On Tuesday, September 9, 2025, Dr. Jean-François Dorville was the guest on (local TV channel) Canal 10’s 7 p.m. Focus on Sargassum following the public meeting of the anti-Sargassum collective held in the Petit-Bourg town hall square on Wednesday, September 3, 2025. For just over 50 minutes, the Sargassum problem was analysed for Guadeloupe, particularly the health effects of anoxic decomposition gases (fermentation). The reproduction (propagation), growth, and transport of the algae were discussed, as well as their death in Guadeloupe’s coastal waters and their effects. Solutions were presented, both technical and political.
The video of the program is available on YouTube at the following address. Feel free to share it.
An English translation will be available very soon.
Dr. Jean-François Dorville during his presentation (photo credit: Philippe Petit)
TCGNRG was invited by Philippe Petit to speak on Saturday, September 6, 2025, about disruptive solutions and evaluation processes for sargassum management during the political back-to-school session of the Union of Democrats and Ecologists of Martinique (UDEM).
Photo of the audience at Paradis des Anges (photo credit: Jean-François Dorville)
In front of just over 50 people, including politicians, supporters, and curious onlookers, Jean-François Dorville presented the need to analyse our current understanding of the sargassum stranding phenomenon and its consequences, to assess the needs for managing the presence of seaweed on the coast, and to adapt solutions. The three-part presentation, spanning 45 minutes, addressed many interrogation from the audience.
Photo of the audience at Paradis des Anges (photo credit: Jean-François Dorville)
The notion of public health was naturally addressed. The event was held at the “Paradis des Anges” guesthouse in the commune of Vauclin in Martinique. The commune of Vauclin has been particularly affected by the stranding of Sargassum. There was also a persistent smell of Hydrogen Sulfide, due to a strip of manatee grass (Syringodium filiforme) and decomposing Sargassum at the entrance to Pointe Faula (see photo).
Photo of a drone view (14,5435°N 60,8302°W, 116 m altitude) of a mix of Sargassum and Manatee Grass tank undergoing anoxic decomposition, causing odours, on Saturday, September 6, on the Vauclin coast.Photo of a view from the shore of a mix of Sargassum and Manatee Grass tank undergoing anoxic decomposition, causing odours, on Saturday, September 6, on the Vauclin coast.
After a year 2025 marked by a long period of strandings of holopelagic sargassum, already spanning nearly seven (7) months, the situation on the Guadeloupe coast is complicated. The solutions implemented (mechanical shovels, sea collection from a barge, and floating barriers to divert or block the algae) appear to be increasingly ineffective and are not adapted to the volumes and frequencies of strandings, nor even to the particularly high sea water temperatures. Concentrations of hydrogen sulfide (H₂S) and ammonia (NH₃) have been elevated for more than four months.
Dr. Jean-François was invited to this public conference. He was able to speak for a little over twenty minutes and answer questions from a relatively large audience, for a weekday meeting after 7 p.m. Dr. Dorville focused on the current limitations of dams and methods of reoxygenating water and Sargassum sludge to limit toxic gas emissions and mitigate risks to human health and the integrity of copper products, allowing time to better organize the management of stranded algae.
An attentive and numerous audience for a weekday (Photo credit: JF DORVILLE)
Mangroves and their ecosystem have an essential role in biodiversity, the renewal of fish stock, the preservation of coastline, the quality of coastal waters, and the attenuation of flood waves. This list is not exhaustive and is growing day by day.
Therefore, preserving these environments is essential for the quality of life of women and men in the coastal zone.
Their preservation is complicated because they most often occupy areas with high tourist, port or real estate value. Making a choice between financially profitable projects and spaces that cannot be monetized is not accessible using a neo-capitalist reading grid.
To ensure the maintenance of these spaces of abundance, life and culture, it is necessary to agree to place the life of a fish, a mollusc, a crustacean, and a bird on the same level as that of ‘a company.
