Snook in Extreme Environments

By Delaney Reynolds, SRC Intern

Earth’s climate is warming, and rising temperatures are impacting animal species and their habitats in alarming ways. Since 1970, temperatures have increased approximately 0.17°C (0.3°F) per decade (Dahlman, 2017). Such changes threaten animals’ ability to adapt to increased heat and induced stress. In the article, “Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study,” researchers observed how migration patterns impacted species’ vulnerability to extreme climate events (ECEs), episodes of uncommon climactic periods in which ecosystem structure is transformed beyond what is characteristically normal (Smith, 2011).

Figure 1: Juvenile Snook

A Juvenile Common Snook caught in the Everglades National Park. Image Source:

The State of Florida enjoys mild lows of 65-41°F during its winter season. Extreme cold fronts, however, occur approximately once every 10 years and can result in colder, more fatal environmental systems. During extreme cold fronts, South Florida’s Everglades National Park often experiences dramatic declines in sportfish populations and, thus, is the experimental ground used to study Snook and climate vulnerability. In 2010, for example, the Park faced one of its most severe cold fronts in a century and saw imperative tropical fisheries decrease 80%.

One of the Park’s residents, the Common Snook, has been useful in studying climate vulnerability because, “the abundance of adult Snook, the most sought after gamefish in the area, decreased by over 90% following the passage of this event” (Boucek, 2017). Once water temperature drops below 60°F, the Snook begin to struggle and become particularly vulnerable.

Looking at Everglades estuaries, Common Snook are observed in various cold-temperature regions. Snook often reside in rivers and for this reason three distinctive areas of the Everglades’ Shark River estuary were studied: the upstream, bay, and downstream zones. The downstream zone consists of the most Snook predators, but also the most Snook prey, and so Snook population and productivity is relatively higher compared to the upstream and bay zones. Passive acoustic telemetry computed Snook distribution patterns predicted for 2012 to 2016 during ECE periods. The researchers found that downstream zones were found to be the warmest, causing little effect on Snook populations, and upstream zones the coldest, killing most tropical fish. When a cold spell is detected in high vulnerability communities, most fish species migrate to areas of higher resistance, ensuring a higher survival rate. When it came to dispersing among less vulnerable habitats, Snook did not portray migration tendencies when detecting ECEs. Another study during the 2010 ECE found that most Everglades Snook showed the same behavior and did not move long distances, but rather made short journeys to areas that would function as a refuge from less severe, but more frequent ECEs (Stevens, 2016).

Figure 2: Snook Habitat Resistance, Animal Distribution, Detection and Response

This figure demonstrates animal distribution in high and low resistance environments, the shaded shapes, as well as their response to ECEs. As shown on the right, when a cold spell is detected in low vulnerability communities, fish will migrate to areas of higher resistance (shown in bright green) and return to their original habitat once it has passed, ensuring a higher rate of survival among the population. Image Source: Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study.

Snook face higher risk of population degradation when they are unable to immigrate to congenial territories, yet their populations did not face large casualties due to the ECEs because they tend to typically dwell in the warmer downstream zone. By staying in warm water areas, the Common Snook helps us better understand how species respond to a change in their habitats’ climate. As ECEs become more common and severe it will be vital to continue to monitor fisheries so as to learn how our warming climate impacts species and their habitats.

Works Cited

Boucek, R. E., Heithaus, M. R., Santos, R., Stevens, P., & Rehage, J. S. (2017, April 7). Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study. Retrieved from file:///C:/Users/derey/Downloads/boucek%20et%20al%202017b.pdf

Dahlman, L. (2017, September 11). Climate Change: Global Temperature. Retrieved October 22, 2017, from

Smith, M. D. (2011, April 15). An ecological perspective on extreme climatic events: a synthetic definition and framework to guide future research. Retrieved from

Effects of Climate Change on the invasive Lionfish: Pterois volitans and Pterois miles

