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Persistent development, population pressures, and increasing natural hazards are unequivocally changing socio-ecological systems in the coastal zone. This essay provides direction and initi...

This study was conducted to compare the sediment parameters of 2 project sites located near Dauphin Island, AL, which each contained a natural shoreline (NS), a living shoreline (LS), and a hardened shoreline (HS) treatment. We collected sediment core samples from the shallow intertidal zone along 3 replicate transects and sectioned them into shallow (0–15 cm) and deep (16–30 cm) fractions. We analyzed sediment subsamples for bulk density, sediment grain size, total carbon, total nitrogen, and extractable phosphorus. At both project sites, HS sediments contained significantly more sand (>90% percent) and higher bulk density than NS and LS sediments. The HS sediments also contained significantly less C and N than the LS and NS. These data suggest that LS treatments over time facilitate conditions that favor organic-matter rich and fine-grained sediments and approach the conditions found in the NS, in contrast to HS sediments that become less suitable for marsh development. These sediment changes in LS treatmnts promote habitat conditions that help facilitate marsh expansion and thereby provide important habitat for estuarine dependent wildlife.

Waldron, M.C.B.; Carter, G.A., and Biber, P.D., 2021. Using aerial imagery to determine the effects of sea-level rise on fluvial marshes at the mouth of the Pascagoula River (Mississippi, USA). Journal of Coastal Research, 37(2), 389–407. Coconut Creek (Florida), ISSN 0749-0208.Coastal marshes provide valuable ecosystem services yet are increasingly vulnerable to sea level rise (SLR).To facilitate a better understanding of how fluvial marshes along the Gulf of Mexico coast are responding to regional SLR of around 3.7 mm per year, this study used aerial imagery to map land cover at the mouth of the Pascagoula River at 20-year intervals, beginning in 1955 and ending in 2014. High-resolution land cover maps were created for each image date based on a maximum likelihood classification scheme using spectral and textural image features. This marsh ecosystem, at the mouth of the largest free-flowing river by volume in the contiguous United States, should be more resilient to sea level rise than other Gulf Coast marshes, with little restriction to sediment supply and relatively low subsidence rates measured nearby. However, the results of this study show that marsh area declined by 1073 ha (17.5%) and rates of marsh conversion to open water increased over the studied time period. Although modeling studies indicate that coastal marshes worldwide may persist under accelerated SLR, these observations suggest that marsh extent in the sediment-rich Pascagoula River Estuary will continue to decline, signifying vulnerability among other marsh ecosystems along the northern Gulf of Mexico coast.

Feedbacks among inundation, sediment trapping, and vegetation productivity help maintain coastal wetlands facing sea‐level rise (SLR). However, when the SLR rate exceeds a threshold, coastal wetlands can collapse. Understanding the threshold helps address key challenges in ecology—nonlinear response of ecosystems to environmental change, promotes communication between ecologists and resource managers, and facilitates decision‐making in climate change policies. We studied the threshold of SLR rate and developed a new threshold of SLR acceleration rate on sustainability of coastal wetlands as SLR is likely to accelerate due to enhanced anthropogenic forces. Deriving these two thresholds depends on the temporal scale, the interaction of SLR with other environmental factors, and landscape metrics, which have not been fully accounted for before this study. We chose a representative marine‐dominated estuary in the northern Gulf of Mexico, Grand Bay in Mississippi, to test the concept of SLR thresholds. We developed a mechanistic model to simulate wetland change and then derived the SLR thresholds for Grand Bay. The model results show that the threshold of SLR rate in Grand Bay is 11.9 mm/year for 2050, and it drops to 8.4 mm/year for 2100 using total wetland area as a landscape metric. The corresponding SLR acceleration rate thresholds are 3.02 × 10−4 m/year2 and 9.62 × 10−5 m/year2 for 2050 and 2100, respectively. The newly developed SLR acceleration rate threshold can help quantify the temporal lag before the rapid decline in wetland area becomes evident after the SLR rate threshold is exceeded, and cumulative SLR a wetland can adapt to under the SLR acceleration scenarios. Based on the thresholds, SLR that will adversely impact the coastal wetlands in Grand Bay by 2100 will fall within the likely range of SLR under a high warming scenario (RCP8.5), highlighting the need to avoid RCP8.5 to preserve these marshes.

Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows.

