Modeling Climate Change: A Gift From the Pliocene

Catalyst VOlume 10

Believe it or not, we are still recovering from the most recent ice age that occurred between 21,000 and 11,500 years ago. And yet, in the past 200 years, the Earth's average global temperature has risen by 0.8 ºC at a rate more than ten times faster than the average ice-age recovery rate.¹ This increase in global temperature, which shows no signs of slowing down, will have tremendous consequences for our planet’s biodiversity and overall ecology.

Climate change is caused by three main factors: changes in the position of the Earth’s continents, variations in the Earth’s orbital positions, and increases in the atmospheric concentration of “greenhouse gases”, such as carbon dioxide.² In the past 200 years, the Earth’s continents have barely moved and its orbit around the sun has not changed.² Therefore, to explain the 0.8 ºC increase in global average temperature that has occurred, the only reasonable conclusion is that there has been a change in the concentration of greenhouse gases.

After decades of research by the Intergovernmental Panel on Climate Change (IPCC), this theory was supported. The IPCC Fourth Assessment Report concluded that the increase in global average temperature is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. Also included in the report is a prediction that global temperatures will increase between 1.1 ºC and 6.4 ºC by the end of the 21st century.²

Though we know what is causing the warming, we are unsure of its effects. The geologists and geophysicists at the US Geological Service (USGS) are attempting to address this uncertainty through the Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) program.³

The middle of the Pliocene Era occurred roughly 3 million years ago-- a relatively short time on the geological time scale. Between the Pliocene era and our current Holocene era, the continents have barely drifted, the planet has maintained a near identical orbit around the sun, and the type of organisms living on earth has remained relatively constant.² Because of these three commonalities , we can draw three conclusions. Because the continents have barely drifted, global heat distribution through oceanic circulation is the same. Additionally, because the planet’s orbit is essentially the same, glacial-interglacial cycles have not been altered. Finally, because the type of organisms has remained relatively constant, the biodiversity of the Pliocene is comparable to our own.

While the eras share many similarities, the main difference between them is that the Pliocene was about 4 ºC warmer at the equator and 10 ºC warmer at the poles.⁴ Because the Pliocene had similar conditions to today, but was warmer, it is likely that at the end of the century, our planet’s ecology may begin to look like the Pliocene. This idea has been supported by the research done by the USGS’s PRISM.³

It is a unique and exciting opportunity to be able to study a geological era so similar to our own and apply discoveries we make from that era to our current environment. PRISM is using multiple techniques to extract as much data about the Pliocene as possible. The concentration of magnesium ions, the number of carbon double bonds in organic structures called alkenones, and the concentration and distribution of fossilized pollen all provide a wealth of information that can be used to inform us about climate change. However, the single most useful source of such information comes from planktic foraminifera, or foram.⁵

Foram, abundant during the Pliocene era, are unicellular, ocean-dwelling organisms adorned with calcium shells. Fossilized foram are extracted from deep-sea core drilling. The type and concentration of the extracted foram reveal vital information about the temperature, salinity, and productivity of the oceans during the foram’s lifetime.⁵ By performing factor analysis and other statistical analyses on this information, PRISM has created a model of the Pliocene that covers both oceanic and terrestrial areas, providing a broad view of our planet as it existed 3 million years ago. Using the information provided by this model, scientists can determine where temperatures will increase the most and what impact such a temperature increase will have on life that can exist in those areas.

Since its inception in 1989, PRISM has predicted, with proven accuracy, two main trends.The first is that average temperatures will increase the most at the poles, with areas nearest to the equator experiencing the least amount of temperature increase.⁵ The second is that tropical plants will expand outward from the equator, taking root in the middle and higher latitudes.⁵

There are some uncertainties associated with the research behind PRISM. Several assumptions were made, such as the idea of uniformitarianism, which states that the same natural laws and physical processes that occur now were true in the past. The researchers also assumed that the ecological tolerances of certain key species, such as foram, have not significantly changed in the last 3 million years. Even with these normalizing assumptions, an important discrepancy exists between the Pliocene and our Holocene: the Pliocene achieved its temperature at a normal rate and remained relatively stable throughout its era, while our temperatures are increasing at a much more rapid rate.

The film industry has fetishized climate change, predicting giant hurricanes and an instant ice age, as seen in the films 2012 and The Day After Tomorrow. Fortunately, nothing as cataclysmic will occur. However, a rise in global average temperature and a change in our ecosystems is nothing to be ignored or dismissed as normal. It is only through the research done by the USGS via PRISM and similar systems that our species can be prepared for the coming decades of change.

