First records of Mnemiopsis leidyi A . Agassiz 1865 off the NW Mediterranean coast of Spain

The comb jelly Mnemiopsis leidyi was first reported in July 2009 along the Spanish coast of the NW Mediterranean Sea and occurred throughout the summer (last report 26 September 2009). Large numbers of the ctenophore were reported by many participants of the “Medusa Project”. The high concentrations of M. leidyi along the Spanish coast, together with its blooms earlier this year in Israel, suggests establishment in the Mediterranean Sea. This is of great concern because of the well-known effects of M. leidyi on marine ecosystems and the consequences for commercial fisheries.

The introduction of Mnemiopsis leidyi A. Agassiz 1865 is one of the best-documented of a non-indigenous gelatinous species in the Mediterranean and adjacent seas.The native range of M. leidyi is along the Atlantic coast of the Americas (reviewed in Purcell et al. 2001).The species favours shallow estuaries and bays (2 -30 m) and coastal waters.It tolerates temperatures from 0°C in northern locations in the winter to 32°C in the southern estuaries during the summer, and salinities from ≤2 to 38.These environments also have high zooplankton biomasses, ranging from 11 to 200 mgCm −3 , and small copepods predominating the mesozooplankton (Purcell et al. 2001).Following its accidental introduction to the Black Sea in the 1980's, M. leidyi has spread to the Caspian, Baltic, and North seas (Mianzan 1999;Shiganova et al. 2001a;Faasse and Bayha 2006;Javidpour et al. 2006).The first occurrence in the Mediterranean Sea was reported in 1990 in the Gulfs of Saronikos and Elefasis in the western Aegean Sea (Shiganova et al. 2001b).The chronology of M. leidyi presence in the Mediterranean Sea (Galil et al. 2009;Shiganova and Malej 2009) shows an increasing number of observations in recent years.
The "Medusa Project", comprised of a network of organizations, has been monitoring the presence of jellyfish along the entire Catalan coast since 2007.The Catalan Water Agency (ACA), which underwrites the project, records the presence of jellyfish daily at more than 300 beaches covering the 69 Municipalities of Catalonia as part of their routine monitoring program.Inspectors record presence of jellyfish at fixed locations on beaches, in near-shore water, and at a distance of 200 m offshore beyond the swimming zone.The project also involves Emergency Services from 26 of the 69 Municipalities that report the presence of jellyfish daily (ACA 2009), and the Fisherman Associations of Catalonia.As part of the project data on water temperature and salinity are recorded.All the information is summarized on the ACA web page and is available to the public (ACA 2009).
In the summer of 2009, M. leidyi was recorded along the entire length of the Catalan coast and in some other locations along the Mediterranean coast of Spain (Figure 1).We report only the confirmed observations (Table 1).We were unable to confirm many records from other locations along the Catalan coast, but believe M. leidyi may have been commonly distributed.Confirmed records of large swarms lasted from early July to the end of August along the entire coast from Cap de Creus to Alcanar.Mnemiopsis leidyi was recorded also in Denia (Valencia) and in Cabrera (Balearic Islands) (Table 1, Figure 2), where emergency services reported several instances of gelatinous organisms on the beaches during summer 2009.The presence of large numbers of M. leidyi at several locations off the Spanish Mediterranean coast suggests there may have been more than one point of origin.It is unclear whether M. leidyi was transported by currents or ships from other areas of the Mediterranean Sea.
Semi-quantitative data been compiled in the NW Mediterranean on large gelatinous plankton, predominantly the scyphomedusae Pelagia noctiluca Forsskål, 1775, Rhizostoma pulmo Macri 1778, and Cotylorhiza tuberculata Macri 1778 since 2000.The abundance of stranded (beached) jellyfish was classified in three categories: 1 (few, < 10 animals per beach), 2 (many, < 1 medusa m -2 ), and 3 (a lot, > 1 medusa m -2 ) (Gili and Pagés 2005;Gili et al. 2007Gili et al. , 2008)).The ACA beach observation program followed this classification scheme; most of the M. leidyi observations during summer 2009 were in category 3.Although large numbers of M. leidyi were reported off the Spanish Mediterranean coast in July 2009, the ctenophores may have been present earlier but unnoticed until the populations increased.Earlier occurrences of M. leidyi may be established by examination of formalinpreserved plankton samples, as in Purcell (1988).
The observations of M. leidyi along the Spanish coast during summer 2009 coincided with the presence of large swarms of this species along the entire Mediterranean coast of Israel (Galil et al. 2009;Dror Angel pers. com.) and Italy (Boero et al. 2009).Although there are no data that conclusively show that M. leidyi has established permanent populations in Mediterranean waters, the fact that large numbers of M. leidyi occurred along the Mediterranean coastlines of both Israel, Italy and Spain during summer 2009 suggests an established population.
The coastal waters of the Catalan Sea (NW Mediterranean) during the summer months of 2009 (from May to September) were characterized by salinities between 34 and 38.2 and temperatures between 22 and 25ºC.In general, the Catalan Sea is characterized by the presence of a permanent shelfbreak density front defined by salinity differences between oceanic waters and shelf waters.The shelf has high spatial variability due to freshwater inputs from continental runoff that interact with topography and local conditions (Salat et al. 2002).During summer, a clear vertical stratification exists that increases stability of the water column.This situation has important effects on the distribution of nutrients, resulting in increased prokaryotic picoplankton that predominate the biomass of primary producers (Cushing 1989).The areas where M. leidyi was reported were along the coast and were not estuarine.All of these conditions in the Catalan Sea are suitable for M. leidyi, as was predicted by Siapsis et al. (2008), who modelled the potential habitat of the species.
The success of introduced M. leidyi has been attributed mainly to reduced competition due to over-fished populations of zooplanktivorous fish and the lack of predators (Oguz et al. 2008;Siapsis et al. 2008).In the NW Mediterranean Sea, overfishing is believed to be one reason that gelatinous zooplankton seem to be increasing in abundance in recent decades (Gili and Pages 2005).In its native range, M. leidyi is eaten by other ctenophores (Beroe spp.) and scyphomedusae (Chrysaora sp.; reviewed in Purcell et al. 2001).In the Western Mediterranean Sea, the ctenophores Beroe cucumis and Beroe forskalii are abundant (Shiganova and Malej 2009) and can be potential predators of M. leidyi; however, Beroe spp.normally are abundant only in spring and early summer along the Catalan coast (Pagés pers.com.), suggesting that these species were not abundant in the area when M. leidyi occurred in high numbers (July and August 2009).Nevertheless, at the beginning of July 2009, both M. leidyi and Pelagia noctiluca were present in the coastal waters and P. noctiluca ate M. leidyi in the laboratory (Fuentes pers.obs.).In late July 2009, P. noctiluca almost disappeared from the Catalan coast; their absence coincided with high abundances of M. leidyi.The importance of P. noctiluca and other species as predators and competitors of M. leidyi in Mediterranean waters remains to be investigated.
The success of M. leidyi and the consequences for the environment have not been studied yet in Mediterranean waters.The presence and possible establishment of M. leidyi populations could have serious consequences for the Mediterranean ecosystem and fisheries as in other previously-invaded regions (e.g., Purcell et al. 2001;Shiganova et al. 2001a).

Table 1 .
Records of Mnemiopsis leidyi along the Spanish NW Mediterranean coast during summer 2009.ACA is the Catalan Water Agency