Article

A simple, fast, and reliable method to predict Sargassum washing ashore in the Lesser Antilles

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Since 2011, the Lesser Antilles have faced major events of the washing ashore of pelagic Sargassum. Windward, exposed island coasts receive tons of algae that alter the quality of coastal ecosystems and the environment. The events repeated in 2012, 2014, 2015 and 2016. A major concern for local governments is to predict arriving floating algae and assess the risk of washing ashore. Here, we present a method to use a Sargassum Watch System (SaWS), based on satellite imagery and numerically-modelled surface currents, for near-real-time tracking of floating algae in the central Atlantic. The analysis of satellite data and numerical HYCOM surface ocean currents was used to predict washing ashore events days before they occur. These online products are integrated and made available to users in Keyhole Markup Language (KML) format and uploaded in Google Earth. Tracking of Sargassum slicks, combined with distance from coast and HYCOM current vectors’ direction and speed, can provide an effective prediction tool for possible washing-ashore in specific locations. Comparisons of events between the years 2011 and 2015 show some intensification of the presence of Sargassum in the western Atlantic and a significant increase in the risk of Sargassum washing ashore on the beaches of small islands. The demonstration using simple analyses of existing near real-time online products provides a template for governmental agencies and environmental groups to use, effectively, existing resources towards coastal management.
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... Comme montré à la Figure 1, les sargasses prolifèrent dans l'Atlantique Nord équatorial, soit au large du Brésil, se rassemblent en des bancs de forte densité et de grandes surfaces qui atteignent fréquemment, par l'intermédiaire de courants et de vents favorables, les côtes des Caraïbes. Au début de la décennie, les échouages commencaient plutôt vers le mois de mars, mais depuis trois ans les côtes des Antilles Françaises (AF) sont touchées depuis le mois de Janvier [3], voire toute l'année ( Le Tableau 1 montre qu'en 2018, l'événement a été sans précédent car des centaines de baies se sont remplies en une dizaine d'heures dans toute la région. Ces échouages aboutissent à des cumuls élevés de biomasse, laissant les autorités sans réponses immédiates avec des moyens sous dimensionnés face à l'ampleur des dégâts écologiques et socio-économiques provoqués [4]. ...
... Ces échouages aboutissent à des cumuls élevés de biomasse, laissant les autorités sans réponses immédiates avec des moyens sous dimensionnés face à l'ampleur des dégâts écologiques et socio-économiques provoqués [4]. La communauté scientifique internationale s'est aussi mobilisée, avec une large contribution portant sur l'identification, la caractérisation, le dénombrement de l'ensemble des impacts et l'évaluation du potentiel d'échouage, tout en utilisant aussi bien les résultats d'observations in situ que la télédétection [1,2,3,5,6]. Du point de vue biologique, bien que les tapis dérivants constituent un habitat important pour la faune et la flore en pleine mer [7,8,9], ils deviennent après échouages des pièges souvent mortels pour les animaux. ...
... utilise un produit d'analyse fondé sur des images satellites issues du radiomètre spectral pour imagerie de résolution moyenne (MODIS), ceux de MERIS et les capteurs du dispositif Landsat et VIIRS [14,15,16]. Récemment, quelques auteurs se sont préoccupés du contexte océanographique, en associant les observations par des satellites à des modèles numériques [3,17,18]. ...
Conference Paper
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Abstract : The unprecedented influx of Sargassum that reached the French Antilles on several occasions, especially during 2015 to 2018 constitutes a major threat to the ecology, health and economy of these islands. These small islands can each receive an average of 150 000 m 3 of seaweed during major stranding episodes. The predictability of these has not been investigated and is likely related with thermodynamic conditions that cause a build-up and ocean transport that brings the problem to east-facing beaches and bays, mainly since 2011. The increased volume of seaweed has closed some tourism resorts and made some beaches uninhabitable. A research effort becomes necessary to reduce these uncertainties and thereby apprehend future episodes of seaweed stranding. We present here the results from a series of ocean models that examine surface transport, east of the Antilles, for several cases of massive stranding on the coasts 24 ème Congrès Français de Mécanique Brest, 26 au 30 Août 2019 of Guadeloupe and Martinique. The Operational Mercator global ocean analysis and forecast system at 1/12 degree was used and includes daily mean files of temperature, salinity, currents, sea level, and mixed layer depth. The atmospheric fields forcing the ocean model are taken from the ECMWF (European Centre for Medium-Range Weather Forecasts) Integrated Forecast System. We will explore the dynamical and statistical relationships between surface currents and Sargassum cover observed by satellites in the Atlantic near these islands and on reaching the coastal areas.
... Using large-scale observations with ocean color satellite remote sensing, historical hydrographic observations, time series of 45 Sargassum volume collected on ships, multi-year reanalysis of wind and current, numerical models estimated both the role of subsurface nutrient supply and surface current transport. Several authors have contributed to the understanding of the mechanisms and physicochemical processes governing the phenomenon (Gower et al., 2006;Gower and King, 2011;Gower et al., 2013;Maréchal et al., 2017;Johns et al., 2020). Operational systems have been developed such as the satellite based Sargassum Watch System SaWS (Hu, 2009;Hu et al., 2015) and the Sargassum Early Advisory System (SEAS) (Webster and Linton, 2013). ...
... Tropical Atlantic currents and winds seasonally aggregate and carry these algae towards the Caribbean (Franks et al., 2016;Brooks et al., 2018;Cuevas et al., 2018). Modeling studies mainly focused on the transport properties of Sargassum rafts by offshore currents (Wang and Hu, 2017;Brooks et al., 2018;Maréchal et al., 2017;Putman et al., 2018Putman et al., , 2020Wang et al., 2019;Berline et al., 2020). Johns et al. (2020) extended this analysis to highlight anomalous transport due to the 2009-2010 NAO anomaly and seasonal aggregation by the Inter Tropical Convergence Zone (ITCZ). ...
... Johns et al. (2020) extended this analysis to highlight anomalous transport due to the 2009-2010 NAO anomaly and seasonal aggregation by the Inter Tropical Convergence Zone (ITCZ). 60 A combination of MODIS AFAI Satellite images with HYCOM surface current forecast data were used by Maréchal et al. (2017) to short-term predict Sargassum strandings for Guadeloupe and the French Antilles islands. Maréchal et al. (2017) showed that this short-term prediction system (i.e., detection starting within 50-100 km of the coasts) worked efficiently during the year 2015 with a performance percentage of 62% and a stranding forecast date uncertainty below one day. ...
Preprint
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The massive Sargassum algae strandings observed over the past decade are the new natural hazard that currently impacts the island states of the Caribbean region (human health, environmental damages, and economic losses). This study aims to improve the prediction of the surface current dynamic leading to beachings in the Lesser Antilles, using clustering analysis methods. The input surface currents including windage effect were derived from the Mercator model and the Hybrid Coordinate Ocean Model 10 (HYCOM). Past daily observations of Sargassum stranding on Guadeloupe coasts were also integrated. Four representative current regimes were identified for both Mercator and HYCOM data. The analysis of the backward current sequences leading to strandings showed that the recurrence of two current regimes is related to the beaching peaks observed respectively in March and in August. A decision tree classifier was built and its accuracy reaches 73.3% with 0.04°-scale HYCOM data and 50.8% with 0.08°-scale Mercator data. This significant accuracy difference highlights the need of very small-scale current data (i.e., lower than 5 km scale) 15 to assess coastal Sargassum hazard in the Lesser Antilles. The present clustering analysis predictive system would help improve this risk management in the islands of this region.
... A better understanding of how Sargassum moves at the ocean surface (specifically relative to Global HYCOM velocity estimates) is needed to improve predictions of the timing of its entry into the Caribbean Sea as well as where and when it will hit the coast [Maréchal et al., 2017;Putman et al., 2018]. Here, we evaluated how closely synthetic particles tracked in HYCOM followed the paths of actual Sargassum. ...
... 91.2) hindcasts [Chassignet et al., 2009] and wind fields (10 m above the ocean surface) from NOAA Blended Sea Winds [Zhang et al., 2006] (Fig. 1B). Global HYCOM has been used extensively in the Caribbean Sea to simulate the movements of diverse marine organisms and shows good agreement with relevant observations [Foster et al., 2012;Putman and Naro-Maciel, 2013;Jaimes et al., 2016;Maréchal et al., 2017;Baeza et al., 2019]. Likewise, Blended Sea Winds has been widely used to provide context for ecological processes ranging from coral bleaching [Eakin et al., 2010] to sea turtle behavior [Mansfield et al., 2017]. ...
... In addition to providing insight into existing biogeographic patterns, results from this study will be critical in the development of a forecasting tool to identify where Sargassum is likely to wash ashore, providing coastal zone managers warning in advance of Sargassum inundations [Maréchal et al., 2017;Wang and Hu, 2017]. However, additional work will also be needed to determine how widely the results obtained here can be generalized and whether explicit consideration of other physical (e.g., tides, waves, 3-dimensional inertial effects) and biological (e.g., growth and mortality of the algae) processes can further improve predictions of Sargassum movement. ...
Article
A mechanistic understanding of organismal movement provides context for existing biogeographic and ecological patterns and improves our ability to predict changing patterns in dynamic environments. Here, we examined the movement ecology of pelagic Sargassum in the northern Caribbean Sea, where major inundation events of this brown algae have become increasingly problematic to coastal communities. We used GPS-trackers affixed to Sargassum mats, standard oceanographic drifters, and “pseudo-Sargassum” drifters to acquire empirical data on the movement of Sargassum and ocean currents. We related these observed movements to ocean surface velocity fields from a global ocean circulation model and wind velocities derived from models and satellite observations. Specifically, we assessed whether adding a windage component to ocean surface velocities improved predictions generated by synthetic particles tracked within an ocean circulation model. We found that the inclusion of a windage factor of 1 to 3% reduced separation distances between synthetic particles and the tracks of Sargassum mats, pseudo-Sargassum drifters, and un-drogued oceanographic drifters. When similar analyses were conducted for oceanographic drifters with drogues centered at 15 m depth (which are designed to minimize the influence of winds and waves and thus served as a control for this technique), inclusion of a windage factor did not improve particle-tracking predictions. These findings indicate that adding a windage calculated from satellite-derived winds to the surface layer of an ocean circulation model produces particle-tracking results that are more relevant to Sargassum, likely by accounting for the buoyant nature of the algae and the influence of the direct forcing of wind (and waves, implicitly) on the part of the object extending above the surface. However, the estimates of an appropriate windage coefficient for Sargassum may differ depending on the wind and surface current products used as well as the particular oceanic region being studied. Future work to identify and resolve systematic biases in the representation of winds and currents will be an important step toward eventually forecasting Sargassum movement and coastal inundation events.
... Major and unexpected accumulation of Sargassum occurred near and along the islands of the eastern Caribbean starting in 2011 and continued through December of that year (Gower et al., 2013;Hu et al., 2016). A similar event occurred in 2012 (Marechal et al., 2017), followed by even greater Sargassum inundation events throughout the Caribbean in 2014 through 2015 Hu, 2016, 2017). These anomalous events caused widespread negative impacts to the fishing and tourism economies throughout the region. ...
