Shoreline Stabilization Research Articles

Moving Toward L‐Band NASA‐ISRO SAR Mission (NISAR) Dense Time Series: Multipolarization Object‐Based Classification of Wetlands Using Two Machine Learning Algorithms

AbstractGiven the key role wetlands play in climate regulation and shoreline stabilization, identifying their spatial distribution is essential for the management, restoration, and protection of these invaluable ecosystems. The increasing availability of high spatial and temporal resolution optical and synthetic aperture radar (SAR) remote sensing data coupled with advanced machine learning techniques have provided an unprecedented opportunity for mapping complex wetlands’ ecosystems. A recent partnership between the National Aeronautics and Space Administration (NASA) and the Indian Space Research Organization (ISRO) resulted in the design of the NASA‐ISRO SAR (NISAR) mission. In this study, the capability of L‐band simulated NISAR data for wetland mapping in Yucatan Lake, Louisiana, is investigated using two object‐based machine learning approaches: Support vector machine (SVM) and random forest (RF). L‐band Unmanned Aerial Vehicle SAR (UAVSAR) data are exploited as a proxy for NISAR data. Specifically, we evaluated the synergistic use of different polarimetric features for efficient delineation of wetland types, extracting 84 polarimetric features from more than 10 polarimetric decompositions. High spatial resolution National Agriculture Imagery Program imagery is applied for image segmentation using the mean‐shift algorithm. Overall accuracies of 74.33% and 81.93% obtained by SVM and RF, respectively, demonstrate the great possibility of L‐band prototype NISAR data for wetland mapping and monitoring. In addition, variable importance analysis using the Gini index for RF classifier suggests that H/A/ALPHA, Freeman‐Durden, and Aghababaee features have the highest contribution to the overall accuracy.

Sediment Exchange Between the Created Saltmarshes of Living Shorelines and Adjacent Submersed Aquatic Vegetation in the Chesapeake Bay

Rising sea levels and the increased frequency of extreme events put coastal communities at serious risk. In response, shoreline armoring for stabilization has been widespread. However, this solution does not take the ecological aspects of the coasts into account. The “living shoreline” technique includes coastal ecology by incorporating natural habitat features, such as saltmarshes, into shoreline stabilization. However, the impacts of living shorelines on adjacent benthic communities, such as submersed aquatic vegetation (SAV), are not yet clear. In particular, while both marshes and SAV trap the sediment necessary for their resilience to environmental change, the synergies between the communities are not well-understood. To help quantify the ecological and protective (shoreline stabilization) aspects of living shorelines, we presented modeling results using the Delft3D-SWAN system on sediment transport between the created saltmarshes of the living shorelines and adjacent SAV in a subestuary of Chesapeake Bay. We used a double numerical approach to primarily validate deposition measurements made in the field and to further quantify the sediment balance between the two vegetation communities using an idealized model. This model used the same numerical domain with different wave heights, periods, and basin slopes and includes the presence of rip-rap, which is often used together with marsh plantings in living shorelines, to look at the influences of artificial structures on the sediment exchange between the plant communities. The results of this study indicated lower shear stress, lower erosion rates, and higher deposition rates within the SAV bed compared with the scenario with the marsh only, which helped stabilize bottom sediments by making the sediment balance positive in case of moderate wave climate (deposition within the two vegetations higher than the sediment loss). The presence of rip-rap resulted in a positive sediment balance, especially in the case of extreme events, where sediment balance was magnified. Overall, this study concluded that SAV helps stabilize bed level and shoreline, and rip-rap works better with extreme conditions, demonstrating how the right combination of natural and built solutions can work well in terms of ecology and coastal protection.

