Over the past few years, fisherman and tourists have reported an increasing number of jellyfish in many coastal areas. Scientists confirmed that the population patterns of jellyfish are changing, and increasing for certain areas.

The regions with a high risk of increase are the east coast of the United-States, the East China Sea, the Sea of Japan and the west coast of southern Africa.

There are about 2000 recorded species of jellyfish. They vary in size and degree of dangerousness.  One of the biggest species of jellyfish, Nomura’s jellyfish, is increasingly appearing in Japanese waters. This giant jellyfish can measure up to 2 meters wide and weight 200 kilograms, and is causing problems to Japanese fishermen as it tends to get caught in their nets.

Along the east cost of America, the moon jellyfish are scaring tourists. While it may be only twelve inches wide and have a subtle sting, there are many beaches that have had to close.

Apparently overfishing is causing jellyfish population to increase. A decreasing population of fish opens new possibilities for jellyfish as there is less competition for food and living space. The fact that they have few predators and are not massively harvested by humans enables their population to grow fast.

Nutrient-rich water runoff, often coming from agricultural processes, enhances algae growth. This rapid increase in the algae population has lead to a reduced amount of oxygen in the water. Many fish cannot live in water with such low levels of oxygen. Jellyfish, however, can. Jellyfish can adapt easily to different conditions.

In other regions however, the jellyfish population are declining. It is the case for the west coast of South America and around Kuril islands (Pacific Russia). There is no clear explanation for these irregularities in the population patterns of jellyfish over the world.

Scientist cannot conclude that there is an invasion before recording the populations over many years. A better understanding about the jellyfish populations is needed; however Jellyfish are not easy creatures to study.

Image courtesy of Creative Commons.

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