast. Species distribution models (SDMs) link ecological conditions species occurrence across landscapes, and can predict the distribution of species across un-sampled or hard to sample areas and support the development of habitat maps. To predict SAV distribution in coastal Louisiana, a SDM was developed and projected across the landscape to create a spatial likelihood of occurrence (SLOO) model describing the probability of SAV presence in aquatic habitats. SAV presence and absence data were examined from over 500 field observations in relation to physical and hydrologic variables, including exposure, turbidity, water level, and salinity. A binary logistic regression model (p < 0.0001) identified three significant predictors of SAV presence: mean winter salinity, exposure, and turbidity. As each of these variables increased, the probability of SAV presence in the summer growing season decreased. The spatial application of this SDM helps to predict the likelihood of occurrence across the coastal landscape, creating a valuable tool to describe un-sampled SAV habitat and estimate future changes in habitat availability.

In Situ Effects of Shoreline Type and Watershed Land Use on Submerged Aquatic Vegetation Habitat Quality in the Chesapeake and Mid-Atlantic Coastal Bays

Submerged aquatic vegetation (SAV) is an ecologically and economically valuable component of coastal estuaries that acts as an early indicator of both degrading and improving water quality. This study aimed to determine if shoreline hardening, which is associated with increased population pressure and climate change, acts to degrade SAV habitat quality at the local scale. In situ comparisons of SAV beds adjacent to both natural and hardened shorelines in 24 subestuaries throughout the Chesapeake and Mid-Atlantic Coastal Bays indicated that shoreline hardening does impact adjacent SAV beds. Species diversity, evenness, and percent cover were significantly reduced in the presence of riprap revetment. A post hoc analysis also confirmed that SAV is locally affected by watershed land use associated with increased population pressure, though to a lesser degree than impacts observed from shoreline armoring. When observed over time, SAV recovery at the local level took approximately 3 to 4 years following storm impacts, and SAV adjacent to natural shorelines showed more resilience to storms than SAV adjacent to armored shorelines. The negative impacts of shoreline hardening and watershed development on SAV shown here will inform coastal zone management decisions as increasing coastal populations and sea level rise drive these practices.

Submerged aquatic vegetation, topography and flow characteristics in the upper, tidal Hudson River: Progress toward a predictive habitat model

Submerged aquatic vegetation (SAV) plays a critical role in biogeochemical cycling, primary productivity, sediment dynamics and current flow within the systems they inhabit. SAV communities in the Upper Hudson River Estuary are comprised of species assemblages dominated by two very morphologically distinct species: the native Vallisneria americana, which has wide-strap shaped leaves that are completely submerged underwater, and the invasive Trapa natans, which produces leaf rosettes that float at the water’s surface. Using characteristics of modeled tidal/riverine flow, we examined the distribution and composition of the predominant SAV in the estuary. SAV habitat space was, on average, well described by depth and flow. From a hydrodynamic standpoint however, the two species occupied very similar niche spaces. Species-specific distribution patterns and co-occurrence rates did not appear to be strongly controlled by physical tolerances of topography or flow. Other ecological drivers such as disturbance regimes, dispersal strategies, plant-animal interactions, and sediment chemistry and composition might explain distribution patterns and T. natans expansion more accurately, rather than hydrodynamics alone. Sixty years after reaching the Hudson River Estuary, T. natans appears unable to fully displace V. americana, despite significant overlap in habitat space and spatial distribution. Future management of the exotic T. natans should consider its role as an ecosystem engineer, adding to overall habitat diversity, rather than the current focus on its perceived invasibilty.