... There are three main surface dynamical oceanographic features whereby Sargassum travel from the Equatorial Atlantic into the Caribbean Sea: (1) along the continental shelf break of South America via the Guiana Current, (2) across the deep ocean translated via North Brazil Current Rings, and (3) initially moving eastward with the North Brazil Current Retroflection before being swept westward by the North Equatorial Current (Johns et al., 2014) (Fig. 1). With increased understanding of how these advection processes influence the distribution of Sargassum, it may be possible to better assess and predict the occurrence and timing of Sargassum accumulation in the Caribbean Sea, an important first step to assessing the potential for beaching (Marechal et al., 2017) as Sargassum abundance in the Caribbean appears to be directly related to beaching events (Wang and Hu, 2017). ...
... In 2011, Sargassum beaching was only reported east of 71°W (Franks et al., 2016), yet including 1% windage greatly increased the probability of transport west of this longitude ( Fig. 4A and B). In 2012, Sargassum beaching was restricted to areas in the Caribbean even further to the east (Marechal et al., 2017). The scenario without windage is consistent with this observation, predicting much less transport from the Equatorial Atlantic into the Caribbean than usual (Fig. 4C). ...
Article
Full-text available
Since 2011, beach inundation of massive amounts of pelagic Sargassum algae has occurred around the Caribbean nations and islands. Previous studies have applied satellite ocean color to determine the origins of this phenomenon. These techniques, combined with complementary approaches, suggest that, rather than blooms originating in the Caribbean, they arrive from the Equatorial Atlantic. However, oceanographic context for these occurrences remains limited. Here, we present results from synthetic particle tracking experiments that characterize the interannual and seasonal dynamics of ocean currents and winds likely to influence the transport of Sargassum from the Equatorial Atlantic into the Caribbean Sea. Our findings suggest that Sargassum present in the western Equatorial Atlantic (west of longitude 50 W) has a high probability of entering the Caribbean Sea within a year's time. Transport routes include the Guiana Current, North Brazil Current Rings, and the North Equatorial Current north of the North Brazil Current Retroflection. The amount of Sargassum following each route varies seasonally. This has important implications for the amount of time it takes Sargassum to reach the Caribbean Sea. By weighting particle transport predictions with Sargassum concentrations at release sites in the western Equatorial Atlantic, our simulations explain close to 90% of the annual variation in observed Sargassum abundance entering the Caribbean Sea. Additionally, results from our numerical experiments are in good agreement with observations of variability in the timing of Sargassum movement from the Equatorial Atlantic to the Caribbean, and observations of the spatial extent of Sargassum occurrence throughout the Caribbean. However, this work also highlights some areas of uncertainty that should be examined, in particular the effect of "windage" and other surface transport processes on the movement of Sargassum. Our results provide a useful launching point to predict Sargassum beaching events along the Caribbean islands well in advance of their occurrence and, more generally, to understand the movement ecology of a floating ecosystem that is essential habitat to numerous marine species.
... Although the statistics-based prediction is supported by physics, because the forcing terms (winds, currents, and Sargassum growth rate [Webster and Linton, 2013;Carpenter and Cox, 1974;Lapointe, 1996;Lapointe et al., 2014;Ardron et al., 2011;Brooks, 2016;Maréchal et al., 2017]) are not explicitly included in the prediction, the prediction may only be applicable to future years when these forcing terms are similar to the hindcast years used here. The fundamental question is as follows: are the years in this study "normal" years so the prediction can be applied to future normal years? ...
... In reality, whether or not a bloom will end up on beaches depends on local winds and currents, which can only be studied through high-resolution modeling or a combination of nearshore daily observations and currents/winds. For example, the Sargassum Early Advisory System [Webster and Linton, 2013] used periodic Landsat observations for short-term predictions of potential beaching events, while Maréchal et al. [2017] used MODIS daily imagery for the same predictions. Nevertheless, as Sargassum blooms are unlikely to diminish in the coming years, the simple forecast system developed here will provide timely information to the Caribbean residents and management agencies on the potentials of Sargassum blooms with several months of lead time. ...
Article
Recurrent and significant Sargassum beaching events in the Caribbean Sea (CS) have caused serious environmental and economic problems, calling for a long-term prediction capacity of Sargassum blooms. Here we present predictions based on a hindcast of 2000 – 2016 observations from Moderate Resolution Imaging Spectroradiometer (MODIS), which showed Sargassum abundance in the CS and the Central West Atlantic (CWA), as well as connectivity between the two regions with time lags. This information was used to derive bloom and non-bloom probability matrices for each 1o square in the CS for the months of May – August, predicted from bloom conditions in a hotspot region in the CWA in February. A suite of standard statistical measures were used to gauge the prediction accuracy, among which the user's accuracy and kappa statistics showed high fidelity of the probability maps in predicting both blooms and non-blooms in the eastern CS with several months of lead time, with overall accuracy often exceeding 80%. The bloom probability maps from this hindcast analysis will provide early warnings to better study Sargassum blooms and prepare for beaching events near the study region. This approach may also be extendable to many other regions around the world that face similar challenges and opportunities of macroalgal blooms and beaching events.
... This new 'sargassum crisis', caused at least in part by a combination of ocean eutrophication and climate change is now being considered the 'new norm' [13,14], to which Caribbean nations must find ways to adapt. The negative impacts on national economies and coastal livelihoods have initiated a rapidly growing interest in utilizing stranded sargassum as a raw material for developing a wide range of potentially valuable products; ...
... Despite ongoing important advances in sargassum detection, monitoring and prediction addressing these uncertainties (e.g., [2,13,[18][19][20][21][24][25][26][27][28][29][30][31]), significant technical challenges and knowledge gaps remain. These continue to inhibit accurate forecasting of sargassum influx events in real time, especially over hours (which is necessary for automated harvest solutions) and over time frames greater than three months to allow advanced planning for high abundance sargassum seasons or years. ...
Article
Full-text available
Over the last decade, the Caribbean has seen massive, episodic influxes of pelagic sargassum negatively impacting coastal ecosystems, people’s livelihoods and climate-sensitive sectors. Addressing this issue solely as a hazard has proven extremely costly and attention is slowly turning towards the potential opportunities for sargassum reuse and valorization. However, turning the ‘sargassum crisis into gold’ is not easy. In this study we use a multi-method approach to learn from sargassum stakeholders (researchers, entrepreneurs and established businesses) across the Caribbean about the constraints and challenges they are facing. These can be grouped into five broad categories: (1) unpredictable supply of sargassum; (2) issues related with the chemical composition of the seaweed; (3) harvest, transport and storage; (4) governance; and (5) funding. Specific issues and potential solutions associated with each of these categories are reviewed in detail and recommended actions are mapped to five entry points along a generalized value chain to demonstrate how these actions can contribute to the development of sustainable sargassum value chains that promote economic opportunities and could help alleviate impacts of massive influxes. This paper offers guidance to policy makers and funding agencies on existing gaps and challenges that need to be addressed in order to scale-up successful and sustainable solutions to the sargassum crisis.
... In Fiji, there is a very rapid proliferation of Gracilaria edulis and S. polycystum (N'Yeurt and Iese 2015a), but also in French Polynesia, where a proliferation of S. pacificum and T. ornata began in the 1990s (Stiger and Payri 1999a,b, Andréfouët et al. 2004, Zubia et al. 2008). On the Caribbean coasts, the problem of mass beaching of Sargassum species has not been solved yet (Smetacek and Zingone 2013, Gower et al. 2013, Johnson et al. 2013, Oyesiku and Egunyomi 2014, Wang and Hu 2016, Maréchal et al. 2017, Ody et al. 2019). Since 2011, the Caribbean has been suffering recurrently from massive strandings of pelagic Sargassum. ...
... Numerous remote sensing observations around 7°N, might indicate the presence of a new "Sargasso Sea" in the Tropical North Atlantic ( Gower et al. 2013). In 2015 the mean Sargassum summer coverage was estimated to be 20 times higher than that observed for summers between (Wang and Hu 2016, and the risk of Sargassum washing onshore increased in the Lesser Antilles between 2011(Maréchal et al. 2017). The factors leading to the Sargassum blooms remain unknown with regard to both the dynamics and the source regions of these rafts. ...
Article
This review focuses on the diversity of French tropical overseas macroalgae and their biotechnological applications. After listing the specific diversity, i.e. 641 species in French Antilles in the Atlantic Ocean, 560 species in the Indian Ocean, and 1015 species in the South Pacific Ocean, we present the potential of their metabolites and their main uses. Among the great diversity of metabolites, we focus on carbohydrates, proteins, lipids, pigments and secondary metabolites, in particular terpenes and phenolic compounds. The main applications of reef macroalgae are described in human and animal consumptions, phycocolloids extraction, production of active ingredients for health, cosmetics, agriculture, and bioremediation. For each application, we list what has been done, or will be done in French tropical overseas territories and point out the challenges faced when using this chemo-diversity, and problems linked to their exploitation. Finally, we discuss challenges to develop seaweed farming, their uses in carbon sequestration and resilience to global change, their uses for alternative proteins together with the production of bioenergy and biomaterials. As a conclusion, we encourage the research on the chemo-diversity of French reef macroalgae for industrial applications as these organisms represent a reservoir of active ingredients that is still insufficiently explored.
... In Fiji, there is a very rapid proliferation of Gracilaria edulis and S. polycystum (N'Yeurt and Iese 2015a), but also in French Polynesia, where a proliferation of S. pacificum and T. ornata began in the 1990s (Stiger and Payri 1999a,b, Andréfouët et al. 2004, Zubia et al. 2008). On the Caribbean coasts, the problem of mass beaching of Sargassum species has not been solved yet (Smetacek and Zingone 2013, Gower et al. 2013, Johnson et al. 2013, Oyesiku and Egunyomi 2014, Wang and Hu 2016, Maréchal et al. 2017, Ody et al. 2019. Since 2011, the Caribbean has been suffering recurrently from massive strandings of pelagic Sargassum. ...
... Numerous remote sensing observations around 7°N, might indicate the presence of a new "Sargasso Sea" in the Tropical North Atlantic (Gower et al. 2013). In 2015 the mean Sargassum summer coverage was estimated to be 20 times higher than that observed for summers between 2000 and 2010 (Wang and Hu 2016), and the risk of Sargassum washing onshore increased in the Lesser Antilles between 2011 and 2015 (Maréchal et al. 2017). The factors leading to the Sargassum blooms remain unknown with regard to both the dynamics and the source regions of these rafts. ...
Article
This review focuses on the diversity of French tropical overseas macroalgae and their biotechnologi- cal applications. After listing the specific diversity, i.e. 641 species in French Antilles in the Atlantic Ocean, 560 species in the Indian Ocean, and 1015 species in the South Pacific Ocean, we present the potential of their metabolites and their main uses. Among the great diver- sity of metabolites, we focus on carbohydrates, proteins, lipids, pigments and secondary metabolites, in particular terpenes and phenolic compounds. The main applications of reef macroalgae are described in human and animal consumptions, phycocolloids extraction, production of active ingredients for health, cosmetics, agriculture, and bioremediation. For each application, we list what has been done, or will be done in French tropical overseas territories and point out the challenges faced when using this chemo-diversity, and problems linked to their exploi- tation. Finally, we discuss challenges to develop seaweed farming, their uses in carbon sequestration and resil- ience to global change, their uses for alternative proteins together with the production of bioenergy and biomate- rials. As a conclusion, we encourage the research on the chemo-diversity of French reef macroalgae for industrial applications as these organisms represent a reservoir of active ingredients that is still insufficiently explored.
