Aims To investigate the physiological processes underlying freshwater utilisation in halophytes under nonuniform salinity conditions in order to determine whether preferential uptake of freshwater occurs and whether transient freshwater availability improves plant water relations and photosynthesis Methods In a split-root experiment, we grew Avicennia marina (Forssk.) Vierh. at uniform salinity conditions (35:35 ppt) and then lowered (35:5 ppt) or increased (35:65 ppt) salinity to one compartment. Using δ 18 Olabelled water we calculated the extent of preferential water uptake of either source. Results When given a 35:5 treatment, A. marina tookup three times more water from the fresher compartment than predicted by a root-weighted-no-salinitypreference model. No difference between compartments was observed in the 35:65 treatment, suggesting that avoidance of the more saline water did not occur. In the 35:5 treatment, stomatal conductance increased within 1.5 h, but photosynthetic rates were not enhanced over the 48-h period of the experiment and rapidly decreased in the 35:65 treatment. Conclusions Avicennia marina responds to transient freshwater patches by increasing water uptake from areas of the root zone where the salinity is better for growth. However, photosynthetic rates respond to the highest salinity in the root zone; thus, reductions in salinity in part of the root zone may enhance water storage in stem tissues but positive effects on photosynthesis may require longer periods.

Long-term data with high-precision chronology are essential to elucidate past ecological changes on coral reefs beyond the period of modern-day monitoring programs. In 2012 we revisited two inshore reefs within the central Great Barrier Reef, where a series of historical photographs document a loss of hard coral cover between c.1890–1994 AD. Here we use an integrated approach that includes high-precision U-Th dating specifically tailored for determining the age of extremely young corals to provide a robust, objective characterisation of ecological transition. The timing of mortality for most of the dead in situ corals sampled from the historical photograph locations was found to coincide with major flood events in 1990–1991 at Bramston Reef and 1970 and 2008 at Stone Island. Evidence of some recovery was found at Bramston Reef with living coral genera similar to what was described in c.1890 present in 2012. In contrast, very little sign of coral re-establishment was found at Stone Island suggesting delayed recovery. These results provide a valuable reference point for managers to continue monitoring the recovery (or lack thereof) of coral communities at these reefs.

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