Volume 10, Number 32: 8 August 2007
Coral reefs of the eastern Pacific Ocean, according to Guzman and Cortes (2007), "suffered unprecedented mass mortality at a regional scale as a consequence of the anomalous sea warming during the 1982-1983 El Niņo." At Cocos Island (5°32'N, 87°04'W), for example, they found in a survey of three representative reefs, which they conducted in 1987, that remaining live coral cover was only 3% of what it had been prior to the occurrence of the great El Niņo four years earlier (Guzman and Cortes, 1992). Based on this finding and the similar observations of other scientists at other reefs, they predicted that "the recovery of the reefs' framework would take centuries, and recovery of live coral cover, decades." In 2002, therefore, nearly 20 years after the disastrous coral-killing warming, they returned to see just how prescient they might have been after their initial assessment of the El Niņo's horrendous damage, quantifying "the live coral cover and species composition of five reefs, including the three previously assessed in 1987."
So what did they find?
The two researchers report that overall mean live coral cover increased nearly five-fold, from 2.99% in 1987 to 14.87% in 2002, at the three sites studied during both periods, while the mean live coral cover of all five sites studied in 2002 was 22.7%. In addition, they found that "most new recruits and adults belonged to the main reef building species from pre-1982 ENSO, Porites lobata, suggesting that a disturbance as outstanding as El Niņo was not sufficient to change the role or composition of the dominant species."
Another interesting aspect of the study was the fact that a second major El Niņo occurred between the two assessment periods; and Guzman and Cortes state that "the 1997-1998 warming event around Cocos Island was more intense than all previous El Niņo events," noting that temperature anomalies "above 2°C lasted 4 months in 1997-1998 compared to 1 month in 1982-83." Nevertheless, they report that "the coral communities suffered a lower and more selective mortality in 1997-1998 [our italics], as was also observed in other areas of the eastern Pacific (Glynn et al., 2001; Cortes and Jimenez, 2003; Zapata and Vargas-Angel, 2003)," which is indicative of some type of thermal adaptation following the 1982-83 El Niņo.
As for the source of the expanded coral cover that Guzman and Cortes discovered in their 2002 census of the Cocos Island reefs, they opine that "recovery may have begun with the sexual and asexual recruits of the few surviving colonies of P. lobata and Pavona spp. and with long distance transport of larvae from remote reefs," the latter of which phenomena is suggested by the fact that some of the species found, such as L. scabra, P. maldivensis, P. frondifera, P. chiriquensis and P. inflata, "had not been reported before the mid-1990s for Cocos Island."
In concluding their revealing paper, Guzman and Cortes thus state that "for Cocos Island (Guzman and Cortes, 1992) and for most areas of the tropical eastern Pacific (Glynn, 1990; Glynn et al., 2001; Guzman et al., 2004) there are recovery processes (e.g., reproduction, larvae dispersion, recruitment) and possibly short-term thermal adaptation, that ensured the recovery [our italics] of the more degraded reefs." Consequently, seeing no reason why these same phenomena should not continue to operate in the future, we presume they will also ensure the recovery of earth's coral reefs from future warming events.
Sherwood, Keith and Craig Idso
References
Cortes, J. and Jimenez, C. 2003. Corals and coral reefs of the Pacific of Costa Rica: history, research and status. In: Cortes, J. (Ed.) Latin American Coral Reefs. Elsevier, Amsterdam, The Netherlands, pp. 361-385.
Glynn, P.W. 1990. Coral mortality and disturbance to coral reefs in the tropical eastern Pacific. In: Glynn, P.W. (Ed.) Global Ecological Consequence of the 1982-83 El Niņo-Southern Oscillation. Elsevier, Amsterdam, The Netherlands, pp. 55-126.
Glynn, P.W., Mate, J.L., Baker, A.C. and Calderon, M.O. 2001. Coral bleaching and mortality in Panama and Ecuador during the 1997-98 El Niņo-Southern Oscillation event: spatial/temporal patterns and comparisons with the 1982-1983 event. Bulletin of Marine Science 69: 79-109.
Guzman, H.M. and Cortes, J. 1992. Cocos Island (Pacific of Costa Rica) coral reefs after the 1982-83 El Niņo disturbance. Revista de Biologia Tropical 40: 309-324.
Guzman, H.M. and Cortes, J. 2007. Reef recovery 20 years after the 1982-1983 El Niņo massive mortality. Marine Biology 151: 401-411.
Guzman, H.M., Guevara, C.A. and Breedy, O. 2004. Distribution, diversity, and conservation of coral reefs and coral communities in the largest marine protected area of Pacific Panama (Coiba Island). Environmental Conservation 31: 111-122.
Zapata, F.A. and Vargas-Angel, B. 2003. Corals and coral reefs of the Pacific coast of Columbia. In: Cortes, J. (Ed.) Latin American Coral Reefs. Elsevier, Amsterdam, The Netherlands, pp. 419-447.