10:10-12:10 Session I Biology of Coral Reef
Developing predictive and reactive tools for monitoring coral health
B Willis, K Anthony, R Berkelmans, K Michalek-Wagner, C Page, J True
James Cook University, Townsville, Qld. 4811
Australia
bette.willis@jcu.edu.au
Identifying sublethal indicators of coral health is important for the development of tools to monitor potential impacts of global climate change on coral reefs. Here we report on a variety of indicators of sublethal stress in corals and comment on their usefulness for developing predictive or reactive tools for monitoring coral health.
Our results indicate that, in corals, tissue growth is much more sensitive to environmental stressors than skeletal growth. Large reductions in tissue thickness were detected within a month of a natural bleaching disturbance whereas skeletal growth rates were only marginally reduced. In a separate study, energy investment into tissues showed stronger correlations with light level and sediment load than did skeletal growth. Tissue growth and energetics may thus be useful tools in reactive monitoring programs. Patterns of change in reproductive tissues further substantiate this. We found that both the number and size of eggs were reduced in hard and soft corals following a natural bleaching disturbance. Also, differential reductions in fecundity following moderate and heavy bleaching disturbances (experimentally simulated) suggest that measures of fecundity are correlated with the level of disturbance and thus have potential for evaluating the severity of an impact. Since fecundity integrates the impact of a disturbance over the relevant portion of the gametogenic cycle, it is a useful long-term reactive monitoring tool. Use of tissue thickness, tissue energetics and fecundity as indicators of coral health, however, requires knowledge of baseline values of these parameters, particularly as long-term studies have shown that tissue thickness varies seasonally. Whereas tissue thickness can be used independently of season, fecundity can generally only be applied at the time of reproductive maturity.
Finally, analysis of 12 years of temperature, light, barometric pressure and wind data indicate that of these, sea temperature is the most important physical parameter to monitor as a predictor of environmental conditions likely to cause coral stress and bleaching. Use of temperature as a predictive monitoring tool requires knowledge of maximum thermal tolerances for local indicator species. Time-temperature relationships likely to trigger a bleaching response can be constructed from long-term records of bleaching and in situ sea temperature data. In combination with automated monitoring of sea temperature, such time-temperature relationships for bleaching responses can be used to generate automated warnings of conditions stressful to coral communities.
