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A simple, fast, and reliable method to predict Sargassum washing ashore in the Lesser Antilles
Abstract and Figures
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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... Thus, these main aggregations were larger than 3000 m and 140 m length for OLCI and MSI, respectively. In addition, Sargassum aggregations near coasts were discarded because of the FC high values in such areas due to the turbidity and shallow water [7,24,65,66]. The distance was set to 15 km away from coasts for OLCI and 200 m for MSI images. ...
... These extra ID pixe associated with turbid water that the ID method used here as an undiscarded ref [59]. All the false detection origins presented here are also confirmed by different au [7,23,24], namely the extra-detection rate in OLCI images is close to the false detectio observed by Podlejski et al. [24] using the ID method on MODIS images. Such estim confirm that a large part of the extra-detections is linked to false detection and lead overestimation of the coverage of Sargassum (FC) by 50%. ...
... These extra ID pixels are associated with turbid water that the ID method used here as an undiscarded reference [59]. All the false detection origins presented here are also confirmed by different authors [7,23,24], namely the extra-detection rate in OLCI images is close to the false detection rate observed by Podlejski et al. [24] using the ID method on MODIS images. Such estimations confirm that a large part of the extra-detections is linked to false detection and leads to an overestimation of the coverage of Sargassum (FC) by 50%. ...
Since 2011, the proliferation of brown macro-algae of the genus Sargassum has considerably increased in the North Tropical Atlantic Sea, all the way from the Gulf of Guinea to the Caribbean Sea and the Gulf of Mexico. The large amount of Sargassum aggregations in that area cause major beaching events, which have a significant impact on the local economy and the environment and are starting to present a real threat to public health. In such a context, it is crucial to collect spatial and temporal data of Sargassum aggregations to understand their dynamics and predict stranding. Lately, indexes based on satellite imagery such as the Maximum Chlorophyll Index (MCI) or the Alternative Floating Algae Index (AFAI), have been developed and used to detect these Sargassum aggregations. However, their accuracy is questionable as they tend to detect various non-Sargassum features. To overcome false positive detection biases encountered by the index-thresholding methods, we developed two new deep learning models specific for Sargassum detection based on an encoder–decoder convolutional neural network (CNN). One was tuned to spectral bands from the multispectral instrument (MSI) onboard Sentinel-2 satellites and the other to the Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3 satellites. This specific new approach outperformed previous generalist deep learning models, such as ErisNet, UNet, and SegNet, in the detection of Sargassum from satellite images with the same training, with an F1-score of 0.88 using MSI images, and 0.76 using OLCI images. Indeed, the proposed CNN considered neighbor pixels, unlike ErisNet, and had fewer reduction levels than UNet and SegNet, allowing filiform objects such as Sargassum aggregations to be detected. Using both spectral and spatial features, it also yielded a better detection performance compared to algal index-based techniques. The CNN method proposed here recognizes new small aggregations that were previously undetected, provides more complete structures, and has a lower false-positive detection rate.
... During the periods 2011-2012 and then 2014-2019, massive Sargassum beachings impacted most coasts of the Lesser Antilles (LA), mainly those facing east and southeast (Franks et al., 2012;Gower et al., 2013;Johnson et al., 2014;Hu et al., 2016;Wang and Hu, 2016). The LA received large amounts of algae on the windward Atlantic coastline, while leeward Caribbean coastal areas remained slightly affected (Maréchal et al., 2017). These beachings in terms of frequency and intensity can now be considered a new natural hazard for the Caribbean islands and American coasts. ...
... Using large-scale observations with ocean color satellite remote sensing, historical hydrographic observations, time series of Sargassum volume collected on ships, multiyear reanalysis of wind and current, and numerical models, the roles of both subsurface nutrient supply and surface current transport were estimated. 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 (SargassumWatch System, 2021;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 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 North Atlantic Oscillation (NAO) anomaly and seasonal aggregation by the Intertropical Convergence Zone (ITCZ). ...
The massive Sargassum algae beachings observed over the past decade are a
new natural hazard currently impacting 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 were derived from the Mercator model and the Hybrid
Coordinate Ocean Model (HYCOM) outputs in which we integrated the windage
effect. Past daily observations of Sargassum beaching on Guadeloupe coasts and
satellite-based Sargassum offshore abundance were also integrated. Four
representative current regimes were identified for both Mercator and HYCOM
data. The analysis of the current sequences leading to beachings showed that
the recurrence of two current regimes is related to the beaching peaks
respectively observed in March and August. The performance score of the
predictive model showed that the HYCOM data seem more suitable to assess
coastal Sargassum hazard in the Lesser Antilles. For 1 year of tests (i.e., 2021),
the decision tree accuracy respectively reached 70.1 % and 58.2 % for
HYCOM and Mercator with a temporal uncertainty range ±3 d around the
forecast date. The present clustering analysis predictive system, requiring
lower computational resources compared to conventional forecast models, would
help improve this risk management in the islands of the region.
