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Coral Reefs (History - General) -- Summary
In an article entitled "Reefs Happen," which presents an overview of the findings of a number of papers in a special issue of Global Change Biology that address the potential impacts of global environmental change on the planet's coral reefs, Kinzie and Buddemeier (1996) note that coral reefs have persisted through geologic periods of huge environmental transformation. They are survivors, they state, "because they do not simply tolerate environmental changes." Rather, "they exhibit an impressive array of acclimations in the short term, adaptations at the population level in the longer term, and responses in the form of changes in community composition ... over even longer time periods." As a result, they conclude that corals and other reef organisms are "well adapted to surviving natural environmental change," such as global warming, noting that "the growing human population and its direct effects [our italics]" provide the "most dominant impact" on coral reef health and stability.

Writing in the same issue of Global Change Biology, Wilkinson (1996) examined the ability of coral reefs to cope with the potential changes in climate that are predicted by many coupled ocean-atmosphere general circulation models. In doing so, he concluded that "reefs on average should cope well with regional climate change, as they have coped with similar previous fluctuations," noting, for example, that coral reefs survived the most bitter cold of the last ice age, when sea levels were over 100 meters lower than at present and mean temperatures were 8C cooler. In addition, he notes that reefs weathered the rapid rise in sea level that accompanied the demise of the Last Glacial Maximum, as well as large changes in a number of other environmental parameters, including atmospheric CO2 concentration, rainfall, cloud cover, storms and ocean currents. Hence, he writes that if rates of sea level rise do indeed increase as suggested by model simulations, they will still be low "compared to Holocene rates of rise."

Yet a third person writing in the special coral issue of Global Change Biology was Chadwick-Furman (1996), who reviewed what is known about the evolution of reef-building corals over the past 240 million years and used this knowledge to infer potential impacts on coral reef diversity in light of predictions of future changes in temperature and sea level. Her assessment of the literature led her to conclude that any future rise in sea level would likely benefit the world's coral reefs, as she reports that "many coral reefs have already reached their upward limit of growth at present sea level, and may be released from this vertical constraint by a rise in sea level." In addition, she notes that rising sea levels may allow "more water circulation between segregated lagoons and outer reef slopes," which could "increase the exchange of coral propagules between reef habitats and lead to higher coral diversity in inner reef areas." She also points out that at different times in the past, coral reefs have survived sea level rises of "more than twice the rate" that is predicted by current ocean-atmosphere general circulation models.

As for changes in sea surface temperature, Chadwick-Furman suggests that although the warming predicted by global climate models for the next century might well cause higher rates of coral mortality in some cases, it may positively impact coral diversity in reefs of "latitudinally marginal areas, which presently are temperature limited." On the whole, therefore, as she summarized the situation, "coral reefs are likely to survive predicted rates of global change," with a much more dire threat being "regional anthropogenic stress" due to pressures that "are most intense near human population centers."

Three years later Wilkinson (1999) again reviewed what was known about coral reefs and a number of current and potential threats to their well-being. With respect to local or direct anthropogenic stresses, he concluded that the prognosis "is indeed grim, with major reductions almost certain in the extent and biodiversity of coral reefs, and severe disruptions to cultures and economies dependent on reef resources." With respect to more global or indirect anthropogenic stresses, however, he concluded that the prognosis "is more encouraging because coral reefs have remarkable resilience to severe disruption and will probably show this resilience in the future when climate changes either stabilize or reverse." He also noted that although no one can predict the future with certainty, his review of the literature led him to conclude "there is little doubt that coral reefs will eventually recover from the present ranges of human-induced pressures and continue to exist and evolve in changing environments into the future," suggesting, in fact, that "they should outlive the species causing most damage at the moment, Homo sapiens."

In an original research study, Greenstein et al. (1998) broached the problem of the "shifting baseline syndrome," stating the obvious but oft-neglected truth that "it must be demonstrated that the classic reef coral zonation pattern described in the early days of coral reef ecology, and upon which 'healthy' versus 'unhealthy' reefs are determined, are themselves representative of reefs that existed prior to any human influence." Hence, they conducted systematic censuses of life and death assemblages on healthy modern patch reefs in the Florida Keys and the Bahamas, and compared the results to censuses of ancient reef assemblages preserved in Pleistocene limestones in close proximity to the modern reefs. This work revealed that living patch reefs of the Florida Keys were "representative of patch reefs that flourished prior to any human influence in that area." In the Bahamas, however, they observed a recent rapid decline of A. cervicornis that they described as "a unique event that contrasts with the long-term persistence of this taxon during Pleistocene and Holocene time."

So what do these results imply?

