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14.3 Medusae (Cnidaria)
W.M. Graham and K.M. Bayha
14.3.1 Phyllorhiza punctata (Scyphozoa)
The scyphomedusa Phyllorhiza punctata appeared suddenly and in spectacular
numbers in the northern Gulf of Mexico during the summer of 2000 (Graham
et al. 2003). Phyllorhiza punctata was first described from Pt. Jackson,
Australia (von Lendenfeld 1884), and, presumably due to its conspicuous
medusa stage, has a relatively well-documented history of invading tropical
and subtropical environments around the globe over the past 200 years. The
first recorded invasion of P. punctata was into the Swan-Canning estuary,
Perth (Western Australia) between 1837–1838, presumably by early Australian
shipping (Rippingale and Kelly 1995). P. punctata subsequently
appeared in Pearl Harbor, Hawaii, USA (1941; Devaney and Eldridge 1977),
Laguna Joyunda, Puerto Rico (1945 at the latest; Garcia-Sais and Durbin
1993), San Diego, California, USA (1990 at the latest; Colin and Arneson 1995),
Danajon Bank, Bohol Island, The Philippines (Heeger et al. 1992), and Bahia
de Todos os Santos, Brazil (between 1991–1999; da Silveira and Cornelius
2000). P. punctata also appeared in the eastern Mediterranean (in 1965, as referenced
by Galil et al. 1990), but apparently did not persist there. This welldocumented
history of invasion over an extended period may make P. punctata
a particularly instructive model toward understanding invasions of
jellyfish in particular, and of invasive marine species in general.
The occurrence of the very large population estimated at 10 ¥ 10 6 medusae
across the north-central Gulf of Mexico (Alabama, Mississippi, and Louisiana)
in the summer of 2000 was unexpected, as the species had never been
documented north of the Caribbean Sea. The timing of the occurrence was
coincident with the incursion of tropical water from the Caribbean into the
Gulf of Mexico. Using a modeling approach to assess transport mechanisms
via currents measured during the 2000 bloom, Johnson et al. (2005) were able
to suggest a plausible advection of medusae out of the Caribbean Sea by the
northward-flowing Loop Current in the Gulf of Mexico. However, in the
absence of direct evidence of transport of medusae from the Caribbean to the
northern Gulf via this current (Johnson et al. 2005), we must also consider
that cryptic populations have existed for some time in the Gulf of Mexico.
This is supported by anecdotal reports by fishermen of this species occurring
as small populations around coastal Louisiana for at least several years prior
to 2000. P. punctata has been documented in the coastal waters of south-central
Louisiana in each summer since 2000 (unpublished data).
The potential ecological and economic impacts of P. punctata were judged
as high, and it was feared that the ecology of the northern Gulf of Mexico
would be altered permanently, along with the valuable fishing industry that
depends on it (Graham et al. 2003). These fears were fueled by the costs of P.