The Jamaican Green Desalination Project is glad to announce that the MPhil associated with the project was validated, in September 2020, by the University of the West Indies, Mona Campus. The thesis is entitled “RENEWABLE ENERGY FOR DESALINATION PROCESS: EFFICIENCY AND ENVIRONMENTAL IMPACTS IN A TROPICAL ISLAND USING DIGITAL TOOLS”
Title page of the Williams MPhil thesis
It is an initial project of three years, fruit of collaboration of the TCG•NRG and UWI Mona. This research is innovative for Jamaica and proposes the use of the Reverse Osmosis process to be run with Renewable Energy. The work done took a snapshot of the freshwater and Renewable Energy resource based on up to 50 years of data. Maps of the best locations to produce freshwater based on the Renewable Energy resource (i.e., wind, solar and wave), freshwater need and the impact of the waste aka by-product (i.e., brine) on the coastal environment have been produced for Jamaica. The impacts of a desalination plant powered by Renewable Energy have been evaluated in equivalent carbon dioxide tons saved and volume of sea water needed to dilute the brine produced by the desalination process.
Jamaica has a new Master of philosophy in Applied physics named Zachary Williams. The Thesis will be available for download in the couple of months.
These three years of research set methodology to select:
the type of Desalination process based on the environmental conditions.
the Renewable Energy hybrid farm based on the available resources.
The study allows the conception of a numerical simulator, using among other GIS methods, to evaluate the Renewable Energy production based on historical data. Those tools allow for evaluation of the production of freshwater and waste for the next decades.
One of the main output is the generation of map of the best location a Green Powering Desalination plant (see figure)
From 23 to 26 October Regional Council of Guadeloupe wants to be the convergent point of know-how and techniques for mitigating Sargassum algae effects through the organization of the international conference financed by the European program of regional cooperation InterReg Caraïbe.
The objectives of this conference were presented during the steering committee set up on April 16, 2016 are
better understand the Sargassum phenomenon at the Caribbean level;
share experiences in collection, processing and recovery of algae;
sign on the international political agenda issues of massive sargassum invasion.
The answer to the first point can only come from research and technological innovations. This objective therefore requires a real investment in competent human resources.
The second point raises the question of the effectiveness of methods already tested, all of which have major drawbacks which considerably aggravate the environmental resource. The current level of knowledge is too limited to assess medium and long-term consequences.
The third point, on the other hand, is a pious wish. How politically collaborate to mitigate a phenomenon whose origins and modes of growth, spatial and temporal distribution, are as poorly known. The absence of boundaries and natural barriers when pelagic algae is advected makes it necessary to regulate invasion situations at local scales. The hope of have a turnkey solution rests solely on the convictions of predatory vendors.
A first analysis
Fig. 1: Distribution of subjects in hourly amount during the International Conference Sargassum2019 in Guadeloupe, FWI
The planning for the international conference was unveiled last week (week # 36). Without access to the detailed program, a quantitative analysis can be conducted nevertheless to understand the essence of this conference.
During the four days of that event, we can note the large number of communication actions with the public screening of a documentary , a televised debate, a public debate and a press conference with a total duration of 5h52 min (2h30min + 1h30min + 1h + 52min).
The state of knowledge, reserved to the first day is limited to 3h15min, coffee break included. The rest of the day is planned for the TV debate and presentation of the projects selected for the Sargassum call for projects .
Experience sharing of Friday, October 25th 2019 seems more provided spread over 4h30min, leaving the best place to the case of the Dominican Republic and Mexico, where their main issues are the preservation of sites operated by the tourism industry (>8 M of visitors for 2018 in Quintana Roo -Mexican state- and >6.5 M to Dominican Republic). The rest of the day is reserved for presentation of funding opportunities and the public debate.
The last day dealt with the cooperation to fight sargassum and international strategies during almost 3 hours. We hope that this morning will allow states and territories which are all concurrent in tourism, fishing and marine mining resources, to take stock of the situation put theirs differences other side and share their human resources and knowledges. Announced presence of the Prime ministry of the French Republic, Édouard Philippe, should not change nothing. Despite the Paris Agreement France are doing little choice in favour of nature and public health.
Conclusion
This
succinct analysis gives a vision of the objectives of this
conference, unfortunately far from the TCGNRG vision and
possibly of the resolution of this situation.
It should be remembered what the named Sargassum crisis is in fact an imbalance of nutriments (nitrogen, phosphorus, etc.) across the Atlantic and most of the coastal area which promote the growth of algae. We must noted that during their pelagic phase the growth and reproduction (by cuttings) rates of Sargassum algae is not stopped.
