Glen and Kelsey Dennison reveal the underwater discoveries they made while diving Howe Sound's reefs and islands, March 8. Visitors to Unity Church, 5840 Oak St., can learn more about 3D underwater mapping techniques used to study glass sponge biotherms on deep sea mounts. The free talk starts at 7:30 p.m. For more information, see naturevancouver.ca or phone 604-737-3074.