Volcanoes: I don’t know – Ian Plimer says it’s significant. Many more undersea volcanoes get discovered than expected. But I doubt it. Too much thermal mass in the oceans.
Coral reefs: They expel their algae and reload different algae when conditions change; that’s a bleaching event. In the Red Sea corals thrive at 29 deg C water temperature. They like it warm. Deep sea corals in the North Sea like it cold. Extremely versatile genus. Practically indestructible.