The recent complete die-off of once-dominant Acropora cervicornis and its subsequent replacement by Porites porites, which Greenstein et al. say "does not have a Pleistocene precedent," argues strongly against global warming being its cause, since the Pleistocene record is replete with evidence of climatic changes of large magnitude -- reaching significantly greater warmth than what currently prevails on earth -- and those changes had essentially no effect on this long-term dominant species of Caribbean coral reefs. Consequently, whereas the lack of long-term data on coral community composition has long confounded attempts to determine whether various faunal replacements are natural components of long-term ecological cycles or unprecedented phenomena resulting primarily from anthropogenic disturbances, it now seems clear that direct assaults of humanity are likely what have brought about the demise of this particular Caribbean coral. Global warming, by itself, does not appear to be implicated.

Considerably more evidence for this line of thinking has been provided by a host of other researchers, as described in our editorial of 26 June 2002, where we note that the scleractinian corals, which are the major builders of the reefs of today (Achituv and Dubinsky, 1990), appeared in the mid-Triassic some 210 million years ago (Wells, 1956), when the earth was considerably warmer than it is currently (Chadwick-Furman, 1996). They were also present throughout the Cretaceous, when temperatures were as much as 10-15C higher than at present (Chadwick-Furman, 1996). Last of all, they survived the numerous warm interglacials that have punctuated the great Pleistocene ice ages (Pandolfi, 1999).

Of these latter warm periods, the most pertinent, of course, are the most recent, as their thermal conditions would have impacted the most immediate predecessors of today's corals; and we are fortunate in this regard to have a 420,000-year record of Antarctic temperatures that was derived from the Vostok ice core by Petit et al. (1999). Their extensive data set clearly indicates that all four interglacials that preceded the current interglacial were warmer than the one in which we presently live by an average thermal increment in excess of 2C. Furthermore, the most recent of the prior four interglacials was fully 3C warmer.

Of course, one can always say these data pertain to Antarctica, which is not the part of the world where most corals are found. However, Muhs et al. (2002) published a review of a vast array of globally-dispersed faunal records -- including marine invertebrates, such as mollusks, ostracodes and corals themselves -- from which Last-Interglacial ocean temperatures can be inferred. Beginning with their own work, they note that both Oahu, Hawaii and Bermuda, which they studied in great detail, exhibit evidence of a number of "extralimital southern species of mollusks, suggesting warmer-than-present waters during the Last Interglacial period." Warmer Last-Interglacial waters are similarly suggested for localities around North America, including Alaska, Greenland, Baffin Island, Nantucket Island, southern Florida, Baja California, California and Oregon. In addition, Muhs et al. note that "studies in Japan, the Mediterranean Basin and Western Australia also show evidence of warmer-than-modern Last-Interglacial waters." And in many of the cases of high-temperature-induced latitudinal displacement of species, the distances involved spanned hundreds -- and in some instances even thousands -- of kilometers. Also, in a study of marine sediment cores obtained along the western coast of North America from the southern tip of the Baja Peninsula to Oregon, Herbert et al. (2001) determined that "the previous interglacial produced surface waters several degrees warmer than today," such that "waters as warm as those now at Santa Barbara occurred along the Oregon margin."

Even the several-thousand-year-long central portion of the current interglacial was considerably warmer than it has been recently. On the basis of temperature reconstructions derived from studies of latitudinal displacements of terrestrial vegetation (Bernabo and Webb, 1977; Wijmstra, 1978; Davis et al., 1980; Ritchie et al., 1983; Overpeck, 1985) and vertical displacements of alpine plants (Kearney and Luckman, 1983) and mountain glaciers (Hope et al., 1976; Porter and Orombelli, 1985), it has been concluded (Webb et al., 1987; COHMAP, 1988) that mean annual temperatures in the Midwestern United States were about 2C warmer than those of the past few decades (Bartlein et al., 1984; Webb, 1985), that summer temperatures in Europe were 2C warmer (Huntley and Prentice, 1988), as they also were in New Guinea (Hope et al., 1976), and that temperatures in the Alps were as much as 4C warmer (Porter and Orombelli, 1985; Huntley and Prentice, 1988). In the Russian Far East, temperatures are also reported to have been from 2 C (Velitchko and Klimanov, 1990) to as much as 4-6C (Korotky et al., 1988) higher than they were over the past few decades; while the mean annual temperature of the Kuroshio Current between 22 and 35N was 6C warmer (Taira, 1975).

