Are jellyfish blooms truly increasing, or is it just our imagination? Here is what marine scientists are discovering.

A post from the Weekly Jellyfish Blog Series

In recent years, it seems like everyone is talking about an increase in jellyfish blooms. Beaches are being closed, fishing nets are clogged, and swimmers hesitate to enter the water.

But is there truly an increase in jellyfish numbers, or is it just a temporary impression? To answer that, we have to look past the human calendar and understand a creature that has been swimming in our oceans for nearly half a billion years.

Natural Cycles vs. A Changing Ocean

It is important to understand that changes in jellyfish populations cannot be measured based on a single year.

The most comprehensive long-term study on jellyfish occurrence was conducted along the coasts of France. Data collected at the Oceanographic Center of Monaco—one of the world’s earliest marine research institutions—enabled scientists to track the Mauve Stinger jellyfish for more than one hundred years.

The conclusion: Significant population blooms naturally occurred in cycles of approximately ten years. In other words, “a sudden year with many jellyfish” is a normal, natural phenomenon.

DID YOU KNOW? Jellyfish are the ultimate survivors. They can be found in all marine environments, from warm tropical seas to the freezing depths beneath kilometers of Arctic ice.

However, this is where the story changes. In recent years, there has been broad agreement among marine research laboratories worldwide: jellyfish blooms are indeed increasing beyond their natural cycles. The same jellyfish that once appeared in large numbers only every decade now appear at the beginning of summer almost every year.

The sea is becoming more “gelatinous.”

The Main Culprit: Overfishing

While climate change and warming waters play a role, the most widely accepted explanation for the rapid rise in jellyfish populations is overfishing.

Here is how the ecological imbalance works:

1. Less Competition: Edible fish and jellyfish often compete for the same food source: zooplankton. When commercial fishing removes massive amounts of these fish from the ecosystem, an abundance of food is left behind for the jellyfish.

2. Rapid Reproduction: With unlimited food, jellyfish reproduce at astonishing rates.

3. The Death Spiral for Fish: As jellyfish numbers explode, they begin eating the eggs and larvae of the remaining fish.

This creates a reinforcing cycle that strengthens jellyfish populations while devastating fish stocks. The extreme result is an ecosystem dominated by jellyfish rather than fish—a phenomenon scientists refer to as a “gelatinous sea.” In regions where overfishing is severe—such as the South China Sea, the Mediterranean, West Africa, and the northeastern United States—scientific agreement confirms that jellyfish blooms are permanently on the rise.

The Black Sea Collapse

The most famous example of this ecological shift occurred in the Black Sea. Gelatinous organisms (specifically a type of comb jelly) took over the ecosystem to such an extent that the local anchovy fisheries completely collapsed. This led to the devastation of the fishing industry and the abandonment of historic fishing villages along the coast.

Global Migration: The Ballast Water Problem

Beyond overfishing, human activity is physically moving jellyfish into brand-new territories.

When a massive cargo ship is empty of cargo, it pumps seawater into its “ballast tanks” to maintain stability. This water often contains various microscopic stages of the jellyfish life cycle (like the planula or polyp stages we discussed in previous blogs).

After crossing an ocean, the ship discharges this ballast water in another port, releasing the jellyfish into a completely new environment without natural predators. Because of this, massive new blooms have been documented along coastlines in the Mediterranean and Brazil where they had never previously existed.

What Does This Mean for Beachgoers?

The sea is changing. In places where the ecological balance is disrupted, jellyfish are simply filling the vacuum. They were here long before us, and they will undoubtedly remain long after us.

While we must support global efforts to protect marine balance and reduce overfishing, we must also adapt to the reality of the ocean today. Knowing how to enter the sea safely and responsibly is more important than ever.

You don’t have to abandon the beach just because the ocean is changing. Safe Sea is clinically proven to deactivate the stinging mechanism of jellyfish, allowing you to share the water safely with these ancient survivors.

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