... 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. ...
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. ...
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.
... 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]. ...
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.
... Because of the high sensitivity of the MODIS instrument, floating Sargassum may be detected with only 0.2% (2,000 m 2 ) overall coverage of a 1 km 2 pixel (Wang & Hu, 2016). Using near real-time AFAI images and the Floating Algal density product distributed via the Sargassum Watch System (SaWS; Hu et al., 2016), the trajectories of large holopelagic Sargassum aggregations have been modeled to predict beaching events (Marechal, Hellio & Hu., 2017;Marsh et al., 2021;Trinanes et al., 2021). However, after applying the AFAI algorithm and neural network deep learning to high-resolution sensor data, Wang & Hu (2021) concluded that floating Sargassum density is greatly underestimated using MODIS, the magnitude to which has not been ground-truthed. ...
... With the desire to predict and prepare for potentially catastrophic beaching events, communities have come to rely upon bulletins based on satellite-derived estimates of floating Sargassum distribution and abundance (Hu et al., 2016;Marechal, Hellio & Hu., 2017;Trinanes et al., 2021). AFAI strength is used to assign fractional coverage estimates of floating Sargassum to remote sensing pixels for algorithm outputs. ...
Between 2011 and 2020, 6,790 visual observations of holopelagic Sargassum were recorded across the North Atlantic Ocean to describe regional distribution, presence, and aggregation state at hourly and 10 km scales. Influences of oceanographic region and wind/sea conditions as well as temporal trends were considered; marine megafauna associates documented the ecological value of aggregations. Holopelagic Sargassum was present in 64% of observations from the western North Atlantic. Dispersed holopelagic Sargassum fragments and clumps were found in 97% of positive observations whereas aggregated windrows (37%) and mats (1%) were less common. Most field observations noted holopelagic Sargassum in quantities below the AFAI algorithm detection limit for the MODIS sensor. Aggregation state patterns were similar across regions; windrow proportion increased with higher wind speeds. In 8 of 10 years in the Sargasso Sea holopelagic Sargassum was found in over 65% of observations. In contrast, the Tropical Atlantic and Caribbean Sea exhibited greater inter-annual variability (1–88% and 11–78% presence, respectively) that did not align with extremes in central Atlantic holopelagic Sargassum areal coverage determined from satellite observations. Megafauna association patterns varied by taxonomic group. While some study regions were impacted by holopelagic Sargassum dynamics in the equatorial Atlantic, the Sargasso Sea had consistently high presence and operated independently. Field observations capture important dynamics occurring at fine spatiotemporal scales, including transient aggregation processes and ecological value for megafauna associates, and therefore remain essential to future studies of holopelagic Sargassum .
... 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. ...
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 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. . ...
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.
... 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. ...
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 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. ...
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.
... Sargassum mats are visible from space due to their characteristics: floating, long lasting and a distinctive spectral response (Gower and King, 2008). They can, therefore, be monitored using different vegetation indices, such as the Maximum Chlorophyll Index (MCI), Normalized Difference Vegetation Index (NDVI), Floating Algal Index (FAI) and Alternate Floating Algae Index (AFAI) (Hu, 2009;Gower and King, 2011;Hu et al., 2015;Marećhal et al., 2017;Hernańdez et al., 2020). Sargassum does not always aggregate in large mats, thus, it is not detectable by some coarse spatial resolution optical sensors (e.g., MODIS at 250m, Sentinel-3 at 300m), requiring high spatial resolution sensors for local tactical monitoring. ...
