Spreading and reproduction limitations of the American comb jelly Mnemiopsis leidyi in the Baltic Sea

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1 Not to be cited without prior reference to the author ICES CM 2010/K:07 Spreading and reproduction limitations of the American comb jelly Mnemiopsis leidyi in the Baltic Sea Maiju Lehtiniemi 1*, Andreas Lehmann 2, Jamileh Javidpour 2 and Kai Myrberg 1 1 Finnish Environment Institute, Marine Research Center, P.O.Box 140, FI Helsinki, Finland *Contact author: maiju.lehtiniemi@ymparisto.fi, phone: Leibniz Institute of Marine Sciences, Duesternbrookerweg 20, Kiel, Germany Extended abstract Based on the information on salinity and temperature needed for survival and reproduction, areas within the Baltic Sea have been identified where the American comb jelly, Mnemiopsis leidyi could potentially survive and reproduce. In addition physical drift modeling has been used to investigate the potential dispersion of Mnemiopsis with the assumption that the invasion occurred via advection from the Kattegat through the Danish Straits into the western Baltic Sea. In the low saline surface layer the dispersion is mainly driven by the wind, in the lower saline layer the dispersion is controlled by the baroclinic flow field and bottom topography. Model runs showed that the natural spreading via deep water currents from the Bornholm Basin where it presently occurs, towards north and east is limited by topographic obstacles and low advection velocities. However, if Mnemiopsis would be transported in the ballast water of a ship to the northern latitudes it might survive but not reproduce in a sufficient rate to establish a new population. Thus due to combined effects of low salinity and low temperature it is not probable that Mnemiopsis could establish permanent populations in the central or northern Baltic Sea. It seems that Mnemiopsis could only reproduce at higher rate in the southern parts of the sea. If under climate change the salinity in the Baltic Sea will further decrease the establishment of Mnemiopsis would be even less probable in the north although water temperature would increase. Keywords: American comb jelly, Baltic Sea, physical factors, reproduction, survival, drifting The most important global pathway for new species introductions is ship traffic including transfers by both ballast water (and sediments) and ship fouling (Molnar et al. 2008). Shipping is very effective in species transport due to easy overcome of natural dispersal barriers e.g. too saline or cold water in the open ocean. It is important to note that over 80 % of all marine introductions have been unintentional and 31 % of the marine introductions have happened via ballast waters of ships (Molnar et al. 2008). After establishment a non-indigenous species may also spread further from the primary site of introduction via a combination of natural dispersal and human-associated transport mechanisms. Currents and related drifts are among important natural dispersal pathways, which transport particles and organisms both vertically and horizontally, and may serve as a pathway for secondary spread for alien species as well. The Baltic Sea is one of the largest brackish seas in the world. It is a semi-enclosed basin connected to the main Atlantic Ocean only via the Danish Straits. The water exchange through these straits is limited, and as a consequence of the positive freshwater balance the Baltic Sea water mass is brackish, with mean salinity of about 7 one fifth of the salinity of normal ocean waters (Fig. 1.). All euryhaline and eurythermal species are potential invaders to the Baltic Sea. Since most originate from

2 warmer areas, global warming can be expected to increase future invasions (e.g. Paavola et al. 2005). However, the ability of these species to survive and reproduce in low salinity is a key factor to determine their invasion success. Figure 1. Bottom salinity measured on R/V Aranda in June 2009 and Mnemiopsis leidyi observations. The northern and easternmost areas (blue squares; Haslob et al. 2007, Huwer et al. 2008, Janas and Zgrundo 2007) and stations (blue dots; observations done on R/V Aranda 2010) where M. leidyi has been observed and stations where it has not been observed (red dots) in the Baltic based on observations of adult individuals with lobes or genetic analyses. The stations for temperature-salinity plots are included in the map. One of the recent invaders is the American comb jelly, Mnemiopsis leidyi A. Agassiz 1865, which has caused large ecosystem perturbations in the Black Sea and the adjacent areas (Vinogradov et al. 1989). The first records of M. leidyi in northern European waters were made in 2005 in Oslofjorden, Norway (Oliveira 2007), then later in the North Sea, off the western coast of the Netherlands (Faasse and Bayha 2006), and on the Swedish west coast, in Skagerrak and in the Kiel Bight, southern Baltic Sea in autumn 2006 (Javidpour et al. 2006, Hansson 2006). In it was widely distributed in the Danish waters (Tendal et al. 2007). The species is easily identified from other ctenophores when the lobes have been developed, which are characteristic for adult specimens. However, small individuals i.e. cydippid stage larvae are difficult to identify to species without applying genetic methods (Gorokhova et al. 2009). This identification problem led to confusion to widely think that M. leidyi has spread to almost the whole Baltic Sea (e.g. Lehtiniemi et al. 2007). However, based on genetic analysis the species occurring in the central and northern Baltic Sea is proved to be an arctic comb jelly (Mertensia ovum) (Gorokhova et al. 2009). In light of the new accumulating genetic evidence it seems most probable that M. leidyi has not been found north or east of the Bornholm Basin and the Bay of Gdansk (Fig. 1). Although showing wide tolerance to physical parameters, M. leidyi is clearly close to the limit of its occurrence in such conditions where both salinity and temperature are near the lowest tolerance limits. To be able to establish permanently, M. leidyi should be able to reproduce, which

