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The recent aquatic invasive species American comb jelly Mnemiopsis leidyi in the northern Baltic Sea
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Key message
The American comb jelly (Mnemiopsis leidyi) invaded the southern Baltic Sea in autumn 2006, and was found from the northern Baltic in August 2007. The abundances increased until midwinter 2008 in the Åland Sea and the Gulf of Finland. The decrease in the abundances was observed in all sub-basins of the northern Baltic Sea during spring and summer.
Figure 1. The abundances of the American comb jelly (Mnemiopsis leidyi) at three monitoring stations in the northern Baltic Sea during the first year of the invasion. Click image to enlarge.
Results and assessment
Relevance of the indicator for describing developments in the environment
Introduction of alien invasive species (AIS) has been identified as one of the major threats to marine ecosystems causing biodiversity loss and adverse environmental, economic and social impacts from the local level upwards. The Baltic Sea is a young and simple ecosystem, hence vulnerable to ecological changes. For invasive species this gives an opportunity to find a free ecological niche and consequently establish permanent populations. The present eutrophic conditions and rapid expansion in shipping increases the risk of new AIS establishments, increasing the threat to the ecosystem.
Assessment
The most recent invader in the Baltic Sea is the American comb jelly Mnemiopsis leidyi A. Agassiz 1865, which has earlier been transferred unintentionally via ballast waters to the Black and Caspian Seas from the eastern coast of North, Central and South America. It was found for the first time in the southern Baltic in autumn 2006 and a year later in the northern Baltic. During 2008 the abundances have strongly fluctuated being highest in midwinter and lowest in August. However, the August 2008 abundances were 40-60 % higher compared with the abundances of August 2007 indicating adaptation to Baltic Sea conditions.
The highest comb jelly abundances ranged from 800 to 3800 ind m-2 in the Gulf of Finland and the Åland Sea, respectively in January 2008. The densest layers of ctenophores were observed near and below halocline (max 94 ind m-3). The populations have been dominated by larval stages (0.5-3 mm) while adults have been rare. No individuals were found from the Bothnian Bay.
Figure 2. Mnemiopsis leidyi in the central Baltic Sea in January 2008. Photo Jan-Erik Bruun, Finnish Institute of Marine Research.
References
Javidpour J, Sommer U, Shiganova T 2006. First record of Mnemiopsis leidyi A. Agassiz 1865 in the Baltic Sea. Aquat Invasions 4:299-302.
Javidpour J, Molinero J, Peschutter J, Sommer U 2008. Seasonal changes and population dynamics of the ctenophore Mnemiopsis leidyi after its first year of invasion in the Kiel Fjord, Western Baltic Sea. Biological Invasions DOI 10.1007/s10530-008-9300-8
Lehtiniemi, M, Pääkkönen, J-P, Flinkman, J, Gorokhova, E, Karjalainen, M, Viitasalo, S, Björk, H 2007: Distribution and abundance of the American comb jelly (Mnemiopsis leidyi) – A rapid invasion to the northern Baltic Sea during 2007. Aquat Invasions 2(4):445-449.
Leppäkoski E, Gollasch S, Gruszka P, Ojaveer H, Olenin S, Panov V 2002. The Baltic—a sea of invaders. Can J Fish Aquat Sci 59:1175-1188.
Vinogradov ME, Shushkina EA, Musayeva EI, Sorokin PY 1989: A new exotic species in the Black Sea: the ctenophore Mnemiopsis leidyi (Ctenophora: Lobata). Oceanology 29: 220-224.
Metadata
Technical information
1. Data source: The collection and microscopic counting of Mnemiopsis leidyi were made during FIMR research and monitoring cruises in January, May-June and August 2008. The data produced by FIMR is kept at the FIMR database.
2. Description of data: Ctenophores were collected by vertical net tows with a 500 µm WP-2 plankton net mainly in three vertical parts; from the bottom to the halocline, from the halocline to the thermocline and from the thermocline to the surface. The specimens were counted directly after sampling under research microscope to prevent misidentification due to lost body parts and fragmentation.
3. Geographical coverage: Sampling covered the northern part of the Baltic Proper, the western part of the Gulf of Finland, the Bothnian Sea and Bay.
4. Temporal coverage: January, May-June and August 2008.
5. Methodology and frequency of data collection: Samplings were done on three monitoring cruises 2008 during 12 weeks.
Quality information
6. Strength and weakness (at data level): Data covers well the different parts of the northern Baltic Sea although station grid is scarce. The future monitoring of M. leidyi, which would be important in terms of value as an indicator, is not clear yet due to difficulties in proper preservation of the animals.
7. Reliability, accuracy, robustness, uncertainty (at data level): Data gives reliable estimates of abundances of both larvae and adults of M. leidyi, but underestimates the densities of eggs because of the large mesh sized net used.
8. Further work required (for data level and indicator level): The fragility of M. leidyi in the most common preservatives makes the frequent monitoring of the species difficult because the specimens have to be counted fresh immediately after sampling.
Links:
Global Invasive Species database: Mnemiopsis leidyi. http://www.issg.org/database/welcome/
FIMR: http://www.itameriportaali.fi/en/tietoa/artikkelit/ihminen/en_GB/kampamaneetti/
Mnemiopsis video:
For reference purposes, please cite this indicator fact sheet as follows:
[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2008. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.
Last updated: 10 October 2008