Red tide is a common term for harmful algal blooms, or HABs, which are caused by an overgrowth of microscopic algae. These organisms, often dinoflagellates such as Karenia brevis, can multiply rapidly under certain conditions. While some algal blooms are harmless, others produce toxins that can negatively impact marine ecosystems and human activities. These blooms can last from a few days to several months, affecting coastal environments.
The Distinctive Odor
Red tide often comes with a distinctive and unpleasant smell. Many people describe it as a strong odor similar to rotting fish, decaying seaweed, or a sulfur-like scent, sometimes compared to rotten eggs. This intense odor can travel miles inland. The strength of the odor can vary significantly depending on the severity of the bloom, how close one is to the affected water, and prevailing wind conditions. The actual toxins produced by the algae are odorless, so the smell itself is not a direct indicator of toxin presence.
What Causes the Smell
The distinctive smell associated with red tide primarily originates from the decomposition of marine organisms. When red tide blooms produce toxins, they can cause large-scale die-offs of fish, invertebrates, and other marine life. As these dead animals wash ashore and decompose, they release gases, including hydrogen sulfide, which is responsible for the rotten egg-like smell. Additionally, the microscopic algae themselves, particularly Karenia brevis, contribute to the odor as their cells break down. This process releases various organic materials and volatile compounds into the water, which are then further broken down by bacteria, intensifying the unpleasant scent.
Other Sensory Clues and Visibility
Beyond the smell, several other sensory clues can indicate the presence of a red tide. Visually, the water can appear discolored, ranging from reddish-brown to green, or even remain clear, depending on the specific algal species and its concentration. Dead or dying marine life, such as fish and shellfish, washed up along the shoreline is another sign. In some instances, certain types of red tide algae can also cause the water to glow blue at night, a phenomenon known as bioluminescence, which might be observed before the strong odors develop.
Health Considerations
The primary health concern associated with red tide, particularly blooms of Karenia brevis, stems from airborne toxins. This specific algae produces neurotoxins called brevetoxins, which can become aerosolized when waves break open the algal cells. Inhaling these airborne toxins can lead to respiratory irritation, causing symptoms like coughing, sneezing, and a burning sensation in the eyes, nose, and throat. Individuals with pre-existing respiratory conditions, such as asthma or emphysema, may experience more pronounced or severe reactions. To minimize exposure, it is advisable to avoid affected beaches, stay indoors, and consider wearing a particle filter mask when in areas with strong onshore winds during a bloom.