3 requires better environmental conditions compared with the conditions in which it survives. The aim of this study is to identify most probable areas where M. leidyi could disperse, survive and furthermore reproduce in the Baltic Sea with respect to circulation and hydrographic conditions. Baltic Sea Ice-Ocean Model (BSIOM) -the numerical model, used in this study, is a general threedimensional coupled sea ice-ocean model of the Baltic Sea (Lehmann and Hinrichsen 2000). The coupled sea ice-ocean model is forced by meteorological data taken from the Swedish Meteorological and Hydrological Institute (SMHI Norrköping, Sweden) meteorological database (Lars Meuller, pers. comm.) which covers the whole Baltic drainage basin on a regular grid of 1 x 1 with a temporal increment of 3 hours. The database, which for modelling purposes is further interpolated onto the model grid, includes surface pressure, precipitation, cloudiness, air temperature and water vapour mixing ratio at 2 m height and the geostrophic wind. BSIOM has been run for the period starting from an existing model run covering the period Three-dimensional fields of temperature and salinity as well as the current field have been extracted as daily averages from the model to be further used in a Lagrangian particle tracking model (Hinrichsen et al. 1997). Thus, circulation and drift track model are operated subsequently. Drifters were released in two areas where Mnemiopsis leidyi was reported to occur in May and November 2007: Bornholm Basin and Stolpe Channel (Fig. 2.). All drift experiments run until the end of the year To be able to predict the invasion and survival possibilities of M. leidyi in the central and northern Baltic Sea we searched salinity and temperature information from certain port areas, which could be either source or destination ports in the translocation of this species via ship's ballast water (Table 1). Table 1. Details of the ports chosen for the port survey. Port Country Source / destina tion Rotterdam Port Gothenburg Port Port of New Orleans The Netherlands S Description of the port Largest seaport in Europe with an annual throughput of more than 400 million tons of goods Sweden S Largest container terminal in the Nordic region Alabama, USA S Most visited US port in 2009 by the ships which transport cargo directly to Finnish (northern Baltic) harbors Primorsk Port Russia D Largest port in the Baltic by export volume Klaipeda Port Lithuania D 8 th largest port by export volume Tallinn harbour Port Kokkola of Estonia D Third largest port by traffic volume as well as by export volume in the Baltic Finland D 15 th largest port in the Baltic by transported dry bulk volume Mnemi present Yes Location North-eastern coast of the Atlantic Yes In a transition area between the North and Baltic Seas Yes In the native area of M. leidyi on the western coast of the Atlantic No No No Eastern end of the Gulf of Finland Eastern coast of the central Baltic at the mouth of the Curonian lagoon Southern coast of the Gulf of Finland Reference Faasse Bayha 2006 & Hansson et al Purcell et al. 2001, Statistics of FTA Saurama et al Saurama et al Saurama et al No Bothnian Bay Saurama et al To identify typical temperature and salinity conditions of the different sub-basins of the Baltic Sea (stations marked in Fig. 1) we used TS-diagrams (modified form Leppäranta and Myrberg 2009).

