Coral Growth Rates Revisited after 31 Years: What is Causing Lower Extension Rates in Acropora Palmata?

Linear extension of branches in the same Acropora palmata (Lamarck, 1816) population in Curaçao was measured, employing exactly the same methods, in 1971–1973 and in 2002–2004, and the resulting coral growth rates are compared. Linear growth shows the same pattern over seasons in both periods with growth being significantly higher in summer than in winter. Growth in the 2002–2004 time interval was significantly slower than in 1971–1973. Mean monthly growth ranged from 0.69 cm (winter) to 0.81 cm (summer) in 1971–1973 and from 0.62 cm (winter) to 0.75 cm (summer) in 2002–2004. This means that linear growth rates in 2002–2004 were 7.2% lower in summer and 10.7% lower in winter compared with 1971–1973. Considering possible causative environmental factors relating to these decreases in growth rate, we cannot preclude the possibility that a change in ocean pH could be responsible for the drop in extension rate.