Reef accretion and coral growth rates are decoupled in Holocene reef frameworks

Abstract

A central assumption of Holocene reef models is that reef accretion rates are directly related to coral growth rates, with reefs dominated by faster growing corals having higher accretion rates. Yet, few studies have explicitly tested this assumption, particularly in Indo-Pacific region. Through high-precision UTh dating and palaeoecological reconstructions of coral community structure, this study explores patterns of reef accretion (mm yr−1) among late Holocene reef frameworks from the inshore central Great Barrier Reef. Modern assemblages were dominated by either slow-growing Goniopora (9.6 ± 2 mm yr−1) or rapid-growing branching Acropora (89 ± 6 mm yr−1) framework building corals. Despite a nearly 10-fold difference in coral growth rates, rates of reef accretion were comparable between frameworks dominated by slow-growing Goniopora (8.6 ± 1.3 mm yr−1) and rapid-growing branching Acropora (7.1 ± 1.4 mm yr−1). UTh chronologies indicate that accretion rates were continuous throughout the past 750 years (R2 = 0.96–0.98) despite a temporal shift in framework building corals from Acropora to Goniopora that occurred ~250 years ago. That coral growth rates are decoupled from reef accretion at Holocene scales indicates that previous models of accretion in Pacific coral reefs may be based upon inaccurate assumptions. The finding that ecological processes are decoupled from geological processes has implications for the management of modern coral reefs, and suggests that maintenance of living corals, regardless of taxonomic identify, is important for accretion of reef frameworks.