Multi-decadal shoreline morphodynamics of a shelf-edge reef island, Great Barrier Reef: Implications for future island persistence

Future climatic change and sea-level rise threaten the persistence of reef islands potentially making them uninhabitable over the next century. Improved understanding of island morphodynamics at multiple time scales is required for resolving major drivers of shoreline change and predicting future island resilience. Utilising 45 individually mapped shorelines, the morphodynamic change of a shelf-edge reef island (Raine Island, Great Barrier Reef) has been quantified over a 57-year time scale in the context of environmental change and anthropogenic impacts. Results show that between 1963 and 2020, there has been an average net shoreline movement (NSM) of −4.71 m and an average rate of retreat of −0.11 m/yr. However, only 23% of the shoreline has exhibited statistically significant erosion while the remaining 77% has remained stable. Importantly, data reveal a remarkable level of long-term shoreline stability despite large seasonal fluctuations in wind and wave climate, episodic storm events, and a regional sea level rise currently outpacing the global mean. Direct human impact, through modifications of the beach profile since 2014, have resulted in localised increases in rates of shoreline change but have only slightly decreased the proportion of stable shoreline (91% since modifications commenced versus 96% prior to modifications). Interestingly, there is a significant decreasing trend in island planform area over the 57-year period and especially over the last decade. However, the length of the observation interval between sampled shorelines has a strong effect on the change in planform area recorded over the interval, suggesting increased sampling frequency, rather than sea level rise, is a more likely cause of the decreasing trend. The findings of this study have direct implications for more accurate assessments of past, present and future shoreline change on reef islands. They also support the concept of 21st century island persistence in the face of climate change although the relative resilience of a given island to change (e.g., sea level, human modifications) will depend on a continuous adequate supply of sediment from organisms living on the surrounding reef, which may or may not be threatened in the future.

Technical and Social Approaches to Study Shoreline Change of Kuakata, Bangladesh

In recent years, shoreline determination has become an issue of increasing importance and concern, especially at the local level, as sea level continues to rise. This study identifies the rates of absolute and net erosion, accretion, and shoreline stabilization along the coast of Kuakata, a vulnerable coastal region in south-central Bangladesh. Shoreline change was detected by applying remote sensing and geographic information system (RS-GIS)-based techniques by using Landsat Thematic Mapper (TM), Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) satellite images at 30-m resolution from 1989, 2003, 2010, and 2020. The band combination (BC) method was used to extract the shoreline (i.e., land-water boundary) due to its improved accuracy over other methods for matching with the existing shoreline position. This study also used participatory rural appraisal (PRA) tools which revealed the societal impacts caused by the shoreline changes. Coupling RS-GIS and PRA techniques provides an enhanced understanding of shoreline change and its impacts because PRA enriches the RS-GIS outcomes by contextualizing the findings. Results show that from 1989 to 2020, a total of 13.59 km2 of coastal land was eroded, and 3.27 km2 of land was accreted, suggesting that land is retreating at about 0.32 km2 yr–1. Results from the PRA tools support this finding and demonstrate that fisheries and tourism are affected by the shoreline change. These results are important in Kuakata, a major tourist spot in Bangladesh, because of the impacts on fisheries, recreation, resource extraction, land use planning, and coastal risk management.

Sand resource geology of the Southern North Carolina inner shelf

Beach nourishment is a popular engineering-with-nature (EWN) strategy used globally for shoreline stabilization and coastal storm damage reduction. Large-scale projects require dredging from offshore sand borrow sources. However, suitable sands for nourishment are not ubiquitous offshore, especially in sediment-starved southern NC. In 2015, >300 nautical miles (555 km) of sub-bottom, sidescan, bathymetry and 38 cores/grabs were collected in data gaps offshore southern NC and interpreted for geologic horizons and potential nourishment-compatible sand thickness. In addition, hundreds of paleochannels were mapped and evaluated for fill patterns and resource potential. Various forms of hardbottom were delineated, sometimes in close proximity to sand resources. Results show high spatial variability in the distribution of beach-compatible sands across the southern NC shelf, where only a thin sand veneer is observed in many locations, although some regions contained continuous deposits exceeding 3 m. The thickest shoal deposits (>5 m) were observed offshore New Hanover County Region. Underlying strata and bathymetry appear to affect channel shape and distribution. Channels with acoustically transparent fill may be suitable as nourishment sources, yet many channels show complex and variable fill suggestive of tidal and estuarine environments. Seafloor reconnaissance data are valuable in preventing multi-use conflicts on the shelf as shelf areas are increasingly being explored for other functions (e.g, wind farms, oil/gas, fish habitat). These findings provide a useful starting point for coastal managers seeking sufficient offshore sediment resources for nourishment in response to future storm events and sea-level rise.

