• 17.06.2025

Compass Jellyfish in the Bay of Kotor – Beautiful, but Beware!



Univerzitet Crne Gore
Univerzitet Crne Gore

In recent days, one of the most recognizable jellyfish species of the Mediterranean – Chrysaora hysoscella, also known as the compass jellyfish – has been increasingly observed in the Bay of Kotor. Although it moves gracefully through the water, this species can cause unpleasant skin reactions due to the stinging cells located on its long tentacles.

Its bell is usually 10–15 cm in diameter, but can grow up to 30 cm! It is easily identified by dark radial stripes on the bell, which resemble the points of a compass. Its long oral arms are used for feeding, while the whitish tentacles along the bell margin contain stinging cells (cnidocytes) that can cause redness, pain, and irritation upon contact with skin.

In Montenegro, the compass jellyfish was first recorded in 2006, and since 2013 it has appeared every year, usually from April to early June. This year, it appeared a bit later, likely due to a warm autumn, mild winter, and increased rainfall, all of which influence its life cycle.

Two-stage life cycle:
Chrysaora hysoscella goes through a polyp stage (attached to the seabed) and a medusa stage (free-swimming). The appearance and abundance of jellyfish depend on the development and budding (strobilation) of the polyps.

This species is highly tolerant of temperature fluctuations (from 4°C to 28°C), but salinity plays a more critical role in its reproduction. Weather conditions, rainfall, sea currents, and temperature all affect when and in what numbers jellyfish appear. They are often more visible in bays and inlets, carried by waves and currents.

 What to do in case of contact with a jellyfish?
Do not rinse with fresh water!
Do not touch the affected area with bare hands!

 Rinse with seawater, and carefully remove tentacle remnants using a card or similar object.
 If available, rinse the area with 4–6% vinegar or baking soda dissolved in seawater.
 Apply a cold compress (ice wrapped in fabric, no direct contact with freshwater).
 Use antihistamine creams if needed.
 In case of a stronger reaction – consult a pharmacy or medical professional.

 Please report any sightings of this or similar jellyfish to the Institute of Marine Biology – your observations are important for monitoring marine ecosystems.

Photo: Vesna Mačić

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