These several observations, as well as a host of others not cited, bear witness to the fact that many times in the past, the coral species that currently inhabit the planet have successfully endured temperatures well in excess of what climate alarmists typically claim should pretty much spell their doom; and the fact that they are still with us speaks volumes about their resiliency. For the past several centuries, however, a number of direct and localized human activities have degraded coastal environments the world over to the point where today's corals can no longer respond to rising temperatures with the resiliency that served them so well in the past, being subject, as they are, to so many other anthropogenic-induced stresses (Idso et al., 2000). Thus, it is becoming more and more commonplace that periods of higher-than-usual temperatures do indeed result in deadly episodes of coral bleaching; and this synergism is showing signs of reaching mammoth proportions.

In another intriguing paper, Jackson et al. (2001) addressed, not just the health of coral reefs, but the well-being of all coastal ecosystems. The primary hypothesis advanced by the authors of this landmark study is that "humans have been disturbing marine ecosystems since they first learned how to fish." To truly understand the reasons for ecosystem changes that have occurred over the past several decades, therefore, they feel it is necessary to know what occurred to them over the past several centuries; and they provide this historical background via well-dated biological, biogeochemical, physical and historical proxies, as well as via archaeological discoveries in human coastal settlements spanning the last 10,000 years, historical records from documents, journals and charts dating from the 15th century onward, and ecological data from the scientific literature of the past hundred years.

Two examples of this approach, which Jackson et al. describe in some detail, concern the near disappearance over the past 20 to 30 years of subtidal seagrasses in the offshore half of Moreton Bay near Brisbane, Australia, and the simultaneous die-off of turtlegrass in Florida Bay and the Gulf of Mexico. Before humans appeared on the scene, these grasses provided forage and habitat for enormous numbers of large dugongs (sea cows) and sea turtles, as well as many commercially-important fish and invertebrates. Even before the arrival of Europeans, however, the aboriginal people of Australia had already harvested dugongs extensively; but as late as 1893, the authors note that herds comprising "tens of thousands of large individuals" were still observed in Moreton Bay. Shortly thereafter, however, they report that "widespread colonial exploitation of dugongs for their flesh and oil resulted in the crash of the dugong fishery." So drastic was the reduction in the dugong population that the report of a mere 300 individuals in Moreton Bay in 1978 was considered an important "discovery."

So what's the significance of these observations for seagrasses? Jackson et al. note that moderate-sized herds of dugongs can remove over 90% of leafy seagrass blades and up to 70% of their roots. This "systematic plowing " of the bay floor, say the authors, provides space for colonization by competitively inferior species of seagrasses, while producing massive amounts of floating debris and dung that are exported to -- and used by -- adjacent ecosystems. It also provides for shorter grass blades, as do the grazing activities of sea turtles. In the near absence of green turtles today, for example, Jackson et al. note that "turtlegrass beds grow longer blades that baffle currents, shade the bottom, start to decompose in situ, and provide suitable substrate for colonization by the slime molds that cause turtlegrass wasting disease." They also report that "deposition within the beds of vastly more plant detritus also fuels microbial populations, increases the oxygen demand of sediments, and promotes hypoxia." All of these deleterious consequences of massive human destruction of dugong and sea turtle populations tend to weaken seagrasses and make them more susceptible to other anthropogenic-induced assaults upon their environment, such as increased eutrophication, sedimentation and water turbidity, until there finally comes the proverbial "straw that breaks the camel's back," which can be any number of things of either human or natural origin.

Other examples of the deleterious cumulative consequences of mankind's long history of harvesting sea life that are described by Jackson et al. deal with kelp forests, oyster beds, offshore benthic communities and, of course, coral reefs, the recent troubles of which are routinely blamed on global warming. However, as Jackson et al. and we have both noted (see much of the material filed under Coral Reefs in our Subject Index), there are many much more direct anthropogenic assaults upon coral reefs and their environment that have historically combined to place a truly heavy burden upon the backs of these fragile ecosystems.

In yet another seminal paper to address this subject, Pandolfi et al. (2003) began by noting that "the long-term historic sequence of ecosystem decline is unknown for any reef, thereby obscuring the potential linkage and interdependence of the different responsible factors that must be unraveled for successful restoration and management." Hence, they take their own advice and reconstruct multi-century histories of fourteen coral reefs from around the world, employing a common set of consistent criteria, before attempting to prescribe a restorative treatment program.

This exercise revealed, in the words of the twelve contributing scientists, that "all reefs were substantially degraded long before outbreaks of coral disease and bleaching," which phenomena currently garner the lion's share of attention when it comes to assessing reef health. In fact, they report that the "degradation of coral reef ecosystems began centuries ago," when, of course, the world was still in the midst of the Little Ice Age.

So how far down the slippery slope that leads to extinction are the world's coral reefs currently? And what has propelled them to this unfortunate position?