4 Experiments to determine egg production and larval survival at different salinities were conducted in the laboratory. Experiments were done at five salinity levels (5, 10, 15, 20 and 30 ) representative for the Baltic Sea gradient and at 18 C temperature. Adult Mnemiopsis leidyi (ca 2 cm) were sampled from Kiel Fjord during summer 2008 for the experiments. Figure 2. Patterns of dispersal of Mnemiopsis leidyi in the central Baltic Sea by using the Lagrangian particle-tracking model. Launching positions of drifters (black circles in squares) released in May 2007 (upper panel) and November 2007 (lower panel) in the area where M. leidyi is known to occur and end positions (red circles) in December Colors denote sub-basins of origin: green (Bornholm Basin) and yellow (Stolpe Channel). In May the drifters were launched from m and in November from m depths according to the observations (Haslob et al. 2007, Huwer et al. 2008). The drifters released in areas and water column parts where Mnemiopsis leidyi is reported to occur in May and November 2007 show that in months time the northernmost drifters end up to the northern Baltic Proper (Fig. 2). However, the majority of the drifters stay in the Bornholm Basin and in the central Baltic Sea. Small part of the drifters turns back with the cyclonic circulation in the eastern side of Gotland. No drifters released in May 2007 end up to the coastal areas, but all stay in the deeper parts of the southern and central Baltic basins. In addition to natural dispersal M. leidyi may spread in ships' ballast waters over the central Baltic Sea to the northern parts. If the ballast water is taken in when the ship leaves the harbors in the east (Rotterdam port) or west (port of New Orleans) coast of the Atlantic it is possible that the salinity difference is too large (even > 30 ) between the ballast water and the ambient water in a Baltic port. This would mean that ctenophores in the ballast water could not survive when discharged to any of the central or northern Baltic ports. The reproduction experiments conducted in different salinities show that M. leidyi produces eggs at a sufficient rate in salinities from 10 to 20 to establish permanently, although in 10 salinities the production rate is significantly lower than in 15 and 20 salinities (Tukey HSD test:

5 p=0.001 and p=0.003, respectively). In 5 or 30 no eggs were produced (Fig. 3). Larval survival was high in salinities ranging from 15 to 30, 10 being the lowest salinity were larvae survived. In 5 no larvae survived. M n e m i o p s i s e g g p r o d u c t i o n N r. e g g s d i n a d -1 y s a l i n i t y M n e m i o p s i s l a r v a e s u r v i v a l -1 % o f l a r v a e s u r v i v e d 6 d a y s a l i n i t y Figure 3. Egg production (number of eggs produced by one ctenophore per day) and larval survival (percentage of larvae survived per day) of Mnemiopsis leidyi in 18 C in different salinities from 5 to 30. Average ± SD. The hydrographic conditions (temperature and salinity) enabling M. leidyi to survive and reproduce in the Baltic Sea are marked in the Temperature-Salinity diagrams for stations in all sub-basins of the sea (Fig. 4). The required environmental conditions for survival are met on all studied stations and subbasins except in the northernmost basin, the Bothnian Bay (station F2), where all TS measurements fall outside the survival range. The salinity and temperature requirements for reproduction are much higher and therefore not met in most of the sub-basins (Fig. 4). The only areas where TS measurements lay inside the range enabling reproduction are in the western Baltic Sea: in the Kiel Bight.

6 Figure 4. Temperature-Salinity plots for stations from different sub basins of the Baltic Sea (starting from the southern and westernmost stations in Kiel Fjord in upper left corner and ending to the northernmost station F2 in lower right corner). Black dots show temperature and salinity measurements taken by CTD on board research vessels (except for Kiel Fjord ). The light blue indicates the temperature and salinity ranges where Mnemiopsis leidyi could survive and light orange indicates the ranges for reproduction.

2006 2007 2008 2009 Figure 5. Maps showing hypoxic: oxygen level between 0-2 ml l -1 (grey) and anoxic: oxygen <0 ml l -1 (black) areas in August 2006-2009.

7 Figure 5. Maps showing hypoxic: oxygen level between 0-2 ml l -1 (grey) and anoxic: oxygen <0 ml l -1 (black) areas in August Oxygen measurements are taken onboard R/V Aranda (Finnish Environment Institute) during HELCOM monitoring cruises. One important factor, in addition to salinity and temperature, influencing survival of M. leidyi is the oxygen content of the water. The strong stratification, which prevents mixing of the water column, causes deep-water anoxia and hypoxia in the central Baltic Sea (Fig. 5). This most probably affects M. leidyi survival during slow drifting from the southern Baltic Sea via deep water currents (Fig. 2).