Introduction: Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico

IntroductionCoastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico Patrick Biber* and Hyun Jung Cho* This special issue compiles original research and reviews of previous research on an important geographic constitution at the water-land interface: the seagrass/Submerged Aquatic Vegetation (SAV) beds in the Gulf of Mexico (GoM) coastal zone. SAV are a group of vascular plants that grow underwater; and seagrass is a specialized subgroup of SAV that have adapted to live in the high salinity coastal and marine waters. Presence of, types of, and seasonality of SAV beds have substantial influences on geography, ecology, landscape, culture, and economy in the coastal zone. Healthy SAV beds help shape, maintain, and modify coastal landscapes by buffering wave energy, modifying water currents, protecting shorelines from erosion, aiding sediment deposition, consolidating substrate, and changing littoral profiles and water depth. Coastal seagrass resources are among the most productive ecosystems on Earth. Seagrass beds perform numerous vital ecological functions and provide food and shelter for commercially and ecologically important organisms, including blue crabs, shrimp, turtles, manatees, and waterfowl. Therefore, assessment of SAV distribution, composition, and abundance has been of particular interest to coastal environmental managers, scientists, developers, and recreationists as this information serves as an excellent indicator of estuarine environmental quality. Coastal areas containing seagrass and SAV beds carry geographical and historical importance in the Southeast, especially throughout the GoM. The GoM and its resources have immense ecological, economical, and historic values to the U.S. but have been going through several major environmental disturbances and disasters including, but not limited to, major hurricanes (e.g., 2005 Hurricane Katrina), the 2010 Deepwater Horizon Oil Spill, red tides, rapid subsidence, marsh erosion, threats from sea level rise, and river water diversions. Man-made levees [End Page 208] along major rivers (e.g., Mississippi River) prevent natural flooding from the rivers that historically used to deliver the necessary nutrients and sediments for coastal wetland growth and delta formation. This has resulted in coastal wetland retreat and subsidence. In addition, environmental quality has been significantly degraded, which in turn, results in the loss of ecological/economical services in the region. Loss of coastal land and environmental degradation are projected to be amplified with changing global climate, which is a growing threat to coastal SAV beds (Scavia et al. 2002, Doyle et al. 2010, Unsworth et al. 2014). The low-lying coastal areas of the GoM are particularly vulnerable to natural/anthropogenic disturbances due to the effects of sea-level rise, increases in population density, extensive landscape alternation, modification, and armoring of natural shorelines, as well as natural/man-made disasters. Documentation of habitat conditions, change over time, and interactions with the human environment are critical needs to better assess current status and predict future trends for SAV/seagrass habitats, a critical component of coastal geography. However, many regionally focused relevant studies on these habitats have not been addressed in the increasingly international scope of many pertinent scientific journals. We, the Guest Editors, agreed that compiling regional studies on a unifying topic would help enhance understanding of long-term and larger scale trends in SAV/seagrass beds of the GoM. In response, requests for manuscripts on sea-grass and other SAV occurring in tidally-influenced GoM coastal habitats were sent out to several regional seagrass/SAV scientists. In order to comply with the scope of Southeastern Geographer, the papers in this issue present studies on SAV/seagrass with a regional geography focus, particularly relating to issues of temporal variation and changes related to land use change, human alteration, and climate change. The five papers published in this special issue synergistically help to summarize change occurring across the GoM. Geographically, this special issue covers coastal habitats from Texas (the Coastal Bend and Laguna Madre), Louisiana (Terrebonne Bay, the Pontchartrain basin), areas around the borders of Mississippi and Alabama (Grand Bay National Estuarine Research Reserve), and west Florida (Tampa Bay). The topics of the papers extend from (1) evaluation of SAV for nekton habitat value in comparison to marshes during one season (Jerabek et al.), (2) test of a model to assess carbon stocks in seagrass meadows in a single year (Congdon & Dunton), (3) temporal...

Editors’ Introduction

Editors’ Introduction Hilda E. Kurtz and Deepak R. Mishra In Volume 57, Issue 3 of the Southeastern Geographer, we are pleased to offer a special issue on “Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico” guest edited by Patrick Biber and Hyun J. Cho. Seagrass and Submerged Aquatic Vegetation (SAV) communities found along the coastlines of northern Gulf of Mexico (GoM) and southeast Atlantic are highly productive coastal ecosystems which provide extremely valuable ecosystem services. These critical ecosystems provide habitat for fish and food resource for waterfowl. They absorb wave energy and prevent sediment resuspension which is required to maintain water clarity. They also prevent algal blooms in coastal waters because of their significant nutrient uptake of nitrogen and phosphorous. These coastal habitats are increasingly threatened by anthropogenic activities and climate change induced sea level rise. The impact of these threats would most likely impair the ecologic and economic serviced provided by these habitats. Therefore, this special issue, which compiles five regional studies documenting the distribution and long-term trends of SAV and seagrass communities in GoM, is very important and timely. The Guest Editors have done a fantastic job in introducing their special issue in the next section. It has been a real pleasure to work with the guest editors and authors on this special issue in the physical geography category. We hope that readers will find the work gathered here to be as informative and invigorating as we have. This special issue also includes a full book review section. As always, we conclude by inviting more proposals for themed issues of Southeastern Geographer, as well as inviting readers to continuing submitting excellent work to the journal. If you would like to organize a themed issue, please send a 2-page proposal highlighting the summary, justification, list of specific research areas, and potential author names/affiliation (if already known) to segeditors@uga.edu. On a final note, we are excited to announce that Southeastern Geographers will now accept color figures for its online version. Printed versions will still be grayscale. For more information, please refer to the article submission guidelines document at http://sedaag.org/southeastern-geographer/ [End Page 207] Hilda E. Kurtz and Deepak R. Mishra University of Georgia Copyright © 2017 Southeastern Division of the Association of American Geographers

