The effects of temperature on embryonic development and larval survival in two scleractinian corals

Increased temperatures are deleterious to early life stages in many organisms; however, the biological effects of decreased temperatures are rarely explored. For example, the tolerance of marine invertebrate larvae to temperatures lower than ambient might affect the capacity of species to disperse from tropical to subtropical locations. In addition, reduced rates of development are likely to affect the proportion of larvae retained on natal reefs. Here, we explore the relationship between temperature, embryonic development and larval survival over an 8 degrees C temperature range (-4 to +4 degrees C around the ambient temperature at the time of spawning of 24 degrees C) in 2 reef-building corals, Goniastrea favulus and Acropora spathulata from One Tree Island in the southern Great Barrier Reef. Rates of development were generally slower at lower temperatures: embryos of both species took longer to complete gastrulation and to become motile at temperatures below ambient. In contrast, temperatures below ambient did not affect larval survivorship in either species. A. spathulata larvae were more sensitive to increased temperatures than G. favulus, which also had higher survivorship than A. spathulata at all temperatures except 20 degrees C. These results suggest that fluctuations in temperature at the time of spawning will influence patterns of coral larval dispersal. Furthermore, cold water is unlikely to prevent the dispersal of tropical corals to subtropical locations.