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14.3.3 Rhopilema nomadica (Scyphozoa)
W.M. Graham and K.M. Bayha
Another example of Lessepsian invasion (Chap. 5) is the tropical medusa,
Rhopilema nomadica. Recognized by sea bathers as a painful stinger, seasonal
blooms of R. nomadica create problems along recreational beaches of the
eastern Mediterranean (Lotan et al. 1993, 1994; Gusmani et al. 1997). Medusae
concentrations reported by Lotan and colleagues during the late 1980s were
on the order of ‘600,000 per nautical mile’ (Lotan et al. 1992, 1993), sufficient
to create local problems such as clogging of fishing nets. Kideys and Gucu
(1995) suggest the first appearance of this species into the Mediterranean to
be in the mid-1970s. Subsequent to the initial period of colonization, populations
were qualitatively noted to increase (Galil et al. 1990). The species
appears to be limited to the eastern Mediterranean Sea, with reports of it
occurring along the coasts of Egypt, Israel, Lebanon, Syria, and Turkey (Galil
et al. 1990; Kideys and Gucu 1995).
14.3.4 Aurelia spp. (Scyphozoa)
The genus Aurelia, known as moon jellyfish, is a conspicuous member of
coastal ecosystems from polar to tropical seas (Kramp 1961, 1970).As perhaps
the most studied of all the scyphomedusae (literally 100s of publications,
ranging from fundamental ecology to microgravitational impacts on sensory
development), the genus is known to school children and scientists alike.
Until recently, three generally accepted species had been recorded within the
genus: the polar A. limbata, the north Pacific A. labiata, and the cosmopolitan
A. aurita (Dawson and Jacobs 2001). However, recent molecular genetic work
by Dawson and colleagues has described a far more diverse genus (Dawson
and Jacobs 2001; Dawson and Martin 2001; Dawson 2003; Dawson et al. 2005),
with most species considered ‘cryptic’, since general morphological characters
alone are not sufficient to differentiate between these (sensu Mayr and
Ashlock 1993). Surprising to many, the common moon jellyfish was not a single
species, A. aurita, but perhaps as many as 12 species (Dawson 2003) with
enough morphological similarity to confuse traditional taxonomists (Sect.
14.6).
Since medusae of Aurelia spp., similarly to those of most scyphomedusae,
persist for weeks to months, diffusion processes, ocean currents, and active
swimming could potentially disperse this stage over 1,000s of kilometers (e.g.,
Johnson et al. 2005). However, Dawson et al. (2005) showed that, despite the
high dispersal potential of Aurelia spp., a molecular phylogeny of the genus
exhibits substantial biogeographic regionalization, indicating that genetic
isolation is more common than previously recognized.