Remote Sensing Application for Exploring Land Use and Land Cover Dynamics in and Around Chatra Wetland, English Bazar, West Bengal

Wetlands are often called as biological “supermarket” and “kidneys of the landscape” due to their multiple functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines and support of aquatic lives. Unfortunately, although being dynamic and productive ecosystem, these wetlands have been affected by human induced land use changes. India is losing wetlands at the rate of 2 to 3 per cent each year due to over-population, direct deforestation, urban encroachment, over fishing, irrigation and agriculture etc (Prasher, 2018). The present study tries to investigate the nature and degree of land use/land cover transformation, their causes and resultant effects on Chatra Wetland. To fulfil the purpose of the study, GIS and remote sensing techniques have been employed. Satellite imageries have been used from United States Geological Survey (USGS) Landsat 7 Enhanced Thematic Mapper plus and Landsat 8 Operational Land Imager for the year 2003 and 2018. Cloud free imageries of 2003 and 2018 have been downloaded from USGS (https://glovis.usgs.gov/) for the month of March and April respectively. Image processing, supervised classificationhas been done in ArcGis 10.5 and ERDAS IMAGINE 14. The study reveals that the settlement hasincreased by about 90.43 per cent in the last 15 years around the Chatra wetland within the bufferzone of 2 Sq km. Similarly agriculture, vegetation, water body, swamp and wasteland witnessed asignificant decrease by 5.94 per cent, 57.69 per cent, 26.64 per cent 4.52 per cent and 55.27 per centrespectively from 2003 to 2018.

Monitoring Impact of Salt-Marsh Vegetation Characteristics on Sedimentation: an Outlook for Nature-Based Flood Protection

Salt marshes can protect coastlines against flooding by attenuating wave energy and enhancing shoreline stabilization. However, salt-marsh functioning is threatened by human influences and sea level rise. Although it is known that protection services are mediated by vegetation, little is known about the role of vegetation structure in salt-marsh accretion. We investigated the role of vegetation presence, vegetation type and structural vegetation characteristics in sedimentation and sediment grain size. We established 56 plots on a salt marsh on the Dutch Wadden island of Texel. Plots were divided over four vegetation types contrasting in vegetation structure and varied in elevation and distance to creeks. Vegetation presence was controlled by clipping in subplots. Within each plot, we measured seven vegetation characteristics, sedimentation and the sediment grain size distribution. Furthermore, we explored the effect of the natural variation in vegetation structure on wave attenuation with a simple model approach. For this, we developed vegetation scenarios based on the field measurements of stem height, diameter and density. We found that vegetation presence increased sedimentation on average by 42%. Sedimentation was highest in Salicornia vegetation and increased with stem height and branching level. Grain size also seemed to increase with branching level. Modelled wave attenuation was 7.5 times higher with natural vegetation compared to topography only, was strongest for Spartina vegetation and most sensitive to the natural variance in stem density. Our results can be used to improve predictions of salt-marsh accretion and the implementation of salt marshes in nature-based flood defences.

Detecting hydrodynamic changes after living shoreline restoration and through an extreme event using a Before-After-Control-Impact experiment

Stabilization of eroding estuarine shorelines using living shoreline techniques, including native vegetation and nearshore structural components, has the potential to combat erosion while increasing shoreline ecotone function. However, there are few detailed field studies and little quantitative data available to assess hydrodynamic changes that occur immediately following living shoreline implementation. To address this gap, detailed hydrodynamic observations were made along eroding and stable reference shorelines over a 16-month period spanning living shoreline stabilization, which included the landfall of a major hurricane (Irma) 9 weeks after stabilization. In the months following stabilization, planted vegetation was sparse and shoreline hydrodynamics were governed by water level relative to breakwater structures. When water levels were at or below breakwater crest elevation, current velocities were initially reduced by 62% and wave heights by up to 83%; however, at higher water levels, shoreline velocities at the stabilized site vastly exceeded those observed at a nearby bare control site. Sixteen months after stabilization, flow-vegetation interactions had become a dominant control over shoreline hydrodynamics, and current attenuation was similar to that observed in nearby mature mangrove vegetation. Additionally, turbulence dissipation rates at the stabilized site (2.2∙10−5 m2/s3) and vegetated reference site (1.1∙10−5 m2/s3) were an order of magnitude greater during boat wake events compared to the bare shoreline site (1.6∙10−6 m2/s3,p < 0.001). This first experimental assessment of hydrodynamic effects related to living shoreline stabilization indicates that more than one year may be required before planted vegetation meaningfully influences shoreline hydrodynamics.

