By default legend is plot right side and I want to change it to bottom of plot.
levelplot(CHL1, xlim=c(30,130), ylim=c(-20,30),
xlab="", ylab="", margin=FALSE, col.regions=pal,
at=seq_along(brks), colorkey=ckey) +
layer(sp.polygons(msk, fill='black', col='transparent'))