A proposal to create marine parks off the coast of California has led to shouting matches between environmentalists and scientists on the one side and the fishing industry and recreational anglers on the other. The proposal would prevent fishing and other human activities in as much as 20 percent of state waters — a 100-fold increase over the current 0.2 percent protected by state law. Opponents, some of whom threw fish at the plan’s authors when it was unveiled, question the science behind the proposal and say it would devastate angling in California. Proponents, however, argue that marine species would be best protected by habitat conservation. That position might be bolstered by the work of the Pew Oceans Commission, which heard testimony yesterday that unchecked growth in the nation’s coastal cities is leading to polluted oceans and damaged marine habitat.