To this
imbalance one must added a structural and intellectual incapacity to
rethink the management of organic matter in an overly industrialized
environmental system.
Sargassum (Sargassum fluitans and natans) have been the main species of visible pelagic floating algae since 2011, stranded on the Caribbean coast. Their stranding are strongly influenced by sea currents and configuration of the coastlines (human making included). Arrival of dense or scattered rafts causes ecological disturbances because of the quantity of organic matter (composed by carbon C, hydrogen H, Oxygen O, Nitrogen N, Phosphorus P and sulphur S) which it brings and the speed of stranding. Rafts of Sargassum move under effects of wind, waves, sea currents and tide. They are home to a wide variety of plankton, fish and shellfish colonies. Sargassum oxygen needs coupled with the poor quality of shallow coastal waters cause asphyxiation and anoxic decomposition -fermentation- generating toxic gases such as hydrogen sulphide (H2S), ammonia (NH3), thiols (R -SH) but also greenhouse gases such as methane (CH4).
These processes of decomposition without oxygen are the subject of many controversies, health, economic and ecological crises. The solutions adopted in the French West Indies are mechanized pickups and emergency dredging, causing extensive destruction of beaches and harbours. The concentrations of two of the most toxic gases (H2S & NH3) are controlled so that populations can be evacuated if there is a risk. Despite measured rates of more than 10ppm H2S (Limit Value-Short-Term Exposure VLCT) no evacuation has been done since 2011.
Remarkable
sites
Many beaches are considered to be
remarkable sites. They attract many visitors and constitute the
tourism potential of our developing countries. The presence of
sargassum causes degradation of bathing water quality, landscape
potential and air quality. These sites, which are highlighted and
exploited by the tourism industry, offer significant profitability
due to the lack of maintenance required to date.
The management of these sites is mostly
complex and is pooling of many stakeholders, but this can not in any
case justify their long-term pollution.
Porte-d-Enfer
Beach
Map describing the configuration of Porte-d’Enfer beach and creek
The
range of Porte-d-Enfer (16.48 ° N, 61.44 ° W) in Anse-Bertrand
(known as the Trou à Man Coco) has been known for the last years of
numerous massive sargassum stranding massive (see photo) provoking
the fact of its geographical configuration the partial or complete
blockage of the creek and a thick layer (more than 15 cm in height)
of decomposed compacted algae. Under favourable conditions the
production of bio-gases takes place on the whole column of wet
Sargassum. It can be observed by the presence of bubbles (under
columns shape) or by the dispersion of biofilms of sulpho-reducing
bacteria greyish colour on the surface.
In these cases of mass stranding (example September 2018, January and July 2019) swimming is impossible and dangerous for health. The presence in the zone (up to 500m) of the basin is risky because the production of biogas is important, non-homogeneous and highly variable. The temperature of the water favours the production of hydrogen sulphide (H2S) and ammonia (NH3) during the sunniest hours of the day (9am-5pm) and therefore the risk during periods of affluence. Time variations such as wind failure or pressure drops favour high concentrations.
Cleaning – mitigating the effects of stranding
The site is naturally cleaned during
the phases of strong increase of swell which warranty a ebb of the
organic matter and the re-oxygenation of the basin.
The rainy season lets in the mouth
which encourages the ebb and feeding of the sand beach.
The mechanized methods of collection
are put in place by the municipality and the services of the French
State are only for small quantity stranded algae. An attempt to set
up a floating dam was a failure. Collection with crawler excavator
help to strongly damaged the beach and nearby roads as well as
pollution from petroleum products (see image of a tractor-excavator).
Manual cleaning stay the more efficient
and ecologically respectful of the site, but unfortunately it is not
set up.
Protection
of populations
There have been 22 surveys of H2S and NH3 since 2018 with 15-minute portable measurements. No measures have indicated overtaking of the limit values for exposure, the maximum values recorded are 1.9 ppm for H2S (24/04/2018) and 36 ppm for NH3 (28/05/2018). We can question the validity of these measures when we know that the potential area of biogas production in case of total coverage is 14,000m2 while stranding areas producing biogas is rarely greater than 5,000m2 in Guadeloupe (case of the fishing port of Capesterre-Belle-Eau). Comments made by users in the area confirm this question.
