Caribbean Corals: What's Really Been Giving Them a Hard Time?

In introducing their newest study of the subject, Cramer et al. (2012) write that "Caribbean reef corals did not appear to be affected by human activities until the 1980s (Hughes, 1994)," but they say that "since this period, coral cover in the Caribbean has declined by an average of 80% (Gardner et al., 2003) and branching species of Acropora and Porites corals have been replaced by non-branching species of Agaricia and Porites," citing Aronson et al. (2004, 2005) and Green et al. (2008). They also indicate that "surveys of fossil reefs have revealed that such drastic changes in Caribbean coral communities are unprecedented over the last c. 200,000 years despite large fluctuations in sea level and climate (Pandolfi and Jackson, 2006; Greer et al., 2009), implicating [some non-climatic] anthropogenic disturbance in the recent decline." Nevertheless, they write that "the appearance and intensification of mass coral disease and bleaching events in the Caribbean and elsewhere have been widely attributed to anthropogenic climate change."

So what, or who, is the real culprit? And how was the guilty party identified?

In terms of their contribution to the search effort, Cramer et al. "analyzed coral and molluscan fossil assemblages from reefs near Bocas del Toro, Panama to construct a timeline of ecological change from the 19th century to the present." This work revealed "large changes before 1960 in coastal lagoons coincident with extensive deforestation, and after 1960 on offshore reefs." Some of the "striking changes" they identified include "the demise of previously dominant staghorn coral Acropora cervicornis and oyster Dendrostrea frons that lives attached to gorgonians and staghorn corals." And they say that "reductions in bivalve size and simplification of gastropod trophic structure further implicate increasing environmental stress on reefs."

In discussing their findings, the five researchers say that "the dramatic historical transformations we quantified on reefs near Bocas del Toro are consistent with results of previous qualitative surveys from other regions of the Caribbean," noting that Pandolfi et al. (2003) demonstrated that "reef corals including Acropora spp. were depleted at sites across the Caribbean as early as the 19th century," and that Jackson et al. (2001) had determined that "the proportion of sites dominated by Acropora corals in particular had declined before the 1980s." In addition, they state that "paleoecological data from the opposite end of the southern Caribbean in Barbados showed that A. palmata underwent a dramatic decline within the past centuries concurrent with large-scale land clearing during the onset of European colonization," citing Lewis (1984).

In summing up the implications of their findings and commenting on their significance, Cramer et al. write, in the concluding sentence of their paper's abstract that, "our paleoecological data strongly support the hypothesis, from extensive qualitative data, that Caribbean reef degradation predates coral bleaching and disease outbreaks linked to anthropogenic climate change." And they state, in the concluding sentence of the body of their paper, that their results - "coupled with increasing evidence that protection from local disturbances may increase reef resilience to climate change (Hughes et al., 2007; Knowlton and Jackson, 2008)" - "highlight the importance of managing local impacts such as fishing and land clearing to stem the tide of reef decline." And it thus becomes ever more clear, from these real-world findings, that each coastal location on Earth must be accountable to itself - or to regions upstream if located at the mouth of a river - for whatever coral reef degradation may be occurring off its shores.

Additional References
Aronson, R.B., Macintyre, I.G., Wapnick, C.M. and O'Neill, M.W. 2004. Phase shifts, alternative states, and the unprecedented convergence of two reef systems. Ecology 85: 1876-1891.

Aronson, R.B., Macintyre, I.G., Lewis, S.A. and Hilbun, N.L. 2005. Emergent zonation and geographic convergence of coral reefs. Ecology 86: 2586-2600.

Gardner, T.A., Cote, I.M., Gill, J.A., Grant, A. and Watkinson, A.R. 2003. Long-term region-wide declines in Caribbean corals. Science 301: 958-960.

Green, D.H., Edmunds, P.J. and Carpenter, R.C. 2008. Increasing relative abundance of Porites astreoides on Caribbean reefs mediated by an overall decline in coral cover. Marine Ecology Progress Series 359: 1-10.

Greer, L., Jackson, J.E., Curran, H.A., Guilderson, T.P. and Teneva, L. 2009. How vulnerable is Acropora cervicornis to environmental change? Lessons from the early to middle Holocene. Geology 37: 262-266.

Hughes, T.P. 1994. Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral reef. Science 265: 1547-1551.

Hughes, T.P., Rodrigues, M.J., Bellwood, D.R., Ceccarelli, D., Hoegh-Guldberg, O. and McCook, L. 2007. Phase shifts, herbivory, and the resilience of coral reefs to climate change. Current Biology 17: 360-365.

Jackson, J.B., Kirby, M.X., Berger, W.H., Bjorndal, K.A., Botsford, L.W., Bourque, B.J., Bradbury, R.H., Cooke, R., Erlandson, J., Estes, J.A., Hughes, T.P., Kidwell, S., Lange, C.B., Lenihan, H.S., Pandolfi, J.M., Peterson, C.H., Steneck, R.S., Tegner, M.J. and Warner, R.R. 2001. Historical overfishing and the recent collapse of coastal ecosystems. Science 293: 629-637.

Knowlton, N. and Jackson, J.B.C. 2008. Shifting baselines, local impacts, and global change on coral reefs. PLoS Biology 6: 215-220.

Lewis, J.B. 1984. The Acropora inheritance: a reinterpretation of the development of fringing reefs in Barbados, West Indies. Coral Reefs 3: 117-122.

Pandolfi, J.M. and Jackson, J.B.C. 2006. Ecological persistence interrupted in Caribbean coral reefs. Ecology Letters 9: 818-826.

Pandolfi, J.M., Bradbury, R.H., Sala, E., Hughes, T.P., Bjorndal, K.A., Cooke, R.G., McArdle, D., McClenachan, L., Newman, M.J.H., Paredes, G., Warner, R.R. and Jackson, J.B.C. 2003. Global trajectories of the long-term decline of coral reef ecosystems. Science 301: 955-958.