Habitat-specific growth, survival and diet of late juvenile hatchery-reared spotted seatrout (Cynoscion nebulosus)

As a key recreational fishery species throughout the Gulf of Mexico, the spotted seatrout (Cynoscion nebulosus Cuvier) requires sound management practices (VanderKooy and Muller, 2003; Fulford and Hendon, 2010). Accordingly, it is imperative to fully understand the ecology of spotted seatrout (Lorio and Perret, 1978), especially factors affecting the successful recruitment of this estuarine-dependent carnivore. Considering the large gap in knowledge about the ecology of late juvenile stage spotted seatrout, as well as the need to evaluate current stock enhancement practices for this species, the objective of this study was to assess the growth, survival and diet of late juvenile hatchery-reared (HR) spotted seatrout within three prospective nursery habitats in a shallow bay system: submerged aquatic vegetation (SAV), non-vegetated shoreline (NVS), and non-vegetated open water (NVO). While caged under natural conditions for 4weeks, relative growth was significantly greater for fish caged in SAV and NVS habitats compared to NVO habitat. Mortality was relatively high in the first week of the study during acclimation. Stomachs of HR fish contained prey, and the diet composition of HR fish included common prey types consumed by comparable sizes of wild fish. Findings indicate that habitats within or in close proximity to SAV or marsh shoreline offer more favorable conditions than deeper open water habitat for late juvenile HR spotted seatrout. Moreover, HR fish can acclimate to natural conditions and successfully transition to a natural diet, in the absence of predators and competitors.

The Relationship Between Shoreline Armoring and Adjacent Submerged Aquatic Vegetation in Chesapeake Bay and Nearby Atlantic Coastal Bays

Shoreline armoring is an ancient and globally used engineering strategy to prevent shoreline erosion along marine, estuarine, and freshwater coastlines. Armoring alters the land water interface and has the potential to affect nearshore submerged aquatic vegetation (SAV) by changing nearshore hydrology, morphology, water clarity, and sediment composition. We quantified the relationships between the condition (bulkhead, riprap, or natural) of individual shoreline segments and three measures of directly adjacent SAV (the area of potential SAV habitat, the area occupied by SAV, and the proportion of potential habitat area that was occupied) in the Chesapeake Bay and nearby Atlantic coastal bays. Bulkhead had negative relationships with SAV in the polyhaline and mesohaline zones. Salinity and watershed land cover significantly modified the effect of shoreline armoring on nearshore SAV beds, and the effects of armoring were strongest in polyhaline subestuaries with forested watersheds. In high salinity systems, distance from shore modified the relationship between shoreline and SAV. The negative relationship between bulkhead and SAV was greater further off shore. By using individual shoreline segments as the study units, our analysis separated the effects of armoring and land cover, which were confounded in previous analyses that quantified average armoring and SAV abundance for much larger study units (subestuaries). Our findings suggest that redesigning or removing shoreline armoring structures may benefit nearshore SAV in some settings. Because armoring is ubiquitous, such information can inform efforts to reverse the global decline in SAV and the loss of the ecosystem services that SAV provides.