References

1. Earth Observatory. http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php (accessed Oct. 1, 2016).
2. Pachauri, R.K., et. al. IPCC 4th Assessment 2007, 104.
3. PRISM4D Collaborating Institutions. Pliocene Research Interpretation and Synoptic Mapping. http://geology.er.usgs.gov/egpsc/prism/ (Oct. 3, 2016).
4. Monroe, R. What Does 400PPM Look Like?. https://scripps.ucsd.edu/programs/keelingcurve/2013/12/03/what-does-400-ppm-look-like/ (accessed Oct. 19, 2016).
5. Robinson, M. M., J. Am. Sci. 2011, 99, 228

Corals in Hot Water, Literally

Catalyst VOlume 10

Coral reefs support more species per unit area than any other marine environment, provide over half a billion people worldwide with socio-economic benefits, and produce an estimated USD $30 billion annually.¹ Many people do not realize that these diverse ecosystems are at risk of extinction as a result of human activity--the Caribbean has already lost 80% of its coral cover in the past few decades² and some estimates report that at least 60% of all coral will be lost by 2030.¹ One of the most predominant and direct threats to the health of these fragile ecosystems is the enormous amount of carbon dioxide and methane that have spilled into the atmosphere, warming the planet and its oceans on unprecedented levels.

Corals are Cnidarians, the phylum characterized by simple symmetrical structural anatomy. Corals reproduce either asexually or sexually and create stationary colonies made up of hundreds of genetically identical polyps.³ The major reef-building corals belong to a sub-order of corals, called Scleractinia. These corals contribute substantially to the reef. framework and are key species in building and maintaining the structural complexity of the reef.³ The survival of this group is of particular concern, since mass die- offs of these corals affect the integrity of the reef. Corals form a symbiosis with tiny single-celled algae of the genus Symbiodinium. This symbiotic relationship supports incredible levels of biodiversity and is a beautifully intricate relationship that is quite fragile to sudden environmental change.³

The oceans absorb nearly half of the carbon dioxide in the atmosphere through chemical processes that occur at its surface.⁴ Carbon dioxide combines with water molecules to create a mixture of bicarbonate, calcium carbonate, and carbonic acid. Calcium carbonate is an important molecule used by many marine organisms to secrete their calcareous shells or skeletons. The increase of carbon dioxide in the atmosphere shifts this chemical equilibrium, creating higher levels of carbonic acid and less calcium carbonate.⁴ Carbonic acid increases the acidity of the ocean and this phenomenon has been shown to affect the skeletal formation of juvenile corals.⁵ Acidification weakens the structural integrity of coral skeletons and contributes to heightened dissolution of carbonate reef structure.³

The massive influx of greenhouse gases into our atmosphere has also caused the planet to warm very quickly. Corals are in hot water, literally. Warmer ocean temperatures have deadly effects on corals and stress the symbiosis that corals have with the algae that live in their tissues. Though coral can procure food by snatching plankton and other organisms with protruding tentacles, they rely heavily on the photosynthesizing organism Symbiodinium for most of their energy supply.³ Symbiodinium provides fixed carbon compounds and sugars necessary for coral skeletal growth. The coral provides the algae with a fixed position in the water column, protection from predators, and supplementary carbon dioxide.³ Symbiodinium live under conditions that are 1 to 2° C below their maximum upper thermal limit. Under warmer conditions due to climate change, sea surface temperatures can rise a few degrees above their maximum thermal limit. This means that a sudden rise in sea temperatures can stress Symbiodinium by causing photosynthetic breakdown and the formation of reactive oxygen species that are toxic to corals.³ The algae leave or are expelled from the coral tissues as a mechanism for short-term survival in what is known as bleaching. Coral will die from starvation unless the stressor dissipates and the algae return to the coral’s tissues.³

Undoubtedly, the warming of the seas is one of the most widespread threats to coral reef ecosystems. However, other threats combined with global warming may have synergistic effects that heighten the vulnerability of coral to higher temperatures. These threats include coastal development that either destroys local reefs or displaces sediment to nearby reefs, smothering them. Large human populations near coasts expel high amounts of nitrogen and phosphorous into the ecosystem, which can increase the abundance of macroalgae and reduce hard coral cover. Increased nutrient loading has been shown to be a factor contributing to a higher prevalence of coral disease and coral bleaching.⁶ Recreational fishing and other activities can cause physical injury to coral making them more susceptible to disease. Additionally, fishing heavily reduces population numbers of many species of fish that keep the ecosystem in balance.

