Climate change and human activity have impacts that ripple through all ecosystems. Their negative effects can lead to population imbalances across these various ecosystems. While populations of many species are declining because they are unable to survive the rapid environmental changes, this is often not the case for venomous aquatic life like sea urchins and jellyfish. In fact, these populations are increasing across the globe, with damaging effects on other living aquatic organisms and human activity.

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Jellyfish are one of the main types of marine animals that have experienced rapid population growth in recent years. Jellyfish are not actually fish — they are a type of plankton. Instead of swimming, plankton drift through the ocean, pushed by the currents. Jellyfish have been around for 500 million years and are one of the few types of plankton that is visible to the naked eye. Because of their classification as plankton, they are at the bottom of the ocean’s food pyramid and are consumed by seabirds, fish (including sharks), turtles and whales.

Jellyfish can range from about one centimeter to 40 centimeters (0.4 to 15 inches) in size, but some can be much larger. This includes the Lion’s Mane jellyfish which can be up to 1.8 meters (5.9 feet) wide with tentacles stretching over 15 meters (49 feet)!

Related: Europeans eat jellyfish as Mediterranean population spikes

Jellyfish in an aquarium floating

Why are jellyfish populations rising?

Warming oceans

Studies show that over the last century, average ocean surface temperatures have risen by approximately 0.9 degrees Celsius. This increase in surface temperature indicates that, since the 1980s, the ocean has acquired one billion times the heat energy of the atom bombs dropped on Hiroshima and Nagasaki. The excess heat is a result of human-related factors such as industrial activity and pollution that induce global warming.

While 0.9 degrees Celsius still may not seem like much of a temperature increase, it has an immense impact on weather patterns and climate change. This is because warmer surface water evaporates easily and can affect precipitation, humidity and phenomena like cyclones.

These rising sea temperatures also impact aquatic populations. Warming oceans mean that sea creatures can live in areas that have historically been too cold for them to survive. This includes movement towards the temperate regions and even the poles. Through these migrations, these new species may take over the endemic species of that region and cause problems within the food chain. For example, warm-water jellyfish species are typically smaller and less nutritious than cold-water species. This can impact the health of marine life which depend on jellyfish for food.

Marine oxygen levels

As a result of rising temperatures and pollution, oxygen in aquatic ecosystems has dropped by 2% in the last 50 years. While many species struggle to adapt to low-oxygenated environments, jellyfish (unlike other species of plankton) can tolerate them quite well. This is believed to be because of their reduced oxygen use in low-oxygen conditions and their ability to store it in their gelatinous tissues. These physical properties lead to an abundance of jellyfish in these areas and the dominance of jellyfish in low-oxygenated environments compared to other marine species.


Overfishing of certain species has led to decreasing populations of jellyfish’s predators. These include species of fish like tuna and swordfish, which could otherwise help regulate increasing jellyfish populations. There has also been an increase in fishing for the species that have a similar diet to jellyfish, such as anchovies. Without these species to compete with for food, jellyfish populations inevitably increase and overpopulate the ocean.

Jellyfish that look blue and yellow

Why is it a big deal?

Painful stings

One of the reasons why increasing jellyfish populations is harmful is because of their unwanted interactions with humans. As a result of warmer coastlines, large numbers of jellyfish drift to the seashore and can potentially sting humans. In Queensland, Australia, one week in June 2019 alone had a reported number of 13,000 jellyfish stings.

Most of the time, jellyfish stings are more painful than harmful to humans. This is because of venom transmitted through millions of microscopic barbs in jellyfish tentacles. Typically, pain, redness and swelling are localized to the area(s) where the barbs made contact with skin. However, depending on the species and the individual, there can be full-body reactions or symptoms like nausea and headaches.

On the odd occasion, jellyfish stings can be lethal. This too depends on the venom of particular species, such as the box jellyfish. These stings can result in death within a few minutes of contact. Unfortunately, the population of box jellyfish is growing like other species of jellyfish and they are now being more commonly found along coastlines.

Impacts on industries

Besides ruining beach excursions, jellyfish can impact industrial activities situated along the coast. One such example is preventing nuclear power plants from functioning. Nuclear power plants can seawater to cool reactors or desalinate it for purification. Jellyfish can easily disrupt these activities by clogging cooling filters or over-saturating a water supply, which can require these plants to shut down for lengthy periods of time. Instances such as these have occurred in Scotland at the Torness power plant and the Oskarshamn power plant in Sweden.

Another example of jellyfish negatively impacting human activity is by impeding farming and harvesting activities that take place near the shoreline. In Ireland, jellyfish have hindered salmon farming, while in the Caspian Sea, they have prevented beluga caviar farming, thus impacting local livelihoods and trade.

What can we do?

There are a few ways we can prevent the ideal conditions for jellyfish population growth. One example is by limiting global warming and pollution. This can be done by switching to clean energy and practices that do not emit greenhouse gases. Through sustainable practices, ocean surface temperatures can also be regulated at appropriate levels, preventing jellyfish from venturing into warm and/or low-oxygenated environments.

We can also opt for sustainable fishing practices and limit the consumption of fish. In doing so, predatory species can increase in number and assist to regulate jellyfish overpopulation.

Finally, some species of jellyfish are considered edible. This is a potential approach to dealing with the over-abundant populations. Recently, chefs have experimented with this concept and tried incorporating them into gastronomy. Some creations include crunchy “jelly” wafers and sushi rolls.

via World Economic Forum, Forbes, The Economist

Images via Pexels and Shirah Kinder