Climate Change effects on sea turtles

By Molly Rickles, SRC intern

Climate change has become an increasing threat to species across the planet. With hotter average temperatures and less predictable weather patterns, humans have undeniably influenced the global climate. The effects of a changing climate are translated to the ocean, where warmer sea surface temperature and rising sea level can alter the marine ecosystem on many levels. These changes can decrease biodiversity and alter the balance of marine ecosystems (Fuentes et al. 2010). These far-reaching effects have extreme consequences for marine life, but some species are impacted more than others. Sea turtles are heavily affected by climate change because of their wide range of habitats (Butt et al. 2016). Since sea turtles lay eggs on beaches but spend their lives in the ocean, they are affected by climate change on both fronts. In addition, climate change may affect survival of juvenile sea turtles, decreasing adult population numbers. Since sea turtles can be widely affected by the far-reaching effects of climate change, it is necessary to implement measures of protection for them. There are ongoing research projects to determine how climate change directly impacts sea turtles and what the best policy options are to combat these effects. This is important because there is little information on how to protect these species from the effects of climate change.

In A, the mean air temperature is shown (black points) against the mean sand temperature (white points) to show how the temperature fluctuates throughout the year. In B, the proportion of nesting by loggerhead turtles for 2005, 2007, 2008, 2009. (Source: Perez, E. A., Marco, A., Martins, S., & Hawkes, L. (2016). Is this what a climate change-resilient population of marine turtles looks like? Biological Conservation, 193, 124-132. doi:10.1016/j.biocon.2015.11.023)

Over the past forty years, sea level has risen at an average of 2mm each year (Butt et al. 2010). This is an alarming statistic especially for low-lying and coastal areas. This is also bad news for sea turtles, which lay their eggs on beaches, which have already been affected by rising sea levels. Beaches are at a high risk for flooding from sea level rise, and when this does occur, the sea turtle eggs are washed away or swamped (Perez et al. 2016). This is especially devastating for endangered species of turtles such as the Hawksbill Turtle or the Australian Loggerhead Turtle, whose numbers are already low and cannot afford a sharp decrease in reproductive output (Butt et al. 2016).

Another major threat to sea turtles is rising sea surface temperature. One of the major effects of climate change is an increase in air temperature, which correlates to an increase in sea surface temperature. This excess thermal stress has especially hard consequences for reptiles, who are exothermic animals that rely on outside temperature to regulate their internal temperature (Perez et al. 2016). An increased sea surface temperature creates a more stressful environment for the sea turtles, but the increased sand temperature has proven to be even more harmful. Since sea turtles lay eggs on beaches, the hotter sand leads to less ideal conditions for laying eggs, which leads to decreased reproductive output. In addition, the sex of the embryos is partially determined by the outside temperature. In this case, a warmer environment leads to a higher percentage of females. It has been estimated that a 2°C increase will lead to a 99.86% female hatching rate (Butt et al. 2016). This, of course, will lead to a very lopsided sex ratio within sea turtle populations, further decreasing the reproductive output and population size.

The image shows all of the nesting sites identified in Australia. This shows that sea turtles have a wide range of habitats. This is beneficial because it allows policy makers to protect certain beaches where sea turtles are known to use for nesting. (Source: Butt, N., Whiting, S., & Dethmers, K. (2016). Identifying future sea turtle conservation areas under climate change. Biological Conservation, 204, 189-196. doi:10.1016/j.biocon.2016.10.012)

All of these threats to sea turtles could have devastating effects on their populations. Decreases in sea turtle populations have already been observed, and most sea turtle species are already on the endangered species list. Due to the fact that sea turtles are dealing with a multitude of threats, it becomes increasingly difficult to find management techniques to combat these issues (Fuentes et al. 2010). Some of the more straightforward strategies deal with the sea turtle’s habitat on land, since it is easier to manage beaches than the open ocean. Since sea turtles rely on certain beaches for nesting, it is possible to protect these areas to preserve the nesting habitat (Fuentes et al. 2010). This has already been implemented in many coastal areas, where nesting sites are blocked off from public use. In addition, many coastal areas have regulations to control nighttime lighting near nesting beaches so the sea turtle hatchlings have a better chance of making it to the ocean. By protecting these important nesting areas, sea turtles will continue to be able to lay eggs safely, and more hatchlings will survive to adulthood. This will lead to an increase in sea turtle population, thus preventing their numbers from decreasing even more rapidly.