Along the mainland coastline of eastern Mississippi Sound, the seagrass species Ruppia maritima (Wigeongrass) and Halodule wrightii (Shoalgrass) co-occur in persistent and sometimes extensive beds within Grand Bay. This paper presents seasonal and annual changes in those Ruppia-Halodule beds that are part of the Grand Bay National Estuarine Research Reserve in western Grand Bay using 2005–2011 transect survey data of percent cover and 2009–2013 biomass sampling data. The seagrass beds exhibited significant interannual variation in areal coverage and seasonal variations in biomass, with peak total aboveground biomass (up to 140 g dry wt/m2) in July and August. Intact R. maritima and H. wrightii seeds were found in the sediment, with densities as high as 4160 seeds/m2. The Ruppia-Halodule beds did not show any short-term declines in their growth or abundance following 2005 Hurricanes Katrina and Rita nor the 2010 Deepwater Horizon oil spill. Resumen: A lo largo de la costa continental del este del Mississippi Sound, las especies de pastos marinos Ruppia maritima (Wigeongrass) y Halodule wrightii (Shoalgrass) coexisten en camas persistentes ya veces extensas dentro de Grand Bay. Este articulo presenta cambios estacionales y anuales en los lechos de Ruppia-Halodule que forman parte de la Reserva de Investigacion Estuarina Nacional de Grand Bay en el oeste de Grand Bay usando datos de la encuesta de transectos de 2005–2011 de cobertura porcentual y datos de muestreo de biomasa 2009–2013. Los lechos de pastos marinos mostraron una variacion interanual significativa en la cobertura aerea y las variaciones estacionales en la biomasa, con el pico de biomasa total sobre el suelo (hasta 140 g de peso seco/m2) en julio y agosto. Se encontraron semillas intactas de R. maritima y H. wrightii en el sedimento, con densidades tan altas como 4160 semillas/m2. Las camas Ruppia-Halodule no mostraron disminuciones a corto plazo en su crecimiento o abundancia despues de los huracanes Katrina y Rita en el 2005 ni en el derrame de petroleo Deepwater Horizon del 2010.

Recent technological advances in marine shrimp and finfish aquaculture alleviate many of the environmental risks associated with traditional aquaculture, but challenges remain in cost-effective waste management. Liquid effluent from freshwater aquaculture systems has been shown to be effective in agricultural crop production (i.e., aquaponics), but few studies have explored the potential for reuse of marine aquaculture effluent, particularly the solid fraction. The purpose of this study was to investigate the use of marine aquaculture solid waste as a nutrient source for the nursery production of two salt tolerant plants commonly used in coastal salt marsh restoration, Spartina alterniflora (smooth cordgrass) and Juncus roemerianus (black needlerush). Specifically, measurements of plant biomass and tissue nitrogen and phosphorus allocation were compared between plants fertilized with dried shrimp biofloc solids and unfertilized controls, as well as between plants fertilized with dried fish solids and unfertilized controls. In both experiments, S. alterniflora plants fertilized with marine aquaculture solids showed few significant differences from unfertilized controls, whereas fertilized J. roemerianus plants had significantly greater biomass and absorbed and incorporated more nutrients in plant tissue compared to unfertilized controls. These results suggest that J. roemerianus may be a suitable plant species for the remediation of marine aquaculture solid waste. Keywords: Marine aquaculture, Salt marsh plants, Solid waste, Phytoremediation

We studied the ecological resilience of salt marshes by deriving sea level rise (SLR) thresholds in two estuaries with contrasting upland hydrological inputs in the north-central Gulf of Mexico: Grand Bay National Estuarine Research Reserve (NERR) with limited upland input, and the Pascagoula River delta drained by the Pascagoula River, the largest undammed river in the continental United States. We applied a mechanistic model to account for vegetation responses and hydrodynamics to predict salt marsh distributions under future SLR scenarios. We further investigated the potential mechanisms that contribute to salt marsh resilience to SLR. The modeling results show that salt marshes in the riverine dominated estuary are more resilient to SLR than in the marine dominated estuary with SLR thresholds of 10.3 mm/yr and 7.2 mm/yr respectively. This difference of >3 mm/yr is mainly contributed by larger quantities of riverine-borne mineral sediments in the Pascagoula River. In both systems, sediment trapping by the above-ground vegetation appears to contribute more to marsh platform accretion than organic matter from below-ground biomass based on the medians of the accretion rates. However, below-ground biomass could contribute up to 90% of accretion in the marine dominated estuary compared to only 60% of accretion in the riverine dominated estuary. SLR thresholds of salt marshes are more sensitive to vegetation biomass in the marine dominated estuary while biomass and sediment similarly affect SLR thresholds of salt marshes in the riverine dominated estuary. This research will likely help facilitate more informed decisions on conservation/restoration policies for these two types of systems in the near-term needed to minimize future catastrophic loss of these coastal marsh habitats once SLR thresholds are exceeded.

