How does rising atmospheric CO2 affect marine organisms?

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Ocean Acidification (Effects on Marine Animals: Sea Urchins) -- Summary
As the atmosphere's CO2 content continues to rise, the pH of the world's oceans is expected to decline, driving a phenomenon described by climate alarmists as ocean acidification, to which they are already ascribing a host of imminent catastrophic consequences. Writing in Marine Ecology Progress Series, however, Vézina and Hoegh-Guldberg (2008) state that "without an understanding of how such a slow and continuous decline in pH is likely to affect ocean ecosystems, we may miss important aspects of this global ocean pH change," and that "to compound this uncertainty, recent research reveals counter-intuitive, positive/neutral effects of acidification on some organisms and processes." In what follows, therefore, we review a few of these "counter-intuitive, positive/neutral effects," primarily as they apply to sea urchins.

We begin with the earlier review of Kurihara (2008), who reported on the effects of ocean acidification on early developmental and reproductive stages of a number of different calcifiers, which periods of their life are believed to be "the most vulnerable stages to environmental change within a life cycle." In doing so, he indeed found that several studies suggested that "ocean acidification has negative impacts on the fertilization, cleavage, larva, settlement and reproductive stages of several marine calcifiers, including echinoderm, bivalve, coral and crustacean species," and he concluded that "future changes in ocean acidity will potentially impact the population size and dynamics, as well as the community structure of calcifiers, and will therefore have negative impacts on marine ecosystems."

Interestingly, however, most of the studies Kurihara cites did not observe statistically significant negative effects of atmospheric CO2 enrichment until very large increases in the air's CO2 content were employed. In studies of sea urchins, for example, statistically significant reductions in egg fertilization rates did not occur in Echinometra mathaei until the atmospheric CO2 concentration was raised a full 5,000 ppm above that of the ambient air; and in Hemicentrotus pulcherrimus, even a 10,000 ppm increase in the air's CO2 concentration was insufficient to elicit a statistically significant decline in egg fertilization rate. In addition, Kurihara himself suggests that the great degree of scatter in the data may reflect "a degree of genetic variation for CO2 tolerance within populations," which may allow the species to readily adapt to a long-term upward trend in the air's CO2 content. And in the conclusion to his review, he acknowledges that "recent research has revealed that organisms could evolve within decades in response to strong pressures, which Stockwell et al. (2003) termed 'contemporary evolution'," citing the work of Collins and Bell (2004), to which can be added the studies of Collins and Bell (2006) and Collins et al. (2006).

In a subsequent study, Byrne et al. (2009) investigated the effects of ocean acidification state (pH values of 8.2-7.6, corresponding to atmospheric CO2 concentrations of 230-690 ppm) and seawater temperature (20-26°C, where 20°C represents the recent thermal history of indigenous adults) on the fertilization of sea urchin (Heliocidaris erythrogramma) eggs and their subsequent development in what they call "the eastern Australia climate change hot spot," which is located near Sydney. In doing so, they say that over the ranges of seawater pH and temperature they studied, there was "no effect of pH" and "no interaction between temperature and pH" on sea urchin egg fertilization. In addition, they report that "comparative data on the effect of increased CO2 and decreased pH as a single stressor on sea urchin fertilization and development are available for five species," and that "these studies show that sea urchin fertilization and early development are only affected by pH < 7.4 (above 1000 ppm CO2)," citing the work of Bay et al. (1993), Kurihara and Shirayama (2004) and Carr et al. (2006).

Seawater pH also had no effect on the longer-term development of fertilized sea urchin eggs; but the six scientists say that warming led to "developmental failure at the upper warming (+4 to +6°C) level, regardless of pH." Even here, however, they appear quite hopeful, stating that "it is not known whether gametes from H. erythrogramma adults acclimated to 24°C would have successful development in a +4°C treatment," stating that their study "highlights the potentiality that adaptive phenotypic plasticity may help buffer the negative effects of warming, as suggested for corals." In fact, they note that "single stressor studies of thermotolerance in a diverse suite of tropical and temperate sea urchins show that fertilization and early development are robust to temperature well above ambient and the increases expected from climate change," citing the work of Farmanfarmaian and Giese (1963), Chen and Chen (1992) and Roller and Stickle (1993). All things considered, therefore, it would appear that sea urchins may be well equipped to deal with the challenges of projected ocean acidification and global warming, and then some, even if they were to occur simultaneously.

Most recently, Byrne et al. (2010) have noted that changes in seawater chemistry -- such as the pH decline that may be caused by rising atmospheric CO2 concentrations -- have the potential to negatively impact fertilization kinetics in free-spawning marine invertebrates, but that ocean warming could do the opposite and "may enhance fertilization due to positive effects on sperm swimming speeds and heightened sperm-egg collisions," such that the net effect of both phenomena acting in unison could well be negligible. Therefore, to explore the degree of likelihood of this scenario occurring in the real world, they investigated the effects of projected near-future oceanic warming and acidification for conditions that have been predicted for southeast Australia within the timeframe of 2070-2100: an increase in sea surface temperature of 2 to 4°C and a decline in pH of 0.2 to 0.4 unit. This they did in a fertilization study of the sea urchin Heliocidaris erythrogramma via multi-factorial experiments that incorporated a titration of sperm density (10-103 sperm per ml) across a range of sperm-to-egg ratios (10:1-1500:1).