Coastal resilience surges as living shorelines reduce lateral erosion of salt marshes.

A growing suite of research has demonstrated that nature-based shoreline stabilization methods can increase resilience of coastal ecosystems by improving their capacity to return to predisturbance states. Previous work suggests that during hurricanes, living shorelines promote vertical accretion and experience less damage than traditional shoreline stabilization alternatives. Nevertheless, there is limited research looking at the impacts of major storm events on living shorelines and most studies have investigated a small number of sites. This study used in situ real-time kinematic (RTK)-GPS surveys to quantify the resilience (via the lateral change in shore position) of 17 living shoreline sites before and after a Category 1 hurricane event (Hurricane Florence, 2018). By doing so, this study seeks to understand the capacity of living shorelines (marsh with seaward breakwater or sill) to provide storm protection as compared to unaltered natural fringing salt marshes. After Hurricane Florence, living shorelines on average experienced significantly less lateral erosion compared to unprotected control segments (shoreline change rates of 0.015 and -0.31 m year-1 , respectively). This study also explores how environmental siting variables (i.e., scarp presence, fetch, and bottom sediment) and sill design variables (i.e., sill material, width, and height) influence short- and long-term erosion. living shorelines were found to reduce erosion of fringing marsh edge among projects with a range of installation ages, structural materials, sill widths, and sill heights, and they were able to provide protection from erosion across a range of fetch, scarp, and bottom sediment conditions. Living shoreline siting and sill design may be suitable for broader environmental conditions than previously known. This study shows that living shorelines can increase resilience by reducing erosion of fringing salt marshes, promoting lateral building up of shoreline zones during short-term disturbance events, and from their long-term presence. Integr Environ Assess Manag 2022;18:82-98. © 2021 SETAC.

Planting after shoreline cleanup treatment improves salt marsh vegetation recovery following the Deepwater Horizon oil spill

The Deepwater Horizon oil spill (2010) resulted in ~100 km of heavily oiled salt marsh shorelines with severe marsh vegetation impacts. Approximately 27 km of these shorelines had marsh cleanup treatments aimed at limiting oil spread and facilitating ecological recovery. Heavy oiling impacts and disturbance from intensive cleanup treatments left marsh shorelines largely bare of live vegetation. Following operational-scale shoreline cleanup and experimental planting of Spartina alterniflora, we compared oiling degree and vegetation recovery among three types of heavily oiled salt marsh plots over three years: oiled control (no cleanup treatment, no planting); mechanical cleanup treatment (unplanted); and mechanical treatment coupled with planting. Nearby reference plots were used to define recovery targets and determine recovery progress. Mechanical treatment with planting showed the most improvement in oiling conditions and was most effective in re-establishing vegetation cover and dominant plant species composition approaching reference conditions. In contrast, the oiled controls and mechanical treatment plots without planting were similar and showed much slower recovery trends. Vegetation planting should be considered as a shoreline treatment or restoration approach for heavily oiled salt marshes, especially where oil impacted areas are left largely unvegetated, natural recovery is delayed, marsh shorelines are at risk of erosion, and as a possible condition for the use of intensive cleanup treatments. Vegetation planting following oil spills could be incorporated into shoreline treatment operations during emergency response as shoreline stabilization and for oil removal via phytoremediation, or as emergency restoration under the Natural Resources Damage Assessment (NRDA) process, to limit the degree and duration of natural resource impacts.

Conservation practice insights from a comparative case study of two shoreline stabilization projects in Boston Harbor, MA

AbstractAs sea levels rise and the frequency of flooding events increases, so do efforts to stabilize coastal shorelines. Nature‐based solutions to shoreline stabilization (“green” solutions, as opposed to traditional “grey” shoreline hardening) have been increasingly adopted in the Gulf of Mexico and mid‐Atlantic regions of the United States, but they are only beginning to be implemented, documented, and understood in the northeastern United States. This case study contrasts two shoreline stabilization projects directly across from each other on the banks of the Mystic River, Boston Harbor, MA. These two projects, one private and one public, employ a spectrum of green‐grey shoreline stabilization techniques. Originally planned as traditional grey shoreline stabilizations, both projects shifted toward greener solutions due to local environmental group advocacy, highlighting the influence of outside groups as advocates for nature‐based solutions. This study documents the evolution of both projects, highlighting common challenges in permitting and vegetation maintenance, as well as critical differences in project goals, funding sources, and biodiversity impacts.