Habitat attributes of submerged aquatic vegetation and floating-leaved aquatic vegetation were analyzed from survey data collected in estuaries and coastal river systems of Mississippi and Mobile Bay, Alabama. The objectives were to: locate aquatic plant beds along tidally influenced areas and characterize landscape parameters of the sites; group the plant species into a manageable number of logical clusters; and characterize the landscape attributes indicative of the plant communities through Classification and Regression Tree (CART) analysis. Based on the cluster analyses, aquatic vegetation was categorized into three groups: (1) downstream estuarine/saline group, (2) brackish tolerant freshwater species group, and (3) upstream freshwater only group. Landscape features used for habitat characterization and plant classification were defined by long-term environmental conditions which would shape plant communities, rather than water quality parameters, such as water transparency and salinity, that exhibit higher variability and reflect the discrete conditions at time of sampling. The CART results suggest that salinity and “energy” (relative exposure to waves/currents) are the two most important abiotic factors that structure plant communities in the river deltas studied. Abstract: Atributos del habitat de vegetacion acuatica sumergida y vegetacion acuatica con hojas flotantes fueron analizados a partir de los datos de encuestas recogidas en los estuarios y sistemas fluviales costeras de Mississippi y la bahia de Mobile, Alabama. Los objetivos fueron: localizar camas de plantas acuaticas a lo largo de las zonas influidas por las mareas y caracterizar los parametros del paisaje de los sitios; Agrupar las especies de plantas en un numero manejable de agrupaciones logicos; y caracterizar los atributos paisajisticos indicativos de las comunidades de plantas a traves del analisis de arboles de clasificacion y regresion (CART). Con base en los analisis de agrupaciones, la vegetacion acuatica se clasifico en tres grupos: (1) Grupo de aguas abajo del estuario / solucion salina, (2) Grupo de especies de agua dulce tolerantes salobres, y (3) grupo de aguas arriba solamente agua dulce. Las caracteristicas del paisaje utilizadas para la caracterizacion del habitat y la clasificacion de plantas fueron definidas por las condiciones ambientales a largo plazo, que darian forma a las comunidades de plantas, en lugar de parametros de calidad del agua, tales como la transparencia del agua y la salinidad, que presentan una mayor variabilidad y reflejan las condiciones discretas en el momento del muestreo. Los resultados del CART analisis sugieren que la salinidad y “energia” (exposicion relativa a las ondas/corrientes) son los dos factores abioticos mas importantes que estructuran comunidades vegetales en los deltas de los rios estudiados.

Nearshore artificial reefs are common coastal features, for instance the Mississippi Sound has 67 inshore artificial reefs, the goal of which is to increase fisheries production. The success of artificial reefs depends in part on the primary production potential available to support the reef-based food web. In this study, we used settlement plates to estimate periphyton community net productivity, chlorophyll-a (chl-a), and biomass at sites adjacent to four artificial reefs in the Mississippi Sound in order to evaluate the potential of these artificial reefs to enhance local primary production. Water column primary productivity, chl-a, and biomass were also measured to assess the contribution of phytoplankton to total net primary production at these four sites. The largely negative net productivity measurements obtained for the periphyton community suggest that artificial structures deployed in the Mississippi Sound are potentially net heterotrophic and that the autotrophic component of the periphyton is not likely to be a major source of primary production to the reef food web for much of the year except in winter. The higher water column productivity measurements suggest that phytoplankton is a more important source of primary production to the reef food web than the benthic periphyton community especially during the summer.

Loss of aquatic plant species has occurred in coastal and freshwater habitats throughout the world. In particular, population and habit loss of the submerged aquatic species, Vallisneria americana Michx., have made it a potential restoration candidate. For successful restoration, reliable seed sources are vital for producing plants or for direct seeding. Seed survival and their ability to retain viability through storage are key components for successful reproduction. Seed storage and subsequent germination of V. americana were studied over a 6-month period to determine the conditions that retain seed vigor. Seeds were stored at three humidity levels 11%, 50%, 95% using saturated salts and ambient humidity for 1, 2, 4, and 6 months at either cold or ambient temperatures. After storage intervals, seed moisture content, embryo viability, and germination were determined. Timing of germination and seed survival were analyzed using semi-and non-parametric analyses. Storing seeds at lower RH levels for longer periods reduced seed survival and resulted in later germination. Germination and seed survival increased in seeds stored at higher relative humidity and led to earlier germination. Seeds of V. americana from the northern Gulf of Mexico were shown to be desiccation tolerant and have orthodox seed characteristics.