... In these nearshore regions, the algorithm's performance for detecting Sargassum is affected by high concentrations of chlorophyll not associated with Sargassum and artefacts from benthic sources. These data gaps in our ability to predict and monitor the coastal inundations of Sargassum, are extremely problematic, because it is in this area where negative impacts are typically the greatest (Maréchal et al. 2017). ...
... Since 2016 and 2018, respectively, MODIS and VIIRS data have been processed to generate AFAI and weekly FA density imagery ( Figure 2) in near real time for The AFAI has been used in a wide array of analyses pertaining to Sargassum ecology including describing seasonal variability in transport, beaching, bloom dynamics and prediction, and wind-effects on transport (Maréchal et al. 2017;Wang and Hu 2017;Putman et al. 2018;Berline et al. 2020) and produces results similar to other satellitebased Sargassum detection methods such as the Maximum Chlorophyll Index (MCI) King 2011, 2020). Since early 2018, the FA density products have also been used to generate monthly Sargassum outlook bulletins for various stakeholders. . ...
Article
Full-text available
Pelagic Sargassum is a buoyant macroalgae that forms rafts at the ocean surface and serves as a biologically rich habitat for hundreds of diverse marine species. Since 2011, massive blooms of Sargassum have occurred in the tropical Atlantic and swept through the western tropical Atlantic, Caribbean Sea, and Gulf of Mexico. These recurring annual events have caused significant disruptions to coastal communities throughout the region, negatively impacting human health, tourism, fishing, navigation, and nearshore ecosystems. We present here the Sargassum Inundation Report (SIR), a product that uses satellite-based methodology to estimate and predict the future coastal inundation of pelagic Sargassum. Results from one year of SIRs show strong spatiotemporal differences in the potential of coastal inundation across the Intra-American Seas, and provide a comprehensive method for assessing its geographic distribution and temporal variation. Comparisons of SIRs to opportunistically collected photographs indicate a qualitative concordance between satellite and in situ observations. This work highlights the value of satellite observations, basin-wide and seasonal monitoring, and emphasises the need for sub-regional and weekly forecasting. SIRs show considerable promise as a tool that can eventually incorporate improved spatiotemporal resolution Sargassum imagery, ocean circulation, wind, and wave conditions to forecast the movement of Sargassum into coastal areas.
... Pelagic Sargassum spp. were also sampled, as unusual and massive amounts of this Phaeophyceae are washed up on the coasts of the Caribbean area since 2011 (Maréchal et al., 2017) and can constitute a substratum for the development of benthic dinoflagellates. Sampling was carried out during both dry and cyclonic seasons in Guadeloupe and Martinique. ...
... Since 2011, large amounts of Sargassum spp. are regularly found washed up on coasts in the Gulf of Mexico, in Africa (from Sierra Leone to Ghana) and along the beaches of islands in the Lesser Antilles, including Guadeloupe and Martinique islands (Gower et al., 2013;Maréchal et al., 2017;Wang and Hu, 2016). This impressive phenomenon, called "Golden tides", involves two species of Phaeophyceae, Sargassum natans, and Sargassum fluitans which form the drifting algal communities found in the Sargasso Sea (de Szechy et al., 2012). ...
Article
Epibenthic dinoflagellates were monitored monthly over an 18 month period in Guadeloupe and Martinique (Lesser Antilles, Caribbean Sea). These islands are located in the second most affected ciguatera fish poisoning (CFP) region of the world. Guadeloupe presented five times more total epibenthic dinoflagellates and two times less abundant Gambierdiscus spp. compared to Martinique, although the area of frequent CFP outbreaks covers Guadeloupe and not Martinique. Results did not show any clear seasonal variations of benthic dinoflagellates abundances. Temperature and salinity were not driving parameters in the evolution of total benthic dino-flagellate abundances. Preferential associations were found between macrophyte species and epibenthic dino-flagellates. The Phaeophyceae Dictyota spp. hosted the highest abundances of total epibenthic dinoflagellates, composed mainly of Ostrepsis and Prorocentrum genera. The seagrass Halophila stipulacea hosted the highest abundances of Gambierdiscus spp. and Sinophysis spp. whilst the highest abundance of Coolia was determined on Galaxaura spp. The pelagic Sargassum spp. hosted the lowest abundances of benthic dinoflagellates including the genus Gambierdiscus.
... 7: Marie Galante. 8-9 Les Saintes[1]. ...
Poster
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The aim of this poster is to use the oceanic reanalyses of the Copernicus Marine Environment Monitoring Service (CMEMS) and other observation means to establish a diagnosis of the most recent possible physico-chemical triggers for proliferation (oceanic and atmospheric nutrient inputs, physical parameters of marine waters, etc.) and the influence of climate variability on a seasonal scale. An update will also be given on the current means of control. This assessment will provide a summary of the current explanation and understanding of the phenomena. It should contribute to the emergence of possible responses to develop and propose new strategies and means of control on the scale of these small territories.
... (hereafter Sargassum) (Gower, Young & King, 2013;van Tussenbroek et al., 2017). Since 2011, these extensive off-shore Sargassum shoals have appeared in unprecedented ways in oceanic waters off the coast of northern Brazil (De Széchy et al., 2012;Gower, Young & King, 2013;Sissini et al., 2017), actually, this events of Sargassum blooms were registered on the African coast as well (De Széchy et al., 2012;Maréchal, Hellio & Hu, 2017). Those shoals likely have origins in the North Equatorial Recirculation Region (NERR) Lewis & Chang, 2006). ...
Chapter
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Training and testing of algorithms used in computing for application in several studies, require datasets previously validated and labeled. In the case of satellite remote sensing, there are several platforms with large volumes of open source data. Aqua and Terra satellite platforms have available the sensor MODIS (Moderate-Resolution Imaging Spectroradiometer) which has available open access data for earth observation. Despite the facilities offered by the MODIS data platform, extracting data from a particular region for the construction of useful dataset requires an arduous work that includes manual, semi-automatic and automatic stages. The present study proposes a methodology for the construction of a geospatial dataset using MODIS sensor data. This methodology has been successfully implemented in the construction of dataset for the analysis of physical and biological variables in the Caribbean Sea, highlighting its application in the monitoring of Sargasso along the coastline of the state of Quintana Roo. Its application can be extended to any of the data and products offered by the MODIS sensor.
... However, events in which copious amounts of sargassum have washed up along the coasts of the Caribbean have intensified in more recent years. Extreme sargassum events have occurred in 2011(Maréchal et al., 2017. Sargassum shows substantial spatial and temporal variability as it is influenced by ocean conditions (such as sea surface temperatures, ocean acidification, and wind disturbances) and even thrives in warmer waters (Huffard et al., 2014). ...
... A number of factors, including nutrients, rising sea temperatures, and Sahara dust storms, have been put forward as potential causes [33]. Specific models developed to analyze satellite imagery and detect floating algae-the Floating Algae Index (FAI) [34] or the Alternate Floating Algae Index (AFAI) [35]-reveal that only in recent years was the area subject to mass proliferation of Sargassum: satellite imagery prior 2011 shows the area to be "largely free from seaweed". Unfortunately, operational warning devices able to anticipate algae washing ashore still have disadvantages related to the inadequate sampling and temporal frequency (MODIS observations, e.g., [36]) and the interposing obstacles such as cloud shadows and sun glint constitute very important issues. ...
Article
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Coastal video monitoring has proven to be a valuable ground-based technique to investigate ocean processes. Presently, there is a growing need for automatic, technically efficient, and inexpensive solutions for image processing. Moreover, beach and coastal water quality problems are becoming significant and need attention. This study employs a methodological approach to exploit low-cost smartphone-based images for coastal image classification. The objective of this paper is to present a methodology useful for supervised classification for image semantic segmentation and its application for the development of an automatic warning system for Sargassum algae detection and monitoring. A pixel-wise convolutional neural network (CNN) has demonstrated optimal performance in the classification of natural images by using abstracted deep features. Conventional CNNs demand a great deal of resources in terms of processing time and disk space. Therefore, CNN classification with superpixels has recently become a field of interest. In this work, a CNN-based deep learning framework is proposed that combines sticky-edge adhesive superpixels. The results indicate that a cheap camera-based video monitoring system is a suitable data source for coastal image classification, with optimal accuracy in the range between 75% and 96%. Furthermore, an application of the method for an ongoing case study related to Sargassum monitoring in the French Antilles proved to be very effective for developing a warning system, aiming at evaluating floating algae and algae that had washed ashore, supporting municipalities in beach management.
... The widespread invasion of the Indian Ocean-native sea vine, Halophila stipulacea across eastern Caribbean seagrass ecosystems (Ruiz and Ballantine 2004;Ambrose 2009, 2012;Maréchal et al. 2013;Willette et al. 2014), in combination with the large-scale dispersion of Sargassum fluitans stranded mats (Maréchal et al. 2017), have represented recent major threats to the persistence of Caribbean native seagrass assemblages. The effects of such emergent factors combined with chronic local factors such as declining water quality, sedimentation, physical disturbance (i.e., anchoring, navigation, hurricanes), and larger scale phenomena such as climate change, can lead to conditions that may reduce the resistance and recovery capacity of seagrasses (Duarte 2002;Unsworth et al. 2015). ...
Article
Category five hurricanes Irma and María (September 2017) caused significant damage to shallow seagrass communities across Puerto Rico. The magnitude and spatial extent of hurricane impacts on representative seagrass habitats of Culebra Island were addressed using a combination of random photo-quadrats and before–after hurricanes GIS-based imagery analyses. There was a significant loss of shallow seagrasses across all nine surveyed locations. Most of the documented impacts were associated with sediment bedload (horizontal transport), which resulted in burial and suffocation. There was also localized physical disruption of the seagrass habitat matrix across locations exposed to stronger wave action, creating major scars and exposing below-ground structure to further disintegration by future storm events. Displaced coral rubble also caused seagrass burial. Aerial imagery analyses (2007, 2010, 2017) showed a significant decline in seagrass percent cover. Seagrass decline was positively correlated with wave exposure (p < 0.05). Seagrass cover, density, and changes in benthic community structure were documented across five of the surveyed locations during 2018, and these data were further compared to data collected in 2004 at these same sites. There was a decline in percent seagrass cover and density and a change in benthic community structure favoring habitat homogenization. A remarkable finding was the rapid recovery, expansion, and increased localized dominance of the invasive seagrass, Halophila stipulacea. This was particularly evident in areas impacted by recurrent land-based runoff pulses, anchoring, sediment resuspension due to navigation, trampling or by the accumulation of decaying Sargassum mats. Hurricanes triggered a localized shift in marine vegetation, favoring the invasion of H. stipulacea, with potentially significant consequences on ecosystem resilience and on the ability of native in seagrasses to persist and adapt to projected climate change impacts.