In conducting these experiments, the five Australian researchers found that "across all treatments there was a highly significant effect of sperm density, but no significant effect of temperature or interaction between factors." In fact, they state that "low pH did not reduce the percentage of fertilization even at the lowest sperm densities used, and increased temperature did not enhance fertilization at any sperm density." In addition, they remark that "a number of ecotoxicology and climate change studies, where pH was manipulated with CO2 gas, show that sea urchin fertilization is robust to a broad pH range with impairment only at extreme levels well below projections for ocean acidification by 2100 (pH 7.1-7.4, 2,000-10,000 ppm CO2)," citing the work of Bay et al. (1993), Carr et al. (2006), and Kurihara and Shirayama (2004). Therefore, neither seawater warming nor seawater acidification (caused by contact with CO2-enriched air) had either a positive or a negative effect on sea urchin fertilization, suggesting, as the five scientists concluded, that "sea urchin fertilization is robust to climate change stressors."

In one final study worth reporting here, Richardson and Gibbons (2008) used coelenterate (jellyfish) records obtained from the Continuous Plankton Recorder (CPR) and pH data obtained from the International Council for the Exploration of the Sea (ICES) for the period 1946-2003 to explore the possibility of a relationship between jellyfish abundance and acidic ocean conditions in a large portion of the North Sea. This work revealed that there were, as they describe it, "no significant relationships between jellyfish abundance and acidic conditions in any of the regions investigated," and that "no observed declines in the abundance of calcifiers with lowering pH have yet been reported." In addition -- and of particular interest to the subject at hand -- they note that the "larvae of sea urchins form skeletal parts comprising magnesium-bearing calcite, which is 30 times more soluble than calcite without magnesium," and, therefore, that "lower ocean pH should drastically inhibit the formation of these soluble calcite precursors [italics added]." Yet they report "there is no observable negative effect of pH." In fact, they say that echinoderm larvae in the North Sea have actually exhibited "a 10-fold increase in recent times [italics added]," which phenomenon they say has been "linked predominantly to warming (Kirby et al., 2007)."

In concluding this summary, we make one other observation; and that is that even in the most recent IPCC report, in the words of Richardson and Gibbons, "there was no empirical evidence reported for the effect of acidification on marine biological systems (Rosenzweig et al., 2007)," in spite of all the concern that has been raised by climate alarmists claiming that such is, or should be, occurring.

Bay, S., Burgess, R. and Nacci, D. 1993. Status and applications of echinoid (phylum Echinodermata) toxicity test methods. In: Landis, W.B., Hughes, J.S. and Lewis, M.A., Eds. Environmental Toxicology and Risk Assessment. American Society of Testing and Materials, Philadelphia, Pennsylvania, USA, pp. 281-302.

Byrne, M., Ho, M., Selvakumaraswamy, P., Nguyen, H.D., Dworjanyn, S.A. and Davis, A.R. 2009. Temperature, but not pH, compromises sea urchin fertilization and early development under near-future climate change scenarios. Proceedings of the Royal Society B 276: 1883-1888.

Byrne, M., Soars, N., Selvakumaraswamy, P., Dworjanyn, S.A. and Davis, A.R. 2010. Sea urchin fertilization in a warm, acidified and high pCO2 ocean across a range of sperm densities. Marine Environmental Research 69: 234-239.

Carr, R.S., Biedenbach, J.M. and Nipper, M. 2006. Influence of potentially confounding factors on sea urchin porewater toxicity tests. Archives of Environmental Contamination and Toxicology 51: 573-579.

Chen, C.P. and Chen, B.Y. 1992. Effects of high temperature on larval development and metamorphosis of Arachnoides placenta (Echinodermata Echinoidea). Marine Biology 112: 445-449.

Collins, S. and Bell, G. 2004. Phenotypic consequences of 1,000 generations of selection at elevated CO2 in a green alga. Nature 431: 566-569.

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Collins, S., Sultemeyer, D. and Bell, G. 2006. Changes in C uptake in populations of Chlamydomonas reinhardtii selected at high CO2. Plant, Cell and Environment 29: 1812-1819.

Farmanfarmaian, A. and Giese, A.C. 1963. Thermal tolerance and acclimation in the western purple sea urchin, Strongylocentrotus purpuratus. Physiol. Zool. 36: 237-343.

Kirby, R.R., Beaugrand, G., Lindley, J.A., Richardson, A.J., Edwards, M. and Reid, P.C. 2007. Climate effects and benthic-pelagic coupling in the North Sea. Marine Ecology Progress Series 330: 31-38.

Kurihara, H. 2008. Effects of CO2-driven ocean acidification on the early developmental stages of invertebrates. Marine Ecology Progress Series 373: 275-284.

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Richardson, A.J. and Gibbons, M.J. 2008. Are jellyfish increasing in response to ocean acidification? Limnology and Oceanography 53: 2040-2045.

Roller, R.A. and Stickle, W.B. 1993. Effects of temperature and salinity acclimations of adults on larval survival, physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea). Marine Biology 116: 583-591.

Rosenzweig, C., Casassa, G., Karoly, D.J., Imeson, A., Liu, C., Menzel, A., Rawlins, S., Root, T.L., Seguin, B., and Tryjanowski, P. 2007. Assessment of observed changes and responses in natural and managed systems. In Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. and Hanson, C.E. (Eds.) Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK, pp. 79-131.

Vézina, A.F. and Hoegh-Guldberg, O. 2008. Effects of ocean acidification on marine ecosystems. Marine Ecology Progress Series 373: 199-201.

Last updated 18 August 2010