Moerisia lyonsi

History of Spread

The hydrozoan Moerisia lyonsi is only known from its type locality, Lake Quarun Egypt (a lagoon of the Nile Delta) and the East, Gulf and West coasts of North America (Boulenger 1908; Rees 1958; Calder and Burrell 1967; Poirier and Mulino 1977; Meek et al. 2012). Other species of Moerisia are known from the Caspian Sea, Japan, and the Mediteranean, in coastal and continental salt lakes (Calder 1971; Dumont 1994). An unidentified species of Moerisia has been introduced to San Francisco Bay (Mills 1999). It is possible that M. lyonsi and other named forms may represent a single, morphologically plastic species of Ponto-Caspian origin (Mills 1999).

Atlantic Coast records are listed from south to north:

Gulf of Mexico, Lake Ponchartrain - Polyps of M. lyonsi were found in the lake spillway in 1975, but disappeared during unusually low salinities (Poirier and Mulino 1977).

South Carolina- Medusae of M. lyonsi were reported as abundant in most areas of low salinity (Calder and Hester 1978). Medusae and polyps invaded an shrimp aquaculture system at Charlestown SC in 1973 (Sandifer et al. 1974).

Chesapeake Bay - M. lyonsi medusae were first collected in 1965 and hydroids in 1965-68 in low-salinity waters of the James and Pamunkey Rivers (Calder and Burrell 1967; Calder 1971). Subsequent reports of the species are sparse, but hydroids of M. lyonsi were found in settling plates from Baltimore Harbor in 1995 (Ruiz et al. unpublished). About 1992-93, M. lyonsi medusae invaded an experimental mesocosm system at the University of Maryland Horn Point Laboratory, and were also collected in the adjacent Choptank river (Purcell et al. 1999).

Delaware River and Bay- M. lyonsi was found in Delaware Bay by Dale Calder (no specific data on locality) (Calder et al. 1974).

In the San Francisco estuary, Moerisia sp. medusae and polyps were discovered in the brackish Petaluma River, a tributary of San Pablo Bay, in 1993 (Mills and Sommer 1995), and were later found in the Napa River, another San Pablo tributary. In 1997, Moerisia sp. medusae were collected in Suisun Slough (Rees and Gershwin 2000). Extensive surveys of non-indigenous hydrozoans in Suisun Marsh, and the Napa and Petaluma rivers were made by Schroeter (2008) and Wintzer et al. (2011a; 2011b). Medusae of Moerisia sp. were the most numerous of the 3 species of nonindigenous hydromedusae in Suisun Marsh, occasionally reaching densities of 100 . M-3 (Schroeter 2008l; Wintzer et al. 2008b). The San Francisco Bay hydrozoans have recently beeen found to be identical to M. lyonsi from Chesapeake Bay (Meek et al. 2012). History References - Calder and Burrell 1967;Calder 1971;Calder and Hester 1978; Dumont 1994; Poirrier and Mulino 1977a; Purcell et al. 1999; Ruiz et al. unpublished data; Sandifer et al. 1974

Invasion Comments