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)
In Guadeloupe, for several months, see years, many treatment plants
(micro, small or large) are dysfunctional or broken down. They are
stopped or only work a few days a month. Wastewater (i.e., sewer,
rainwater) is rejected without treatment at the coast. These
discharges can cause pollution , threshold violation can occur for
several days.
Coastal waters represent amounts of shallow water that can dilute physical pollution (temperature, particles), chemical (detergent, antibiotic) and biological (organic matter, bacteria) using sea currents and waves motion. The lack of high tides in the Lesser Antilles limits the ability of coastal areas to buffers discards.
Pollution causes a decrease in amount of dissolved oxygen with eutrophication, especially during warm periods (February-August). Without oxygen fish and seagrass die asphyxiated and organic matter that is to say, leaves, dead wood, algae, faecal matter will decompose following anaerobic pathways producing gases such as methane ( CH4), ammonia (NH3), hydrogen sulphide (H2S) or mercaptan with effects on human health and environment. Methane is a greenhouse gas 25 times more stable than carbon dioxide (CO2) and hydrogen sulphide causes respiratory and sensory disorders (loss of smell) or death in case of high exposure. Probable deaths are reported for concentrations greater than 500 ppm for an exposure of few minutes or heart problems with a daily exposure of around 0.05 ppm.
The case of the station of Sarrault Place at down-town Petit-Bourg (see map) is worrying because its failure is associated with sargassum arrivals, presence of effluents from a second waste water treatment plant malfunctioning (from Ravine Onze Heure), presence of mangrove areas concentrating organic matter and presence of many seagrass beds that lose their leaves with each big swell.
At Petit-Bourg down town , effects of the wastewater treatment plant are mainly olfactory with the smell of wastewater associated with the accelerated decomposition of sargassum blocked and shredded by waves on the coast, in shallow areas.
Sarrault Waste water treatment Plant
Gas rates such as ammonia and hydrogen sulphide are fluctuating due to instability of the wind at the coast and seawater and effluent temperatures. They often exceed the limits used by labour law to define safe spaces.
Other effects are related to water quality and the presence of
bacteria and toxins. Sargassum raft are autonomous ecosystems around
which many species of fish proliferate attracting amateur fishermen
directly into the effluent plume. The method of cooking fish in the
West Indies generally at high temperature (i.e., frying, grilling,
broth) limits the risk of intoxication but does not cancel it.
It is to be hoped that measures will be taken to maintain essential environmental equipment and to ensure public health. Or at least inform the people, about risks and behaviours to hold and if needs ban angling in that area.
Illustration 1 : Oceanographic and Meteorological data for beginning of June 2019
June
1st and 2nd 2019 beaching of sargassum were observed on the
Caribbean coast of Martinique (Fort-de-France, Schoelcher). This type
of beaching has been rare since 2011 and the over-abundance of
drifting sargassum rafts in the North Atlantic and the Caribbean Sea.
Each year one or two beaching are observed on this coast from Fort-de-France to the Prêcheur. They take place only under favourable oceanographic and meteorological conditions.
The breakdown of the Trade Wind felt after the passage of a tropical wave favoured the action of the Southwest currents. Sargassum beds generally extend northward along the Caribbean coast pushed by the East wind and sea currents. This Sunday June 2nd pelagic algae were trapped by the shallow waters of creeks and bays.
In two
days of presence, the decomposition of algae forced their collection
on the small artificialized Cove of Batelière at Schoelcher (500 on
200m), due to emanation of di-oxyde of sulphide and ammonia (SO2,
NH3). This rapid decomposition can obviously be explained by the age
of the rafts that went aground. But also by relatively high water
temperatures (27.9-28.5 ° C) which decreases dissolved oxygen
concentrations in the water of the order of 1 to 2 mg per litre and
therefore anoxic decomposition (i.e., without oxygen ).
The quality of the water is another element to take into account. Only the quality for bathing is continuously monitoring. The last map, published by the Regional Office of Health (ARS), available from (illustration 2) indicates for the beach of Batelière a ‘good’ quality. This measure is misleading because it indicates only the frequency of the presence of certain bacteria of faecal origin but not the capacity of the ecosystem to withstand anthropogenic or natural pollution.
Illustration 2 : Map of Water Quality for Martinique’s bathing of 2018
The
runoff water related to this tropical wave (give a name) to degrade
the quality of the water, on the biological and physiochemical point,
making this area more sensitive to the presence of large amount of
living organism.
It is
essential to take better account of bathing water quality in the
determination of areas exposed to the risk of decomposition pollution
of seaweed-type algae. To better prepare the pickup procedures and
necessary equipment.
TCGNRG can help you design better risk maps for over-concentration of seaweed based on environmental conditions and better organised your organic matter collection and your recovery procedures. Do not hesitate to contact us
