Tokyo stocks opened lower Thursday as investors locked in gains after the benchmark Nikkei index rose to a two-month high the previous day, while an overnight rise in crude oil futures also weighed on the market. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 256.48 points, or 0.91 percent, from Wednesday to 27,783.68. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 16.85 points, or 0.85 percent, to 1,961.85. Decliners were led by marine transportation, metal product and precision instrument issues. At 9 a.m., the dollar fet…