SMHI mapping of jellyfish

Have invading comb jellies spread to the Baltic? Do jellyfish eat zooplankton that would otherwise feed fish? How do jellyfish affect the food chain? BAZOOCA (Baltic Zooplankton Cascades) is a research collaboration between countries around the Baltic to find out how changes in jellyfish stocks affect the food chain in the sea.

SMHI has also started mapping the extent of jellyfish in the southern Baltic, the Kattegat and the Skagerrak. The work started following an increased awareness of the important role of jellyfish in the ocean ecosystems and the introduction of a new species in northern European waters – the warty comb jelly scientifically known as Mnemiopsis leidyi.

The warty comb jelly

Origin and spread

These small carnivorous animals originally come from the US east coast. They do not sting but are very greedy and periodically occur in very large numbers. They eat zooplankton, including fish eggs and small fry and this huge consumption can decimate the population of important zooplankton groups.

The warty comb jelly has previously spread to both the Black Sea and the Caspian Sea, where it contributed to the crash of economically important anchovy fisheries. In these areas it is feared that jellyfish can have started a chain reaction capable of spreading all the way up the food chain to the Caspian seal. The Black Sea and Caspian Sea are quite similar to the Baltic and there is concern about the effects of the comb jelly if it multiplies and spreads in our northern waters.


The warty comb jelly was first observed in Swedish waters in 2006. It was probably introduced accidentally after travelling in the ballast water of a ship. An adult grows to 1–10 cm long and large numbers have been recently observed along the west coast during late summer. Since these jellyfish are hermaphroditic and can fertilise themselves they are able to reproduce quickly if conditions are right. They can survive in both salt water and brackish water.
More information about the warty comb jelly:

The BAZOOCA project follows jellyfish

BAZOOCA (Baltic Zooplankton Cascades) is a project that is part of the larger BONUS Baltic programme, financed by organisations including the Swedish Research Council FORMAS, the Swedish Environmental Protection Agency and the EU. Since jellyfish can have a significant effect on fish stocks the Swedish Board of Fisheries is also interested in the results.

Measurements of the extent and volume of jellyfish are necessary to calculate their effect on the ecosystem in the waters around Sweden. SMHI is the largest Swedish producer of marine environmental data and thus has a logical role in the project. By combining the jellyfish research cruises with SMHI’s routine sampling expeditions, the project has made efficient use of resources, and collaboration between SMHI personnel and university researchers has been strengthened.

During 2009 - 2010 year, scientists from Göteborg University and Denmark’s Technical University have participated in SMHI’s monthly expeditions where they complement the ordinary sampling with measurements of jellyfish and the optical properties of seawater.

BAZOOCA homepage