In response to hurricane and oil-spill environmental impacts along the northern Gulf of Mexico, coastal and marine habitat restoration has become a priority. In particular, restoration of submerged aquatic plants is vital for ecosystem health. To facilitate restoration, developing propagation protocols for Gulf coast plants is necessary, but challenging due to the lack of information on many species. Previous seed germination research of Vallisneria americana, a submerged aquatic species with declining abundance in coastal habitats, from northern latitudinal populations reported germination percentages between 80–90%. Germination experiments using Mississippi Gulf coast plants revealed unexpected outcomes. Less than 8% germination occurred when seeds were germinated in a 16 hr photoperiod or 24 hr dark period at 10, 20, 30 or 40 °C. To enhance germination, cold stratification and gibberellic acid soak treatments were conducted, but germination was below 10%. A subsequent seed scarification experi...

Two small-scale Black needlerush (Juncus roemerianus) marsh restoration designs were examined for cost-effectiveness by analyzing a suite of morphological and physiological metrics, along with vegetated area over time. The restoration was conducted by harvesting marsh sods from an adjacent natural marsh and planting in the restoration site. Both restoration designs are on suitable scales for private property owners to conduct, but differed in initially planted coverage area. One design was fully planted (100% coverage of planted marsh sods; termed full density design) and the other design was planted at half the density of the fully planted design (50% coverage of planted marsh sods; termed half density design). We found no consistent differences in the measured metrics between the two restoration designs and few differences between restored sites and reference natural marsh stands. These findings suggest the potential similar functionality across all treatments. The only metrics with consistent differences among treatments were increased leaf nutrient and chlorophyll content in the restored plots when compared to natural stands. These differences are potentially attributable to nutrient-rich runoff from an adjacent parking lot to the restoration site. Total vegetated coverage area for half density plots was similar to full density plots at 2.1 years after planting. Cost-effectiveness analysis of both designs across eight differing restoration scenarios (based on hiring or donation of cost categories) resulted in half density plots having higher or equal cost-effectiveness in seven of the eight scenarios. Half density plots were approximately twice as cost-effective in scenarios with donated pre-planting site construction. Based on the similar vegetated area between the two designs and lower cost and restoration effort, we suggest the half density design as a more cost-effective restoration strategy than the full density design and should be considered for small-scale Black needlerush restoration projects.

Chlorophyll fluorescence is a well established technique to rapidly and non-invasively determine photosynthesis parameters in plant leaves. It can be used in both laboratory and field settings, and frequently dark-adaptation of a leaf sample is called for. In the field, this can be accomplished on flat leaves using standard leaf clips supplied by instrument manufacturers. However, not all plant leaves are flat, many are cylindrical or otherwise three-dimensional in shape. The standard leaf clip does not close fully on three-dimensional leaves, therefore, does not allow the sample to be properly dark adapted in the field. A new leaf “wand” was developed that can be slipped over an entire cylindrical leaf or culm of rushes and sedges for both light- and dark-adapted measurements. This new leaf wand is compared to the standard leaf clip (DLC-8) using a Walz mini-PAM on Juncus roemerianus(Black needlerush). Results indicate that dark-adapted yield measurements are not significantly different between leaf clips, while light-adapted yields are higher with the leaf wand. The potential sources of difference in the optical path of the excitation light and fluorescence return are discussed and compared between leaf clips. Construction of specialized leaf wands should be considered for any leaves are not flat and therefore that do not fit the standard leaf clip for complete dark-adaptation under field conditions.

Vertical aerial image data were used with an edge-detection procedure and visual image interpretation to determine yearly to decadal changes in seagrass (predominantly Halodule wrightii Ascherson) coverage on the Mississippi barrier islands. On Horn Island, seagrass coverage declined from 77 ha in 1940 to 19 ha in 1971, but returned to its 1940 value by 2006. Coverage on Petit Bois declined from 54 ha in 1940 to 8–19 ha from 1952 through 2007. On East Ship, seagrass coverage varied at 2–19 ha from 1963 to 2007. On West Ship, coverage dropped to zero in 2003, but by 2007 it had increased to approximate its 1975 value of 1.8 ha. On Cat Island, coverage increased from 22 ha in 2003 to 71 ha in 2007. There was no apparent negative impact of Hurricane Camille or Hurricane Katrina on seagrass coverage, which could vary annually by a factor of two or more.

