Red Tide

What you see in the picture above is not a gruesome pool of blood, but it is a natural phenomenon known as an "Algal Bloom." Algal blooms generate red tide, a phenomenon in which algae become so numerous that they stain coastal waters (hence the name "red tide"). The algae bloom might also deplete oxygen levels in the water and release poisons that make humans and other animals sick.

Although many people refer to these blooms as "red tides," experts prefer to classify them as "harmful algal blooms." One of the most well-known HABs happens nearly every summer along Florida's Gulf Coast. Like many HABs, this bloom is caused by microscopic algae that create toxins that kill fish and render shellfish unsafe to eat. Toxins may also make breathing difficult in the surrounding area. 

Warm ocean surface temperatures, low salinity, high nutrient content, calm seas, and rain followed by bright days throughout the summer months are significant variables causing red tide episodes. Furthermore, red tide-related algae can be disseminated or carried across vast areas by winds, currents, storms, or ships. Red tide is a worldwide phenomenon, but damaging red tide outbreaks have become increasingly pervasive since the 1980s. Higher knowledge of Red tide, better equipment for detecting and analyzing red tide, and nutrient loading from farming and industrial runoff can potentially influence the detection of a spread. France, Guatemala, Hong Kong, India, Argentina, Australia, Brazil, Canada, Chile, Denmark, England, and Ireland have experienced numerous red tide episodes.

Apart from just changing the color of the water, these phenomena do have significant lasting effects. Red tide algae produce natural poisons. It's unclear why these toxins exist, but biomagnification and bioaccumulation processes can make some of them dangerous to larger organisms. Toxins have little effect on grazers like fish and krill, so as they eat the algae, the toxins concentrate and build to a toxic level to organisms that feed on them. Consumption of shellfish during red tide algal blooms robustly correlates with many fish fatalities and various mammalian diseases and deaths. Paralytic and Amnesic Shellfish Poisoning are two such diseases that can afflict people.

Nonetheless, not all algal blooms are hazardous. Instead, most blooms are beneficial since the small plants provide food for marine creatures. They are, in fact, the primary source of energy for the ocean food web.

However, a small percentage of algae generate potent toxins that can kill fish, shellfish, animals, and birds while causing disease in humans. Blooms of non-toxic species that disrupt marine ecosystems are also classified as HABs. For example, when large amounts of algae die and decompose, the decomposing process can reduce oxygen in the water, leading creatures to flee or perish.

Thankfully though,  science has evolved to tackle this phenomenon. Scientists can now better detect and monitor harmful algae blooms because of technological breakthroughs like satellite imaging. Tracking and monitoring red tide algae helps mitigate the algae's detrimental impacts by issuing warnings about eating contaminated seafood and swimming in affected seas.