... Since summer of 2011, a massive influx of pelagic Sargassum took place in the Caribbean. In 2012, a non-common arrival of pelagic Sargassum was reported at the southern coast of Cuba [36] and in middle of 2014, many Caribbean islands began to be affected [37,38]. On the other hand, the Mexican golf coasts have been dramatically impacted during the last years. ...
Article
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The use of algal biomass as a renewable source of energy is potentially promising. The literature on biofuels derived from Sargassum is limited compared to other macroalgae. The unusual seaweed bloom of Sargassum from 2011 to date can be caused by the following factors: eutrophication of the sea, climate change, and other oceanographic patterns. The atypical invasion has had great ecological and economic effects in the affected regions. Traditionally, Sargassum has been recovered from coasts and beaches for use as fertilizer, but new markets need to be found to exploit the large volumes produced by the seaweed influx and mitigate its impact. The biochemical composition of Sargassum biomass defines it as a potential feedstock for biofuel production. However, the high moisture and ash content constitute the limitations for the development of some energy extraction methods. On the other hand, the costs associated with the removal of high volumes of accumulated Sargassum from coasts and beaches, transportation, cleaning, and storage are relatively high. Therefore, the production of biofuels from Sargassum seaweed is still a technical, economic, and energy challenge. This review proposes a multifactorial approach to the potential use of Sargassum biomass as feedstock for energy production, especially by thermochemical conversion (combustion, gasification, pyrolysis, and hydrothermal liquefaction). The survey analyses the chemical composition, biomass productivity and coastal impact, energy output, thermochemical conversion processes, techno-economic challenges, and future perspectives. In addition, a Sargassum biomass biorefinery approach with a circular bioeconomy approach is proposed.
... Scientific researches are conducted to gain an understanding of the evolution of the Sargassum [3,4]. Remote sensing techniques can provide interesting information regarding standing stock forecasts in terms of spatial location, period of occurrence and abundance [5]. ...
Article
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The invasive species of brown algae Sargassum gathers in large aggregations in the Caribbean Sea, and has done so especially over the last decade. These aggregations wash up on shores and decompose, leading to many socio-economic issues for the population and the coastal ecosystem. Satellite ocean color data sensors such as Sentinel-3/OLCI can be used to detect the presence of Sargassum and estimate its fractional coverage and biomass. The derivation of Sargassum presence and abundance from satellite ocean color data first requires atmospheric correction; however, the atmospheric correction procedure that is commonly used for oceanic waters needs to be adapted when dealing with the occurrence of Sargassum because the non-zero water reflectance in the near infrared band induced by Sargassum optical signature could lead to Sargassum being wrongly identified as aerosols. In this study, this difficulty is overcome by interpolating aerosol and sunglint reflectance between nearby Sargassum-free pixels. The proposed method relies on the local homogeneity of the aerosol reflectance between Sargassum and Sargassum-free areas. The performance of the adapted atmospheric correction algorithm over Sargassum areas is evaluated. The proposed method is demonstrated to result in more plausible aerosol and sunglint reflectances. A reduction of between 75% and 88% of pixels showing a negative water reflectance above 600 nm were noticed after the correction of the several images.
... Data with high temporal resolution (minutes) and large footprint ( km 2 ), providing drift direction and velocities of sargassum under a large range of hydrodynamic conditions, can give further insight in the conditions that govern sargassum drift from the ocean to the beach. Such insight is also essential for the improvement of sargassum early warning systems Maréchal et al., 2017;Trinanes et al., 2021;Webster & Linton, 2013), which provide information that can help coastal communities to better manage massive sargassum beachings. ...
Article
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Massive quantities of the pelagic brown macroalgae Sargassum spp. (sargassum) have been invading the Caribbean and West African shores since 2011, causing devastating effects on the coastal ecosystem and local economy. Little is known about sargassum beaching dynamics and the capacity of the coastal system to naturally remove beached sargassum. Here, we characterize the temporal variation in arriving and beached sargassum in a reef lagoon using a 5.2‐year data set of hourly optical imagery, and identify the governing hydrometeorological conditions. Image classification reveals interannual variability in the start, duration, and intensity of the sargassum arrival season. Arrivals are associated with relatively low energy onshore directed winds and waves, and offshore abundance of sargassum. Furthermore, nearshore sargassum mat size is found to decrease with decreasing wave/wind energy. Once sargassum beaches, a berm of wrack is formed. Natural wrack removal was observed under elevated water levels and increased wave action. Three types of wrack removal were distinguished, depending on the water level η with respect to the berm crest height zc and berm crest toe zt: gradual berm destruction with gaps developing in the seaward berm edge that grow larger with time (Type I; zt<η<zc) and abrupt berm destruction with part of the wrack depositing on the upper beach (Type II; η>zc) or in the dunes (Type III; η≫zc). Higher energy waves activate the reef circulation, which is suspected to flush part of the wrack out of the reef lagoon. We propose a conceptual model of nearshore sargassum dynamics in a reef lagoon system.
... During the past decade, unprecedented volumes of the pelagic brown macroalgae Sargassum spp. (S. natans and S. fluitans) have inundated Caribbean, West African, and northern Brazilian coastlines (Gower et al., 2013;Smetacek and Zingone, 2013;Oyesiku and Egunyomi, 2014;Maréchal et al., 2017;Sissini et al., 2017;Wang et al., 2019;Rodríguez-Martínez et al., 2016. Reliable quantitative data on the scale of these beaching events is limited but reported amounts are huge: in the Mexican Caribbean a total of 522,226 t was reportedly removed from managed parts of its c450 km coastline in 2018 (Espinosa and Ng, 2020). ...
Article
Since 2011, pelagic Sargassum has inundated Caribbean, West African, and northern Brazilian shorelines in increasing volumes. These events are linked to the emergence of a major new Sargassum bloom region in the Atlantic Ocean, and annual high-volume Sargassum beachings are seemingly becoming an established norm. Resultant socio-economic and ecological implications are widespread and potentially serious, but an important question that has so far received no attention is whether these Sargassum inundations might represent a new source of carbonate sediment in affected coastal areas. This sediment derives from calcareous epiphyte communities that colonise Sargassum (e.g., bryozoans, serpulid worms, and red algae), and if volumetrically significant, may help to counteract aspects of Sargassum beachings thought to reduce sediment supply and decrease coastal stability. Here we determine the carbonate contents of Sargassum from coastal waters of the Mexican Caribbean. Integrating these with volumetric data on beached Sargassum, we then estimate total epiphytic carbonate import during 2018 at 11 sites along a 60 km section of the Quintana Roo coast, Mexico. Based on measured mean carbonate content of Sargassum (2.09% wet weight; 95% confidence interval [CI]: 1.83–2.32), and estimates of annual beached Sargassum (7.0 × 103 kg drained weight⋅m− 1 of shoreline; 95% CI: 6.9–7.2), our findings indicate that Sargassum beachings in the Mexican Caribbean contributed an average of 179 kg CaCO3⋅m− 1 of shoreline (95% CI: 173–185) in 2018: close to our upper estimate of seagrass epiphyte contri- butions (210 kg⋅m− 1). Although quantitative data on Sargassum beachings from other locations are sparse, numerous media reports suggest the scale of these events is comparable for many exposed tropical Caribbean and Atlantic shorelines. This represents the first documentation of pelagic Sargassum as a major vector of coastal sediment import, the significance of which has likely only arisen since the onset of large-scale inundations in 2011.
... (hereafter Sargassum) (Gower, Young & King, 2013;van Tussenbroek et al., 2017). Since 2011, these extensive off-shore Sargassum shoals have appeared in unprecedented ways in oceanic waters off the coast of northern Brazil (De Széchy et al., 2012;Gower, Young & King, 2013;Sissini et al., 2017), actually, this events of Sargassum blooms were registered on the African coast as well (De Széchy et al., 2012;Maréchal, Hellio & Hu, 2017). Those shoals likely have origins in the North Equatorial Recirculation Region (NERR) Lewis & Chang, 2006). ...
Article
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Recently, Caribbean coasts have experienced atypical massive arrivals of pelagic Sargassum with negative consequences both ecologically and economically. Based on deep learning techniques, this study proposes a novel algorithm for floating and accumulated pelagic Sargassum detection along the coastline of Quintana Roo, Mexico. Using convolutional and recurrent neural networks architectures, a deep neural network (named ERISNet) was designed specifically to detect these macroalgae along the coastline through remote sensing support. A new dataset which includes pixel values with and without Sargassum was built to train and test ERISNet. Aqua-MODIS imagery was used to build the dataset. After the learning process, the designed algorithm achieves a 90% of probability in its classification skills. ERISNet provides a novel insight to detect accurately algal blooms arrivals.
... Wang and Hu (2016) developed a novel approach to detect Sargassum's presence and to quantify Sargassum coverage using the Moderate Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI). Moreover, Maréchal et al. (2017) used Sargassum Watch System (SaWS), based on MODIS Rayleigh-corrected reflectance analysis and surface currents from the Hybrid Coordinate Ocean Model (HYCOM) to detect floating algae Sargassum in the central Atlantic. According to Hu (2009) algorithms have been developed to detect certain phytoplankton on sea surface based on their unique optical properties. ...
Conference Paper
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Since 2011, large amounts of seaweed Sargassum species were observed in sea water and on West African beaches, among them the Nigerian coast which is significantly affected. Through satellite observations, based on fluorescence values (0.2 – 0.3 W·m −2·μm −1 ·sr −1 ), we were able to detect recurrent occurrence of Sargassum throughout these last years in Nigeria. GPS coordinates from previous studies and satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS Aqua) were used to monitor the expansion Sargassum patterns from 2011 to 2016. During this period, the fluorescence spread along the Eastern to Western coasts, and the seasonal distribution resulted in difficulties impacting the livelihood of the population. Consequently, fishery, tourism activities and food security are threatened. However, further studies using remote sensing techniques need to done in order to differentiate the species and appropriately estimate the masses.
... There has been much effort expended over the last few years to understand pelagic Sargassum arrival and transport throughout the Wider Caribbean (e.g., Wang and Hu 2016, Brooks et al. 2018, Putman et al. 2018, Johns et al. 2020. New and experimental products have been developed, which provide valuable insight into the comparative presence of pelagic Sargassum blooms across the Caribbean and GOM, and visual assessment of the probability of inundation (e.g., Webster and Linton 2013, Wang and Hu 2017, Arellano-Verdejo et al. 2019 Maréchal et al. (2017), Sutton (2019) and Bernard et al. (2019). To date however, there are few examples of longer-term (seasonal) forecasting of pelagic Sargassum arrival. ...