Pandolfi et al.'s analysis revealed that the 14 coral reefs they studied are fairly evenly distributed between just under 30% to just under 80% of the way from what they call "pristine" to "ecologically extinct," and they find that "the most important guilds influencing the trajectories of decline are large herbivores and carnivores," which they report "were almost nowhere pristine by the beginning of the 20th century, when these guilds were already depleted or rare in more than 80% of the 14 regions examined."

With regard to the present, the scientists note that "recent widespread and catastrophic episodes of coral bleaching and disease have distracted attention from the chronic and severe historical decline of reef ecosystems." Noting that "all of the reefs in our survey were substantially degraded long before the first observations of mass mortality resulting from bleaching and outbreaks of disease," they conclude that "the only reasonable explanation for this earlier decline is overfishing, although land-derived pollution could have acted synergistically with overfishing in some localities."

In describing the practical implications of their findings, Pandolfi et al. say that "coral reef ecosystems will not survive for more than a few decades unless they are promptly and massively protected from human exploitation," which is what we have advocated from the very beginning of this discussion on our website (see, for example, our Editorials of 1 Jan 1999 and 26 Mar 2003). It should be abundantly clear to most thinking people, therefore, that to claim that we must halt global warming to save these precious ecosystems, as most climate alarmists do, is to look beyond the mark and to therefore likely fail to implement the more mundane (but absolutely necessary) protective measures that must be put in place now. Taking the other course may well give folks who have been misled by Al Gore and his minions a warm fuzzy feeling, but it will consign earth's corals to oblivion. We cannot be distracted by tilting at windmills when a clear and present danger is staring us right in the face.

Somewhat surprisingly, another group of coral researchers (Aronson et al., 2003) had some major problems with the study of Pandolfi et al., claiming that coral reefs in many parts of the world did not begin to suffer to any significant degree "until recent decades," and questioning Pandolfi et al.'s hypothesis that prior overfishing was the leading cause of long-term reef degradation. In their response to this challenge, however, Pandolfi et al. (2003b) remained unmoved from their original position, as the following series of quotes from their rebuttal clearly demonstrates.

"Coral reef ecosystems were degraded long before more recent changes attributable to climate change or disease" "Recent changes represent an ongoing degradation that long predates modern ecological studies" ... "Although we agree that bleaching and disease are becoming more prevalent, the ability of reefs to absorb these impacts will clearly depend on the extent to which they are already degraded" ... "So-called proximal causes [bleaching and disease] are not the ones that have acted over long time periods or that have caused the most intense degradation of reefs and associated ecosystems" ... "The ultimate causes of coral reef ecosystem decline are more subtle than recent proximal ones and reach further back in time than events observed in the past few decades."

What would a qualified third party have to say about this debate? Fortunately, one has weighed in on the issue; and it is a group to which Aronson et al. actually appealed in their critique of Pandolfi et al. (2003a), when they said that a review by Hughes et al. (2003) "concludes that climate change and disease are the primary agents of increased coral mortality and that degraded reefs will survive, albeit with altered species composition."

Normally, one would not think that such a brief remark -- which does not question the findings of the third party and actually cites them approvingly -- would elicit a response from them. Nevertheless, the third group (Hughes et al.) took it upon themselves to respond to Aronson et al. in language that clearly supports Pandolfi et al.'s original thesis.

"We focused more on contemporary threats and future solutions" ... "Human impacts and the increased fragmentation of coral reef habitat have undermined reef resilience, making them much more susceptible to current and future climate change" ... "In particular, we presented clear, unambiguous evidence that over-harvesting of herbivorous fishes can impair the resilience of coral reefs and inhibit their recovery from bleaching and other disturbances" ... "We do not consider our findings to be in conflict with those of Pandolfi et al."

In light of this further discussion of the causes of both long- and shorter-term coral reef degradation, we continue to hold to our belief that to save earth's fast-fading coral reef ecosystems we must focus our attention on alleviating the many direct effects of human activities that have (1) negatively affected them in the past, (2) continue to plague them in the present, and (3) will destroy them in the not too distant future, unless we act soon and properly. To believe that we will save these incomparable ecosystems by implementing the almost totally ineffective Kyoto Protocol, or anything like it, is simply wishful thinking -- or worse! -- for the resulting neglect of the real problem, about which we actually can do something, is to allow earth's coral reefs to continue unimpeded down the road to extinction, which most reefs have already halfway traversed and from whence there is no hope of their ever returning.

In concluding this Summary, we report on the paper of Precht and Aronson (2004), which is like a breath of fresh air compared to what is typically 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 above, 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.

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Last updated 16 January 2008