Meeting Abstract
Coral growth rates are often used as a metric of coral health and have been measured extensively in the lab under controlled conditions to better understand the potential impacts of future climate change. However, in the field corals live in dynamic environments, which can have extreme daily variability. Most field-based studies have measured growth rates over periods of time that are greater than the time over which environmental conditions vary. On Ofu Island in American Samoa, corals living in the back-reef can experience a range of conditions within a day due to the structure of the reef and the tide. Data from continuous-recording pH sensors show that, during high tides, the pH in the back-reef is very close to the pH in the fore-reef. However, during low tides, the pH in the back-reef is higher during the day and lower during the night, due to an imbalance between CO2 consumption and respiration. We have recorded pH ranging from 7.78 to 8.31. There are also diurnal fluctuations in dissolved oxygen availability and temperature. We measured linear extension growth rates in Acropora surculosa for three consecutive 5-day periods, each with different environmental regimes. As far as we are aware, this is the first study to use skeletal staining techniques to measure fine-scale growth rates in the field. Linear extension rates were measured using confocal microscopy of skeletal thin-sections of stained coral branches. These results are a first attempt at elucidating the impact that large, natural environmental variation may have on coral fine-scale growth rates. Preliminary analysis suggests that the amplitude of environmental variability does not have a negative effect on fine-scale linear extension growth rates.