Article
Since 2011, pelagic Sargassum has experienced extraordinary blooms in the Tropical Atlantic where a system of persistent but seasonally variable currents has retained and consolidated it in large masses. Although beneficial at sea, principally as a unique pelagic habitat, when Sargassum inundates the nearshore environment it can have catastrophic effects on tourism, fisheries, health, and local ecosystems. Providing advanced warning of arrival dates of large masses of Sargassum is critical for enabling preparations and planning for its removal, use, and mitigation. Predictions of arrival time and location involve satellite identification of Sargassum at sea together with ocean current data for forward model tracking. However, forecast ocean current data are generally valid for only 5—7 days. In this study, ocean currents from 2 models (HYCOM and OSCAR) are validated against satellite tracked drifters from the Global Drifter Program with vector correlation and with skill in replicating a drifter pathway. Various wind additions to the models are also tested. Although both models capture the surface current systems in the Tropical Atlantic, they are mediocre in performance along both boundaries. In contrast, a drifter based current data model with 0.5% wind addition had high skill levels. This skill—tested drifter—based model was then used to determine marine connectivity across the Tropical Atlantic and suggests a much broader spread of Sargassum in the eastern Tropical Atlantic than is presently observed by satellites, conforming to earlier hypotheses. This model forms the basis for seasonal scale Sargassum forecasting.
... The high probability and increased frequency of extreme catastrophic events are also expected, such as floods, droughts, SLR, heavy rains and intense tropical cyclone activity ). Additionally, the secondary impacts including algal blooms of Sargassum seaweed (Maréchal et al., 2017), transcontinental dust clouds (Prospero, 2006), and vector-borne diseases (Confalonieri et al. 2007; Van Bortel et al. 2014) have been observed. ...
Preprint
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Small Island States (SIDS) are among the nations most exposed to climate change (CC) and are characterised by a high degree of vulnerability. Their special nature means there is a need for more studies focused on the limits to CC adaptation on such fragile nations, particularly in respect of their problems and constraints. This paper addressed a perceived need for research into the limitations of adaptation on SIDS, focusing on the many restrictions which are unique to them. The main research question raised by this study was that how and to what extent the challenges by human activities (e.g., agriculture and tourism) posed to coastlines of SIDS could be addressed. This paper identified and described the adaptation limits they have, by using a review of the literature and an analysis of case studies from a sample of five SIDS in the Caribbean and Pacific regions (Barbados, Trinidad and Tobago, Cook Islands, Fiji, Solomon Islands, and Tonga). The findings of this research showed that an adaptable SIDS is characterised by awareness of various values, appreciation and understanding of a diversity of impacts and vulnerabilities, and acceptance of certain losses through change. The implications of this paper are two-fold. It explains why island nations continue to suffer from the impacts of CC, and suggest some of the means via which adequate policies may support SIDS in their efforts to cope with the threats associated with a changing climate. This study concluded that, despite the technological and ecological limits (hard limits) affecting natural systems, adaptation to CC is not only limited by such complex forces, but also by societal factors (soft limits) that could potentially be overcome by more adequate adaptation strategies.
... Inertial effects may be important for efforts aimed at predicting Sargassum beaching events such as the Sargassum Early Advisory System (Webster & Linton, 2013) and the Sargassum Watch System (Maréchal et al., 2017). The difference between inertial particles and a traditional particle model in these experiments often results in differences of tens of kilometers in projected trajectory over just 1 week. ...
Article
Full-text available
The effect of inertia (resistance to a change in velocity of buoyant finite-sized objects) on the advection of pelagic Sargassum, a macroalgae, is a function of the size and density of natural Sargassum rafts. Here we present observations of Sargassum density and an approach for estimating an effective radius of Sargassum rafts from remote-sensing observations. This allows the existing theoretical framework for Lagrangian modeling of inertial effects on spherical particles to be applied to Sargassum. Accounting for inertia yields up to a 20% increase in Sargassum export from the Sargasso Sea southward and provides a return pathway to the tropics that may be important to maintaining a self-sustaining population. Resolving inertial effects also leads to increases in retention in the Gulf of Mexico and Caribbean Sea, where Sargassum inundation events are increasingly common. Including inertial effects in models of Sargassum advection could improve predictions of these events.
... (i.e. Sargassum natans and Sargassum fluitans, a complex of two co-occurring species of floating brown macroalga), have been regularly occurring since 2011 [1]. Such events are more than likely due to both global warming and anthropic activities. ...
Article
This work aims to valorize an invasive brown macroalga (Sargassum spp. consisting of two species Sargassum fluitans and Sargassum natans) by producing biochars (BCs) and activated carbons (ACs). Its abundant and frequent occurrence along the Caribbean coastlines, Florida, Gulf of Mexico during the last past nine years, have triggered human health concerns and have negatively impacted local economy, ecology and the environment. In this paper, BCs and ACs were developed to assess the reduction of chlordecone (CLD) environmental availability in artificial and tropical contamined soils. Such innovative approach was proposed to limit CLD bio-availability to fauna and outdoor reared-animals. The BCs were prepared by pyrolysis at 700°C while ACs samples by chemical or physical activation. Textural characterization, has evidenced that bi-modal structures with micro- and mesopores, various surface and high pore volumes were successfully obtained. Finally, the environmental availability tests resulted in various ability of BCs or ACs to significantly sequestrate CLD on artificial contaminated soils and on a natural nitisol. In particular, the BCs prepared with a 3 h pyrolysis time, exhibited the highest porosities properties and was the best candidate to efficiently sequestrate CLD in soil samples.
... (hereafter Sargassum) (Gower, Young & King, 2013;van Tussenbroek et al., 2017). Since 2011, these extensive off-shore Sargassum shoals have appeared in unprecedented ways in oceanic waters off the coast of northern Brazil (De Széchy et al., 2012;Gower, Young & King, 2013;Sissini et al., 2017), actually, this events of Sargassum blooms were registered on the African coast as well (De Széchy et al., 2012;Maréchal, Hellio & Hu, 2017). Those shoals likely have origins in the North Equatorial Recirculation Region (NERR) Lewis & Chang, 2006). ...
Article
Full-text available
Recently, Caribbean coasts have experienced atypical massive arrivals of pelagic Sargassum with negative consequences both ecologically and economically. Based on deep learning techniques, this study proposes a novel algorithm for floating and accumulated pelagic Sargassum detection along the coastline of Quintana Roo, Mexico. Using convolutional and recurrent neural networks architectures, a deep neural network (named ERISNet) was designed specifically to detect these macroalgae along the coastline through remote sensing support. A new dataset which includes pixel values with and without Sargassum was built to train and test ERISNet. Aqua-MODIS imagery was used to build the dataset. After the learning process, the designed algorithm achieves a 90% of probability in its classification skills. ERISNet provides a novel insight to detect accurately algal blooms arrivals.
... The latter relies on near-real-time satellite and modeling results to monitor pelagic Sargassum, which serve to create monthly bulletins and show the distribution maps in the central-west Atlantic Ocean and Caribbean regions (Duffy et al., 2019;Hu et al., 2016). Other tools have been developed to integrate SaWS products for visualization using Google Earth, which facilitates the application of SaWS products through a widely known visualization tool (Maréchal, Hellio & Hu, 2017). Finally, "Citizen Science" platforms, such as Epicollect and iNaturalist, allow groups of researchers to build sets with geo-referenced images of Sargassum. ...
Article
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The atypical arrival of pelagic Sargassum to the Mexican Caribbean beaches has caused considerable economic and ecological damage. Furthermore, it has raised new challenges for monitoring the coastlines. Historically, satellite remote-sensing has been used for Sargassum monitoring in the ocean; nonetheless, limitations in the temporal and spatial resolution of available satellite platforms do not allow for near real-time monitoring of this macro-algae on beaches. This study proposes an innovative approach for monitoring Sargassum on beaches using Crowdsourcing for imagery collection, deep learning for automatic classification, and geographic information systems for visualizing the results. We have coined this collaborative process “Collective View”. It offers a geotagged dataset of images illustrating the presence or absence of Sargassum on beaches located along the northern and eastern regions in the Yucatan Peninsula, in Mexico. This new dataset is the largest of its kind in surrounding areas. As part of the design process for Collective View, three convolutional neural networks (LeNet-5, AlexNet and VGG16) were modified and retrained to classify images, according to the presence or absence of Sargassum. Findings from this study revealed that AlexNet demonstrated the best performance, achieving a maximum recall of 94%. These results are good considering that the training was carried out using a relatively small set of unbalanced images. Finally, this study provides a first approach to mapping the Sargassum distribution along the beaches using the classified geotagged images and offers novel insight into how we can accurately map the arrival of algal blooms along the coastline.
... Additionally, the secondary impacts, including algal blooms of Sargassum seaweed [104], transcontinental dust clouds [105] and vector-borne diseases [106,107] have been observed. ...
Article
Full-text available
Small Island States (SIDS) are among the nations most exposed to climate change (CC) and are characterised by a high degree of vulnerability. Their unique nature means there is a need for more studies focused on the limits to CC adaptation on such fragile nations, particularly regarding their problems and constraints. This paper addressed a perceived need for research into the limitations of adaptation on SIDS, focusing on the many unique restrictions. To this end, the study identified and described the adaptation limits they have by using a review of the literature and an analysis of case studies from a sample of five SIDS in the Caribbean and Pacific regions (Barbados, Trinidad and Tobago, Cook Islands, Fiji, Solomon Islands and Tonga). This research’s findings showed that an adaptable SIDS is characterised by awareness of various values, appreciation and understanding of a diversity of impacts and vulnerabilities, and acceptance of certain losses through change. The implications of this paper are two-fold. It explains why island nations continue to suffer from the impacts of CC and suggest some of the means via which adequate policies may support SIDS in their efforts to cope with the threats associated with a changing climate. This study concluded that, despite the technological and ecological limits (hard limits) affecting natural systems, adaptation to CC is limited by such complex forces and societal factors (soft limits) that more adequate adaptation strategies could overcome.
... In the recent years, modeling effort mainly focused on the transport properties of Sargassum rafts by offshore currents (Wang and Hu, 2017;Brooks et al., 2018;Maréchal et al., 2017;Putman et al., 2018Putman et al., , 2020Wang et al., 2019;Berline et al., 2020;Beron-Vera and Miron, 2020), with significant advances on the role of inertia in the drift trajectories (Brooks et al., 2019;Beron-Vera and Miron, 2020) and the importance of considering windage to properly resolve the drift of the Sargassum mats (Putman et al., 2020;Berline et al., 2020). To our knowledge, Brooks et al. (2018) were the first to integrate Sargassum physiology along the trajectories and showed that considering growth and mortality improved the modeling of the large-scale distribution of Sargassum. ...
... The challenge of predicting sargassum has grown alongside studies of how and why these blooms are developing. On short timescales, of up to several days, satellite imagery and operational 7-day ocean current forecasts are used to predict beaching events (e.g., Maréchal et al., 2017). On much longer timescales, other approaches must be adopted, involving the use satellite observations (Wang and Hu, 2017), drifters (Johnson et al., 2020) FIGURE 2 | (A) Beached sargassum at Sanzule, on 20 June 2020, located in the centre of (B), which shows sites on the western coast of Ghana recording beached sargassum in June 2020. ...
