Although the crisping air and Starbuck’s reintroduction of the pumpkin-spice latte mean that fall has officially arrived, sculptor Michael Krebber is keeping the summer alive with his whimsical yet conceptually rigorous show of chopped-up windsurfing boards. The brightly hued results, mounted on the walls of Greene Naftali gallery till October 18, suggest the work of a refined shark with a taste for Donald Judd and unsuspecting beachgoers alike.