Measurements of DMSP production from Acropora intermedia collected fromHeron Island, in the southern Great
Barrier Reef (GBR) from 2001 to 2003, show a distinct seasonal cycle of increased production in summer, and
lower production in winter, despite severe coral bleaching in 2002. Increasing seawater temperatures by
+2 °C in summer and winter increased DMSP production from A. intermedia by approximately 45%. Compared
with winter 2001 and summer 2002, marked increases in cellular DMSP occurred in A. intermedia in the winter
of 2002 and summer 2003, five to six months after coral bleaching, and seemed to be related to high seawater
temperatures and high rainfall. In contrast to these results cellular Chl a concentrations in A. intermedia decreased
from2001 to 2002 and then increased in summer 2003 as the coral slowly recovered. A parallel study conducted
on Pocillopera damicornis froma fringing reef offMagnetic Island in the central GBR, highlightedmarked variation
in cellular concentrations of Chl a, DMSP, and algal symbionts, in colonies that were collected five months after a
severe bleaching event. The increases in cellular DMSP at both low and high symbiont concentrations, and the
highly significant correlation between cellular DMSP and Chl a, could reflect an adaptive response to enhanced
levels of reduced oxygen species produced during the bleaching event, and may have aided the coral's recovery.
The increases in cellularDMSP could also be explained by a change in the symbiont community. Comparisonwith
measurements made mainly on Acropora coral from different locations in the GBR over different years, suggests
that changes in the cellular or tissue concentration of DMSP are a sensitive indicator of coral stress.
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