Massive influxes of holopelagic Sargassum spp. (Sargassum natans and S. fluitans) have been causing major economic, environmental and ecological problems along the Caribbean coast of Mexico. Predicting the arrival of the sargassum as an aid to addressing these problems is a priority for the government, coastal communities and the society; both mitigating the impacts and providing opportunities for its use. Lack of data concerning precise locations and times of sargassum beachings means that public and private funds are being spent inefficiently and most actions are reactive. The dynamic nature of sargassum beachings/influxes render conventional ground-based monitoring insufficient. Earth observation and cloud-based processing services offer tools to track, quantify and understand sargassum beaching remotely in a frequent, systematic and reliable manner with the temporal and spatial resolutions required for its management. In order to find the right solutions to address this problem, in this paper the needs and requirements of stakeholders are taken into consideration for the development of an Earth observation-based service to monitor sargassum along the Mexican Caribbean coast. Routine monitoring of sargassum over a large area will be cost effective and help mitigate the negative effects of sargassum influxes. The combination of imagery from Planet, Frontiers in Marine Science specifically their SuperDove systems that provide daily data at 3 m spatial resolutions, with the freely available EU Copernicus data would be useful for many different stakeholders and potential users. A prototype of the service is presented, based on the main user requirements. The system would enable public and private organizations to allocate resources appropriately in affected areas quickly and efficiently, thereby minimizing economic, social and environmental impacts and enhancing the resilience of local communities. It would also assist the sargassum industry in the collection of fresh algae for onward processing. The system could easily be implemented for similar types of environmental monitoring in the Greater Caribbean and beyond.
... Monitoring and forecasting Sargassum beaching events are necessary to improve mitigation and clean-up responses, work towards long-term adaptive management operations, and provide information to the growing entrepreneurial community attempting to valorize these influxes of Sargassum (Lopez-Miranda et al. 2021;Oxenford et al. 2021). The widespread nature of this phenomenon presents significant challenges for efforts to synoptically monitor coastal J o u r n a l P r e -p r o o f inundations (Maréchal et al. 2017;Johnson et al. 2020;Bernard et al. 2022). The application of satellite-based sensors with the capability of detecting Sargassum from space has been used to develop monitoring tools, such as the Sargassum Inundation Reports (SIRs) produced by the National Oceanographic and Atmospheric Administration (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML). ...
... In 2015 the Sargassum summer coverage was 20 times higher than that observed for summers between 2000 and 2010 (Wang and Hu 2016). Moreover, the risk of Sargassum washing onshore has increased in the Lesser Antilles between 2011 and 2015 (Maréchal et al. 2017). Species responsible of these strandings concern the genus Sargassum which is highly diversified in the order Fucales as 360 worldwide species are currently listed (Guiry and Guiry 2023). ...
Human populations in the Caribbean region, suffer recurrently for 12 years from brown tides followed by significant strandings of Sargassum spp. which cause environmental, economic and health issues. Given current interest in new renewable sources of chemicals, proteins, and polymers, this underexploited biomass represents a potential source to be explored in a biorefinery concept. Up the value chain in biorefinery process, seaweeds should be rapidly stabilised. Stabilisation by drying would permit to reduce the storage and transport costs and to obtain a product stable all year round. The aim of this work was to investigate oven drying and air impingement drying at two air velocities (7 and 21 m s⁻¹) on three species of Sargassum: S. fluitans III, S. natans I and S. natans VIII. The drying kinetics were studied. The apparent diffusivity coefficients were calculated thanks to the Fick’s diffusional model. Seven thin-layer equations were used to fit drying kinetics, namely Page, Modified Page, Diffusion approach, Verma, Two-term, Midilli-Kucuk and Henderson-Pabis modified. Freeze-drying, as a reference drying method, was applied on Sargassum in order to compare the effects of drying processes on several phytochemical components, which are neutral sugars, proteins, polyphenols, uronic acids and mineral matter. According to these results, air impingement drying was the better process to dry these three Sargassum species, but it also depended on the seaweed chain of valorisation after the stabilisation process.
... Carbon derived from blooming Sargassum can account for up to 18% of the total particulate organic carbon present in the top layers of the ocean . In 2015 the 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 up on the shore has increased in the Lesser Antilles between 2011 and 2015 (Maréchal et al. 2017). The factors leading to the Sargassum blooms for a time remained hypothetical, with regards to both the dynamics and the source regions of these rafts (Oyesiku and Egunyomi 2014;Schell et al. 2015). ...
Sargassum C. Agardh is a highly diverse genus within the brown algae, with 615 currently recognized species, varieties and forms worldwide. This high level of species diversity led early taxonomists, using morphological-anatomical criteria only, to divide the genus into up to five sub-genera and several lower-ranking taxonomic units (e.g., sections, tribes). With the advent of molecular data, subsequent authors revised this complex and archaic classification, with the genus now comprising only two sub-genera: Sargassum and Bactrophycus. Whilst most Sargassum species are benthic, only two are known to be holopelagic and responsible for strandings along tropical Atlantic coasts. The rest of the genus is cosmopolitan, occurring from tropical to temperate regions. Sargassum has not yet been reported in polar regions. Where Sargassum is present, macroalgal populations can grow in large quantities, and the resulting biomass can be valuable to the local communities for a variety of uses. Here we review the genus Sargassum from a taxonomic, ecological and physiological perspectives, and explore the different ways of taking advantage of this extraordinary biomass, which while becoming an invasive pest in some countries, could represent opportunities for coastal populations worldwide.