Seagrasses are considered important indicators of decline in water quality resulting in increased light attenuation that negatively influences their growth and survival. Chronic light-limitation interspersed with unpredictable acute attenuation events have had poorly understood effects on seagrass recovery dynamics. Zostera marina (eelgrass) and Halodule wrightii (shoalgrass) were subject to a matrix of light-deprivation events followed by recovery periods to mimic repeated acute shading events. Plant survival, morphology, biomass, chlorophyll content, and Fv/Fm were assessed over time to determine recovery. At the end of the experiment, all plants were harvested and species-specific treatment effects were determined. Significant differences due to treatments were noted in all parameters measured. In general, responses were similar for both life-stages and between species, suggesting similar physiological tolerance to repeated acute light-attenuation events. Only plants in treatments where light-deprivation was followed by a recovery interval of at least the same duration showed signs of long-term survival. Chlorophyll fluorescence (Fv/Fm) was an important metric for assessing recovery, but it failed to detect the onset of mortality in many plants. Other metrics of plant condition need to be assessed and coupled with chlorophyll fluorescence data to assess seagrass “health”. This is of particular importance in field studies, where the history of the plants is largely unknown.

Spartina alterniflora (smooth cordgrass) is a widespread intertidal salt marsh plant that is frequently used in coastal restoration projects. Seeds collected in 2004 were tested for seed germination and seedling survival after 6 months of cold seed storage to determine differences among collection locations (experiment 1). Seeds collected in 2005, after Hurricane Katrina, were tested for seed germination and seedling survival from 0 to 15 months of cold seed storage time to determine minimum and maximum storage time and seedling survival rates (experiment 2). Seed germination increased from 1-4 months of cold, wet storage (stratification) and then began to decline. Survival of the seedlings was highest after 2 months of stratification. In experiment 1, seedling size was found to vary widely among seedlings of the same source and age. Seedling height at 22 days after planting ranged from 2-16 cm, despite identical environmental conditions. Selective breeding could target plants with fast early growth characteristics to promote strains that can be raised quickly in a nursery in response to demands for restoration.

Seagrasses are typically light limited in many turbid estuarine systems. Light attenuation is due to water and three optically active constituents (OACs): nonalgal particulates, phytoplankton, and colored dissolved organic matter (CDOM). Using radiative transfer modeling, the inherent optical properties (IOPs) of these three OACs were linked to the light attenuation coefficient, K PAR, which was measured in North River, North Carolina, by profiles of photosynthetically active radiation (PAR). Seagrasses in the southern portion of Albemarle-Pamlico Estuarine System (APES), the second largest estuary in the USA, were found to be light limited at depths ranging from 0.87 to 2 m. This corresponds to a range of K PAR from 0.54 to 2.76 m−1 measured during a 24-month monitoring program. Turbidity ranged from 2.20 to 35.55 NTU, chlorophyll a from 1.56 to 15.35 mg m−3, and CDOM absorption at 440 nm from 0.319 to 3.554 m−1. The IOP and water quality data were used to calibrate an existing bio-optical model, which predicted a maximum depth for seagrasses of 1.7 m using annual mean water quality values and a minimum light requirement of 22% surface PAR. The utility of this modeling approach for the management of seagrasses in the APES lies in the identification of which water quality component is most important in driving light attenuation and limiting seagrass depth distribution. The calibrated bio-optical model now enables researchers and managers alike to set water quality targets to achieve desired water column light requirement goals that can be used to set criteria for seagrass habitat protection in North Carolina.

Drifting macroalgae are unattached seaweeds that are commonly found in many South Florida and Gulf of Mexico shallow-water seagrass habitats. They are primarily comprised of species of red algae (Rhodophyta) and some brown algae (Phaeophyta). Because of the unattached nature of these species, drift algae have the ability to be moved around the landscape primarily by tidal, as well as wind-driven and alongshore currents. Numerous invertebrates and some fish species are typically found associated with drift algal clumps and aggregations. Transport of drift algae is an important dispersal mechanism for both the plants and their associated fauna. Dispersal distances have been studied in numerous locations over a range of spatial scales. However, little is known about quantities of algal material that are involved. In this study I report on composition and biomass of drifting algae that are transported through a tidal inlet in Biscayne Bay, Florida. Sargassum (a brown alga) and about 12 genera of red algae were found in three seasonal collections (Aug., Dec., May). Total biomass collected varied among seasons, with larger average amounts of drift algae collected in May than the other two months sampled. From this data, I calculate the approximate quantities of drift algae that are potentially moving in, or out of, Biscayne Bay, about a half to one ton of biomass per day.

