How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic


Coral Reef Recovery Following the 1982/1983 ENSO Event
Reference
Glynn, P.W., Colley, S.B., Ting, J.H., Mate, J.L. and Guzman, H.M. 2000. Reef coral reproduction in the eastern Pacific: Costa Rica, Panama and Galapagos Islands (Ecuador). IV. Agariciidae, recruitment and recovery of Pavona varians and Pavona sp.a. Marine Biology 136: 785-805.

What was done
The authors studied the responses of two eastern Pacific zooxanthellate coral species to the El Nio-Southern Oscillation disturbance of 1982/1983 in Costa Rica, Panama and the Galapagos Islands (Ecuador).

What was learned
The warming of the sea produced by the 1982/1983 ENSO event devastated coral communities in the three localities studied and was, in the authors' words, "the most severe ever reported over such a broad coral-reef region." Mean coral mortality in Costa Rica, for example, was approximately 50%, while in Panama it ranged from 75 to 85% and in the Galapagos Islands it was 97%. Immediately thereafter, however, the corals began to make a comeback, slowly at first, but gradually increasing with time. Moreover, recruitment was positively correlated with sea surface temperatures (SSTs), as increasingly-higher water temperatures increasingly enhanced coral reproduction up to a positive temperature anomaly of 1.56C. Thus helped by warmer waters, the corals returned to pre-ENSO abundances in about a decade, after which they were again devastated by the 1997/1998 ENSO event.

What it means
Even in the face of the monumental mortality associated with the high SSTs of the 1982/1983 ENSO event, the corals studied in this long-term observation program returned to pre-ENSO conditions within a mere ten years of their near-annihilation; and the warmer it was in those subsequent years, the bigger were the strides they made in reestablishing themselves. These observations demonstrate the resiliency of corals and testify to their ability to overcome tremendous hardships; but they also raise a provocative question. Why did annual recruitment in these corals rise higher and higher in response to increases in SSTs, only to crash once again when the positive temperature anomaly rose but a mere 0.02C, from 1.56C to 1.58C? It does not seem logical that such a tiny increase in temperature would not only halt the positive effects that increasing SSTs had had to that point, but that they would lead to the actual death of the corals. Clearly, there must be another factor at work in this strange coral history.


Reviewed 6 September 2000