... Early efforts to clean-up beached sargassum were ad hoc and involved multiple actors: government agencies, community volunteers, and private sector actors including hotel staff and fishers, often with little communication or coordination among them. A review of sargassum policies from 2011-2020 [29] across the Wider Caribbean Region (WCR) found varying degrees of effort by national and regional institutions, with no sustained increase in initiatives until 2017 when policy makers realised that sargassum influxes appeared to constitute a new normal [37]. Further, the first iteration of sargassum plans, policies and guidance documents took between four and ten years to be produced after the first impact in 2011 (figure 2). ...
Climatic and anthropogenic changes appear to be driving the emergence of new ecosystem and human health risks. As new risks emerge, and the severity or frequency of known risks change, we ask: what evidence is there of past adaptations to emergent risks? What scientific and policy processes lead to adaptive solutions that minimise the impacts of these events, and draw out opportunities? We identify science and policy lessons learned from coping with, and responding to, the sudden arrival of brown macroalgae (pelagic sargassum) that has proliferated across the tropical Atlantic since 2011. Drawing on an evidence base developed from a systematic search of literature relating to sargassum seaweed, and using event timelines and word clouds, we provide an analysis of lessons learned from a case study of adaptive responses across three continents to an emergent risk over the course of a decade. We reflect on successes and failures as well as opportunities taken in building adaptive capacity to address the risk in four key domains: policy, knowledge and evidence, monitoring and early warning, and technology and valorisation. Failures include: lack of environmental risk registries; missed opportunities to share monitoring data; and lack of a shared approach to manage the risk. Successes include: development of national management strategies; open-access knowledge hubs, networks and webinars sharing information and best practice; semi-operational early advisory systems using open access remote sensing data; numerous innovations customising clean-up and harvesting equipment, and research and development of new uses and value-added products.
... hundreds of millions of dollars to national economies 8,23 . Influx events are now considered a new norm to which countries must adapt 12,24 . There is a rapidly growing interest in utilizing Sargassum and turning it into business opportunities [25][26][27][28] . ...
The recent proliferation of pelagic Sargassum spp. in the Tropical Atlantic causes major ecological and socioeconomic impacts to the wider Caribbean when it washes ashore, with regional fisheries and tourism industries particularly affected. The Caribbean influxes have been tracked to a new bloom region known as the North Equatorial Recirculation Region (NERR) encompassing the area between the South Equatorial Current and the North Equatorial Counter Current and extending from Africa to South America. The vast biomass of Sargassum presents serious problems when it washes ashore but also represents significant commercial opportunities, especially with biofuel and fertilizer. The floating Sargassum mats are themselves diverse ecosystems that vary both in their biodiversity and biochemical attributes. Two major species (Sargassum fluitans and S. natans) have been identified as well as several distinguishable morphotypes of each. Oceanic mixing tends to blend the morphotypes together making it difficult to determine if there are regions of the NERR that favour bloom and growth of the distinct types. In this study, we quantify the species and morphotype composition of Sargassum strandings in Barbados and test if this is related to separate oceanic origins and routes travelled using a backtracking algorithm based on ocean drifter data. We found significant seasonal variation in the relative abundance of three morphotypes and this could be traced to two distinct easterly sub-origins and/or transport pathways; one area around 15° N that travels directly E-W across the Atlantic, and another area generally south of 10° N that takes a more meandering route coming close the coast of South America. These findings contribute towards our understanding of why the Tropical Atlantic bloom is presently occurring as well as towards addressing valorisation constraints surrounding variation in the supply of the three commonly occurring morphotypes.
... Au plan écologique, les sargasses couvrent les sites de pontes des tortues marines, ce qui constitue un obstacle non seulement à leur nidification, mais aussi une entrave à l'accès en mer des nouveau-nés. Ce phénomène entraîne la perte de centaines, voire de milliers de nouveau-nés de tortues marines (Johnson et al., 2012 ;Maréchal et al., 2017). À ce jour, aucune solution efficace n'a été trouvée pour lutter contre la pollution des plages par les sargasses, et aucun moyen de valorisation n'existe en Côte d'Ivoire. ...