Nevertheless, these measurements are much higher than the chronic and sub-chronic exposure limits of 0.02 ppm for H2S and 0.714 ppm for NH3 [HCSP 08/06/2018]. The sub-chronic exhibition is an exhibition of one to several months which was the case between March and July 2018 according to the statements published by the ARS Guadeloupe (i.e., Regional Health Agency).
Two last values of H2S measured Thursday, July 18, 2019 and Monday, August 12th 2019 reach respectively 5.2 and 4.2 pm which are alert values (>5 ppm) for workers in French Labour Law.
No signboard is visible to alert passers-by (and tourists) of the health risks during periods of beaching and fumes of toxic gas. Without knowledge of the site, many passers-by, children and the elderly, admire the stranding without taking into account the serious health risk.
In
the case of the crisis of green algae (Ulva aka sea-lettuce) of
Brittany it took nearly ten years, dead wild boars, horses, dogs and
several joggers before appearing on the beaches of official
information boards.
It
is therefore urgent to recognize that human health is worth more than
the reputation (or image) of a tourist site. It is essential that the
authorities protect people and tourists by intelligently informing
about the non-permanent risk of stranding sargassum. This is
particularly true for territories that rely on sustainable tourism
development.
The Caribbean Geophysics and Numerical Research Group (TCGNRG) remains at your disposal to assist you (communities, collection companies and individuals) to secure the best places taking into account environmental conditions.
Last update (9/07/2019)
Municipal decree 8/20/2019
Display area of the decree
Since 20 August 2019 a municipal decree (see photo above) prohibits all nautical activities. This first plain decision of common sense is to be commended. But despite all the poor visibility of the display and the lack of pictogram for people who do not read the French prevents to really warn the risks associated with the presence of anoxic decomposing (fermentation) seaweed for more than two months.
At
the moment the photos were taken an under water spear fisherman was
coming out of the water without noticing the posters
From October 23 to 26, Guadeloupe organizes an event on Sargasso at the regional level (America – Caribbean). At eight (8) weeks of this event let’s make a point of situation.
It should be noted that at least two events have already occurred in 2019 on the subject in the Caribbean area :
Regional Sargassum Forum, Mona Campus, Kingston July 26 2019 Led by Jamaican Ministry of Tourism and the Global Tourism Resilience and Crisis Management Centre (GTRCM)
https://www.sargexpo.fr/
The limited information available nevertheless allows to know that there will be a trade fair Sargass’Expo aiming to gather exhibitors around of (in order of importance)
remote sensing – prevision;
collection;
recovery;
storage;
and health surveillance.
We may be surprised that the sanitary surveillance is thus misplaced, knowing that the main impact of sargassum is first sanitary with olfactory risks (potential complete loss of smell), ocular, cardiac, respiratory, intestinal, etc. In 2018 in Martinique in 31 weeks more than 8500 consultations related to sargassum emanation were counted by the network of sentinel doctors.
The second event is the international scientific conference Sargassum2019. No information is currently available, only the steering committee was presented in April 15, 2019 . The lack of information (i.e. call for communication) and detailed program questions about its progress and the ability to produce useful information for people (residents, schoolchildren, workers, tourists, etc.) and economic actors impacted (fishermen, restaurateur, hotel keeper, sailing sector).
The third event which is Off of sargassum 2019 is a Caribbean Conference, from 19 to 22 October 2019. It is part of the Caribbean Science and Innovation Meeting. It will benefit the presence of some researchers on topics such as Biodiversity, Health,Natural Hazards, Renewable Energy and the Circular Economy. The latter seems much better organized, may produce very interesting results. Deadline for registration is 16 September 2019 Contact the University of Antilles (Research Office).
TCGNRG wonders about the usefulness of using public funds to communicate on a subject where very little to any has been made since 2014. The methods used at this time are re-employment, most often come from construction industry in opposition with concepts of nature protection and biodiversity. The common sense might have been to wait until 2020 to organize a real cross-cutting conference on the topic on at least a week, giving scientists time to be really prepared.