Mediterranean Tapeweed Posidonia oceanica (L.) Delile, an Endangered Seagrass Species

THE MOST plentiful and important seagrass in the Mediterranean Sea is Posidonia oceanica L. (Delile) because of its ability to create a three-dimensional habitat with high biodiversity and to build the “matte”(a terrace of interlaced rhizomes and roots trapping sediment). This matte highly influences coast features in terms of wave attenuation and shoreline stabilization. In addition, P. oceanica meadows, which could extend along the coast, from the shoreline until 40m depth, are directly exposed to anthropic pressure coming from the coastal zones and it is particularly sensitive to the environmental conditions. In the last decades, human activities in coastal areas impacted sedimentary processes severely affecting P. oceanica meadows with consequent seagrass loss. This review aims to shed light on the importance of this plant, the extent of its dangerous status, and to urge the international community and governments to try to protect it in all possible ways, especially in Egypt.

Acoustic camera and net surveys reveal that nursery enhancement at living shorelines may be restricted to the marsh platform

Rapid human development in coastal areas is introducing significant amounts of novel habitat and leading to widespread habitat simplification. To predict how species will respond to these changes, it is important to understand how organisms interact with novel habitats versus naturally existing habitats. In this study, we used traditional fish sampling gear (fyke nets and minnow traps) and a Dual-Frequency Identification Sonar (DIDSON) to conduct fish surveys along natural and modified estuarine shorelines in North Carolina, USA. The overall objective of our study was to investigate how fish abundance and other community metrics change as a function of shoreline type (natural marsh, living shoreline, or bulkhead), sampling location (marsh platform or the shallow subtidal area offshore of the structure), and time of day (day or night). Using fyke nets, we caught significantly more fish and recorded higher species richness on the marsh platform at living shorelines versus natural marsh shorelines. However, we found no significant differences in fish abundance in the shallow unvegetated habitats seaward of the different shoreline types, which may have been affected by low sampling efficiency and replication when sampled using minnow traps and the DIDSON. Our findings, in conjunction with similar studies, may reflect a localized shoreline effect where the nursery enhancement observed at living shoreline sites is restricted to the living component of the shoreline (i.e., the marsh). Additionally, the preliminary results from our limited daytime versus nighttime DIDSON sampling show no significant differences in fish detections. This contrasts with many previous studies using traditional fish sampling techniques that report substantially higher fish catches at night. This unexpected finding is worthy of additional research as it may suggest that traditional fish sampling techniques are underestimating fish abundances during the day, perhaps due to visual gear avoidance. Ultimately, a careful consideration of the social and ecological goals of any shoreline stabilization project is needed before choosing a final design; however, maximizing habitat restoration and limiting the use of artificial materials is likely to confer the greatest ecological benefit.

Salvando el planeta con biotecnología apropiada: 5. Un plan de acción

We evaluate suggestions to harness the ability of calcifying organisms (molluscs, crustacea, corals and coccolithophore algae) to remove permanently CO2 from the atmosphere into solid (crystalline) CaCO3 for atmosphere remediation. Here, we compare this blue carbon with artificial/industrial Carbon dioxide Capture &amp; Storage (CCS) solutions. An industrial CCS facility delivers, at some cost, captured CO2, nothing more. But aquaculture enterprises cultivating shell to capture and store atmospheric CO2 also produce nutritious food and perform many ecosystem services like water filtration, biodeposition, denitrification, reef building, enhanced biodiversity, shoreline stabilisation and wave management. We estimate that a mussel farm sequesters three times as much carbon as terrestrial ecosystems retain. Blue carbon farming does not need irrigation or fertiliser, nor conflict with the use of scarce agricultural land. Blue carbon farming can be combined with restoration and conservation of overfished fisheries and usually involves so little intervention that there is no inevitable conflict with other activities. We calculate that this paradigm shift (from ‘shellfish as food’ to ‘shellfish for carbon sequestration’) makes bivalve mollusc farming and microalgal farming enterprises, viable, profitable, and sustainable, alternatives to all CCUS industrial technologies and terrestrial biotechnologies in use today.