Article
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The holopelagic macroalgae sargassum has proliferated across the tropical Atlantic since 2011, of consequence for coastal populations from West Africa to the Caribbean with limited early warning of major beaching events. As part of an interdisciplinary project, ‘Teleconnected SARgassum risks across the Atlantic: building capacity for TRansformational Adaptation in the Caribbean and West Africa’ (SARTRAC), an ensemble forecast system, SARTRAC-EFS, is providing seasonal predictions of sargassum drift. An eddy-resolving ocean model hindcast provides the winds and currents necessary to generate ensemble members. Ensemble forecasts are then obtained for different combinations of ‘windage’, the fractional influence of winds on sargassum mats, and in situ rates of growth, mortality, and sinking. Forecasts for north and south of Jamaica are evaluated with satellite-observed distributions, associated with beaching events in specific years of heavy inundation, 2015 and 2018-20. These seasonal forecasts are evaluated, on lead times of up to 180 days. Forecasts are subject to leading modes of tropical climate variability, in particular the Atlantic Meridional Mode (AMM). More accurate forecasts for a given year are obtained with ensemble members from hindcast years with a similar spring AMM-index. This is most clearly evident during negative AMM phases in spring of 2015 and 2018, when positive sea surface temperature anomalies and anomalously weak trade winds were established across the northern tropics. On this evidence, SARTRAC-EFS is potentially useful in providing early warning of high sargassum prevalence. Extended to sargassum drift off West Africa, extensive cloud cover limits availability of the satellite data needed for full application and evaluation of SARTRAC-EFS in this region, although experimental forecasts off the coast of Ghana are found highly sensitive to the windage that is associated with strong onshore winds during boreal summer. Alongside other forecast systems, SARTRAC-EFS is providing useful early warnings of sargassum inundation at seasonal timescale.
... For example, nursery habitats, such as free-floating Sargassum mats in the tropical Atlantic and Caribbean, which are considered as both a benefit (e.g., by providing a key fish nursery habitat (Wells and Rooker 2004)) and a hindrance (when periodic mass landings of the free-floating macroalgae strain local economies (Webster and Linton 2013;). These mats can now be detected, characterized, and forecast using optical remote sensing imagery (e.g., Maréchal et al. 2017;Wang and Hu 2017;. Hu et al. (2015) overview how remote sensing analysts can use the red-edge in satellite spectra (i.e., the comparison of high reflectance in the near-infrared region to the low reflectance in the red region of the electromagnetic spectrum, characteristic of vegetation) to remotely detect Sargassum presence or absence on the sea surface. ...
Article
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The coast is home to unique ecosystems, where complex ecological processes take place through the interaction of terrestrial, aquatic, atmospheric, and human landscapes. However, there are considerable knowledge and data gaps in achieving effective and future change-proof sustainable management of coastal zones around the world due to both technical and social barriers, as well as governance challenges. Currently, the role of Earth observation (EO) in addressing many of the recognised information gaps is small and under-utilised. While EO can provide much of the spatiotemporal information required for historical analysis and current status mapping, and offers the advantage of global coverage; its uptake can be limited by technical and methodological challenges associated mostly with lack of capacity and infrastructure, product accuracy and accessibility, costs, and institutional acceptance. While new initiatives and recent technological progress in the EO and information technology arena aim to tackle some of these issues so that EO products can be more easily used by non-EO experts, uptake is still limited. This paper discusses how EO can potentially inform transformative practices of planning in the coastal water zone, by using examples to demonstrate the EO potential in providing information relevant to decision-making framed by international agreements, such as the United Nations Agenda 2030, the Convention on Biological Diversity, and the Sendai Framework for Risk Reduction. By presenting evidence for how EO can contribute to innovative opportunities and data synergies at scale, the paper discusses opportunities and challenges for a more solution-led approach to sustainable coastal management.
Article
Since 2011, tropical beaches from Africa to Brazil, Central America, and the Caribbean have been inundated by tons of sargassum seaweed from a new equatorial source of pelagic sargassum in the Atlantic. In recent years the extraordinary accumulations of sargassum make this a nuisance algal bloom for tropical coasts. In 2018 satellite data indicated floating mats of sargassum that extended throughout the Caribbean to the northeast coast of Brazil with the highest percent coverage over the water yet recorded. A literature review suggests that Atlantic equatorial recirculation of seaweed mats combined with nutrients from several possible sources may be stimulating the growth and accumulations of sargassum. In the western equatorial recirculation area, new nutrient sources may include Amazon River floods and hurricanes; in the eastern equatorial recirculation area, nutrient sources that could sustain the sargassum blooms include coastal upwelling and Congo River freshwater and nutrients.
Article
Recently there has been a significant increase in the amount and frequency of seaweed blooms of the holopelagic brown macroalgae Sargassum fluitans and natans (hereafter Sargassum) in the Atlantic Ocean. These blooms impose a major burden on residents (e.g. rotting beached Sargassum, unpleasant odor, toxic gases), the local economy of countries with affected coast lines (e.g. impacting tourism and aquaculture, costs for remediation), and have a significant impact on the environment (e.g. beaches and coastal areas) and local marine wildlife. Here we present a Techno-Economic Analysis to demonstrate how this burden can be turned into an economic, social and environmental asset. The suggested process involves sustainable ship-based harvesting of excess biomass (up to 6.3 MT·year⁻¹) and using hydrothermal liquefaction (HTL) and established fuel refining processes to deliver renewable liquid fuels. Sea-based harvesting of Sargassum addresses the primary cost impediment for algae-based renewable fuel production, reducing capital and operating costs by 78% and 66% respectively compared with currently modelled land-based microalgae renewable fuel production processes. The modelled approach charts a path to cost competitive renewable fuels that reduce CO2 emissions while mitigating the economic, social and environmental problems caused by these large Sargassum algae blooms. The financial analysis of the process yielded an Internal Rate of Return (IRR) between 2.4% and 28.1% based on the scenarios analyzed. The process could generate up to 8500 bbl of crude oil per day profitably at US$43 bbl⁻¹ (10% IRR), equivalent to 470 ML of diesel or jet fuel per year as well as biofertilizers and recycled nutrients, employ around 200 direct personnel and create up to 1000 indirect jobs.
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Background: Since 2011, the coasts of North America, Mexico, and the Caribbean have experienced an unusual increase in the arrival of Sargassum. As a consequence of this massive accumulations of Sargassum holopelagic species in Caribbean Sea have been generated and that threaten local biodiversity and trigger economic losses associated with beach deterioration and impact on fisheries and tourism. Goals: This docu�ment quantifies the occurrence of an excessive drift of Sargassum in two sites (Puerto Viejo and Punta Uva) of the Caribbean coast of Costa Rica, Limón province, in March-April of 2019. A macroalgae species checklist is presented from six sites (Punta Cahuita, Puerto Vargas, Puerto Viejo, Playa Chiquita, Punta Uva and Manza�nillo) in the Caribbean. In addition, the Sargassum morphotypes are quantified for the study area. Methods: Transects (50 m) were located parallel to the shoreline and, in points previously estimated, a quadrat of 25 x 25 cm covered the entire Sargassum band width on the beach until the water line, by fliping the quadrats and collecting the biomass for as many quadrats were necessary for the band. Then, pelagic Sargassum biomass was weighted in every point, and the dry weight biomass was estimated. Three quadrats were collected by the transect method. Associated species were identified as well as Sargassum morphotypes in all sites. Results: Descriptions that illustrate the morphology of the three morphotypes of pelagic species
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Antecedentes: Desde 2011, las costas de América del Norte, México y el Caribe han experimentado un aumento inusual en la llegada de Sargassum de arribazón. Como consecuencia, se han generado acumulaciones masivas de especies holopelágicas del género Sargassum en áreas costeras del Caribe que amenazan la biodiversidad local y desencadenan pérdidas económicas asociadas con el deterioro de las playas y el impacto en la pesca y el turismo. Objetivo: Se cuantifica la presencia de una deriva excesiva de Sargassum en dos sitios (Puerto Viejo y Punta Uva) de la costa caribeña de Costa Rica, provincia de Limón, en los meses de marzo y abril de 2019. Se presenta la lista de especies de macroalgas conspicuas asociadas al fenómeno en seis sitios (Punta Cahuita, Puerto Vargas, Puerto Viejo, Playa Chiquita, Punta Uva y Manzanillo) en el Caribe. Además, se cuantifican los morfotipos de Sargassum para el área de estudio. Métodos: Se ubicaron transectos (50 m) paralelos a la línea de costa y, en puntos previamente estimados, un cuadrante de 25 x 25 cm cubrió todo el ancho de banda de Sargassum en la playa hasta la línea de flotación, volteando los cuadrantes y recolectando la biomasa para tantos cuadrantes como fueron necesarios para la cubrir la zona arribada. Luego, se pesó la biomasa pelágica de Sargassum en cada punto, y se estimó la biomasa en peso seco. Se recolectaron tres cuadrantes mediante el método de transectos. Se identificaron especies asociadas, así como morfotipos de Sargassum en todos los sitios. Resultados: se presenta la morfología de los tres morfotipos de especies pelágicas. El supuestamente raro S. natans VIII dominó el arribo de algas (65% de peso seco), seguido por S. natans I (25% de peso seco), S. fluitans (10% de peso seco). Se identificaron 28 especies de las Divisiones: Chlorophyta (9), Ochrophyta (15) y Rhodophyta (4). Conclusiones: No existen diferencias significativas entre meses (marzo-abril) y sitios (Puerto Viejo y Punta Uva) para la biomasa arribada.
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The tropical Atlantic has been facing a massive proliferation of Sargassum since 2011, with severe environmental and socioeconomic impacts. The development of large-scale modeling of Sargassum transport and physiology is essential to clarify the link between Sargassum distribution and environmental conditions, and to lay the groundwork for a seasonal forecast at the scale of the tropical Atlantic basin. We developed a modeling framework based on the Nucleus for European Modelling of the Ocean (NEMO) ocean model, which integrates transport by currents and waves, and physiology of Sargassum with varying internal nutrients quota, and considers stranding at the coast. The model is initialized from basin-scale satellite observations, and performance was assessed over the year 2017. Model parameters are calibrated through the analysis of a large ensemble of simulations, and the sensitivity to forcing fields like riverine nutrient inputs, atmospheric deposition, and waves is discussed. Overall, results demonstrate the ability of the model to reproduce and forecast the seasonal cycle and large-scale distribution of Sargassum biomass.
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The Tropical Atlantic is facing a massive proliferation of Sargassum since 2011, with severe environmental and socioeconomic impacts. The development of Sargassum modelling is essential to clarify the link between Sargassum distribution and environmental conditions, and to lay the groundwork for a seasonal forecast on the scale of the Tropical Atlantic basin. We developed a modelling framework based on the NEMO ocean model, which integrates transport by currents and waves, physiology of Sargassum with varying internal nutrients quota, and considers stranding at the coast. The model is initialized from basin scale satellite observations and performance was assessed over the Sargassum year 2017. Model parameters are calibrated through the analysis of a large ensemble of simulations, and the sensitivity to forcing fields like riverine nutrients inputs, atmospheric deposition, and waves is discussed. Overall, results demonstrate the ability of the model to reproduce and forecast the seasonal cycle and large-scale distribution of Sargassum biomass.
