Jellyfish in the Mediterranean: what every sailor should know

Jellyfish are one of the most fascinating and most visually striking sea creatures. But it is very different if you are admiring their colourful allure or afraid to jump into the water because they are everywhere. The fact is that not all jellyfish are harmless. Some can cause painful stings that may require immediate first aid and in the warmer months getting stung by one in the Mediterranean is relatively common.

Jellyfish are a potential threat to all passionate swimmers, sailors, and those who enjoy open water bathing. But jellyfish are neither as aggressive nor as harmful to human life as many people think.
Check out these interesting facts associated with this living organisms:

• They are believed to be the oldest living creatures on the planet.
• The species diversity among jellyfish is remarkable, with over 2,000 different species, some of which are still unidentified.
• The most prevalent and recognized species among jellyfish is the orca, which boasts a signature umbrella-like shape and distinctive movements. Some of these species have bioluminescent capabilities, allowing them to glow in the dark. Their sizes vary dramatically, from a few centimetres to as much as five metres in diameter.

The Mediterranean Sea is home to many different species of jellyfish and their abundance is influenced by many factors such as climate, sea condition and water temperature. In the Mediterranean, jellyfish are more common in the warmer months, especially from May to October, which coincides exactly with the peak of the sailing season.

At the same time, however, the occurrence of jellyfish in the Mediterranean is quite unpredictable and can vary considerably from year to year. While some areas of the world have jellyfish year-round, such as the Gulf of Mexico and some parts of the Pacific Ocean, the occurrence of jellyfish in the Mediterranean is more seasonal.

In general, jellyfish tend to be more abundant in the Mediterranean during the summer months when water temperatures are higher and there is more sunlight for plankton to grow and feed on.

The exact timing and location of jellyfish can vary from year to year and is difficult to predict so it's always a good idea to check with local authorities or lifeguards for information on the presence of jellyfish in a particular region.

The abundance of jellyfish in the Mediterranean Sea can be influenced by a number of factors, in particular water temperature, nutrient levels and weather. There are places where they are more frequently encountered, but nowhere is it a year-round problem. Despite this, jellyfish overpopulation needs to be addressed globally.

Jellyfish thrive best in warm water, so areas with higher water temperatures are also more likely to have higher concentrations. In the Mediterranean, temperatures vary depending on the season and location. In some areas, such as the southern coast of Spain, the water may be warm all year round, while in other areas, such as the north coast of Italy, may be warm only in the summer months. This is reflected in the number of jellyfish.

Jellyfish feed on small marine organisms such as plankton, so in areas with higher nutrient levels, jellyfish concentrations may be higher. Nutrient levels may be influenced by coastal run-off, agricultural processes or ocean currents, which can often bring jellyfish into an area.

Storms and other weather events can affect the distribution and concentration of jellyfish in the Mediterranean Sea. For example, strong winds may push jellyfish closer to the coast, while calm weather may allow them to spread more widely. Their distribution is therefore also dependant on the weather and how it changes.

Jellyfish are found in various countries surrounding the Mediterranean Sea:

Greece: Several species of jellyfish are found in the Aegean and Ionian Seas, including the moon jellyfish (Aurelia aurita), the mauve stinger (Pelagia noctiluca — also known as the purple or night-light jellyfish) and the barrel jellyfish (Rhizostoma pulmo). While the moon jellyfish is harmless, the mauve stinger and the barrel jellyfish are poisonous and can cause painful stings. The mauve stinger is usually found in Greek waters from June to September, while the barrel jellyfish can be found between May and August.

In recent years, the countries around the Mediterranean have been facing a very serious outbreak of these purple jellyfish. The situation was most serious in Greece, but it was far from being a local problem. Experts have pointed to rising sea temperatures and overfishing as the reason, but it has also been suggested that a lack of rain is contributing to the jellyfish's presence. During the dry season, freshwater levels in the sea drop, causing a thermal imbalance between the waters off the coast and in the open sea.

