Marine algae can emit strong odors due to the chemical compounds they produce, such as organic sulfides, terpenes, and amines. These substances can be released in greater quantities when the algae decompose or during low tides, contributing to the sometimes intense smell emanating from marine algae.
Marine algae naturally produce certain organic substances to protect themselves from predators or external aggressions. When stressed or decomposing, they release more of these highly odorous molecules. Among these compounds is dimethyl sulfide (DMS), a gas that smells somewhat like rotten cabbage or spoiled eggs, and which gives beaches their sometimes strong and unpleasant characteristic odor. These powerful smells also serve to repel certain marine organisms or to attract other living beings that are beneficial for their defense or reproduction.
When algae smell strong, it is often due to particular chemical compounds that they produce themselves or release while decomposing. Among them is dimethyl sulfide (or DMS for short), a sulfur compound that gives off that famous marine odor, sometimes compared to that of boiled cabbage or sweet corn. Other aromatic stars include compounds called amines, which smell unpleasantly like rotten fish, and certain iodinated derivatives that contribute to that characteristic "ocean smell." It is this specific chemical cocktail that you smell when passing by a pile of algae drying in the sun.
When algae die and begin to decompose, their cells release all sorts of chemical compounds. Among these compounds, there is mainly sulfur. This sulfur is used and transformed by the bacteria present in the sea, which creates particularly odorous substances, such as hydrogen sulfide. You will quickly recognize this gas because it has a smell quite similar to rotten eggs, not really pleasant. The longer the algae remain on the beach, the more they ferment with the help of bacteria, and the stronger and more unpleasant these odors will be.
Water temperature plays a significant role: the warmer the water, the more algae produce and release these strong and characteristic odors. An intense heat period in summer can thus transform a usually quiet beach into an olfactory festival. Salinity also changes the game. Concentrated salty waters facilitate the development of powerful odor compounds. Light intensity acts similarly: high brightness stimulates algae growth, accelerates their life cycle, and boosts their ability to release odoriferous molecules. Pollution and nutrient runoff from human activities further increase the presence and decomposition of algae, significantly amplifying the olfactory phenomenon.
Many microorganisms, including bacteria and fungi, naturally inhabit marine algae. These tiny creatures feast on decomposing dead algae and release various foul-smelling gases during their banquet. Among them, hydrogen sulfide is often found, which has a particularly unpleasant rotten egg smell, as well as other sulfur compounds like dimethyl sulfide, responsible for the typical sometimes pungent marine odor. The more these microorganisms multiply, the more they produce these volatile substances, making certain beaches particularly odorous at low tide.
The strong odor emitted by decomposed seaweed on the beaches sometimes acts as a natural alert, signaling to visitors the presence of an excessive algal bloom, known as a green tide, which may pose health risks.
Marine algae emit a substance called dimethylsulfoniopropionate (DMSP), which plays a key role in the marine sulfur cycle. This substance is partly responsible for the characteristic smell of sea air.
The typical smell associated with the sea – often described as fresh or salty – actually mainly comes from the chemical compounds produced by algae and associated microbial organisms!
Many species of seabirds use the smell of dimethyl sulfide (DMS), released by certain algae, to locate their feeding grounds and identify areas rich in fish.
The growth of algae is favored by certain environmental conditions such as high temperatures, prolonged sunlight exposure, and nutrient inputs from waterways and agricultural runoff. As a result, certain seasons, particularly summer, often experience increased algae proliferation that leads to strong odors.
Yes. Even though the smell may be unpleasant for humans, seaweeds play an important ecological role. They provide habitat for marine species, contribute to carbon fixation, and serve as an essential nutritional resource in the food chain of coastal ecosystems.
The most effective way is to quickly remove the stranded seaweed. Some communities use specific equipment such as seaweed screeners or gatherers. Aerating the sand and regular cleaning also help to limit the intensity of odors by reducing fermentation.
Heat, low oxygen levels, or a poorly renewed bath of stagnant water promote the rapid decomposition of algae. Such conditions accelerate microbial and chemical processes that release compounds responsible for strong unpleasant odors.
Yes, not all algae necessarily emit a strong odor. In fact, fresh and living algae often have little to no smell. It is mainly those in an advanced state of decomposition, covered in microorganisms, that produce these unpleasant characteristic odors.
In general, unpleasant odors from marine algae are not directly dangerous to health. However, large quantities of algae that are fermenting can produce irritating or toxic gases in certain specific cases. Therefore, it is advisable to avoid lingering near large masses of decomposing algae.
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