Aerial exposure influences bleaching patterns

Abstract

[Extract]On the 17th December 2005 Acropora millepora and other reef flat corals at Heron Island (23.44S, 151.91E) were found to have bleached on the west-north-west face of aerially exposed branches (Fig. 1). Visual surveys on the 15th and 16th had not detected any bleaching signs. In the preceding 3 days, water temperatures reached a maximum of 32.0 C on the 15th December and exceeded 31.0 C for only 2.5 h. Past studies suggest this alone is not sufficient to cause bleaching. Analysis of wind speed and direction for the morning of the 17th showed that the low tide at 03:00 hours coincided with 4 h of high winds from the west-north-west. Peak gusts (57 km h)1) were within the highest 2.5% of all reading from the previous 6 years. Analysis of the red absorbing photosynthetic pigments (absorptivity) and dark-adapted fluorescent yield (Ralph et al. 2005) demonstrated a 65% loss of photosynthetic pigments and a 40% decrease in yield on the west-north-west face of exposed corals (Fig. 2) compared to the eastern side.