The first documented global bleaching event in 1998 killed off an estimated 16% of the world’s reefs; the world experienced the destruction of the third global bleaching event occurred only last year.¹ Starting in mid-2015, an El Niño Southern Oscillation (ENSO) weather event spurred hot sea surface temperatures that decimated coral reefs across the Pacific, starting with Hawaii, then hitting places like American Samoa, Australia, and reefs in the Indian Ocean.⁷ The aftermath in the Great Barrier Reef is stunning; the north portion of the reef experienced an average of 67% mortality.⁸ Some of these reefs, such as the ones surrounding Lizard Island, have been reduced to coral skeletons draped in macroalgae. With climate change, it is expected that the occurrence of ENSO events will become more frequent, and reefs around the world will be exposed to greater thermal stress.¹

Some scientists are hopeful that corals may be able to acclimatize in the short term and adapt in the long term to warming ocean temperatures. The key to this process lies in the genetic type of Symbiodinium that reside in the coral tissues. There are over 250 identified types of Symbiodinium, and genetically similar types are grouped into clades A-I. The different clades of these algae have the potential to affect the physiological performance of their coral host, including responses to thermotolerance, growth, and survival under more extreme light conditions.³ Clade D symbiont types are generally more thermotolerant than those in other clades. Studies have shown a low abundance of Clade D organisms living in healthy corals before a bleaching event, but after bleaching and subsequently recovering, the coral has a greater abundance of Clade D within its tissues.^9,10 Many corals are generalists and have the ability to shuffle their symbiont type in response to stress.¹¹

However, there is a catch. Though some algal members of Clade D are highly thermotolerant, they are also known as selfish opportunists. The reason healthy, stress-free corals generally do not have a symbiosis with this clade is that it tends to hoard the energy and organic compounds it creates from photosynthesis and shares fewer products with its coral host.³

Approaches that seemed too radical a decade ago are now widely considered as the only means to save coral reefs from the looming threat of extinction. Ruth Gates, a researcher at the Hawaii Institute of Marine Biology is exploring the idea of assisted evolution in corals. Her experiments include breeding individual corals in the lab, exposing them to an array of stressors, such as higher temperatures and lower pH, and picking the hardiest survivors to transplant to reefs.¹² In other areas of the globe, scientists are breeding coral larvae in labs and then releasing them onto degraded reefs where they will hopefully settle and form colonies.

Governments and policy makers can create policies that have significant impact on the health of reefs. The creation of marine protected areas that heavily regulates or outlaws harvesting of marine species offers sanctuary to a stressed and threatened ecosystem.³ There is still a long way to go, and the discoveries being made so far about coral physiology and resilience are proving that the coral organism is incredibly complex.

The outlook on the future of healthy reefs is bleak; rising fossil fuel consumption rates mock the global goal of keeping rising temperatures below two degrees Celsius. Local stressors such as overfishing, pollution, and coastal development cause degradation of reefs worldwide. Direct human interference in the acclimatization and adaptation of corals may be instrumental to their survival. Rapid transitions to cleaner sources of energy, the creation of more marine protection areas, and rigid management of reef fish stocks may ensure coral reef survival. If humans fail in this endeavor, one of the most biodiverse and productive ecosystems on earth that has persisted for millions of years may come crashing to an end within our lifetime.

References

1. Cesar, H., L. Burke, and L. Pet-Soede. 2003. "The Economics of Worldwide Coral Reef Degradation." Arnhem, The Netherlands: Cesar Environmental Economics Consulting. http://pdf.wri.org/cesardegradationreport100203.pdf (accessed Dec 14, 2016)
2. Gardner, T.A. et al. Science 2003, 301:958–960.
3. Sheppard C., Davy S., Piling G., The Biology of Coral Reefs; Biology of Habitats Series; Oxford University Press; 1st Edition, 2009
4. Branch, T.A.et al. Trends in Ecology and Evolution 2013, 28:178-185
5. Foster, T. et al. Science Advances 2016, 2(2) e1501130
6. Vega Thurber, R.L. et al. Glob Change Biol 2013, 20:544-554
7. NOAA Coral Watch, NOAA declares third ever global coral bleaching event. Oct 8, 2015. http://www.noaanews.noaa.gov/stories2015/100815-noaa-declares-third-ever-global-coral-bleaching-event.html (accessed Dec 15, 2016)
8. ARC Centre of Excellence for Coral Reef Studies, Life and Death after the Great Barrier Reef Bleaching. Nov 29, 2016 https://www.coralcoe.org.au/media-releases/life-and-death-after-great-barrier-reef-bleaching (accessed Dec 13, 2016)
9. Jones A.M. et al. Proc. R. Soc. B 2008, 275:1359-1365
10. Silverstein, R. et al. Glob Change Biology 2014, 1:236-249
11. Correa, A.S.; Baker, A.C. Glob Change Biology 2010, 17:68-75
12. Mascarelli, M. Nature 2014, 508:444-446

Green Sea Turtles: A Shell of What They Once Were

Catalyst Volume 10

Sea turtles appear in many cultures and myths, and are often beloved symbols of longevity and wisdom. However, in spite of the cultural respect shown towards them, green sea turtles have gradually become endangered due to factors such as nesting habitat loss, pollution, egg harvesting, climate change, and boat strikes. Now, there’s a new, even more dangerous threat on the block: herpes. And no, it’s not the herpes you’re thinking of - this kind, known as fibropapillomatosis (FP), is much, much worse.

