Evidence for a decadal-scale decline in the growth rates of juvenile scleractinian corals

Abstract

Juvenile life stages play critical roles in the population dynamics of virtually all organisms, and there- fore precise estimates of juvenile growth and survival are important for accurate demographic analyses. For tropical reef corals, the contribution of juveniles to population dy- namics is strongly determined by their growth rates, which are inversely proportional to the duration of this life stage and the risks of mortality, yet empirical estimates of this important trait are surprisingly rare. Based largely on re- sults published before 1990, it is often assumed that juve- nile corals ≤50 mm diameter grow ~10 to 34 mm yr-1 , and therefore are ~1.5 to 5.0 yr old. In contrast, results pre- sented here show that juvenile corals (≤40 mm diameter) in St. John, US Virgin Islands, have grown at much slower rates on shallow reefs ( 32 yr of peer-reviewed studies that reveal a gradual decline in the growth rates of juvenile corals. The correspondence of this decline with rising seawater tem- perature and depressed aragonite saturation state raises the possibility that the effects of global climate change have already reduced the growth of juvenile corals.