Invasion
Invasion Description
1st Record: Stockton/CA/San Joaquin River (1987, Orsi and Walter 1991)
Geographic Extent
CA/Suisun Bay, Sacramento-San Joaquin Estuary (1987, Orsi and Walter 1991); CA/Port of Stockton-Suisun Bay (1987, Orsi and Walter 1991); CA/Sacramento Turning Basin (Fairey et al. 2002); CA/San Pablo Bay (during high river-flow condtions, Bollens et al. 2011); Bull Island/CA/Napa River (2003-2005, Bollens et al. 2014). In experiments, naupliiP. forbesi tolerated salinities at least as high as 14 PSU, and adults, at least 8 PSU. but since 1993, it has become rare at salinities above 2 PSU, probably because of predation on nauplii by A. sinensis and by Corbula amurensis.
Vectors
| Level | Vector |
|---|---|
| Probable | Ballast Water |
Regional Impacts
| Ecological Impact | Food/Prey | |
| Pseudodiaptomus forbesi was selected against by larval Striped Bass (Morone saxatilis), apparently because of superior escape abilities (Meng and Orsi 1991). However, Pseudodiaptomus spp., mostly P. forbesi, have become the predominant food of small (under 50 mm) Striped Bass (Bryant and Arnold 2007). Pseudodiaptomus forbesi is also now the principal food organism of the endangered Delta Smelt (Hypomesus transpacificus and the threatened Longfin Smelt (Spirinchus thaleichthys) in the Sacramento-San Joaquin Delta (Hobbs et al. 2006). It is considered to be inferior to the previous dominant copepod, Eurytemora carolleeae as a food item for the smelts (Moyle et al. 1992; Nobriga 2002). The shift in dominance from Eurytemora to Pseudodiaptomus was associated with a decrease in average length for Delta Smelt (Glibert 2010). Overall, changes in the fatty-acid and overall nutritional quality in the foodweb are complex, but the shift from more herbivorous native cladocerans to more omnivorous copepods may have increased transfer of contaminants up the food-chain, and increased dominance of cyanobacteria (Kratina and Winder 2015). The effects of introduced copepods are additionally complex, because of the varying size of the life-stages, and the interaction of different species of fish predators (Sullivan et al. 2016). | ||
| Ecological Impact | Competition | |
| After its invasion in 1987, Pseudodiaptomus forbesi has remained the dominant calanoid copepod in low-salinity regions of the San Francisco estuary, while Eurytemora carolleeae (formerly E. affinis) has declined (Orsi and Walter 1991; Baxter et al. 2005). One of many possible factors is that Pseudodiaptomus forbesi was better able to graze selectively than E. caroleeae, thus avoiding the toxic cyanobacterium Microcystis sp., which has been blooming in low-salinity waters of the estuary (Ger et al. 2010). | ||