Sargassum fluitans (Børgesen) Børgesen et Sargassum natans (Børgesen) Børgesen (Sargassaceae) sont deux algues brunes invasives qu’on retrouve dans les eaux et sur les plages du golfe de Guinée, notamment celles de la Côte d’Ivoire. L’objectif de cette étude est de contribuer à la lutte contre la pollution environnementale des sargasses sur les plages ivoiriennes à travers une valorisation de ces algues en additifs alimentaires en aviculture et en cuniculture. Ainsi, la teneur des deux algues en composés phénoliques ainsi que leurs pouvoirs antioxydants ont été évalués. On note une bonne teneur en polyphénols totaux avec les extraits aqueux avec des valeurs de 378,30 ± 0,59 mg/100 g et 549,39 ± 0,00 mg/100 g respectivement pour SF et SN. Au niveau des phlorotannins, on a des teneurs qui varient entre 93,18 ± 1,46 mg/100g et 36,37 ± 0,58 mg/100g selon le solvant utilisé. L’activité antiradicalaire contre le radical ABTS a donné des valeurs moyennes de 3,89 ± 2,28 mg/mL avec SFEth et 3,21 ± 2,29 mg/mL pour SNH2O. Ces résultats obtenus indiquent que Sargassum fluitans (SF) et Sargassum natans (SN) renferment des composés phénoliques et ont des activités antioxydantes intéressantes susceptibles d’encourager vers leur valorisation en tant qu’additifs alimentaires aux pouvoirs immunogènes chez les poulets de chairs (Gallus gallus domesticus) et les lapins (Oryctolagus cuniculus). Sargassum fluitans (Børgesen) Børgesen and Sargassum natans (Børgesen) Børgesen (Sargassaceae) are two invasive brown algae found in the waters and on the beaches of the Gulf of Guinea, particularly those of Côte d'Ivoire. The objective of this study is to contribute to the fight against the environmental pollution of Sargassum on Ivorian beaches through the valorization of these algae in food additives in poultry farming and rabbit farming. Thus, the content of the two seaweeds in phenolic compounds as well as their antioxidant powers were evaluated. A good content of total polyphenols is noted with the aqueous extracts with values of 378.30 ± 0.59 mg/100g and 549.39 ± 0.00 mg/100g respectively for SF and SN. The phlorotannins contents varied between 93.18 ± 1.46 mg/100g and 36.37 ± 0.58 mg/100g depending on the solvent used. The antiradical activity against the ABTS radical gave average values of 3.89 ± 2.28 mg/mL with SFEth and 3.21 ± 2.29 mg/mL for SNH2O. The results obtained show that Sargassum fluitans (SF) and Sargassum natans (SN) contain phenolic compounds and have interesting antioxidant activities likely to encourage their development as food additives with immunogenic powers in broiler chickens (Gallus gallus domesticus) and rabbits (Oryctolagus cuniculus).
... Most of the works related to algae detection in the ocean have been carried out using remote sensing. Several research efforts relate to monitoring and detecting Sargassum have been developed in recent years using data from satellites, such as GOCI-II, Landsat-8, or Sentinel-2 [5][6][7][8][9][10][11][12]. Although remote sensing is a powerful tool, it still has some disadvantages for certain problems, being the main disadvantages the spatial and temporal resolution. ...
Since 2011, significant and atypical arrival of two species of surface dwelling algae, Sargassum natans and Sargassum Fluitans, have been detected in the Mexican Caribbean. This massive accumulation of algae has had a great environmental and economic impact. Most works addressing this topic use high-resolution satellite imagery which is expensive or may be time delayed. We propose to estimate the amount of Sargassum based on ground-level smartphone photographs that, unlike previous approaches, is much less expensive and can be implemented to make predictions almost in real time. Another contribution of this work is the creation of a Sargassum images dataset with more than one thousand examples collected from public forums such as Facebook or Instagram, labeled into 5 categories of Sargassum level (none, low, mild, plenty, and excessive), a relevant difference with respect to previous works, which only detect the presence or not of Sargassum in a image. Several state-of-the-art convolutional networks: AlexNet, GoogleNet, VGG, and ResNet, were tested using this dataset. The VGG network trained under fine-tuning showed the best performance. The results of the carried out experiments show that convolutional neuronal networks are adequate for providing an estimate of the Sargassum level only from smartphone cameras images.