By Patricia Albano, SRC intern

Across the globe, marine environments face anthropogenic stressors that threaten their continued survival. Throughout the world’s oceans, a colorful variety of marine communities exist, each with their own native flora and fauna and unique interspecific and intraspecific interactions. When the balance of these ecosystems is altered, negative ecological impacts can follow. The introduction of invasive species into marine communities in which they do not belong can have significant and long-lasting effects on the health, balance, and abundance of native species in the environment (Carlton, 2000). A well-known culprit, the Indo-Pacific lionfish, Pterois volitans or Pterois miles, has invaded the Western Atlantic ocean where it voraciously preys upon native species and reproduces in abundance. Via the reports of various divers, researchers, and fishing operations, it has been determined that the lionfish distribution along the east coast of North America may span from the Florida Keys to Cape Hatteras, North Carolina and include water depths up to 100m (Whitfield et al., 2002). For such invasive species to thrive in non-native ecosystems, several environmental factors come into play, one of the most notable being climate change. It has already been noted that increasing global ocean temperatures can predictably influence the growth and reproduction of marine fish and invertebrates (Brown et al., 2004). Consequently, increased growth and reproduction rates can directly impact population increases. For native species, this would be less of a concern; however, with the destructive influence that invasive species propose, it has become an epidemic. All of this considered, it can be concluded that climate change likely propagates invasions rather than halting them, especially in the case of lionfish (Côté and Green, 2012).

Indo-Pacific Lionfish: Pterois volitans. Popular in the aquarium trade for their superfluous body shape and coloration, Indo-Pacific lionfish pose a threat to invaded areas due to their voracious appetite and extreme reproductive capacity.  Image source: Wikimedia Commons

Indo-Pacific Lionfish: Pterois volitans. Popular in the aquarium trade for their superfluous body shape and coloration, Indo-Pacific lionfish pose a threat to invaded areas due to their voracious appetite and extreme reproductive capacity. Image source: Wikimedia Commons

After being introduced into coastal Florida waters in the 1980s through the aquarium trade, the Indo-Pacific lionfish has taken over the entire Caribbean basin and much of the Western Atlantic, infiltrating coral reefs, seagrass beds, and mangrove communities. It is predicted that lionfish life-history and behavior are intrinsically temperature-dependent based on observations of their reproduction and diet (Côté and Green, 2012). In a study concerning the effects of warming temperature on lionfish pelagic larval duration and dispersal and predation rate, it was found that increased temperatures set the perfect stage for an invasion to thrive. Due to their generalist diet, ability to expand their introduced range, and high fecundity, lionfish will continue to remain a threat in the Western Atlantic (Côté and Green, 2012). Increased temperature was predicted to drive the present imbalance between prey consumption and production rates, resulting in the lionfish having the upper hand in the ordeal. As oceans continue to warm, the lionfish will be able to expand its range to areas that are currently too cold for their inhabitation, specifically as the 10°C isotherm expands north and south in both of the hemispheres (Morris and Whitfield, 2009; Côté and Green, 2012). Finally, lionfish spend less time in the pelagic larval stage with increased ocean temperature, leading to growth of populations as temperatures continue to rise (Côté and Green, 2012).

Temperature anomaly of average global sea surface temperature from 1880-2015.  This increased warming trend is predicted to continue and proceed to facilitate the lionfish invasion into regions further north and south of the equator. Figure source: United States Environmental Protection Agency (

Temperature anomaly of average global sea surface temperature from 1880-2015. This increased warming trend is predicted to continue and proceed to facilitate the lionfish invasion into regions further north and south of the equator. Figure source: United States Environmental Protection Agency (

