Sampling-standardized expansion and collapse of reef building in the Phanerozoic

Geologists have long suggested that the Phanerozoic record of marine reefs fluctuated considerably through time but exactly how strong these fluctuations were is still a matter of debate. The published graphs of several authors suggest moderate fluctuations in reef abundance over the Phanerozoic (James 1983; Copper 1988; James & Bourque 1992; Hallock 1997), while other authors have depicted substantial variations, which increase with refinements of reef definitions (Wood 1993; Webb 1996; Kiessling et al. 1999, 2000; Kiessling 2002). Although there is more agreement on the timing of reef expansions and declines, the stratigraphic position and significance of reef booms are also poorly constrained. Resolving the issues of the temporal variability (= volatility) of reef growth and the position of reef booms and bursts is important for several reasons: First, identifying true peaks of reef growth can shed light on the global environmental conditions under which reefs tend to flourish. Second, the intensity of temporal fluctuations in reef abundance illuminates the sensitivity of reefs to extrinsic controls, be they environmental or biological. Third, insights can be gained into general processes of reef waxing and waning through time, because gradual increases and declines of reef abundance may suggest linear relationships between control and effect, whereas sharp peaks and drops could indicate non-linear relationships or even self-organization. Two major problems hinder the detection of biologically meaningful patterns in reef production on geological time scales: Genuine variations in the preservation of sedimentary rocks and (economically driven) heterogeneities in exploration intensity (Kiessling 2005a, 2006). Kiessling (2006) has tried to compensate for much of this bias and uncovered the probable pattern of changes in absolute reef abundance and volume through the Phanerozoic. His pattern of a maximum proliferation of reefs in the Silurian and Devonian and a steep decline thereafter, interrupted by short-term peaks, provides insights into absolute changes in reef production, but does not elucidate variations relative to changes in the fossil record. These relative changes, however, can be even more informative than absolute changes. Imagine for example, that reef abundance were determined merely (and linearly) by available shelf area and thus controlled by sea-level fluctuations and hypsography. Then we could use the reef record to trace ancient sea levels but a prefect correlation between reef abundance and sea level would make it unlikely that any additional factors are relevant. Differences between preserved reef abundance and overall sampling of the fossil record can reveal times when exFossil Record 11 (1) 2008, 7–18 / DOI 10.1002/mmng.200700008