In the last week of August 2025, a bizarre and beautiful invasion occurred on the Costa Blanca. The warm, inviting waters of Jávea, Dénia, and Calp were suddenly filled with thousands of floating orbs, transforming the sea into a surreal, otherworldly soup. The culprit? The fried egg jellyfish.

This mass appearance, known as a jellyfish bloom, sparked immediate concern and immense curiosity. Are they dangerous? Why are there so many this year? What does it mean for our sea?

As a local, this guide is here to answer all your questions. We'll dive into the fascinating biology of this harmless creature, explain the perfect storm of environmental conditions that caused this massive jellyfish bloom in Jávea and beyond, and explore what this event tells us about the health of the Mediterranean.

What is the Fried Egg Jellyfish (Cotylorhiza tuberculata)?

The most important fact to know about the fried egg jellyfish is that it is almost completely harmless to humans.

Its scientific name is Cotylorhiza tuberculata, and it is a common native of the Mediterranean. Unlike more dangerous jellyfish, its stinging cells (nematocysts) are very weak and generally cannot penetrate human skin. While sensitive areas like the lips or eyes might feel a mild irritation, most people will feel nothing at all. This is why lifeguards, while vigilant, did not need to raise the red flag.

A Gentle Giant and a Living Nursery

This jellyfish is a gentle giant, often reaching up to 35 cm (14 inches) in diameter. It's a fascinating creature to observe, not least because it often acts as a mobile habitat. Its mild sting and protective bell make it a perfect shelter for juvenile fish, like horse mackerel and jacks, who can be seen darting in and out of its oral arms, safe from larger predators.

How is it Solar-Powered?

One of the most remarkable traits of the fried egg jellyfish is its symbiotic relationship with tiny algae called zooxanthellae, which live within its tissues. These algae photosynthesize, producing energy from the sun and sharing it with their jellyfish host. This "solar power" allows the jellyfish to thrive, giving its bell that distinctive yellowish-white colour.

Why Are There So Many Jellyfish in Spain in 2025? The Perfect Storm

While their appearance in late summer is a normal part of their life cycle, the sheer density of the 2025 bloom was extraordinary. This was caused by a "perfect storm" of environmental factors.

• Record High Sea Temperatures: The intense August 2025 heatwave warmed the coastal waters, creating a perfect incubator. Warmer temperatures accelerate every stage of the jellyfish's life, from the budding of polyps in the spring to the rapid growth of the adults in summer.
• Calm Seas and Lack of Wind: Long periods of calm weather meant that the growing jellyfish population was not dispersed by winds and currents as it normally would be. They remained concentrated in the sheltered bays and coves of the Costa Blanca, leading to the incredible numbers seen from the beaches.

A Bellwether for a Changing Mediterranean

The increasing frequency of large jellyfish blooms is a powerful indicator of broader changes in the Mediterranean ecosystem. Marine biologists point to several long-term factors:

• Decline of Natural Predators: Overfishing has drastically reduced the populations of the fried egg jellyfish's main predators, such as the loggerhead sea turtle and the bluefin tuna. Without these natural controls, jellyfish populations can explode unchecked.
• Coastal Development: The proliferation of man-made structures like marinas and breakwaters has created more hard surfaces on the seabed. These act as unintentional "polyp farms," providing more habitat for the jellyfish to begin their life cycle.
• Pollution and Runoff: Nutrient runoff from agriculture and cities can boost the growth of the plankton that jellyfish feed on, further fuelling their population booms.

The fried egg jellyfish Costa Blanca bloom, while harmless, is a clear and visible symptom of these deeper imbalances.

Suggested Internal Link: The fried egg jellyfish is harmless, but other visitors are not. Read about the [Blue Dragon that forced beach closures earlier this month].

The Human Reaction: From Alarm to Natural Wonder

The initial reaction to the swarm of jellyfish was one of caution. But once the Cruz Roja lifeguards and local authorities confirmed the species was not dangerous, the mood on the beaches of Dénia, Jávea, and Calp shifted from alarm to fascination.

The bloom became a unique natural spectacle. Snorkelers were treated to beautiful underwater scenes, and the event became a talking point and a shared experience for thousands of locals and tourists. It served as a massive, impromptu biology lesson, sparking conversations about marine life and the health of our sea.

Suggested External Link: You can contribute to tracking jellyfish by using citizen science apps recommended by the Marine Institute of Spain (IEO-CSIC).

Frequently Asked Questions (FAQ)

Q1: Are the fried egg jellyfish on the Costa Blanca dangerous?

A1: No, the Cotylorhiza tuberculata, or fried egg jellyfish, is considered harmless to humans. Its sting is very weak and generally not felt, though it's always best to avoid touching any marine life.

Q2: Can you swim with fried egg jellyfish?

A2: Yes, it is generally safe to swim in the water with them. The authorities did not close the beaches, often only raising the yellow flag (Bandera AMARILLA) as a general caution. However, the sheer number of them could be unpleasant for some swimmers.

Q3: Why are they called "fried egg jellyfish"?

A3: They get their name from their distinctive appearance. They have a high, central, brownish-orange dome that looks like an egg yolk, sitting on top of a flattened, whitish bell that resembles a cooked egg white.

Q4: How long will the jellyfish bloom last?

A4: These late-summer blooms are a natural part of the jellyfish's life cycle. They typically last for a few weeks. As the water begins to cool in the autumn, the adult jellyfish will die off, ending the bloom until the next year.