REEF DROWNING VERSUS COMMUNITY DISRUPTION: IMPLICATIONS FOR MITIGATING RECENT REEF DECLINE

The recent decline of coral reefs has spawned vigorous debate over natural vs anthropogenically driven change, and how differentiating the two might inform management strategies. Arguments over “top-down” vs “bottom-up”, and a host of other response pathways illustrate the present breadth of opinion. The recent geologic record provides a temporal perspective that transcends monitoring studies, legislative attention spans or scientists' careers. However, it is a pathway dominated by temporal and spatial scaling differences between biological observation and geologic inference. Two millennial gaps in the record of Acropora palmata during the late Holocene establish that its recent decline is not without precedent. Reefs without A. palmata continued to flourish, and built at rates similar to those before and after the gaps. Earlier in the Holocene, A. palmata reefs off Barbados had been abandoned altogether as sea-level rise accelerated in response to sudden glacial meltwater release. Despite this dramatic change, the new reefs that formed upslope were still dominated by A. palmata, with no apparent change in species dominance. This earlier scenario involves a stable community structure despite a drastic spatial dislocation of the entire reef tract. The later A. palmata gaps suggest dramatic restructuring of the reef community, with or without a similar backstepping of reefs – all without a dramatic sea-level rise. What is the difference between events that spatially dislocate entire reefs but leave community structure unchanged versus those that trigger wholesale changes in the community structure in the absence of rapid sea-level rise? What do these tell us about intrinsic vs extrinsic controls of reef change? How might taphonomic agents have blurred signatures from past events that were temporally consistent with the scale of recent events? Do these make comparisons between monitoring and core studies impossible? Given that recent overexploitation is likely resulting in both accelerated sea-level rise and compromised calcification, how might we use geologic information to resolve arguments over the directional pathways of natural control that must be integrated into effective restoration and management plans? Examples are offered from the Caribbean Holocene record that shed light on these questions.