Long‐term spatial dynamics in vegetated seascapes: fragmentation and habitat loss in a human‐impacted subtropical lagoon

AbstractVegetated coastal seascapes exhibit dynamic spatial patterning, some of which is directly linked to human coastal activities. Human activities (e.g. coastal development) have modified freshwater flow to marine environments, resulting in significant changes to submerged aquatic vegetation (SAV) communities. Yet, very little is known about the spatially complex process of SAV habitat loss and fragmentation that affects ecosystem function. Using habitat mapping from aerial photography spanning 71 years (1938–2009) for Biscayne Bay (Florida, USA), we quantify both SAV habitat loss and fragmentation using a novel fragmentation index. To understand the influence of water management practices on SAV seascapes, habitat loss and fragmentation were compared between nearshore and offshore locations, as well as locations adjacent to and distant from canals that transport freshwater into the marine environment. Habitat loss and fragmentation were significantly higher along the shoreline compared with offshore seascapes. Nearshore habitats experienced a net loss of 3.31% of the total SAV mapped (2.57 km2) over the time series. While areas adjacent to canals had significantly higher SAV cover, they still experienced wide fluctuations in cover and fragmentation over time. All sites exhibited higher fragmentation in 2009 compared with 1938, with four sites exhibiting high fragmentation levels between the 1990s and 2000s. We demonstrate that freshwater inputs into coastal bays modify the amount of SAV and the fragmentation dynamics of SAV habitats. Spatial changes are greater close to shore and canals, indicating that these coastal developments have transformative impacts on vegetated habitats, with undetermined consequences for the provisioning of ecosystem goods and services.

Magnitude and Patterns of Change in Submerged Aquatic Vegetation of the Tidal Freshwater Hudson River

Three aerial photography inventories were used to examine change in submerged aquatic vegetation (SAV) in the tidal freshwater Hudson River over the interval 1997 to 2007. Overall, there was about a 30 % net decline in SAV coverage although there were also many individual areas of expansion. The invasive water chestnut (Trapa natans) did not change appreciably in net cover over the interval, and there was replacement of SAV by water chestnut along with slightly fewer cases of SAV replacing the exotic. A fine-scale (100 m by 100 m quadrats) analysis showed that about 30 % of quadrats that supported vegetation changed by more than 10 % in plant cover and overall SAV was quite dynamic. SAV in the Hudson is limited by light which is in turn controlled by suspended sediment. SAV was rarely found at depths >1 m below low water, and interannual differences in clarity affected the ability of SAV beds to maintain locally supersaturated levels of dissolved oxygen. We found that location within the River channel (proximity to shore) influenced the magnitude and variability in change in SAV between census periods. The physical nature of the adjacent shoreline also affected the magnitude of change with greater declines in cover in areas next to hard-engineered shore types. SAV in the Hudson is highly dynamic, apparently quite resilient, and the control of light by suspended sediment rather than phytoplankton growth offers a contrast to eutrophication-influenced changes in other estuaries. Management and protection of SAV habitat must recognize the highly variable nature of plant cover and that absence in any particular year does not preclude future appearance of submerged plants at that location.

Predicting submerged aquatic vegetation cover and occurrence in a Lake Superior estuary

Submerged aquatic vegetation (SAV) provides the biophysical basis for multiple ecosystem services in Great Lakes estuaries. Understanding sources of variation in SAV is necessary for sustainable management of SAV habitat. From data collected using hydroacoustic survey methods, we created predictive models for SAV in the St. Louis River Estuary (SLRE) of western Lake Superior. The dominant SAV species in most areas of the estuary was American wild celery (Vallisneria americana Michx.). Maximum depth of SAV in 2011 was approximately 2.1m. In regression tree models, most of the variation in SAV cover was explained by an autoregression (lag) term, depth, and a measure of exposure based on fetch. Logistic SAV occurrence models including water depth, exposure, bed slope, substrate fractal dimension, lag term, and interactions predicted the occurrence of SAV in three areas of the St. Louis River with 78–86% accuracy based on cross validation of a holdout dataset. Reduced models, excluding fractal dimension and the lag term, predicted SAV occurrence with 75–82% accuracy based on cross validation and with 68–85% accuracy for an independent SAV dataset collected using a different sampling method. In one area of the estuary, the probability of SAV occurrence was related to the interaction of depth and exposure. At more exposed sites, SAV was more likely to occur in shallow areas than at less exposed sites. Our predictive models show the range of depth, exposure, and bed slope favorable for SAV in the SLRE; information useful for planning shallow-water habitat restoration projects.