Yet More Hurdles for Delta Smelt:
Smaller "Meals" for Their Young

Researcher:

Lindsay Sullivan
Postdoctoral Fellow

Romberg Tiburon Center for Environmental Studies

San Francisco State University
E.: ljswr@sfsu.edu
T.: (415) 435-7127

Tools:

Revised:

June 10, 2010

The tiny Asian copepod Limnoithona tetraspina outnumbers all other copepods by a factor of ten in some parts of the San Francisco Estuary. Credit: D. Marcal/SFSU

June 10, 2010

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

The base of the food chain in San Francisco Estuary is being profoundly altered by a virtually invisible marine crustacean native to Asia.

The species, Limnoithona tetraspina, likely introduced via ships' ballast waters, has become the most abundant copepod (a type of zooplankton) by a factor of ten in some parts of the estuary. Though numerous, the body size of L. tetraspina is much smaller than that of larger copepods, which historically have been the main food source for larval and juvenile fishes.

In a project funded by the Delta Science Program, a scientist examined the effects of the new zooplankton on foraging behaviors and prey selection of larval delta smelt and striped bass. The delta smelt is of particular interest because of its vulnerability to further habitat loss and water diversions.

Based on this project's findings, the Asian copepod, contrary to prevailing view, may be an important food for larval delta smelt, stripped bass and other fishes during their larval period. It is not, however, a preferred food for juvenile delta smelt and stripped bass, which are have bigger mouths and bigger appetites. These larger fishes want to eat larger copepods and will expend energy trying to capture them. In the absence of their preferred prey, juvenile fishes may not be getting enough to eat and/or may be expending extra energy in search of a good meal.

To learn more about this project, visit http://www.csgc.ucsd.edu/BOOKSTORE/Resources/PP2010/RSF-15-Sullivan.pdf