According to the National Ocean and Atmospheric Administration (NOAA), average global sea surface temperature has risen at an average rate of 0.13°F per decade since 1901 (Figure 1). Although this may seem like an insignificant increase, at this rate, global average sea surface temperature is predicted to hover around a 1°F anomaly from historical average by the year 2020, and steadily increase from there. With these elevated sea water temperatures, lionfish will continue to capitalize on climate change if this pattern is not halted. For the time being, one of the only limiting factors that the lionfish invasion faces is the fish’s intolerance to minimum water temperatures of some of its extended ranges away from the equator during the winter time (Kimball et al., 2004). However, this temperature anomaly pattern could facilitate expansion of the depth and latitude range of these invaders. In a study conducted on thermal tolerance and potential distribution of lionfish, it was found that the mean chronic lethal temperature for lionfish was 10°C and mean temperature for them to cease feeding was 16.1°C (Kimball et al., 2004). The average temperature for Florida waters during the winter time is 22°C and about 10°C at the northern limit that lionfish range, Cape Hatteras. These average water temperatures and this study show that as water temperatures continue to increase, the range of lionfish will continue to expand.

Overall, it can be deduced that climate change proposes a large threat to marine communities, especially where invasive species are concerned. As temperatures continue to rise above the norm, lionfish will extend their invasion further along the Western Atlantic.

Works Cited

Brown JH, Gillooly JF, Allen AP, Savage VM, West GB, 2004. Toward a metabolic theory of ecology. Ecology 85: 1771–1789.

Carlton JT, 2000. Global change and biological invasions in the oceans. In: Mooney A, Hobbs RJ ed. Invasive Species in a Changing World. Covelo, Calif ornia: Island Press, 31–53.

Côté IM, Green SJ (2012) Potential effects of climate change on a marine invasion: The importance of current context. Curr Zool 58:1–8

Kimball ME, Miller JM, Whitfield PE, Hare JA (2004) Thermal tolerance and potential distribution of invasive lionfish (Pterois volitans/miles complex) on the east coast of the United States. Marine Ecology Progress Series 283:269–278

Morris JAJ, Whitfield PE, 2009. Biology, ecology, control and management of the invasive I ndo-Pacific lionfish: An updated integrated assessment. NOA A Technical Memorandum NOS NCCOS 99.

Whitfield PE, Gardner T, Vives SP, Gilligan MR, Courtenay WR, Jr., Ray GC, Hare JA (2002) Biological invasion of the Indo-Pacific lionfish Pterois volitans along the Atlantic coast of North America. Mar Ecol Prog Ser 235:289–297


Implications of climate change for the sex ratios of sea turtle hatchlings

By Grace Roskar, SRC Intern

Sea turtles have existed on Earth for over 100 million years and presently inhabit warm waters in tropical and subtropical latitudes. The International Union for the Conservation of Nature has classified six of the seven species of sea turtles as critically endangered, endangered or vulnerable (IUCN, 2014 in Laloë et al., 2016). Threats to sea turtles include being taken as bycatch from fishing, poaching of eggs, and destruction of their habitats on land or at sea. Moreover, all sea turtle species come ashore to lay their eggs on sandy beaches, but these critical habitats face changes in air, water, and sand temperatures and rising sea levels (Santos et al., 2015). These climatic impacts occur at varying timescales and in different geographic locations, which makes it more challenging to respond to and mitigate these various threats (Fuentes and Cinner, 2010).

Like many reptiles, sea turtles possess temperature-dependent sex determination (TSD), which means that the incubation temperature of eggs in the nest determines the sex of an individual. Each species has a certain threshold, or pivotal, temperature, where equal numbers of males and females are produced. Temperatures below this pivotal temperature produce males whiles temperatures above produce females (Standora and Spotila, 1985). The determination of sex occurs in the middle third timeframe of the development of the embryo (Tapilatu and Ballamu, 2015). Due to TSD, increasing temperatures are a concern to sea turtles and were recently determined to be one of the largest threats to sea turtle populations (Fuentes and Cinner, 2010). Sex ratios could become skewed, and in more extreme cases, local extinctions could occur (Janzen, 1994 in Laloë et al., 2016). Warmer nest temperatures may lead to a greater majority of female hatchlings (Howard, Bell and Pike, 2015). Determining what ways increasing temperatures can impact populations is a priority for the conservation of sea turtles (Laloë et al., 2016).