Currents induced by tidal circulation and wind in shallow tropical seagrass habitats can influence the distribution of drifting macroalgae. In Florida, drift algae are mostly comprised of 5 to 10 genera of Rhodophyta (red algae), with 1 or 2 dominant species. Drift clump transport was investigated through manipulative experiments. Increasing flow velocities entrained and transported clumps of drift algae; transport speeds were 50 to 67% of flow velocity and did not vary statistically significantly between clump sizes tested. The roughness of the substratum influenced transport speeds, with moderate to dense monospecific turtlegrass Thalassia testudinum reducing the speed of transport compared to bare substratum. Mixed seagrass substrata (T. testudinum and Halodule wrightii) further inhibited transport of drift clumps by more frequent entangling compared to the bare and monospecific substrata. Persistence of drift algae was inversely related to flow conditions, with longer persistence at low flow velocities.

Seagrass fragments and seeds are important dispersal mechanisms by which individuals can be transported to new habitats. While dispersal distances of these free-floating stages have been recently investigated in some detail, almost nothing is known about how long fragments or seedlings may remain viable in the water-column. This study reports on the results of an experiment in which both mature and seedling life-history stages of the temperate seagrass, Zostera marina L. were successfully maintained hydroponically over a 1-month-period. It is suggested that a potential application of this hydroponic growth approach could be seedling culture for restoration activities.

A model of three functional groups of macroalgae, drift algae, rhizophytic calcareous algae, and seagrass epiphytes, was developed to complement an existing seagrass production model for tropical habitats dominated by Thalassia testudinum(Turtle-grass). The current modeling effort simulates annual biomass dynamics for each of the three functional groups under a variety of stress regimes imposed by nutrient-laden freshwater discharges into a well-flushed coastal bay in South Florida. The model is parameterized based on multiple years of experimental data collected from Biscayne Bay, as well as literature values reported for other Florida and Caribbean seagrass habitats. Calibration of the model yields a good fit of predicted-to-observed biomass (r 2 > 0.85) for sheet-flow and oceanic-influenced sites, but a poor fit ( r 2 = 0.13) under canal-influenced conditions. This is hypothesized to be related to the lack of adequate observed data on seagrass epiphyte dynamics to parameterize the model. Sensitivity analysis showed that the model is easily perturbed by changes in intrinsic growth parameters of the algae (daily growth rate, mortality rate, carrying capacity), while it is much less sensitive to changes in the functional form of the response curves that are used to characterize the stress tolerances of the algae to light, temperature, salinity, and nutrient conditions. This model is considered suitable for use in seagrass habitats similar to those occurring in South Florida, as these are the conditions to which the model was calibrated. © 2003 Elsevier B.V. All rights reserved.

Determination of the percentage cover and residence time of drift algae over perma- nently marked 0.25 m 2 plots at 8 study sites indicated that drift algal cover was relatively low (

1. Hardbottom habitats of Biscayne Bay, a shallow lagoon adjacent to the city of Miami, Florida, USA, contain a limited number of coral species that represent a small subset of the species found at nearby offshore hardbottom and reef habitats of the Florida Reef Tract. Although the physical characteristics of this basin make it a marginal environment for coral growth, the presence of dense populations of Siderastrea radians and Porites furcata indicate that these, as well as other corals that are found at lower densities, are able to tolerate extreme and fluctuating conditions. Three factors, temperature, sedimentation, and salinity, appear to limit coral abundance, diversity, and distribution within Biscayne Bay. 2. Temperatures exhibit high frequencies of extreme high and low values known to cause coral stress and mortality elsewhere. Similarly, sedimentation rates are very high and sediment resuspension caused by currents, storms and boating activities commonly bury corals under sediment layers. Sediment burial was shown experimentally to influence growth and mortality of S. radians. 3. The salinity of Biscayne Bay is influenced by freshwater inputs from canal, sheetflow and groundwater sources that create a near-shore environment with low mean salinity and high salinity fluctuation. Coral communities along this western margin have the lowest coral density and species richness. Chronic exposure to low salinity was shown experimentally to cause a decrease in the growth of S. radians. 4. The location of Biscayne Bay, downstream of a large restoration effort planned for the Everglades watershed, highlights the need to understand the relationship between the physical environment and the health of benthic communities. The data presented here provide the type of scientific information needed so that management decisions can take into account the potential impacts of human activities on the health of coral populations that are already near their tolerance limits for temperature, salinity, and sedimentation. Copyright © 2003 John Wiley & Sons, Ltd.

