Growth response of the reef coral Acropora longicyathus to elevated inorganic nutrients: do responses to nutrients vary among coral taxa?

Rates of linear extension and changes in buoyant weight were measured for transplanted colonies of Acropora longicyathus exposed to elevated concentrations of ammonium and/or phosphate in the ENCORE experiment (One Tree Island, Great Barrier Reef). Linear extension was significantly faster in elevated phosphate treatments compared with controls. Rates of buoyant weight change were significantly increased by elevated ammonium on an annual basis, but significant reductions occurred in winter. Phosphate significantly increased the rate of buoyant weight change in some seasons but had no significant effect on an annual basis. Caution is therefore advised when extrapolating short-term growth data to represent annual trends. Chlorophyll a content of phosphate-treated corals was significantly higher than controls. Unlike other coral taxa in previous studies, elevated chlorophyll a content in Acropora longicyathus in this study did not correlate with reduced calcification. Growth of Acropora corals may be less sensitive to ‘clean’ (i.e. unaccompanied by reduced salinity, elevated sediments, or other pollutants) elevated inorganic nutrient concentrations than growth of other coral taxa used in nutrient enrichment studies to date, and wider use of this cosmopolitan genus in manipulative experiments is recommended.