... These model data are currently obtained from simulations with HYCOM (Chassignet et al., 2007) and NEMO (Madec, 2015) community codes, configured on eddy-resolving (typically 1/ 12°) global meshes, available at time frequencies ranging from daily to weekly. In early dynamical forecasts, satellite imagery and operational 7-day ocean current forecasts were used to predict sargassum drift on timescales of several days (Marećhal et al., 2017). To assess sources and pathways of sargassum, Putman et al. (2018) forward-tracked particles in ensembles released across the tropical Atlantic (0-10°N). ...
Proliferation of sargassum across the tropical Atlantic since 2011 has motivated a range of forecasting methods. Statistical methods based on basin-scale satellite data are used to address seasonal timescales. Other methods involve explicit Lagrangian calculations of trajectories for particles that are representative of drifting sargassum over days-months. This computed sargassum drift is attributed to the combined action of surface currents, winds and waves, individually or in various combinations. Such calculations are undertaken with both observed surface drift and simulated currents, each involving strengths and weaknesses. Observed drift implicitly includes the action on sargassum of winds and waves, assumed equivalent between drifters and sargassum mats. Simulated currents provide large gridded datasets that facilitate computation of ensembles, enabling some quantification of the uncertainty inherent in an eddy-rich ocean, further subject to interannual variability. A more limited number of forecasts account for in situ growth or loss of sargassum biomass, subject to considerable uncertainty. Forecasts provide either non-dimensional indices or quantities of sargassum, accumulated in specified areas or counted across specified transects over a given time interval. Proliferation of different forecast methodologies may reduce uncertainty, if predictions for given seasons are consistent in broad terms, but there is scope to coordinate different approaches with common geographical foci and predicted variables, to facilitate direct inter-comparisons. In an example of forecasting westward sargassum flux into the Caribbean during the first half of 2022, challenges and opportunities are highlighted. In conclusion, prospects for closer alignment of complementary forecasting methods, and implications for sargassum management, are identified.
... This phenomena's ambiguous origin and sizable impacts have led to strong development of forecasting and monitoring efforts. Regional monitoring efforts focused on satellite imagery modeling using various tools such as Moderate Resolution Imaging Spectroradiometer (MODIS) and Sentinel-2 (Wang and Hu, 2016;Maréchal et al., 2017;Putman et al., 2018). Data collected from these tools are often calculated to indices such as the maximum chlorophyll index (MCI), the floating algal index (FAI), and the alternative floating algal index (AFAI) to name a few (Trinanes et al., 2021). ...
During the past decade, massive inundations of holopelagic Sargassum spp. (S. natans I, S. natans VIII, and S. fluitans III), commonly known as sargasso, have drastically affected beaches and coasts throughout the tropical Atlantic, leading to strong forecasting and monitoring efforts. This study aimed to characterize spatiotemporal variation in accumulation levels and morphotype composition of sargasso inundations. Community science initiatives can aid in monitoring sargasso regionally by locally collecting data on morphotype composition and accumulation level. A volunteer network compiled community-contributed photos from the "Sargassum Watch" Epicollect5 digital application. Florida and the Gulf coast showed less susceptibility to high accumulations than other subregions of the tropical Atlantic. S. fluitans III was the most frequently encountered morphotype, though the probability of encountering any of the three morphotypes depended on accumulation level. Despite differences in latitude, the 2021 season demonstrated similar 'peak' sargasso months between South Florida and Mexican Caribbean (May–July), though the intensity and duration of high-accumulation months differed. Much of these composition patterns and accumulation levels were likely related to the proximity of both regions to the Great Atlantic Sargassum Belt and dispersal through wind and water currents. Using community-collected data to outline quantitative trends and patterns in sargasso accumulation levels and composition, this study can be useful for future collaborations and syntheses with other forecasting and monitoring programs.
... Various satellite sensors such as Landsat, Moderate Resolution Imaging Spectroradiometer (MODIS), WorldView-2, QuickBird, and others have been used to study the surface water quality (Maréchal et al. 2017;Wang and Hu 2016). A few studies have suggested reliable models with Landsat data for selected WQPs, including TSS (Wisha et al. 2017), TDS (González-Márquez et al. 2018), and turbidity (Huovinen et al. 2019;Abirhire et al. 2020). ...