In one study, Fuentes and Cinner (2010) used the knowledge of sea turtle experts to estimate how increasing temperatures and other climatic processes will impact sea turtles’ reproductive phases. The turtles of interest were green turtle (Chelonia mydas) populations in the northern Great Barrier Reef of Australia. Twenty-two scientists and managers were surveyed, and both groups agreed that higher sand temperatures could be considered the biggest threat to the reproductive output of these populations. The experts believe that higher sand temperatures will cause “two times more impact to sea turtles’ reproductive output than sea level rise and three times more impacts than altered cyclonic activity” (Fuentes and Cinner, 2010).

However, studies have also showed certain levels of resilience in some sea turtle populations. Howard, Bell, and Pike (2015) studied flatback sea turtles (Natator depressus) that are only native to Australia. Eggs were incubated in a laboratory to examine if the population was vulnerable to higher temperatures while nesting. The eggs were collected from beaches in northeastern Australia, and thus their pivotal temperatures were compared to those of populations from more temperate latitudes in Australia. It was found that the embryos in their study were resilient to incubation at high temperature, able to withstand temperatures almost 4°C above those from more southern populations. Moreover, the pivotal sex-determining temperature was different from past studies. It was previously thought that 29.5°C would produce an equal sex ratio, but for the eggs in this study, 30.4°C was the pivotal temperature. With a higher pivotal temperature, increasing environmental temperatures could drive the sex ratios closer towards equality. Therefore, even under extreme climate change scenarios, this high pivotal temperature adaptation may allow some flatback turtle populations to still produce more equal sex ratios (Howard, Bell, and Pike, 2015).

Not all sea turtle populations have shown such resilience. Fuentes, Hamann, and Limpus (2010) studied sand and air temperatures in the northern Great Barrier Reef. By using models and projections, it was estimated that by 2030, the sex ratios of hatchlings will be greatly skewed towards females. This has also been predicted for other nesting sites such as Cape Canaveral, Florida, and Bald Head Island, North Carolina (Hawkes et al 2007 in Fuentes, Hamann, and Limpus 2010). Laloë et al. (2016) examined historical data for incubation temperatures and sex ratios for green, hawksbill (Eretmochelys imbricata), and leatherback (Dermochelys coriacea) turtles nesting in St. Eustatius in the northeastern Caribbean. Their analysis suggested sex ratios have been skewed towards females for decades, and climate change will only intensify this. It was projected that in St. Eustatius “only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090,” (Laloë et al., 2016). Sex ratios dominated by females have already been reported at nesting sites around the world (e.g. Barbados, Cyprus) and at certain sites, some ratios are as high as 100% female (Binckley et al., 1998 in Laloë et al., 2016).

Projections of increasing incubation temperatures at one site in St. Eustatius. Graph A shows projections for 2030, graph B shows 2060, and graph C shows 2090 (Laloë et al., 2016).

Projections of increasing incubation temperatures at one site in St. Eustatius. Graph A shows projections for 2030, graph B shows 2060, and graph C shows 2090 (Laloë et al., 2016).

Sea turtles have existed for millions of years and have previously shown the ability to adapt during periods of sea level rise and temperature changes, such as changing nesting site locations or utilizing new migratory paths (Fuentes, Hamman, and Limpus 2010). However, modern-day changes in climate have been predicted to occur at a much faster timescale than past changes. Therefore, the capabilities of sea turtles adapting to these changes are still fairly unknown (Fuentes, Hamman, and Limpus 2010). There are several management options that have been suggested in order to mitigate the effects of higher temperatures. Some active methods include artificially changing the sand temperature by sprinkling cool water on the sand, covering areas of the beach with vegetation, or creating artificial shade (Naro-Maciel et al., 1999 in Fuentes, Hamman, and Limpus 2010). Other methods include the use of hatcheries and artificial incubation where temperatures can be controlled, but there is still uncertainty about the risks associated with changing natural sex ratios. Management could also be aimed at population-wide measures, including protecting key habitats, reducing bycatch of sea turtles, and preventing illegal harvest (Fuentes and Cinner, 2010).


