NEMESIS Bioregion Distribution:

Native  Introduced  Cryptogenic  Failed

First Non-native North American Marine/Estuarine Record: 1904
First Non-native West Coast Marine/Estuarine Record: 1904

General Invasion History:

Iais californica was first described by Harriet Richardson in 1904, from specimens collected in Sausalito, San Francisco Bay, California, taken from the pleopods of the isopod Sphaeroma quoianum (as S. pentadon). 'Iais pubescens' from New Zealand, identified by Chilton in 1892, was eventually recognized as synonymous with I. californica, while 'S. pentadon' was synonymized with Australia-New Zealand native S. quoianum (Menzies and Barnard 1051; Hurley 1956). Bot species are now recognized as introductions to the Northeast Pacific (Rotramel 1972). Iais californica is found over most of the introduced range of S. quoianum, from Coos Bay, Oregon to San Diego Bay, California (Rotramel 1972; Iverson 1974; Carlton 1979; Cohen and Carlton 1995; Davidson 2006).

North American Invasion History:

Invasion History on the West Coast:

Iais californica was described from Sausalito, in San Francisco Bay in 1904 (Menzies and Barnard 1951; Carlton 1979), associated with the isopod Sphaeroma quoianum. It is known from the South and Central Bays, and San Pablo Bay (Richardson 1904; Menzies and Barnard 1951: Robinson et al. 2011). It was also found with S. quoianum in fouling on an obsolete cargo vessel moored in Suisun Bay (Llansó et al. 2011), and appears to share some of its host's tolerance for brackish water. The spread of I. californica has depended on the spread of its host, but reports of the commensal have matched, or lagged behind those of the host. This could reflect either slower dispersal of I. californica, or its lesser obviousness.

Iais californica is found in most of the West Coast estuaries where S. quoianum is found, although Iais californica has not been reported from Los Angeles Harbor, where S. quoianum was first reported in 1927 (Johnson and Snook 1927, cited by Carlton 1979), or from northern Yaquina Bay, Oregon (Davidson 2006), or the southern edge of S. quoianum's introduced range at Bahia San Quintin, Baja California (Menzies 1962a). Of course, I. californica could just be overlooked at these sites. Both isopods were probably transported in the fouling communities on hulls of cargo ships coming from New Zealand (Carlton 1979; Cohen and Carlton 1995).