Natural Intertidal Oyster Reef Growth Across Two Landscape Settings and Tidal Ranges

Intertidal oyster reefs are typically restored to offset the loss of reef-associated ecosystem services (e.g., improved water quality, shoreline stabilization, and fish habitat), but the scale of enhanced services is predicated on the health and growth of the restored reef. Previous work on young (<15 years) restored reefs showed the highest growth rates along the sides of reefs where they are aerially exposed 20–40% of the time, but much is still unknown about how those positions in the tidal frame change with landscape setting, tidal range, and reef maturity. This study compared the area of maximum growth among 12 natural intertidal reefs in coastal North Carolina that range between 1395 and 62 years old. The reefs include fringing and patch landscape settings in each of two estuaries with tidal ranges of 0.94 m and 1.51 m. Peak growth rates were similar among landscape and tidal settings and were faster than the rate of sea-level rise (SLR) indicating intertidal reef resilience to accelerating SLR. Flow baffling associated with fringing reefs and higher summer air temperatures in the southern estuary likely contributed to a lower position of the optimal growth zone, where growth rates are highest, in the tidal frame. Intertidal reef growth manifests differently across the range of aerial exposures at varying stages of maturity. Once reefs reached ~50 years old, the elevation of the reef crests equilibrated to ~60–70% aerial exposure and peak growth rates stabilized between 2 and 4 cm year−1 at ~50% aerial exposure. These results are a useful guide for identifying areas and cultch configurations that optimize reef growth rates, enhancing the probability for self-sustaining restored reefs.

Piping plovers demonstrate regional differences in nesting habitat selection patterns along the U.S. Atlantic coast

AbstractHabitat studies that encompass a large portion of a species’ geographic distribution can explain characteristics that are either consistent or variable, further informing inference from more localized studies and improving management successes throughout the range. We identified landscape characteristics at Piping Plover nests at 21 sites distributed from Massachusetts to North Carolina and compared habitat selection patterns among the three designated U.S. recovery units (New England, New York–New Jersey, and Southern). Geomorphic setting, substrate type, and vegetation type and density were determined in situ at 928 Piping Plover nests (hereafter, used resource units) and 641 random points (available resource units). Elevation, beach width, Euclidean distance to ocean shoreline, and least‐cost path distance to low‐energy shorelines with moist substrates (commonly used as foraging habitat) were associated with used and available resource units using remotely sensed spatial data. We evaluated multivariate differences in habitat selection patterns by comparing recovery unit‐specific Bayesian networks. We then further explored individual variables that drove disparities among Bayesian networks using resource selection ratios for categorical variables and Welch’s unequal variances t‐tests for continuous variables. We found that relationships among variables and their connections to habitat selection were similar among recovery units, as seen in commonalities in Bayesian network structures. Furthermore, nesting Piping Plovers consistently selected mixed sand and shell, gravel, or cobble substrates as well as areas with sparse or no vegetation, irrespective of recovery unit. However, we observed significant differences among recovery units in the elevations, distances to ocean, and distances to low‐energy shorelines of used resource units. Birds also exhibited increased selectivity for overwash habitats and for areas with access to low‐energy shorelines along a latitudinal gradient from north to south. These results have important implications for conservation and management, including assessment of shoreline stabilization and habitat restoration planning as well as forecasting effects of climate change.

Living Shoreline Monitoring—How do I evaluate the environmental benefits of my living shoreline?