It is the mauve stinger is the jellyfish that most often plagues the Mediterranean Sea and their long tentacles can deliver a very painful sting. Here, their beauty is truly dangerous. These jellyfish change colour during their lives — while in adolescence they are orange-brown, in adulthood they take on a striking purple or pink colour. They have a bell-shaped body with long, thin tentacles and their distinctive pinkish-purple colour makes them truly beautiful but dangerous creatures.

Although the mauve stinger is relatively small, between 3 and 12 centimetres, it has very long tentacles with which it can span up to 2 metres. As Epaminondas Christou, director of research at the Oceanographic Institute of the Hellenic Centre for Marine Research (HCMR), said last year: "The purple jellyfish is a pelagic species that breeds in the open sea and drifts with the currents to the coasts and beaches. The purple jellyfish is found throughout the Mediterranean Sea, although the persistence in Greek waters suggests that the Aegean Sea may be a breeding ground. Rising sea temperatures are increasing its reproduction rate. On the other hand, the decline of the pelagic fish that feed on them gives the jellyfish a breeding ground. The same applies to the declining numbers of turtles, which are their main predator."

The Mediterranean Sea is home to several species of jellyfish, some of which can be harmful to humans. In addition to Pelagia noctiluca, other common species of jellyfish found in the Mediterranean are:

Aurelia aurita or moon jellyfish is a translucent jellyfish that is also commonly found in the Mediterranean Sea in large numbers. It has a translucent saucer-shaped body with short, powerful tentacles and can range in colour from white to pale blue. Although its sting is not usually harmful, it can cause mild skin irritation.

The occurrence and abundance of jellyfish is difficult to predict because it varies from year to year. However, first aid guidelines for jellyfish stings are important to know when sailing on a yacht.

Jellyfish contact with bathers is usually only incidental, but when it does occur it can be very painful. Stinging cells, called nematocysts, present in the tentacles release filaments that contain venom. The composition of this venom varies from species to species, but in general it is a mixture of proteins and enzymes, along with other stinging agents and neurotoxins that cause pain and paralysis. Each of these elements contributes to the neurotoxic and cardiotoxic properties of the venom.

You may experience a burning sensation, pain and in some cases an allergic reaction when stung by a jellyfish. The severity of the sting depends on the species of jellyfish, the amount of venom injected and the person's reaction to the venom.

Immediate burning from the sting is usually accompanied by swelling and redness. In extreme cases, a severe allergic reaction to the toxin can occur, causing anaphylactic shock that can lead to respiratory failure or drowning of the victim.

If you are stung by a jellyfish, it is important to seek medical attention, especially if the symptoms are severe or if you develop an allergic reaction.

Steps to take when stung by a jellyfish:

1. Definitely avoid scratching. This can activate some of the jellyfish's toxic cells, which still remain inert on our skin.
2. Definitely don't rub the area with a towel or sand.
3. Don't douse the site with fresh water.
4. Rinse the injured area with seawater. Although some sources recommend urine, the safest thing to do is to rinse the site with vinegar. Vinegar is a weak acid and prevents nematocysts from "exploding" on the skin and causing further pain.
5. Cold compresses are recommended for 15 minutes to relieve the symptoms of poisoning
6. In case of intense pain, administer antihistamines such as diphenhydramine.
7. The use of corticosteroid ointments or sunscreen, as well as a homemade mixture of baking soda and water, can also relieve inflammation. Usually, the wound caused can last 24 to 48 hours.

Predicting the occurrence of jellyfish in the Mediterranean, as we have already mentioned, can be challenging because it varies from year to year. However, there are some sources that can help us to get a handle on the current situation.

Local websites, such as the Hellenic Centre for Marine Research, can provide information on the occurrence of jellyfish in Greece. Similarly, the Spanish Marine Biology Research Group provides information on the occurrence of jellyfish in the Mediterranean Sea.

In addition, there are apps to help you monitor the jellyfish in the Mediterranean. For example, the Ibiza Jellyfish App provides information in the waters around Ibiza. Another app, called Jellywatch, allows users to upload photos of jellyfish sightings to help track their movements.