A table outlining possible management measures to reduce climate change impacts on sea turtle reproduction, provided by experts surveyed in the study by Fuentes and Cinner (2010).

A table outlining possible management measures to reduce climate change impacts on sea turtle reproduction, provided by experts surveyed in the study by Fuentes and Cinner (2010).


Sea turtles have key roles in the ecological function of marine ecosystems, as they help maintain seagrass beds and are a valuable part of the tourism industry for many nations. It is vital to understand how the changing environment will influence risks for current and future sea turtle populations around the world. Minimizing further anthropogenic impacts, conserving existing populations and habitats, and further investigation of sea turtles’ ability to adapt to increasing temperatures is critical to protecting these marine organisms.



Howard, Robert, Ian Bell, and David Pike. “Tropical Flatback Turtle (Natator Depressus) Embryos Are Resilient to the Heat of Climate Change.” Journal of Experimental Biology 218 (2015): 3330-335. Web. 1 Feb. 2016.

Fuentes, M.M.P.B., and J.E. Cinner. “Using Expert Opinion to Prioritize Impacts of Climate Change on Sea Turtle’s Nesting Grounds.” Journal of Environmental Management 91 (2010): 2511-518. Web. 1 Feb. 2016.

Laloë, Jacques-Olivier, Nicole Esteban, Jessica Berkel, and Graeme Hays. “Sand Temperatures for Nesting Sea Turtles in the Caribbean: Implications for Hatchling Sex Ratios in the Face of Climate Change.” Journal of Experimental Marine Biology and Ecology 474 (2016): 92-99. Web. 1 Feb. 2016.

M.M.P.B. Fuentes, M. Hamann, and C.J. Limpus. “Past, Current and Future Thermal Profiles of Green Turtle Nesting Grounds: Implications from Climate Chang.” Journal of Experimental Marine Biology and Ecology 383 (2010): 56-54. Web. 1 Feb. 2016.

Santos, Katherine Comer, Marielle Livesey, Marianne Fish, and Armando Camago Lorences. “Climate Change Implications for the Nest Site Selection Process and Subsequent Hatching Success of a Green Turtle Population.” Original Article Mitigation and Adaptation Strategies for Global Change (2015): n. pag. Web. 1 Feb. 2016.

Standora, Edward A., and James R. Spotila. “Temperature Dependent Sex Determination in Sea Turtles.” Copeia 1985 (1985): 711-22. Web. 1 Feb. 2016.

Tapilatu, Ricardo F., and Ferdiel Ballamu. “Nest Temperatures of the Piai and Sayang Islands Green Turtle (Chelonia Mydas) Rookeries, Raja Ampat Papua, Indonesia: Implications for Hatchling Sex Ratios.” Biodiversitas 1st ser. 16 (2015): 102-07. Web. 1 Feb. 2016.

Climate Change to Cause Polar Bear Population Declines

By Laura Vander Meiden, SRC Intern

Over the next 35-40 years polar bear populations have the potential to decrease by more than 30% according to an assessment by the International Union for Conservation of Nature (IUCN). The report cites climate change and the resulting loss of sea ice as the cause of this probable decline.

Photo by Ansgar Walk vie Wikimedia Commons.

Photo by Ansgar Walk vie Wikimedia Commons.


Polar bears are specifically built to survive the harsh conditions of the arctic. Their adaptations include two types of insulating fur, a deep layer of fat to keep warm while in the water, bumps called papillae on the bottom of their feet for grip on ice, and feeding behaviors designed for living on the ice. Ironically it is these adaptations that make polar bears most vulnerable as the climate changes.

