Invasions of nonnative species such as the Asian clam (Portamocorbula amurensis), as well as changes in water transparency and transport, have resulted in precipitous declines in phytoplankton levels in the Sacramento-San Joaquin River Delta since the late 1960s, with far-reaching impacts for the ecosystem’s intricate food web, scientists report in the October-December 2003 issue of the University of California’s California Agriculture journal which can be viewed online at http://danr.ucop.edu/calag/.
Reviewing decades of data, UC Davis research ecologist Alan Jassby and colleagues found that levels of phytoplankton — microscopic, free-floating algae, which form the most important food source on a Delta-wide scale — vary from season to season, but overall are decreasing. Indeed, native fish such as delta smelt and chinook salmon, as well as zooplankton and benthic invertebrates, “all show evidence of food limitation during their first year,” Jassby wrote.
Contact: Jassby, adjassby@ucdavis.edu, (530) 752-7865.

In a second peer-reviewed research article, UC Davis research scientist Inge Werner and colleagues report that biomarkers — in this case, stress proteins and tissue damage — can elucidate the complex ways in which aquatic species respond to environmental stresses such as elevated water temperatures, salinity and heavy-metal contamination.
Contact: Werner, iwerner@ucdavis.edu, (530) 754-8060.

The current issue of California Agriculture also includes several features and news coverage about the Delta and aquatic issues. In an editorial, California Sea Grant advisor Christopher Dewees notes that the state’s aquatic resources, once considered boundless, are stressed to near the breaking point. In the news section, California Agriculture reports on the outbreak of a nonnative algae, Caulerpa taxifolia, which is currently under control in Southern California; on research indicating that invading nonnative aquatic species increase in size; and on efforts to restore Lahontan trout to the Lake Tahoe basin.

Other peer-reviewed articles in the October-December 2003 issue:

Landscape changes in Nevada County: The migration to rural areas by urban dwellers seeking a better quality of life has resulted in concerns about “rural sprawl.” A study of land ownership and landscape changes in Nevada County — about an hour drive from Sacramento in the Sierra Nevada — found dramatic fragmentation of the landscape over the past 50 years, while 40% of the county’s privately owned parcels are zoned for future residential or commercial development. The research in Nevada County also suggests, however, that the ecological effects of rural-residential growth are not always wholly negative, and can be improved through better understanding of the social conditions that shape land-use practices by individual landowners.
Contact: Peter Walker, pwalker@uoregon.edu, (541) 346-4541.

Olive fruit fly populations measured: Considered the most serious global olive pest, the olive fruit fly was first detected in California in 1998. Since then, it has been trapped year-round in olive-growing regions of southern and interior-central California. New trapping studies in the San Joaquin Valley, and Santa Barbara and Ventura counties, demonstrate the susceptibility of the state’s $90 million olive industry to this nonnative pest, although no major damage has been reported to date.
Contact: Richard Rice, rerice@uckac.edu, (559) 646-6542.

Glassy-winged sharpshooter treatments for nursery citrus: Glassy-winged sharpshooter is a proficient vector of Xylella fastidiosa, a bacterium that causes Pierce’s disease in grapevines. A study found that a combination of insecticides effective against mature sharpshooters and emerging nymphs could reduce the transport of this nonnative pest in nursery citrus shipments.
Contact: Beth Grafton-Cardwell, elizabeth.grafton@ucr.edu, (559) 646-6591.

Minute trunk measurements aid almond irrigation: Continuously recorded measurements of minute changes in the trunk diameter of almond trees can be used to efficiently schedule irrigation, maximize yields and accelerate hull-split without any reductions in nut quality. This method could also allow for on-the-tree almond drying, which may reduce dust and nut contamination problems.
Contact: David Goldhamer, dagold@inreach.com, (559) 646-6575.