This study was carried out to apply a cost-effective remote sensing-based methodology to predict water quality parameters of Manchar Lake in Pakistan. Water quality models were developed using level 2 Landsat 8 OLI satellite data for the lake, where regular water quality monitoring is limited in time and space. This study focused only on three water quality parameters (WQPs) with optical properties that can be directly captured using remote sensing tools including total dissolved solids (TDS), total suspended solids (TSS), and turbidity. Twenty-one water samples were collected at various times for pre-monsoon (April 2019), monsoon (August 2019), and post-monsoon (November 2019) seasons on or within 2–3 days the satellite overpass dates. Among them, six samples were randomly selected for models’ validation. Regression analysis was performed on the remaining samples to obtain WQPs’ empirical relationships with bands’ surface reflectance employing single and different band combinations. The linear, logarithmic, and first- and second-degree polynomial regression models were developed and based on the highest R2 values, the “best” models were selected. TDS models performed comparatively well with R2 = 0.9731, 0.7359, 0.7969 in pre-monsoon, monsoon, and post-monsoon periods, respectively. The R2 for the “best” TSS models were 0.7721 (pre-monsoon), 0.8561 (monsoon), and 0.5868 (post-monsoon), whereas their values for turbidity were 0.4807 (pre-monsoon), 0.5212 (monsoon), and 0.6404 (post-monsoon) suggesting relatively weak model performances. Models’ validations produced maximum/minimum root mean square errors of 515/246.9 mg/L, 9.53/8.78 mg/L, and 27.99/13.86 NTU, respectively, for TDS, TSS, and turbidity. Statistically significant values of R2 indicated the suitability of models to predict WQPs of Manchar Lake. However, the models’ performance was reduced in the post-monsoon season, but R2 values were still greater than 0.5. From these results, it can be expected that GIS and remote sensing-based water quality modeling will eventually provide convenient solutions for Manchar Lake’s management and long-term planning.
... 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. ...
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]. ...
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. ...
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.
... 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. ...
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.
... 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. ...
... Additionally, the secondary impacts, including algal blooms of Sargassum seaweed [104], transcontinental dust clouds [105] and vector-borne diseases [106,107] have been observed. ...
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.
... 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. ...
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.
... (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. ...
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.
... 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. ...
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.
... 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. ...
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.
... 7: Marie Galante. 8-9 Les Saintes[1]. ...
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.
... 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). ...
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.
... 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). ...
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.
... 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. ...
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.
... (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). ...
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.
Massive floating
Sargassum
blooms have occurred frequently in many parts of the global ocean, and satellite remote sensing provides an effective way to monitor their spatiotemporal variation. However, coarse-resolution satellite data often suffer from a data gap in nearshore waters and detection uncertainty of
Sargassum
amount especially for smaller patches. These limitations may be ameliorated by high-resolution satellite data, yet such great potential is hindered by the lack of reliable and easy-to-implement methods to detect
Sargassum
slicks. Here, combining the visible and near-infrared top-of-atmosphere reflectance (
R
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) data with random forest model, a new method namely the
R
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-RF model was designed to automatically detect
Sargassum
from high-resolution satellite imagery with four wavebands. Specifically, this model was successfully applied to various satellite sensors, including Gaofen1-Wide Field View Multispectral Camera (WFV; 16m), GF2 - Multispectral Scanner (4m), Gf6-WFV (16m), Huanjing1A/B - Charge Coupled Device (30m), Haiyang1C/D - Coastal Zone Imager (50m). Comparisons with visual inspection and cross-index indicated that all achieved satisfactory performance for detecting
Sargassum
slicks, with the overall accuracy and
Kappa
values greater than 96% and 88% respectively. The sensitivity analysis of the model as example of different sensors suggested the
R
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-RF model can effectively identify
Sargassum
features under complex ocean background, cloud cover and sun glint, even under conditions of surface wave glitter and weak
Sargassum
feature with low false positive rate (<9.60%). The findings here not only pave the way for operational monitoring fine-scale
Sargassum
, but importantly provide thought for developing detection method of macroalgae blooms in global water.
This article highlights the challenge of environmental public policies in French West Indies islands and more particularly in Martinique. It provides answers to the question: What is the effect of the implementation of a Marine Protected Area (MPA) on the professional identity of traditional fishermen? The study, conducted with fishermen at Le Prêcheur in Martinique, brings, in an original way, some key answers on the thoughts of fishermen about biodiversity protection mechanism such as MPA. Overall, fishermen are concerned by the professional transition that the MPA creation will cause as they understand the challenge that ties-up with their identity. Thus, the stake of biodiversity protection faces the one of the preservation of fishermen identity.