Living shorelines are structures made of natural materials such as oyster shell, sand, mangroves, salt marsh plants, and other organic materials built to protect properties from erosion. In addition to increasing shoreline stability, living shorelines enhance many valuable ecosystem functions. In this new 11-page publication of the UF/IFAS Department of Soil and Water Sciences, we provide homeowners, land managers, and Extension agents materials lists, protocols, and data sheets for measuring change in ecosystem function. Measuring and interpreting these measurements will help evaluate living shorelines projects as well as provide the foundation for monetarizing the value of these structures. Written by Laura K. Reynolds, Natalie C. Stephens, Savanna C. Barry, and Ashley R. Smyth.https://edis.ifas.ufl.edu/ss694

Ecological co-benefits from sea cucumber farming: Holothuria scabra increases growth rate of seagrass

Sea cucumber aquaculture is increasing in extent and importance throughout the Indo-Pacific region, supplying a luxury seafood market in Asia. In this context, the grow-out of hatchery-bred juveniles in community-farmed pens is proving to be a viable model, providing increased income security and alternative livelihood options to resource-limited communities. Here, we report a study of the impacts of such sea cucumber farming on the growth of seagrass (a favourable habitat for the animals) at a village-scale aquaculture site in southwest Madagascar. Using experiments, we found that the presence of the hatchery-bred sea cucumberHolothuria scabra(sandfish), at stocking densities of 300 g m-2(similar to the density used in the farmed pens, but relatively high for natural populations), resulted in a large (~30%), statistically significant increase in the leaf extension rate of the locally dominant seagrass speciesThalassia hemprichii. However, the other dominant seagrass species,Cymodocea serrulata, did not significantly change its leaf extension rate in the presence ofH. scabra. Since seagrass is a globally important coastal habitat, supporting high biodiversity, carbon sequestration, shoreline stability and nursery grounds for commercial and small-scale fisheries, the positive effect ofH. scabrafarming on the growth rate of at least one dominant seagrass species implies potential important ecological co-benefits. These co-benefits ofH. scabrafarming are likely to be relevant across the tropical Indo-Pacific coastlines, where this species is cultured.

Evaluation of Lime-Treated Lateritic Soil for Reservoir Shoreline Stabilization

Sedimentation is one of the major problems addressed by reservoir management, and requires extensive effort to control it. This paper aims to evaluate the efficiency of the soil–lime stabilization technique for reservoir shores. The treatment consisted of spraying hydrated lime in slurry form over the surface of a lateritic clay sample with 1, 2, and 4% lime solution and curing times of 1, 7, 28, and 56 days with air-drying and moist-room storage. In addition, a single test with less than 1% lime solution by weight percentage was carried out. The post-cured specimens were mapped with SEM and X-ray analyses. A wave flume test was performed in samples subjected to diverse conditions of lime content, type, and curing time. The results showed that the present technique produces a Ca-rich crust by carbonation rather than stabilizing it and that the lime content and type of curing generate improvements in soil loss reduction, but the curing time does not. The technique gave relative protection against water level variation and wave impacts, but it is necessary to consider a frequent application of lime on the lateritic soil.

Mapping the Intertidal Microphytobenthos Gross Primary Production Part I: Coupling Multispectral Remote Sensing and Physical Modeling

The gross primary production (GPP) of intertidal mudflat microphytobenthos supports important ecosystem services such as shoreline stabilization and food production, and it contributes to blue carbon. However, monitoring microphytobenthos GPP over a long-term and large spatial scale is rendered difficult by its high temporal and spatial variability. To overcome this issue, we developed an algorithm to map microphytobenthos GPP in which the following are coupled: (i) NDVI maps derived from high spatial resolution satellite images (SPOT6 or Pleiades), estimating the horizontal distribution of the microphytobenthos biomass; (ii) emersion time, photosynthetically active radiation (PAR), and mud surface temperature simulated from the physical model MARS-3D; (iii) photophysiological parameters retrieved from Production-irradiance (P-E) curves, obtained under controlled conditions of PAR and temperature, using benthic chambers, and expressing the production rate into mg C h −1 m −2 ndvi −1. The productivity was directly calibrated to NDVI to be consistent with remote-sensing measurements of microphytobenthos biomass and was spatially upscaled using satellite-derived NDVI maps acquired at different seasons. The remotely sensed microphytobenthos GPP reasonably compared with in situ GPP measurements. It was highest in March with a daily production reaching 50.2 mg C m −2 d −1 , and lowest in July with a daily production of 22.3 mg C m −2 d −1. Our remote sensing algorithm is a new step in the perspective of mapping microphytobenthos GPP over large mudflats to estimate its actual contribution to ecosystem functions, including blue carbon, from local and global scales.