How does rising atmospheric CO2 affect marine organisms?

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Coral Reefs: Past, Present and Future
Volume 8, Number 10: 9 March 2005

We have long contended that projections of how living entities and physical phenomena respond to global warming should be based on real-world knowledge of how they have responded to rising temperatures in the past, rather than on the output of idealized conceptual models; and in this regard, the paper of Precht and Aronson (2004), dealing with earth's coral reefs, is like a breath of fresh air compared to what is characteristically served up by the climate alarmists of the world, who seem addicted to computer-based "storylines" and their doom-and-gloom consequences.

Focusing on the planet's past, the two marine biologists note that throughout the early to middle Holocene (from 10,000 to 6,000 years ago), extratropical North Atlantic sea surface temperatures (SSTs) were 2-3C warmer than at present (Balsam, 1981; Ruddiman and Mix, 1991), and that reefs dominated by staghorn coral (Acropora cervicornis) and elkhorn coral (Acropora palmata) were common along the east coast of Florida as far north as Palm Beach County (Lighty et al., 1978).  In addition, they note that this period "correlates with maximal coral diversity at the northernmost position of coral reefs in the Pacific," and that "evidence from both terrestrial and coastal habitats shows that warming during this millennial-scale, high-amplitude climate flicker caused many species from a variety of ecosystems to expand their ranges northwards (COHMAP, 1988; Delcourt and Delcourt, 1991; Dahlgren et al., 2000)."  Of particular interest, in this regard, they note that "Veron's (1992) study of a mid-Holocene fossil reef at Tateyama [the world's highest latitude Pacific coral reef] showed that even a brief period of warming of only 2C doubled species richness from 35 to 72 species at the latitudinal extreme of extant corals."

Citing similar examples from the Southern Hemisphere, Precht and Aronson conclude that the fossil record clearly demonstrates the ability of corals to expand their ranges poleward in response to global warming and to "reconstitute reef communities in the face of rapid environmental change."  In fact, they report that coral range expansions are occurring today, noting that "there is mounting evidence that coral species are responding to recent patterns of increased SSTs by expanding their latitudinal ranges."  And in support of this statement, they cite a number of real-world examples, including (1) the recent establishment of staghorn coral off Fort Lauderdale in Broward County, Florida (Vargas-Angel et al., 2004), (2) the expansion of elkhorn coral as far north as Pompano Beach in northern Broward County, (3) the discovery of elkhorn coral at the Flower Garden Banks in the northern Gulf of Mexico, (4) the identification of eight coral species along the eastern Pacific that are considerably north of their previously known ranges, and (5) the arrival of six new species of coral at Lord Howe Island in Australia within the past decade.

The two researchers also note that "modern reef communities closely resemble fossil reef assemblages (Pandolfi and Jackson, 1997)," and that their "stability and persistence through Quaternary time" suggests they are well equipped to weather the types of climate change predicted for the future.  What is more, they report that "warmer temperatures during the last major interglacial period were not associated with contraction of the southern range of the acroporids or the demise of reef systems in the tropics [our italics]."  Hence, they conclude "it is unlikely that future global warming will lead to the catastrophic collapse of reef systems, the extirpation of acroporid corals, or the contraction of their southern range in the tropical Caribbean, as some have predicted (e.g., Hoegh-Guldberg, 1999; Reaser et al., 2000)."

Interestingly, we have suggested essentially the same thing with respect to terrestrial ecosystems in our Major Report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?, where we show that elevated atmospheric CO2 concentrations enable plants to photosynthesize optimally at temperatures that are considerably greater than those to which they are presently best adapted.  This phenomenon allows them to maintain fairly stable borders at the southern extremes of their ranges in the Northern Hemisphere while their northern borders expand poleward in latitude and upward in elevation in response to global warming.  In addition, we report a number of real-world observations of this phenomenon in the animal kingdom.

An exciting corollary of these facts is that concomitant increases in air temperature and CO2 concentration tend to increase local biodiversity almost everywhere on earth, as plant and animal ranges expand and overlap each other.  In the Specter of Species Extinction, we provide much real-world evidence for the ongoing expression of this phenomenon in both plants and animals of the terrestrial environment; and as noted earlier in this editorial, the warmth of the early to middle Holocene "correlates with maximal coral diversity at the northernmost position of coral reefs in the Pacific," even at lower CO2 concentrations than those of today, which is indicative of an impressive ability of corals to adapt to rising water temperatures, most likely by means of symbiont shuffling.

Taken together, these several real-world observations of both the past and present suggest that earth's coral reefs are quite capable of maintaining themselves, and even flourishing, in the face of rising atmospheric CO2 concentrations and/or temperatures IF humanity's many localized assaults upon them (increased physical destruction, heightened pollution, augmented sedimentation, etc.) do not destroy them first, which is also a primary concern of Precht and Aronson.  It is upon these latter affronts to coral health that we must focus our attention if we ever hope to save them.

Sherwood, Keith and Craig Idso

References
Balsam, W.  1981.  Late Quaternary sedimentation in the western North Atlantic: stratigraphy and paleoceanography.  Palaeogeography, Palaeoclimatology, Palaeoecology 35: 215-240.

COHMAP Members.  1888.  Climatic changes of the last 18,000 years: observations and model simulations.  Science 241: 1043-1052.

Dahlgren, T.G., Weinberg, J.R. and Halanych, K.M.  2000.  Phylogeography of the ocean quahog (Artica islandica): influences of paleoclimate on genetic diversity and species range.  Marine Biology 137: 487-495.

Delcourt, H.R. and Delcourt, P.A.  1991.  Quaternary Ecology - a Paleoecological Perspective.  Chapman and Hall, London, UK.

Hoegh-Guldberg, O.  1999.  Climate change, coral bleaching and the future of the world's coral reefs.  Marine and Freshwater Research 50: 839-866.

Lighty, R.G., Macintyre, I.G. and Stuckenrath, R.  1978.  Submerged early Holocene barrier reef south-east Florida shelf.  Nature 276: 59-60.

Pandolfi, J.M. and Jackson, J.B.C.  1997.  The maintenance of diversity on coral reefs: examples from the fossil record.  Proceedings of the 8th International Coral Reef Symposium 1: 397-404.

Precht, W.F. and Aronson, R.B.  2004.  Climate flickers and range shifts of reef corals.  Frontiers in Ecology and the Environment 2: 307-314.

Reaser, J.K., Pomerance, R. and Thomas, P.O.  2000.  Coral bleaching and global climate change: scientific findings and policy recommendations.  Conservation Biology 14: 1500-1511.

Ruddiman, W.F. and Mix, A.C.  1991.  The north and equatorial Atlantic at 9000 and 6000 yr P.P. In: Wright Jr., H.E., Kutzbach, J.E., Webb III, T., et al. (Eds.).  Global Climates Since the Last Glacial Maximum.  University of Minnesota Press, Minneapolis, MN, p. 94-124.

Vargas-Angel, B., Thomas, J.D. and Hoke, S.M.  2003.  High-latitude Acropora cervicornis thickets off Fort Lauderdale, Florida, USA.  Coral Reefs 22: 465-474.

Veron, J.E.N.  1992.  Environmental control of Holocene changes to the world's most northern hermatypic coral outcrop.  Pacific Science 46: 405-425.