Wu, W.; Huang, H.; Biber, P., and Bethel, M., 2017. Litter decomposition of Spartina alterniflora and Juncus roemerianus: Implications of climate change in salt marshes. Decomposition of plant litter in salt marshes plays an important role in coastal trophodynamics, nutrient cycling, sediment trapping, and short-term carbon storage, all of which are likely to be affected by climate change and accelerated sea-level rise. Warmer temperatures, altered precipitation patterns, longer and more frequent inundation, and saltwater intrusion will all interact to affect decomposition of plant litter in a complex way. A combination of field experiments and model selection techniques was applied to study how these environmental factors affected litter decomposition of two dominant salt marsh species, Spartina alterniflora and Juncus roemerianus, along the northern Gulf of Mexico. The results from summer field experiments conducted between June and August of 2013 showed that S. alterniflora in the low marsh ha...

Mycorrhizal Fungi (Mississippi) Melissa Pratt-Zossoungbo (NOAA National Ocean Service, Policy, Planning and Analysis Division, MBO, RM 13349, 1305 East-West Hwy, Silver Spring, MD 20910, 301/713-3070 x138, melissa.pratt-zossoungbo@noaa.gov) and Patrick D. Biber (University of Southern Mississippi, Gulf Coast Research Laboratory, 703 E Beach Dr, Ocean Springs, MS 39564, 228/740-8402, patrick.biber@usm.edu)

Seagrasses provide habitat for a wide variety of aquatic species, and reduce coastal erosion via sediment stabilization. The areal coverage of seagrass beds on the Mississippi barrier islands appears to have declined substantially since the 1960s. However, difficulties in sampling benthic vegetation, differences among previous studies in survey methods, and a lack of data on year-to-year variation in coverage have impeded quantitative study of this decline. Thus, the goal of the present study was to utilize historical remote sensing data to quantitatively determine changes in seagrass (predominantly Halodule wrightii Ascherson) coverage on the Mississippi barrier islands. Analyses were limited to imagery acquired during late summer through autumn, when seagrass canopies remained fully developed and water turbidity was low. Given these conditions, seagrass beds were readily identifiable in older black-and-white to color aerial photographs as well as in more recent multi-spectral imagery.On Horn, the largest Mississippi island, seagrass coverage declined from 77 ha in 1940 to 19 ha in 1971. Coverage had returned to its 1940 value by 2006, but declined again in 2007. Seagrass coverage on Petit Bois, the most rapidly-migrating island, declined from 54 ha in 1940 to an approximately stable 8-19 ha from 1952 through 2007. Petit Bois was the only island for which decline in seagrass coverage corresponded with decline in island land area. On the smallest island, East Ship, seagrass coverage remained nearly constant at 16-19 ha from 1963-2007 despite dramatic reductions in land area during Hurricanes Camille (1969) and Katrina (2005). On West Ship, coverage dropped to zero in 2003 but increased by 2007 to slightly exceed its 1975 value of 18 ha. Data for Cat Island extended only from 2003-2007. Seagrass coverage more than tripled during this period, from 22 ha in 2003 to 71 ha in 2007. Protection from trawling may have been a significant factor in the post-1995 recovery of seagrass on Horn Island. The absence of a similar recovery on Petit Bois may be linked with its rapid westward migration in combination with a nearly 40% reduction in land area from 1940-2007. There was no discernable negative impact of Hurricane Camille or Hurricane Katrina on seagrass coverage. Methodological differences (e.g., mapping potential seagrass habitat rather than existing seagrass beds) are important in explaining the dramatic decline in seagrass coverage that is apparent when recent data are compared with results of earlier surveys.