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This review provides an overview of the importance of beach accumulations of macrophytes and other organic beach-cast material on the ecology of sandy beach ecosystems. It describes the composition of these allochthonous subsidies, their abundance on beaches in relation to seasonal, lunar, tidal and spatial trends, their decomposition and utilisation by bacterial, meio- and macrofaunal communities. The paper then analyses the community structure and the species succession in both macrophyte wrack and carrion and reports the most important findings on individual wrack-inhabiting species (amphipods, isopods, dipterans). Other aspects, such as feeding and microclimatic preferences of certain species and their interactions in wracks, are also discussed. Links to vertebrate species and other secondary consumers that exploit beach-cast macrophytes and carrion as trophic resource are considered, and the importance of wrack in recycling nutrients to nearshore coastal ecosystems is stressed. The beneficial and detrimental effects of organic beach-cast material on both plants and animals of beach and nearshore communities and on the geomorphology of coastal beach-dune systems are pointed out. Another section is dedicated to human use of beach-cast macrophytes through harvesting of economically important species and of other stranded material through its exploitation for traditional reasons. The effects of harvesting on local faunal communities and on the stability of the dunes is discussed. A final section of the paper includes the positive and negative effects of man-made debris on sandy-beach ecosystems and briefly reviews the major findings.
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The Sargasso Sea, named due to the floating presence of Sargassum fluitans and S. natans, is usually reported for the tropical region of the Northern Hemisphere. On 14 July 2011, at 02°45' N and 48°28' W, samples of pelagic seaweed masses were collected by the Patrol Ship Bracuí of the Brazilian Navy. The seaweed was identified as S. natans, previously considered as of doubtful occurrence in Brazil.
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Pelagic forms of the brown algae (Phaeophyceae) Sargassum spp. and their conspicuous rafts are defining characteristics of the Sargasso Sea in the western North Atlantic. Given rising temperatures and acidity in the surface ocean, we hypothesized that macrofauna associated with Sargassum in the Sargasso Sea have changed with respect to species composition, diversity, evenness, and sessile epibiota coverage since studies were conducted 40 years ago. Sargassum communities were sampled along a transect through the Sargasso Sea in 2011 and 2012 and compared to samples collected in the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone from 1966 to 1975. Mobile macrofauna communities exhibited changes in community structure and declines in diversity and evenness within a 6-month time period (August 2011–February 2012). Equivalent declines in diversity and evenness were recorded in the same region (Sargasso Sea, 25°–29°N) in 1972–1973. Recent community structures were unlike any documented historically, whether compared to sites of the same latitude range within the Sargasso Sea, or the broader historical dataset of sites ranging across the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone. Recent samples also recorded low coverage by sessile epibionts, both calcifying forms and hydroids. The diversity and species composition of macrofauna communities associated with Sargassum might be inherently unstable. While several biological and oceanographic factors might have contributed to these observations, including a decline in pH, increase in summer temperatures, and changes in the abundance and distribution of Sargassum seaweed in the area, it is not currently possible to attribute direct causal links. Electronic supplementary material The online version of this article (doi:10.1007/s00227-014-2539-y) contains supplementary material, which is available to authorized users.
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In the summer of 2011, a major ‘Sargassum event’ brought large amounts of seaweed onto the beaches of the islands of the eastern Caribbean with significant effects on local tourism. We present satellite observations showing that the event had its origin north of the mouth of the Amazon in an area not previously associated with Sargassum growth. A significant concentration of Sargassum was detected in April, when it was centred at about 7° N latitude and 45° W longitude. By July it had spread to the coast of Africa in the east and to the Lesser Antilles and the Caribbean in the west. We have previously used images from MERIS (Medium Resolution Imaging Spectrometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) to show the value of satellite observations in tracking patterns of Sargassum. For the years 2003–2010, we were able to determine the seasonal distribution over the range of 20°–40° N latitude and 100°–40° W longitude covering the ‘Sargasso Sea’ region of the North Atlantic and the Gulf of Mexico. In 2011, satellite data showed a large shift in the distribution, whose cause is unclear.
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The quantity and distribution of Sargassum in the Sargasso Sea, as estimated by various investigators, is reviewed. There has apparently been no significant change in the biomass of Sargassum from 1933 to 1981, except for an area northeast of the Antilles (20 to 25°N, 62 to 68°W), where measurements made in November 1977 and November 1980 were about 0.1% of values measured in February and March 1933. Because of the lack of change in the Bermuda, Bahamas, or Gulf Stream regions, the effect does not appear to be due to pollution or to broad climatic changes; it is most likely due to a seasonal change in Sargassum abundance or to a long-term shift of currents defining the southwestern boundary of the Sargasso Sea.
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We used satellite imagery from the European Space Agency (ESA) Medium Resolution Imaging Spectrometer (MERIS) optical sensor to make the first mapping of the full distribution and movement of the population of Sargassum in the Gulf of Mexico and the western Atlantic. For most of the years for which we have data (2002 to 2008), the results show a seasonal pattern in which Sargassum originates in the northwest Gulf of Mexico in the spring of each year, and is then advected into the Atlantic. The Sargassum appears east of Cape Hatteras as a ‘Sargassum jet’ in July and ends northeast of the Bahamas in February of the following year. This pattern is consistent with historical surveys from ships. MERIS provides a spectral band that greatly improves the discrimination of floating vegetation from confusing signals such as cloud and sunglint.
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Sensor design and mission planning for satellite ocean color measurements requires careful consideration of the signal dynamic range and sensitivity (specifically here signal-to-noise ratio or SNR) so that small changes of ocean properties (e.g., surface chlorophyll-a concentrations or Chl) can be quantified while most measurements are not saturated. Past and current sensors used different signal levels, formats, and conventions to specify these critical parameters, making it difficult to make cross-sensor comparisons or to establish standards for future sensor design. The goal of this study is to quantify these parameters under uniform conditions for widely used past and current sensors in order to provide a reference for the design of future ocean color radiometers. Using measurements from the Moderate Resolution Imaging Spectroradiometer onboard the Aqua satellite (MODISA) under various solar zenith angles (SZAs), typical (L<sub>typical</sub>) and maximum (L<sub>max</sub>) at-sensor radiances from the visible to the shortwave IR were determined. The L<sub>typical</sub> values at an SZA of 45° were used as constraints to calculate SNRs of 10 multiband sensors at the same L<sub>typical</sub> radiance input and 2 hyperspectral sensors at a similar radiance input. The calculations were based on clear-water scenes with an objective method of selecting pixels with minimal cross-pixel variations to assure target homogeneity. Among the widely used ocean color sensors that have routine global coverage, MODISA ocean bands (1 km) showed 2-4 times higher SNRs than the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1 km) and comparable SNRs to the Medium Resolution Imaging Spectrometer (MERIS)-RR (reduced resolution, 1.2 km), leading to different levels of precision in the retrieved Chl data product. MERIS-FR (full resolution, 300 m) showed SNRs lower than MODISA and MERIS-RR with the gain in spatial resolution. SNRs of all MODISA ocean bands and SeaWiFS bands (except the SeaWiFS near-IR bands) exceeded those from prelaunch sensor specifications after adjusting the input radiance to L<sub>typical</sub>. The tabulated L<sub>typical</sub>, L<sub>max</sub>, and SNRs of the various multiband and hyperspectral sensors under the same or similar radiance input provide references to compare sensor performance in product precision and to help design future missions such as the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission and the Pre-Aerosol-Clouds-Ecosystems (PACE) mission currently being planned by the U.S. National Aeronautics and Space Administration (NASA).
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For the past 25 years NIH Image and ImageJ software have been pioneers as open tools for the analysis of scientific images. We discuss the origins, challenges and solutions of these two programs, and how their history can serve to advise and inform other software projects.
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We present satellite imagery that is interpreted as showing extensive lines of floating Sargassum in the western Gulf of Mexico in the summer of 2005. In spite of frequent reports of floating weed covering extended areas in different parts of the world's ocean, this appears to be the first observation of Sargassum from space. Satellite observations were made with the Medium Resolution Imaging Spectrometer (MERIS) on the Envisat satellite launched by the European Space Agency, and subsequently with the Moderate Resolution Imaging Spectroradiometer (MODIS) launched on both the Terra and Aqua satellites by the National Aeronautics and Space Administration. Both instruments cover wide swaths, providing near-daily images. Both have optical spectral bands in the range 670 to 750 nm, which detect the chlorophyll red-edge characteristic of land and marine vegetation, but only MERIS has a band at 709 nm, which was critical to the initial discovery. The combined satellite data from both sensors show the seasonal cycle of weed density in different areas of the Gulf. A wider ranging study is now needed to map its occurrence in other areas, including the Sargasso Sea (named for the weed, but not so far covered in our survey). The satellite observations suggest that Sargassum biomass is greater than previously estimated, and hence plays a more important part in oceanic productivity
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The Sargassum Watch System processes satellite data and feeds results to a Web portal, giving decision makers timely information on seaweed location and warnings for potential beaching events.
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Sargassum washing ashore on the beaches of the Caribbean Islands since 2011 has caused problems for the local environments, tourism, and economies. Although preliminary results of Sargassum distributions in the nearby oceans have been obtained using measurements from the Medium Resolution Imaging Spectrometer (MERIS), MERIS stopped functioning in 2012, and detecting and quantifying Sargassum distributions still face technical challenges due to ambiguous pixels from clouds, cloud shadows, cloud adjacency effect, and large-scale image gradient. In this paper, a novel approach is developed to detect Sargassum presence and to quantify Sargassum coverage using the Moderate Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI), which examines the red-edge reflectance of floating vegetation. This approach includes three basic steps: 1) classification of Sargassum-containing pixels through correction of large-scale gradient, masking clouds and cloud shadows, and removal of ambiguous pixels; 2) linear unmixing of Sargassum-containing pixels; and, 3) statistics of Sargassum area coverage in pre-defined grids at monthly, seasonal, and annual intervals. In the absence of direct field measurements to validate the results, limited observations from the Hyperspectral Imager for the Coastal Ocean (HICO) measurements and numerous local reports support the conclusion that the elevated AFAI signals are due to the presence of Sargassum instead of other floating materials, and various sensitivity analyses are used to quantify the uncertainties in the derived Sargassum area coverage. The approach was applied to MODIS observations between 2000 and 2015 over the Central West Atlantic (CWA) region (0–22°N, 63–38°W) to derive the spatial and temporal distribution patterns as well as the total area coverage of Sargassum. Results indicate that the first widespread Sargassum distribution event occurred in 2011, consistent with previous MERIS findings. Since 2011, only 2013 showed a minimal Sargassum coverage similar to the period of 2000 to 2010; all other years showed significantly more coverage. More alarmingly, the summer months of 2015 showed mean coverage of > 2000 km2, or about 4 times of the summer 2011 coverage and 20 times of the summer 2000 to 2010 coverage. Analysis of several environmental variables provided some hints on the reasons causing the inter-annual changes after 2010, yet further multi-disciplinary research (including in situ measurements) is required to understand such changes and long-term trends in Sargassum coverage.