Nevertheless, TCGNRG offer to individuals, institutions and government our services to assess, analyse or comment on information, methods and equipment will be presented during this event.
Green is not only a buzzword is also a working concept which try to fix the gap between Laws of Nature and human activity. Limited resource of earth can only push human being to better and cautiously used energy, mineral matter and organic molecules (i.e., vegetable & animal) matter.
Somes unconscious person think we will be able to find a second planet to exploit quickly, but that won’t be case before long time. It is better for us to focus on what is already available.
This third post of the Jamaican Green Desalination Project explain main feature of a Desalination plant which can be called Green.
A survey is still running to better understand relation between Jamaican and Freshwater. If you have 5 minutes and reside or have resided in Jamaica please help us and answer to the survey on this link
En Guadeloupe, depuis plusieurs mois, voir années, de nombreuses stations d’épuration (très petites, petites ou grandes) sont en dysfonctionnement voir en panne. Elles sont à l’arrêt ou ne fonctionnent que quelques jours par mois. Les eaux usées (c-a-d égout, eau pluviale) sont rejetées sans traitement sur les côtes. Ces rejets peuvent provoquer des dépassements des seuils de pollution durant plusieurs jours.
Les eaux côtières représentent des quantités peu profonde mais capable de diluer la pollution physique (température, particules), chimique (détergent, antibiotique) et biologique (matière organique, bactérie) à l’aide des courants marins et des vagues. L’absence de grandes marées dans les Petites-Antilles limite la capacité des zones côtières à faire tampon aux rejets.
La pollution provoque la diminution de la quantité d’oxygène dissout avec de l’eutrophisation, particulièrement pendant les périodes chaudes (février-août). Sans oxygène les poissons et les herbes marines meurent asphyxiés et la matière organique c’est-à-dire les feuilles, le bois mort, les algues, la matière fécale vont se décomposer en suivant des filières anaérobiques produisant des gaz tel que le méthane (CH4), l’ammoniaque (NH3), le sulfure d’hydrogène (H2S) ou les mercaptans avec des effets sur la santé humaine et l’environnement. Le méthane est un gaz à effet de serre 25 fois plus stable que le dioxyde de carbone (CO2) et le sulfure d’hydrogène provoque des troubles respiratoires et sensoriels (perte de l’odorat) voir la mort en cas de forte exposition. On parle de décès probable pour des concentrations à plus de 500ppm durant quelques minutes ou des problèmes cardiaques avec une exposition quotidienne de l’ordre de 0,05ppm).
Le cas de la station de la place Sarrault dans la commune de Petit-Bourg (voir carte) est inquiétant car à sa panne est associée à des arrivages de sargasses, la présence des effluents d’une seconde usine de traitement d’eaux usées en dysfonctionnement (depuis la Ravine Onze Heure), la présence de zones de mangrove concentratrices de matière organique et la présence de nombreux herbiers marins qui perdent leurs feuilles à chaque forte houle.
Dans
le centre de Petit-Bourg, les effets de la panne de la station
d’épuration sont surtout olfactifs avec l’odeur des eaux usées
associés à la décomposition accélérée des sargasses bloquées
et déchiquetées par les vagues sur la côte, dans les zones de
faibles profondeurs.
Station d’épuration de Sarrault
Les taux de gaz comme l’ammoniac et le sulfure d’hydrogène sont fluctuants du fait l’instabilité du vent à la côte et des températures de l’eau de mer et des effluents. Ils dépassent souvent les limites utilisées pour la sécurité au travail.
Les
autres effets sont liés à la qualité de l’eau et la présence de
bactéries et de toxines. Les bancs sargasse sont des écosystèmes
autonomes autour desquelles de nombreuses espèces de poissons
prolifèrent attirant les pêcheurs amateurs directement dans le
panache des effluents. Le mode de cuisson du poisson aux Antilles
généralement à haute température (c-a-d friture, grillade,
bouillon) limite les risques d’intoxication mais ne l’annule pas.
Il faut espérer que des mesures seront prises pour assurer la maintenance des équipements environnementaux essentiels et garantir la santé publique. Ou au moins informer les populations, sur les risques et conduites à tenir voir interdit la pêche à la ligne dans cette zone.
