Abstract: The distribution and diversity of species is changing in response to global climate change, particularly increased temperature. However, the specific biotic response, both within and between species, is often dependent on geographical location. For instance, the greatest negative effects of warming are expected to occur in the tropics because tropical species tend to have a narrower range of thermal tolerance when compared with higher latitude species. Coral reef ecosystems are expected to be at a particularly high risk from increased temperatures because thermal anomalies as little as 1°C above average annual summer maximums can cause mass bleaching in adult coral assemblages. Evidence suggests that raised temperatures may also be deleterious to coral larvae (the dispersive life stage), which are crucial for recruitment and replenishment in coral reef ecosystems. However, studies into the effects of temperature on these early life stages have so far been limited to single locations and upper thermal limits. Therefore, the aims of my PhD were to 1) determine thermal tolerance ranges of early development and survival of coral larvae 2) assess the extent to which this tolerance varies across space, specifically I aimed to test whether high latitude species have a broader tolerance and 3) test whether difference between adult coral assemblages across a hypothesized dispersal barrier (Great Barrier Reef to Lord Howe Island) can be predicted by life history traits related to the dispersive larval stages (e.g., mode of larval development, mode of larval nutrition), adult ecology, and/or environmental parameters. To address these aims, I combined small-scale larval experiments at three sites along the east coast of Australia, and large-scale biogeographical analyses. My major findings were that 1) raised temperatures increased the proportion of abnormal embryos, decreased larval lifespan and increased the rate of embryonic development, 2) coral embryos from higher latitudes possessed greater thermal tolerance ranges and 3) the mode of larval development and corallite size were predictors for the differences in coral cover between the Great Barrier Reef and Lord Howe Island. My results support the hypothesis that corals living in regions characterized by larger temperature fluctuations have wider breadths of thermal tolerance. Although local temperature ranges projected by the end of the century exceed thermal tolerance breadths found for each location, rising temperatures pose a greater threat to low-latitude coral populations. Furthermore, the effects of ocean warming are likely to vary among species, and species that brood and have smaller corallites may be better equipped to survive through changing climates because they are successful in marginal conditions..
Biography: Erika grew up in the San Francisco Bay Area and attended Duke University in North Carolina for her undergrad. She moved to Australia in 2007 and received her Masters of Applied Science from the University of Sydney. She began her PhD at the ARC Centre of Excellence for Coral Reef studies in 2010 under the supervision of Andrew Baird, Sally Keith, and Maria Byrne..