Sargassum fluitans (Børgesen) Børgesen et Sargassum natans (Børgesen) Børgesen (Sargassaceae) sont deux algues brunes invasives qu’on retrouve dans les eaux et sur les plages du golfe de guinée, notamment celles de la Côte d’Ivoire. L’objectif de cette étude est de contribuer à la lutte contre la pollution environnementale des sargasses sur les plages ivoiriennes à travers une valorisation de ces algues en additifs alimentaires en aviculture et en cuniculture. Ainsi, la teneur des deux algues en composés phénoliques ainsi que leurs pouvoirs antioxydants ont été évalués. Les résultats obtenus montrent que Sargassum fluitans et Sargassum natans renferment des composés phénoliques et ont des activités antioxydantes intéressantes susceptibles d’encourager vers leur valorisation en tant qu’additifs alimentaires aux pouvoirs immunogènes chez les poulets de chairs (Gallus gallus domesticus) et les lapins (Oryctolagus cuniculus).
The use of biochars (BCs) and activated carbons as a way of sequestering soil-bound pollutants such as chlordecone (CLD) is increasingly being studied. This study aims at assessing the impact of Sargassum BC/AC particle size and Sargassum BC amendment rate on CLD adsorption in Nitisol and in Andosol. Four different types of carbonaceous matrices were tested: Sargasso carbon activated by phosphoric acid (SargH3PO4), Sargasso carbon activated by steam (SargH2O), biochar of Sargasso (Ch Sarg700), and a commercial activated carbon (ORBO™). In a first experiment, CLD contaminated Andosol and Nitisol were amended with 2% of each carbonaceous matrix divided into four particles size classes (< 50 µm, 50–150 µm, 150–200 µm, and > 200 µm). In a second experiment, the contaminated soils were amended with the biochar of Sargasso at five application rates (0, 0.25, 0.5, 1, and 2% (w/w)). After a 4-month aging, environmental availability tests were carried out on the soils of both experiments. The results of the first experiment showed that the best reductions of CLD environmental availability were obtained in both soils with the biochar of Sargasso and the ORBO™. More specifically, in nitisol, particle size under 50 µm of biochar of Sargasso and AC ORBO™ showed a CLD environmental availability reduction up to 72 ± 2.6% and 79 ± 2.6%. In Andosol, there was no significant difference between the three particle sizes (< 50 µm, 50–150 µm, and 150–200 µm) of the biochar of Sargasso on the reduction of environmental availability (average reduction of 43 ± 2.5%). The results of the second experiment showed that an amendment rate increase improves the immobilization of CLD. When the amendment rate was increased from 0.25 to 2%, the environmental availability was reduced by 43% in Nitisol and 50% in Andosol.
Cet article apporte un éclairage sur les défis socio-professionnels de l’écologisation des politiques publiques française et européenne dans les Territoires Outre-Mer. Il présente l’effet de la création d’une Aire Marine Protégée (AMP) sur l’identité professionnelle de pêcheurs traditionnels. La recherche, menée dans une perspective sociologique au Prêcheur, commune de la Martinique, contribue, de manière inédite, à fournir des éléments d’analyse sur la posture professionnelle des pêcheurs vis-à-vis d’un tel mécanisme de protection des écosystèmes marins qui remet en cause leur identité et leur survie. L’enjeu de la protection de la biodiversité se heurte ainsi à celui de la préservation des intérêts catégoriels et identitaires.
This article highlights the challenge of environmental public policies in French West Indies
islands and more particularly in Martinique. It provides answers to the question: What is the
effect of the implementation of a Marine Protected Area (MPA) on the professional identity of traditional fishermen? The study, conducted with fishermen at Le Prêcheur in Martinique, brings, in an original way, some key answers on the thoughts of fishermen about biodiversity protection mechanism such as MPA. Overall, fishermen are concerned by the professional transition that the MPA creation will cause as they understand the challenge that ties-up with their identity. Thus, the stake of biodiversity protection faces the one of the preservation of fishermen identity.
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.
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 document 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 Manzanillo) 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. The putatively rare S. natans VIII dominated the dritf (65 % dry weight), followed by S. natans I (25% dry weight), and S. fluitans (10 % dry). Twenty eight species were identified from Chlorophyta (9), Ochrophyta (15), and Rhodophyta (4) Divisions. Conclusions: There were no significant differences between months (March-April) and sites (Puerto Viejo and Punta Uva) for the dritf biomass.
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.
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
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.
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.
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.
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.
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.
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The online version of this article (doi:10.1007/s00227-014-2539-y) contains supplementary material, which is available to authorized users.
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.
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.
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.
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).
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.
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
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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
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