Scientist’s primary concern is the effect melting sea ice has on the eating habits of the bears. Though polar bears have been seen to opportunistically feed on a variety of organisms, their primary source of food is ring seals which live on the edge of the ice. The seals have a very high calorie content, particularly in their blubber, which is necessary for the polar bear’s frigid lifestyle. This allows the bears to build up large fat reserves which are critical as the bears can only hunt seals when there is ice. When seasonal ice melts in the summer, the bears typically must fast, living off their fat reserves, until the ice returns in the winter.

As climate change continues the ice will melt more quickly each summer and take a much longer time to return each winter. This extends the length of time polar bears must fast, resulting in higher chances of starvation. Melting ice and the subsequent reduced access to food can also lead to an overall decrease in body condition, reduced survival rates of cubs, loss of denning habitat and increased drowning as the bears attempt to swim between ice floes.

Polar bears are found on four different sea ice regions. The populations found in the region where ice is the most seasonal are at present in the most danger from climate change. Also vulnerable are populations in the divergent ice region where ice forms along the shore, but is not always connected to pack ice further out to sea. Safest are populations in the region where convergent ice connects the bears to pack ice and the archipelago region where ice remains year round. The latter region is expected to be the final refuge of the bears, but unless carbon dioxide emissions are reduced even this ice will be melted in 100 years.

Of 19 subpopulations 3 are declining, 6 are stable, 1 is increasing, and 9 have insufficient data to make a determination. Map via Norwegian Polar Institute.

Of 19 subpopulations 3 are declining, 6 are stable, 1 is increasing, and 9 have insufficient data to make a determination. Map via Norwegian Polar Institute.

While the situation for the polar bears appears dire, scientists have not completely lost hope. If significant reductions are made in greenhouse gas emissions, the amount of time before the sea ice melts could be extended. However scientists warn that action must be taken soon, since once a tipping point is reached sea ice will decrease rapidly and no amount of emission reduction will be able to stop the ice from melting.

Effects of Global Warming on Polar Bears in the Arctic

by Dani Ferraro, RJD intern

Global warming and the loss of Arctic sea ice is affecting populations of polar bears (Ursus maritimus) in Hudson Bay. Localized rises in sea surface temperatures (SST) have lead to mortality events and habitat changes for several marine species (Dulvy et al. 2008). While some species have adaptations that allow them to tolerate warming events, the loss of habitat and consequent die-offs of prey species is devastating.  The Hudson Bay Lowlands (HBL), the second largest inland sea in the world and home to polar bears, has warmed approximately three degrees Celsius since the 1990s (Ruhland et al. 2013).  With warmer air temperatures and increasingly rising SST comes the loss of winter ice-cover and reduced snow depth. This has directly caused the mortality of polar bear cubs and their prey, the ringed seal (Phoca hispida) and the bearded seal (Erignathus barbatus). As the forage and movement patterns of ringed seals and closely linked with sea ice, loss of this habitat could explain this mortality. The latest population estimates are about 21,500-25,000 individuals throughout the circumpolar Arctic (Luque et al. 2014).

 Ice formation in early November in Hudson Bay, Canada. Image Source: Wikimedia Commons

Ice formation in early November in Hudson Bay, Canada. Image Source: Wikimedia Commons

As a k-selected species, polar bears have delayed maturation and high adult survival rates, but smaller litter sizes. Sea ice acts as a polar bear’s hunting grounds, with terrestrial habitats as their maternity and breeding grounds. For female polar bears, impacts beyond loss of habitat exist. With reduced sea ice, females will have a cascading loss of adipose stores, causing lowered reproductive rates. This loss of adipose means that females have less fat to invest in their cubs throughout the winter season and subsequent fasting season. With reducing sea ice thickness, it becomes thinner and more pliable to winds and currents. Polar bears will respond with increased walking or swimming, using higher energy in order to retain their habitat range.

