Coral Reef Degradation: Anthropogenic-Induced or Natural?

In a paper published in Global Change Biology, Perry and Smithers (2011) write that "in recent decades, coral cover has markedly declined on coral reefs throughout the Indo-Pacific and Caribbean, with 60%-70% of coral communities now believed to be directly threatened by anthropogenic activities," and in this regard they further indicate that "a wide range of anthropogenic stressors are commonly implicated," including "increased stress from changing marine environmental conditions (especially sea surface temperatures and ocean chemistry changes)," which many believe will lead to "unparalleled reductions in reef accretion potential and accelerated rates of reef framework disintegration," specifically citing in this regard the papers of Hoegh-Guldberg et al. (2007) and Veron et al. (2009).

However, as they continue, "most assessments of changing reef condition fail to consider the additional, but potentially significant, underlying influence a reef's age and evolutionary state exert on its contemporary ecological status and accretionary potential." Hence, they go on to "examine regional histories of mid- to late-Holocene reef establishment and growth to provide a longer-term context for interpretations of contemporary reef geomorphic and ecological states and trajectories," utilizing "reef chronostratigraphic data from the terrigenous sediment-dominated inner-shelf of the Great Barrier Reef, Australia, as a case site," which they say "is arguably the only region globally where sufficient reef accretion data exist to examine these issues at appropriate spatial scales."

The result of this undertaking, as they describe it, was their finding that even throughout the late Holocene, "reef health and growth has fluctuated through cycles independent of anthropogenic forcing." Thus, they concluded -- and rightly so -- that "degraded reef states cannot de facto be considered to automatically reflect increased anthropogenic stress," noting that "in many cases degraded or non-accreting reef communities may reflect past reef growth histories as much as contemporary environmental change."

Additional References
Hoegh-Guldberg, O., Mumby, P.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K., Knowlton, N, Eakin, C.M., Iglesias-Prieto, R., Muthiga, N., Bradbury, R.H., Dubi, A. and Hatziolos, M.E. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318: 1737-1742.

Veron, J.E.N., Hoegh-Guldberg, O., Lenton, T.M., Lough, J.M. and Obura, D.O. 2009. The coral reef crisis: the critical importance of <350 ppm CO₂. Marine Pollution Bulletin 58: 1428-1436.