Does red tide really poison marine life?

(Baonghean.vn) - Red tide is a natural phenomenon that has been observed and documented for thousands of years. However, the sudden increase in this phenomenon in recent years has prompted scientists to reconsider its role.

Sometimes, in areas with relatively shallow water, one can observe the seawater changing color: it can be slightly pink, brown, bright red, orange, purple, yellow, or even turn dark blue or pitch black like sewage water…

That unusual color is due to pigments in the seaweed. When favorable growing conditions arise, some types of seaweed experience explosive growth, causing the seawater to change color.

Why do red tides occur?

The proliferation of microalgae is believed to depend on several factors: sunlight, seawater temperature, and the nutrient content of the seawater.

Red tide – a mesmerizing sight, a natural phenomenon observed for thousands of years. Photo: Internet

Considering natural conditions, the world in general and Vietnam in particular are being affected by the El Niño phenomenon – considered to be the strongest in the past 60 years. Warm ocean currents are causing sea surface temperatures to rise, and coupled with the fact that we are entering an early summer with abundant sunlight, these are favorable conditions for microalgae to thrive.

Meanwhile, human activities and industrial production can also indirectly cause red tides. Domestic and industrial wastewater can be toxic to most aquatic animals but is a rich source of nutrients for microalgae.

Furthermore, maritime transport activities that alter ocean currents can also cause algal blooms, or act as intermediaries in moving algal masses from one sea area to another.

How does red tide affect the ecosystem?

Of the 5,000 species of marine plankton, 300 have the potential to explode in population, causing discoloration of the sea surface – known as red tide. One of the most easily observable phenomena associated with red tide is the mass death of marine life.

However, marine life dies during red tides for a variety of reasons.

In most cases, marine life dies during red tides due to insufficient oxygen in the seawater.When microalgae explode in number, the decomposition activity of bacteria on the algal mass depletes oxygen in the water body, causing the death of marine organisms. In addition, some species of microalgae can damage gills, affecting the respiratory function of marine organisms.

Red tides, caused by non-toxic microalgae, kill fish by depleting oxygen levels but pose no health risks to humans. (Image: Internet)

Therefore, in this case, the marine organisms did not die from poisoning but from lack of oxygen. Consuming these organisms does not lead to poisoning in humans.

Furthermore, among the 300 species of microalgae capable of causing red tides, 80 species can produce toxins, causing deeper and wider impacts on marine ecosystems. Microalgae "poison" the food chain through two pathways:

They produce toxins that directly kill aquatic animals. Some of the "deadly" microalgae commonly mentioned include: Karenia brevis, Noctiluca scintillans, Alexandrium excavatum, etc. The toxins secreted by microalgae can be neurotoxins or heavy metals released through the metal ion exchange process of the algal cells.

In fact, the toxins of the algae Karenia brevis are so potent that they once killed large numbers of manatees in the Gulf of Mexico.

In another instance, microalgae toxins can be absorbed and accumulate in the bodies of some aquatic animals without causing their death.Typically, mollusks such as oysters, clams, mussels, and some species of algae-eating fish are the most ideal intermediate hosts.

When these contaminated organisms are consumed in sufficiently large quantities, it can lead to poisoning in humans and organisms higher up in the food chain.

A warning sign reads: "Do not harvest shellfish; area contaminated by red tide." Photo: Internet

Conclude

Red tide is a natural phenomenon, but its dramatic increase in recent years has prompted scientists to reconsider its role. Human activities may indirectly cause red tides, or they may contribute to the phenomenon, causing broader and deeper impacts on marine ecosystems.

When mass fish deaths occur, suspected to be related to red tide, testing is necessary to confirm the presence of microalgae and identify the species, including whether or not it contains toxins.

To determine the nature of the phenomenon, it is necessary to analyze and identify the species of microalgae causing the red tide. Simultaneously, autopsy and testing of the dead marine organisms are needed to determine the species of microalgae, whether they secrete toxins, and whether the marine organisms died from poisoning or simply from lack of oxygen. Based on this, timely and effective remedial measures can be devised.

Hai Trieu