It’s important to acknowledge the differences in sea ice thickness and location. Polar bears prefer the annual sea ice located over the inter-island archipelagos and continental shelf surrounding the polar basis. This sea ice has declined in near shore areas and in amount of multiyear ice. With this decline comes the decrease in preferred habitat locations for polar bears, as well as other pagophilic species throughout the arctic marine ecosystem. Large expanses of open water due to melting sea ice often separates terrestrial maternity dens from residential pack ice. Pregnant females have a tendency to leave their residential areas during ice break-up and remain separated throughout the summer. In order to endure the summer before they can return to sea ice to feed, females need to have built up sufficient fat stores to sustain themselves for at least 8 months. However, considering the preferred location of polar bears: the deep polar basin, where there is a lower seal density, females will find difficulties obtaining sufficient fat stores. Without having accumulated adequate adipose stores, females have fewer nutrients to pass along to nursing cubs. Due to lower energy and fat stores, females are more likely to give birth to single cub litters, often with low survival rates caused by small body mass (Derocher).

Image 2 Ferraro

Polar Bear (Ursus maritimus) Image Source: Wikimedia Commons



With increasing SST and breaking sea ice, polar bears use more energy moving against the direction of ice drift. If ice moves more quickly, more energy is needed to move and hunt accordingly. Once sea ice concentration falls below 50%, polar bears tend to stick to terrestrial environments. Hunting and hauling prey onto land is energetically costly, requiring older polar bears to consume more, leaving fewer scraps for juveniles to scavenge. Combined with lower female productivity, the loss of food for juveniles doesn’t bode well for polar bear populations in the future. The impacts of climate change and global warming are already being seen with increasing sea surface temperature and decreasing sea ice depth. These habitat changes cause a cascading shift down the Arctic ecosystem, from habitat loss to mass mortality and reduced productivity. There will be shifts in survival rates, maturation age, and reproductive rates in populations of polar bears as well as that of its prey, both the bearded seals and ringed seals. With such a limited habitat in the circumpolar Arctic, global warming and climate change have a drastic effect on their populations, environments, and breeding habits.



Derocher, A. (2004). Polar Bears In A Warming Climate. Integrative and Comparative Biology, 163-176.

Dulvy, N.K., Rogers, S.I., Jennings, S., Stelzenmuller, V., Dye, S.R. & Skjoldal, H.R. (2008) Climate change and deepening of the North Sea fish assemblage: a biotic indicator of warming seas. Journal of Applied Ecology, 45, 1029–1039.

Luque, S., Ferguson, S., & Breed, G. (2014). Spatial behaviour of a keystone Arctic marine predator and implications of climate warming in Hudson Bay. Journal of Experimental Marine Biology and Ecology, 504-515.

Ruhland, K., Paterson, A., Keller, W., Michelutti, N., & Smol, J. (2013). Global warming triggers the loss of a key Arctic refugium. Proceedings of the Royal Society B: Biological Sciences, 20131887-20131887.

Climate Change and Corals: Is it too late?

By Jacob Jerome, RJD Graduate Student and Intern

There have been numerous studies that focus on the alterations that climate change can have on the marine environment and how those alterations affect corals. In the marine science field coral bleaching and the disappearance of coral reefs is widely discussed. One of the primary debates centers around whether or not it is too late to save coral reefs. But is this doom and gloom viewpoint how we should be looking at this situation? Many scientists argue that there is still hope for coral reefs.

It is important to first understand the threats that climate change pose to corals. There are two main threats: a rise in ocean temperatures and a lowering of the ocean’s pH, a process known as ocean acidification.

Higher temperatures stress corals and cause them to lose their symbiotic algae, or zooxanthellae (NOAA,2011). These symbiotic algae are what give corals their color and without them the corals turn white, an event known as coral bleaching. This bleaching can have several negative impacts on the coral polyps. Corals and their symbiotic algae have what is called a mutualistic symbiotic relationship; this is a relationship where both species benefit from interacting with one another. Corals provide their symbiotic algae with a protected environment and compounds they need for photosynthesis. The symbiotic algae, in return, provide corals with the products of photosynthesis, a suite of compounds that provide food for the corals and aid in the production of calcium carbonate. Although still alive, by losing their symbiotic algae, corals experience increased stress and are more prone to disease (NOAA, 2011).


