The Los Angeles Business Journal’s index of largest local public companies gained slightly for the week as the broader markets reacted to positive developments in the European debt crisis.

The weighted LABJ Stock Index closed down 0.75 percent to 136.82 for the week ended Aug. 24. Decliners outpaced gainers 96 to 70, with 10 companies unchanged.

Ceres was among the biggest decliners, sinking 27 percent to $6.38. The Thousand Oaks developer of genetically modified crop seeds held a special shareholders meeting that extended the term of executive stock options that would have expired in December.

Guess Inc. dropped 19 percent to $26.48. The Los Angeles apparel company cut its annual profit and revenue forecasts.

Manhattan Bancorp fell 13 percent to $2.45. Chief Financial Officer Brian Cote notified the El Segundo bank holding company that he was resigning Sept. 14.

Demand Media Inc. lost 13 percent to $9.79. An equity analyst said that the Santa Monica operator of information web sites was no longer in the race to acquire the New York Times’ About.com site.

Among the biggest gainers was Private Bank of California, which jumped 20 percent to $12.25. The Century City bank said that it had agreed to be acquired by First Pactrust Bancorp Inc. of Irvine, in a stock deal valued at roughly $50 million.

MPG Office Trust Inc. rose 11 percent to $3.42, and Thomas Properties Group Inc. rose 7 percent to $5.31. The two Los Angeles real estate companies gained on reports that Thomas Properties may bid for beleaguered competitor MPG.