In deep water, it’s hard to know how to answer a call for help. But that’s what Bernard Dupre, a 48-year-old Santa Rosa man who died in his wetsuit on Bolinas Beach last Saturday, asked from his fellow surfers. Before reaching shore via a surfboard leash and multiple hands, Mr. Dupre lost consciousness. By luck, one M.D. and two nurses were nearby and started CPR. The Marin County Coroner’s Division said the cause of his…