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Remote detection of pelagic Sargassum is often hindered by its spectral similarity to other floating materials and by the inadequate spatial resolution. Using measurements from multi-spectral satellite sensors (Moderate Resolution Imaging Spectroradiometer or MODIS), Landsat, WorldView-2 (or WV-2) as well as hyperspectral sensors (Hyperspectral Imager for the Coastal Ocean or HICO, Airborne Visible-InfraRed Imaging Spectrometer or AVIRIS) and airborne digital photos, we analyze and compare their ability (in terms of spectral and spatial resolutions) to detect Sargassum and to differentiate it from other floating materials such as Trichodesmium, Syringodium, Ulva, garbage, and emulsified oil. Field measurements suggest that Sargassum has a distinctive reflectance curvature of ~ 630. nm due to its chlorophyll c pigments, which provides a unique spectral signature when combined with the reflectance ratio between brown (~ 650. nm) and green (~ 555. nm) wavelengths. For a 10-nm resolution sensor on the hyperspectral HyspIRI mission currently being planned by NASA, a stepwise rule to examine several indexes established from 6 bands (centered at 555, 605, 625, 645, 685, 755. nm) is shown to be effective to unambiguously differentiate Sargassum from all other floating materials Numerical simulations using spectral endmembers and noise in the satellite-derived reflectance suggest that spectral discrimination is degraded when a pixel is mixed between Sargassum and water. A minimum of 20-30% Sargassum coverage within a pixel is required to retain such ability, while the partial coverage can be as low as 1-2% when detecting floating materials without spectral discrimination. With its expected signal-to-noise ratios (SNRs ~ 200:1), the hyperspectral HyspIRI mission may provide a compromise between spatial resolution and spatial coverage to improve our capacity to detect, discriminate, and quantify Sargassum.
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In recent decades, the technology used to detect and quantify harmful algal blooms (commonly known as red tides) and characterize their physicochemical environment has improved considerably. A remaining challenge is effective delivery of the information generated from these advances in a user-friendly way to a diverse group of stakeholders. Based on existing infrastructure, we establish a Web-based system for near-real-time tracking of red tides caused by the toxic dinoflagellate Karenia brevis, which annually threatens human and environmental health in the eastern Gulf of Mexico. The system integrates different data products through a custom-made Web interface. Specifically, three types of data products are fused: 1) near-real-time ocean color imagery tailored for red tide monitoring; 2) K. brevis cell abundance determined by sample analysis; and 3) ocean currents from a nested and validated numerical model. These products are integrated and made available to users in Keyhole Markup Language (KML) format, which can be navigated, interpreted, and overlaid with other products in Google Earth. This integration provides users with the current status of red tide occurrence (e.g., location, severity, and spatial extent) while presenting a simple way to estimate bloom trajectory, thus delivering an effective method for near-real-time tracking of red tides.
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The fauna associated with samples of Sargassum collected from the Gulf Stream has been identified, analyzed, and compared with that reported by other workers from samples collected from the Sargasso Sea. Notable in the present collections are two species of small gastropods not previously reported. The possible significance of these gastropods, as consistent with a benthonic origin of the Gulf Stream Sargassum, is discussed.
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There is a pressing need to assess coastal and estuarine water quality state and anomaly events to facilitate coastal management, but such a need is hindered by lack of resources to conduct frequent ship-based or buoy-based measurements. Here, we established a virtual buoy system (VBS) to facilitate satellite data visualization and interpretation of water quality assessment. The VBS is based on a virtual antenna system (VAS) that obtains low-level satellite data and generates higher-level data products using both National Aeronautics and Space Administration standard algorithms and regionally customized algorithms in near real time. The VB stations are predefined and carefully chosen to cover water quality gradients in estuaries and coastal waters, where multiyear time series at monthly and weekly intervals are extracted for the following parameters: sea surface temperature (°C), chlorophyll-a concentration (mgm-3), turbidity (NTU), diffuse light attenuation at 490 nm [Kd 490, m-1] or secchi disk depth (m), absorption coefficient of colored dissolved organic matter (m-1), and bottom available light (%). The timeseries data are updated routinely and provided in both ASCII and graphical formats via a user-friendly web interface where all information is available to the user through a simple click. The VAS and VBS also provide necessary infrastructure to implement peer-reviewed regional algorithms to generate and share improved water quality data products with the user community. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).
Article
Eleven satellite-tracked drifting buoys were deployed in the central South Atlantic Ocean during two austral summer and two austral winter cruises. Between 7°S and 11°S and 23°W and 31°W during austral winter, net buoy drift was to the west. Surface geostrophic flow was to the east between 7°S and 9°S. It is proposed that strong southeast trade winds can induce directly driven surface flows to the west that are more intense than the eastward geostrophic flows associated with the South Equatorial Countercurrent (SECC). A sustained period of eastward drift within the SECC was observed during austral summer, when the trades are weaker. The trajectories indicate surface waters north of 8°S have a mean northward meridional component and those south of 8°S a southward component. The buoys which drifted north became entrained into the North Brazilian Coastal Current (NBCC) and those that drifted south into the Brazil Current. One buoy left the NBCC at about 5°N to drift northeastward in the North Equatorial Countercurrent (NECC). This trajectory and historical ship drift reports suggest that the NECC may extend only to 35°W to 40°W during boreal winter. Temperature data obtained as the buoys drifted westward and northward suggest that increases in upper layer heat content can be attributed to heat fluxes through the sea surface.
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The long survival of the free-floating plant Sargassum in the wind-mixed surface waters of the oceans is poorly understood. Evidence is presented here that the amounts of Sargassum collected by net tows at the sea surface decrease with increased wind speed. From this new finding and additional evidence in the marine literature, it is hypothesized that the plant is adapted to a cyclic submergence in the wind-induced vortical currents of these waters, returning to the surface only when the currents are less than the plant's rise rate. Such adaptation, readily testable, indicates the plant's capacity to maintain its density and rise rate independent of depth, thus adding to our understanding of its survival at sea.
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Various types of floating algae have been reported in open oceans and coastal waters, yet accurate and timely detection of these relatively small surface features using traditional satellite data and algorithms has been difficult or even impossible due to lack of spatial resolution, coverage, revisit frequency, or due to inherent algorithm limitations. Here, a simple ocean color index, namely the Floating Algae Index (FAI), is developed and used to detect floating algae in open ocean environments using the medium-resolution (250- and 500-m) data from operational MODIS (Moderate Resolution Imaging Spectroradiometer) instruments. FAI is defined as the difference between reflectance at 859 nm (vegetation “red edge”) and a linear baseline between the red band (645 nm) and short-wave infrared band (1240 or 1640 nm). Through data comparison and model simulations, FAI has shown advantages over the traditional NDVI (Normalized Difference Vegetation Index) or EVI (Enhanced Vegetation Index) because FAI is less sensitive to changes in environmental and observing conditions (aerosol type and thickness, solar/viewing geometry, and sun glint) and can “see” through thin clouds. The baseline subtraction method provides a simple yet effective means for atmospheric correction, through which floating algae can be easily recognized and delineated in various ocean waters, including the North Atlantic Ocean, Gulf of Mexico, Yellow Sea, and East China Sea. Because similar spectral bands are available on many existing and planned satellite sensors such as Landsat TM/ETM+ and VIIRS (Visible Infrared Imager/Radiometer Suite), the FAI concept is extendable to establish a long-term record of these ecologically important ocean plants.
Article
Many beach management practices focus on creating an attractive environment for tourists, but can detrimentally affect long-term dune integrity. One such practice is mechanical beach raking in which the wrack line is removed from the beach front. In Texas, Sargassum fluitans and natans, types of brown alga, are the main components of wrack and may provide a subsidy to the ecosystem. In this study, we used greenhouse studies to test the hypothesis that the addition of sargassum can increase soil nutrients and produce increased growth in dune plants. We also conducted an analysis of the nutrients in the sargassum to determine the mechanisms responsible for any growth enhancement. Panicum amarum showed significant enhancement of growth with the addition of sargassum, and while Helianthus debilis, Ipomoea stolonifera, Sporobolus virginicus, and Uniola paniculata responded slightly differently to the specific treatments, none were impaired by the addition of sargassum. In general, plants seemed to respond well to unwashed sargassum and multiple additions of sargassum, indicating that plants may have adapted to capitalize on the subsidy in its natural state directly from the ocean. For coastal managers, the use of sargassum as a fertilizer could be a positive, natural, and efficient method of dealing with the accumulation of wrack on the beach.
Article
The increasing usage of sandy beaches as recreational resources has forced regional authorities of many tourist countries to remove all litter of fabricated origin and natural wrack from the beach. Consequently, a variety of heavy equipment has been developed during the last decades and is now used almost daily at many beaches. A field experiment, following a 'before-after-control-impact' (BACI) design, was conducted at the strandline of De Panne (Belgium) to investigate the impacts of mechanical beach cleaning on the strandline-associated meiofaunal assemblages, focussing on the free-living nematodes. Natural strandline assemblages were exposed to a one-off 5 cm deep mechanical beach cleaning and observed for 24 h. Differences between cleaned plots and those from control plots in terms of decreased percentage of organic matter, decreased total abundance and changed community structure were noticed from immediately after the experimental cleaning onwards and recovered to initial values after the following high water. Any impacts due to cleaning on species richness, Pielou's evenness and taxonomic diversity were shown to be minor in relation to the daily changes. Recolonization in the cleaned sediments is assumed to occur from the underlying sediments initiated by the elevated water table during the rising tide.
Sargassum: erosion and biodiversity on the beach
  • R A Feagin
  • A M Williams
Feagin, R.A., Williams, A.M., 2010. Sargassum: erosion and biodiversity on the beach. In: Spatial Sciences Laboratory, Dept. Ecosystem Science & Management, Texas A & M University, p. 23.
Unprecedented influx of Pelagic Sargassum along Caribbean Island Coastlines during summer
  • J S Franks
  • D R Johnson
  • D.-S Ko
  • G Sanchez-Rubio
  • J R Hendon
  • M Lay
Franks, J.S., Johnson, D.R., Ko, D.-S., Sanchez-Rubio, G., Hendon, J.R., Lay, M., 2012. Unprecedented influx of Pelagic Sargassum along Caribbean Island Coastlines during summer 2011. Proc. Sixty Four Annu. Gulf Caribb. Fish. Inst. 64, 6-8.
  • C Hu
  • B Murch
  • A A Corcoran
  • L Zheng
  • B B Barnes
  • R H Weisberg
  • K Atwood
  • J.-P Maréchal
Hu, C., Murch, B., Corcoran, A.A., Zheng, L., Barnes, B.B., Weisberg, R.H., Atwood, K., J.-P. Maréchal et al. Remote Sensing Applications: Society and Environment 5 (2017) 54-63
The Sargassum invasion of the eastern Caribbean and dynamics of the equatorial North Atlantic
  • D Johnson
  • D S Ko
  • J S Franks
  • P Moreno
  • G Sanchez-Rubio
Johnson, D., Ko, D.S., Franks, J.S., Moreno, P., Sanchez-Rubio, G., 2014. The Sargassum invasion of the eastern Caribbean and dynamics of the equatorial North Atlantic. Proc. Sixty Fifth Annu. Gulf Caribb. Fish. Inst. 65, 102-103.
  • J.-P Maréchal
J.-P. Maréchal et al. Remote Sensing Applications: Society and Environment 5 (2017) 54-63