Salvinia molesta Mitchell, a floating invasive aquatic plant, is one of the top 10 worst invasive aquatic weeds in the world. It was discovered in the lower Pascagoula River in 2005 and evidence suggests that this non-native species is spreading along the northern Gulf of Mexico. These plants exhibit rapid growth and nutrient uptake rates, allowing them to out compete other plants in similar habitats. Distributional observations suggest that non-native S. molesta is able to survive in salinities of up to 7 ppt in the lower Pascagoula River. The response of S. molesta to three salinity levels (0, 5, 10 ppt) was tested using chlorophyll fluorescence. The health of the plants was measured over a period of one month, using a log scale series of observation intensities (hourly, daily, weekly). Plant responses indicated an acute salinity effect after about 4-6 hrs and then a gradual chronic decline. Compared to initial measurements, the final actual quantum yield (∆F/Fm’) dropped by 5%, 6% and 29%, while the final potential quantum yield (Fv/Fm) dropped 6%, 27% and 39% in the 0, 5, and 10 ppt treatments, respectively. Only plants in the 0 ppt treatment showed significant new growth. Plants in 5 ppt appeared to maintain themselves, but plants at 10 ppt all exhibited signs of severe stress and loss of color, turgor, and tissue viability after 10 d. Tolerance to brackish salinities has been reported in the past, and has implications for the use of the biological control agent, the weevil Cyrtobagous salviniae, that can only tolerate freshwater conditions. IntroductIon Aquatic plants can be grouped into three types: emergent, floating, and submerged (Pieterse and Murphy 1993), with some of the most successful invasive aquatic plants being in the floating group (e.g., Eichhornia crassipes and Salvinia molesta). These plants exhibit rapid growth rates, rapid nutrient uptake rates, are aggressive, and are competitive species that can impact aquatic environments, local economies, and human health (Holm et al. 1977). The impact of these species on a freshwater body is dramatically illustrated by S. molesta, one of the top 10 worst non-native invasive aquatic weeds in the world (Room and Julien 1995, Carley and Brown 2006). Salvinia molesta has become a worldwide problem, with invasions into freshwater bodies in most tropical countries, and was introduced into the United States in 1995 (Julien and Tipping 2002, USGS 2005). Salvinia molesta has a doubling time of 4-6 d (Mitchell and Tur 1975) and was found in the lower Pascagoula River in 2005 (MS DMR 2005). Evidence reported in McFarland et al. (2004) suggests that this non-native species is spreading into the northern Gulf of Mexico (GOM). In Alabama and Mississippi, there are many suitable habitats for native and non-native invasive aquatic plants; there are four river drainage systems along the 121 km (75 mile) coastline of the state of Mississippi alone. The largest of these is the Pascagoula River, which holds the distinction of being the longest un-dammed, natural river remaining in the continental USA and provides habitat for numerous important and endangered salt marsh species (Schueler 2002). Much of this river system remains relatively unimpacted by development, except for the very lower reaches between the towns of Gautier and Pascagoula, MS. Distributional observations during an outbreak in 2005 by personnel with the Mississippi Department of Marine Resources (DMR) suggest that non-native S. molesta was able to survive in salinities of up to 7 parts per thousand (ppt) in the lower Pascagoula River; a similar tolerance has been reported earlier by Divakaran et al. (1980) from growth tests conducted on salinities of 0 to 11 ppt. This has implications for the use of the biological control agent Cyrtobagous salviniae on this infestation, as this weevil can only tolerate freshwater conditions (Thomas and Room 1986, Julien et al. 2002). This observation is distressing in two respects: (1) potential for a portion of the non-native S. molesta population in the Pascagoula River to escape biological control; and (2) a more salinity-tolerant variety of this species could easily spread into similar habitats that abound along the GOM and elsewhere. Pulse amplitude modulated (PAM) fluorescence is a tool to measure photophysiological processes in vivo. While it cannot be used to directly measure the mechanisms of osmoregulation, it has been used successfully to demonstrate the physiological stress resulting from salinity change in a number of aquatic plant species (Ralph 1998, Kamermans et al. 1999, Murphy et al. 2003, Biber 2006). PAM fluorescence has been used in submerged aquatic plants to measure acute stress, such as desiccation (Adams and Bates 1994, Bjork et al. 1999), temperature or salinity shifts (Ralph et al. 1998, Ralph 1999), and even changes in ambient light over short time durations (Beer and Bjork 2000

Coral communities worldwide are undergoing intense degradation in response to natural and human disturbances, and many reef systems have already experienced significant declines in live coral cover associated with an increase in macroalgal abundance. Here, we document the seasonal dynamics of the macroalgal communities of the Northern Florida Reef Tract, providing a baseline for long-term studies of coral-algal competition in the area. Both macroalgal biomass and percent cover on reefs showed an increasing trend from January to July, when both light and temperature conditions were favorable for growth. Maximum percent cover (56.7 %) was found in July and minimum levels in December (25.8 %). During these peaks in algal cover, many corals were completely covered by dense mats of algae. Two genera, Halimeda and Dictyota, represented the largest proportion (77299 %) of the total algal biomass. In the summer, Dictyota spp. dominated the algal community, occupying up to 40 % of the reef bottom with a dry biomass of up to 20 g.m 22 . In addition, two species, Stypopodium zonale and Trichogloea requienii, showed a significant bloom in April 1998, covering a significant percentage of the bottom (up to 25 %) at an inshore reef. Species that exhibited rapid space monopolization on Florida reefs, such as Dictyota spp. and Stypopodium zonale, also showed rapid growth in microcosm and field growth studies. No correlations were found between fish grazer abundance and algal biomass or percent cover, indicating that present grazer population abundance and composition are not adequate to prevent space monopolization and coral overgrowth by algae such as Dictyota spp. and Halimeda spp. Only a continued monitoring effort will determine whether the seasonal dynamics of the algal community may result in the decline of coral populations in the Northern Florida Reef Tract.