Effects of thermal stress on fertilization and early embryogenesis in coral species from the Great Barrier Reef and Japan

Favites chinensis colonies were collected from the reef flat off Sesoko Island, Okinawa and transported to aquaria at Sesoko Station. After spawning, sperm and eggs were separated and then used in fertilization experiments at 7 temperatures (25.5, 26.4, 27.0, 27.8, 28.9, 30.2 and 31.6°C). Early fertilization (first and second cleavage) was assessed after 3 hours using a dissecting microscope.Acropora millepora were collected from Davies Reef on the Great Barrier Reef and transported to aquaria at the Australian Institute of Marine Science. Similar fertilization experiments were carried out at 28.3, 30.4, 31.8, 32.8 and 34.1°C. Embryos were sampled at 2 and 4 hours, fixed in Bouins solution and later assessed for fertilization success and gamete quality.Acropora millepora, Favites abdita and Mycedium elephantotus, were collected from Davies Reef. In this experiment, eggs and sperm were separately pre-exposed to temperatures of 26, 28, 30 and 32°C for 30 minutes prior to fertilization at these tempertures. The embryos were sampled and fixed at 2 and 4 hours and assessed for fertilization success, abnormal embryo development and cell cleavage rates. This research was undertaken to examine the influence of seawater temperature on fertilization success and early embryogenesis of reef-building corals, in different families, from the Great Barrier Reef and Japan. Gametes were subjected to temperatures ranging from 2°C below average temperatures during the spawning period at each location to 5-6°C above average, which encompasses the range of increases that might be expected under climate change scenarios.