FP has been observed across all species of sea turtles for years, but it has recently become especially widespread among green sea turtles (Chelonia mydas). The alarming incidence of FP is exacerbating the decline of this already vulnerable population. Among green sea turtles, the number of cases of FP increased 6000% from the 1980s to the mid-1990s, with FP becoming so globally pervasive that the outbreak has been classified as “panzootic,” the animal equivalent of “pandemic.” Now, you might think, “That sounds bad, but why are these turtles dying?” In humans, herpes is unpleasant, but it is seldom life-threatening. Unfortunately, in green sea turtles, the outlook isn’t nearly as optimistic. FP causes the development of tumors on the soft tissues, the shells, and even the eyes of infected turtles. When these growths are left untreated, they can grow to immense sizes, impairing the animal's vital activities, such as breathing and swallowing. So, while the tumors aren’t directly lethal, they invite hordes of secondary infections and pathogens that ultimately result in death.

To make matters worse, treatment for FP is still in development. A landmark study identified the specific pathogen responsible for FP as Chelonid herpesvirus 5 (ChHV5), a close relative of human genital herpes.¹ This discovery was the first step to a cure, but it raised an important question - how had this variant of herpesvirus become so prevalent? Until recently, the answer to that question was elusive.

Fortunately, several recent discoveries offered new explanations for FP’s rise. One study reported a significant positive correlation between serum concentrations of heavy metals and the severity of FP, as well as a significant negative correlation between serum cholesterol concentrations and FP.² In a related find, a team at the University of São Paulo discovered that many green sea turtles have been exposed to organochlorine compounds, which are known to have carcinogenic effects.³ Further research could potentially determine a direct causal relationship between the development of FP and exposure to heavy metals or organochlorine compounds. If such a relationship were found, projects that strive to decrease the prevalence of said compounds in the turtles’ habitats could prove effective in mitigating the spread of FP.

So what’s the prognosis for the green sea turtle? Unfortunately, even knowing what we now know, it may not be good. A study by Jones et. al. found almost all of the infected turtles are juveniles, potentially creating a big problem for the population.⁴ Jones believes the most optimistic explanation for this trend is that current adults and hatchlings have never been exposed to the disease, so only one generation (the juveniles) has been infected. Another optimistic possibility is that once infected turtles recover from the disease, they will simply acquire immunity as adults. However, there is another, devastating possibility: all of the affected juveniles will perish before they reach adulthood, leaving only the unaffected alive and dooming the species. In a heartbreaking aside, Jones reported that FP “grows on their [the turtles’] eyes, they can't see predators, they can't catch food, so sometimes they slowly starve to death — it's not a nice thing for the turtles to experience. Severely affected turtles are quite skinny and have other pathogens affecting them – that’s why they die.”

Eradicating such a devastating disease will no doubt take many more years of specialized research, and significant efforts are needed immediately to rehabilitate the green sea turtle population. Luckily, conservation groups such as The Turtle Hospital, located in the Florida Keys, are making an active effort to save infected sea turtles. They perform surgeries that remove FP tumors, rehabilitate the turtles, and then release them back into the wild. In addition, they collaborate with universities to study the virus and educate the public on sea turtle conservation. To date, the Turtle Hospital has successfully treated and released over 1,500 sea turtles. Through the hard work of conservation organizations and researchers across the globe, we may still be able to save the green sea turtle.

References

1. Jacobson, E. R. et al. Dis. Aquat. Organ. 1991, 12.
2. Carneiro da Silva, C., et al. Aquat. Toxicol. 2016, 170, 42-51.
3. Sánchez-Sarmiento, A. M. et al. J. Mar. Biol. Assoc. U. K. 2016, 1-9.
4. Jones, K., et al. Vet. J. 2016, 212, 48-57.
5. Borrowman, K. Electronic Theses and Dissertations. 2008
6. Monezi, T. A. et al. Vet. Microbiol. 2016, 186, 150-156.
7. Herbst, L. H. et al. Dis. Aquat. Organ. 1995, 22.
8. The Turtle Hospital. Rescue, Rehab, Release. http://www.turtlehospital.org/about-us/ (accessed Oct. 4, 2016).