A clear depiction of coral bleaching (Joe Bartoszek 2010/Marine Photobank)

Ocean acidification occurs due to the overwhelming amount of carbon dioxide that is absorbed into the ocean from the Earth’s atmosphere. When carbon dioxide is absorbed into the water, the pH of the water decreases and the water becomes more acidic. Low pH waters limit the rate at which corals can produce calcium carbonate and also increase the rate at which calcium carbonate dissolves (Andersson et al., 2014). Corals use calcium carbonate to build their hard exoskeleton. If corals are not able to produce calcium carbonate quicker than the rate at which it dissolves, they cannot grow.

Knowing these threats, many assume that corals have little hope for surviving through the end of this century. According to the Status of Coral Reefs of the World: 2008, 19 percent of the world’s coral reefs are gone or cannot recover, 15 percent are seriously threatened, and 20 percent are under the threat of loss within the next 20 to 40 years. So, is it too late for corals? Are these threats too great for us to effectively manage them? New scientific research indicates that not all corals are quite ready to give up.

Figure 2

A table summarizing the status of the world’s coral reefs in 2008 (Wilkinson, C. 2008)

Just last year, Australian scientists discovered that coral animals alone are able to produce dimethylsulphoniopropionate (DMSP), a sulphur-based molecule with properties that can provide protection on a cellular level to corals in times of heat stress (Raina et al., 2013). This was the first time that an animal had been discovered to produce DMSP. They also found that corals increased their production of DMSP when subjected to higher water temperatures (Raina et al., 2013). This new information illustrates that corals, even without their symbiotic algae, can “fight” against temperature shifts. While this does not mean that corals can entirely defend themselves against rising temperatures, it does indicate an ability to adapt, to an extent, to these changes.

In addition, a study in the Cayman Islands revealed that a coral reef system that suffered a 40 percent reduction in corals due to bleaching and diseases was able to recover seven years later (Manfrino et al., 2013). The corals in the Cayman Islands are known to be healthy and are afforded some protection from fishing and anchoring. This protection definitely aided in their recovery along with their isolation, a small human population, and a generally healthy ecology (Manfrino et al., 2013). Nonetheless, the Cayman Islands can serve as an example of what can happen when reef management is taken seriously.

In Palau, something remarkable has been discovered. By taking water samples from 9 different locations that stretched from open ocean, across a barrier reef, and into a lagoon and bays, scientists discovered that the sea water became increasingly acidic as they moved toward land (Shamberger et al., 2014). What was even more surprising was that the level of acidity was as high as scientists had predicted for the open ocean by the end of this century. Even so, healthy and diverse coral reefs were found in these areas. In fact, the corals appeared healthier in the more acidic areas than they did in the less acidic areas (Shamberger et al., 2014). While these results are incredible, caution should be taken when interpreting them. The environment surrounding the corals of Palau might create a “perfect storm” for environmental conditions that allow the corals to survive in the acidic waters. Even so, this area has been functioning the same way for thousands of years and may have unintentionally modified the corals in that area genetically. If this is the case, those corals can essentially be put in other acidic environments and survive. This discovery could have huge implications for the survival of corals.

It is important that we do not lose sight of the fact that these new discoveries do not mean that corals are safe under ocean conditions that have resulted from climate change. It does mean, however, that there is still hope for some corals. Climate change is difficult to prevent and changing human habits can be even harder. But if we can release the myriad of other stresses that are put on corals and think about our carbon footprint, corals just might stand a chance for their beauty to be enjoyed for generations to come.



Andersson, A. J., Yeakel, K. L., Bates, N. R., de Putron, S. J. (2014). “Partial offsets in ocean acidification from changing coral reef biogeochemistry.” Nature Climate Change, 4(1): 56–61.

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