Non-indigenous hydromedusae in California's upper San Francisco Esturary: life cycles, distribution, and potential environmental impacts

New observations and corrections concerning the trio of invasive hydromedusae <i>Maeotias marginata (=M. inexpectata), Blackfordia virginica</i>, and <i>Moreisia</i> sp. in the San Francisco Estuary

“…Further observation of living specimens in August 1995 and on subsequent occasions showed unquestionably that Maeotias does indeed have numerous marginal statocysts (see also Rees and Gershwin, 2000). Such statocysts are clearly described and illustrated by Ostroumoff (1896b), as well as by Borcea (1928), Hummelinck (1941) and Denayer (1973), so any questions about their existence can be laid to rest.…”

“…Within the San Francisco Estuary, Maeotias marginata medusae have recently been found in additional low-salinity locations in north San Francisco Bay, including the Napa River and Suisun Slough (Rees and Gershwin, 2000 Mills and Sommer (1995) reported only male medusae in the Petaluma River, a few female M. marginata (among numerous males) were found in the Napa River in September 1998. Eggs produced by these females were fertilized in the laboratory and developed into tiny, simple, primary polyps without tentacles (see Rees and Gershwin, 2000), very different than those polyps figured as Maeotias by Mills and Sommer (1995) (see below under Moerisia), but not out of character with other known limnopolyps such as Craspedacusta.…”

“…Eggs produced by these females were fertilized in the laboratory and developed into tiny, simple, primary polyps without tentacles (see Rees and Gershwin, 2000), very different than those polyps figured as Maeotias by Mills and Sommer (1995) (see below under Moerisia), but not out of character with other known limnopolyps such as Craspedacusta. Growth of these primary polyps did not occur in laboratory culture and they subsequently disintegrated without further development.…”

First record of the invasive stinging medusa Gonionemus vertens in the southern hemisphere (Mar del Plata, Argentina)

“…Examples include high concentrations of medusae clogging fishing nets and stinging species creating problems along recreational beaches (Graham et al, 2003;Graham & Bayha, 2007). Hydromedusae (Cnidaria, Hydrozoa) can be transported through ballast water, but if the species has a meroplanktonic life cycle, their benthic stage can also be introduced as a part of the ship's fouling fauna (Rees & Gershwin, 2000;Genzano et al, 2006;Miglietta & Lessios, 2009). …”

A pandeid hydrozoan, <i>Amphinema</i> sp., new and probably introduced to central California: life history, morphology, distribution and systematics

“…The hydrozoan fauna of bays and harbors of the central California coast has been altered through non-indigenous species introductions over the past 50 years or more (Hand and Gwilliam, 1951;Mills and Sommer, 1995;Rees and Gershwin, 2000) and the rate of successful establishment of all nonindigenous species in San Francisco Bay appears to be accelerating in recent decades (Cohen and Carlton, 1998). The present paper describes what is believed to be a recently-introduced species of Amphinema, family Pandeidae, in Bodega Harbor, California, a shallow, sandy harbor located about 80 km north of San Francisco.…”