8 We have shown that the probability for Mnemiopsis leidyi spreading from the Bornholm basin with currents to the central or northern parts of the Baltic Sea is very low due to the combination of short life cycle of these ctenophores, low drift speed near the halocline and large anoxic areas in the central Baltic. The survival of the species -if it would anyhow spread to the north- would be possible although the difficult combination of low salinity, low temperature and low food availability would lower the survival rate. We predict that the only real possibility for M. leidyi introduction would be via ballast waters of ships coming from the southern Baltic when the source population would be already adapted to a more close salinity with northern salinities. The higher requirements of temperature and salinity for reproduction make effective reproduction possible only in the western parts of the Baltic Sea. In the central and northern Baltic Sea the species could not reproduce and thus establish permanent populations. References: Faasse MA and Bayha KM (2006) The ctenophore Mnemiopsis leidyi A. Agassiz 1865 in coastal waters of the Netherlands: an unrecognized invasion? Aquatic Invasions 1 (4): Gorokhova E, Lehtiniemi M, Viitasalo-Frösen S, Haddock SHD (2009) Molecular evidence for the occurrence of ctenophore Mertensia ovum in the northern Baltic Sea and implications for the status of the Mnemiopsis leidyi invasion. Limnol Oceanogr 54(6): Hansson HG (2006) Ctenophores of the Baltic and adjacent Seas the invader Mnemiopsis is here! Aquat Invasions 1(4): Haslob H, Clemmesen C, Schaber M, Hinrichsen HH, Schmidt JO, Voss R et al. (2007) Invading Mnemiopsis leidyi as a potential threat to Baltic fish. Mar Ecol Prog Ser 349: Hinrichsen, H. H., A. Lehmann, M. A. St. John & B. Bru gge, Modelling the cod larvae drift in the Bornholm Basin in summer Continental Shelf Research 17(14): Huwer, B., Storr-Paulsen, M., Riisgård, H. U., Haslob, H. (2008) Abundance, horizontal and vertical distribution of the invasive ctenophore Mnemiopsis leidyi in the central Baltic Sea, November Aquat. Inv., 3, Janas U, Zgrundo A (2007) First record of Mnemiopsis leidyi A. Agassiz, 1865 in the Gulf of Gdańsk (southern Baltic Sea). Aquat Invasions 2(4): Javidpour J, Sommer U, Shiganova T (2006) First record of Mnemiopsis leidyi A. Agassiz 1865 in the Baltic Sea. Aquat Invasions 1(4): Lehmann, A. & H. H. Hinrichsen (2000). On the wind driven and thermohaline circulation of the Baltic Sea. Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere 25: Lehtiniemi M, Pääkkönen JP, Flinkman J, Katajisto T, 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 Aquat Invasions 2(4): Leppäranta M, Myrberg K (2009) Physical Oceanography of the Baltic Sea. Springer-Verlag Berlin- Heidelberg-New York, 378 pp.

9 Molnar, JL, Gamboa, RL, Revenga, C. and Spalding, MD (2008) Assessing the global threat of invasive species to marine biodiversity. Front Ecol Environ 6(9): , doi: / Oliveira OMP (2007) The presence of the ctenophore Mnemiopsis leidyi in the Oslofjorden and considerations on the initial invasion pathways to the North and Baltic Seas. Aquatic Invasions 2 (3): Paavola, M, Olenin, S, Leppäkoski, E (2005) Are invasive species most successful in habitats of low native species richness across European brackish water seas? Estuarine, Coastal and Shelf Science 64 (2005) Purcell JE, Decker MB (2005) Effects of climate on relative predation by scyphomedusae and ctenophores on copepods in Chesapeake Bay during Limnol Oceanogr 50(1): Purcell JE, Shiganova TA, Decker MB, Houde ED (2001) The ctenophore Mnemiopsis in native and exotic habitats: U.S. estuaries versus the Black Sea basin. Hydrobiol 451: Saurama, A, Särkijärvi J, Helminen, R, Holma, E, Hytti, M, Tarkki, V and Haapakangas, E-L (2008) Baltic Port List 2007 Annual cargo statistics of ports in the Baltic Sea Region. University of Turku, Merenkulkualan koulutus- ja tutkimuskeskus, p Tendal OS, Jensen KR and Riisgård HU (2007) Invasive ctenophore Mnemiopsis leidyi widely distributed in Danish waters. Aquatic Invasions 2 (4): Vinogradov ME, Shushkina EA, Musayeva EI and Sorokin PY (1989) A new exotic species in the Black Sea: the ctenophore Mnemiopsis leidyi (Ctenophora: Lobata). Oceanology 29:

Distribution and abundance of the American comb jelly (Mnemiopsis leidyi) - a rapid invasion to the northern Baltic Sea during 2007

https://helda.helsinki.fi Distribution and abundance of the American comb jelly (Mnemiopsis leidyi) - a rapid invasion to the northern Baltic Sea during 2007 Lehtiniemi, Maiju 2007 Lehtiniemi, M, Pääkkönen,