In addition to managing habitat on land, it is also important to protect sea turtles in the ocean. One way to do this is to implement marine protected areas in important habitats for the turtles, such as areas where their young mature. However, the main issue affecting sea turtles is climate change, and this must be dealt with at a larger scale. To reduce the overall impact of climate change not only on sea turtles, but every other species, it is necessary to reduce the emissions of greenhouse gases and create a more sustainable way of life. There have already been steps made towards this goal, including the Paris Climate Accord, along with numerous clean air emission standards, but it is not enough. Stricter environmental regulations and environmental conservation education will help reach a more sustainable life, as well as protect sea turtles along with a multitude of other species

References

Fuentes, M., & Cinner, J. (2010). Using expert opinion to prioritize impacts of climate change on sea turtles’ nesting grounds. Journal of Environmental Management, 91(12), 2511-2518. doi:10.1016/j.jenvman.2010.07.013

Butt, N., Whiting, S., & Dethmers, K. (2016). Identifying future sea turtle conservation areas under climate change. Biological Conservation, 204, 189-196. doi:10.1016/j.biocon.2016.10.012

Perez, E. A., Marco, A., Martins, S., & Hawkes, L. (2016). Is this what a climate change-resilient population of marine turtles looks like? Biological Conservation, 193, 124-132. doi:10.1016/j.biocon.2015.11.023

Sea-ice loss boosts visual search: fish foraging and changing pelagic interactions in polar oceans

By Nicole Suren, SRC Intern

Light availability is one of the most important factors in the success of visual foraging. It can be controlled by many variables such as turbidity or weather, but in polar ecosystems ice cover and seasonality are the primary controls for light availability. Climate change has had and will continue to have a huge effect on polar ecosystems through temperature and weather changes, but one of the most notable side effects examined in this study is how increased light availability caused by receding ice and reduced snow cover will affect the success of polar visual foragers. The study modeled the success of planktivorous, visually foraging fish, with the underlying principle of the model being that increased ambient light will increase visual range, thereby making prey detectable at a larger distance and increasing foraging efficiency. The results showed that declines of polar sea ice would boost the visual search of planktivorous fish, but only seasonally. While light availability related to ice cover can be variable due to climate change, the long dark periods caused by polar seasonality are factors independent of climate, and therefore will still place limits on visual foraging during those seasons.

Figure 1

(a) The blue line shows how sea ice extent has decreased over the past decades, and below is a diagram demonstrating that prey will become more likely to be visually detected as the thickness of sea ice decreases. (b) A variety of factors influence prey detection, including the nature and angle of incoming light. Predator, prey, and visual range are not drawn to scale. (Langbehn & Varpe, 2017)

The models predict that several things will change due to light availability caused by loss of ice cover. First, primary productivity may increase, depending on nutrient availability. Second, seasonal feeding migrations into the poles are expected due to the removal of the limiting factor of lack of light for visual foragers. This prediction has already been verified by real-world data; increased feeding forays by Atlantic Salmon, Atlantic Mackerel, and Atlantic Herring have been recorded, and these coincide with decreasing ice cover over the past 35 years. More generally, mobile, fast-swimming predators are predicted to take advantage of these foraging opportunities the most. However, increased light availability can also increase the likelihood of planktivorous predators being spotted and predated upon by larger visual predators in a higher trophic level. This means that not only will the ideal user of these seasonal foraging grounds be mobile and fast-swimming, but they will either be apex predators or schooling fish, which can use the technique of schooling to forage in relative safety despite being visible.

Figure 2

The extent of sea ice is averaged from 2010-2015 in (a) and (b), and (c) and (d) show how visual range correlates with these averages. Data from the Bering Sea and the Barents Sea are shown. (Langbehn & Varpe, 2017)

No matter how efficiently visual foragers learn to take advantage of increased light availability at the poles during the summer months, the darkness of winter will still be a significant limiting factor in regards to permanent habitat expansion. Polar winters will always be long and dark, even if climate change alters the ice cover in that time. This means that the permanent inhabitants of the poles will likely remain the only permanent inhabitants due to their specialized adaptations for living in darkness, while trophic interactions are likely to change during the summer.

Work Cited

Langbehn, T. J., & Varpe, Ø. (2017). Sea-ice loss boosts visual search: Fish foraging and changing pelagic interactions in polar oceans. Global Change Biology, (November 2016). https://doi.org/10.1111/gcb.13797

Polar Bears are Vulnerable to Loss of Sea Ice

By Rachael Ragen

Figure 1

Polar Bear, https://sealevel.nasa.gov/ system/news_items/main_images/ 74_polarbear768.jpeg

Polar bears are currently facing a major problem: declining sea ice. As greenhouse gases continue to increase due to anthropogenic factors causing temperatures to rise and ice to melt. Since polar bears rely on sea ice as they search for prey, the decline in sea ice makes hunting much more difficult. The current population of polar bears is estimated to be 26,000 with 19 subpopulations in 4 ecoregions (Figure 2). It is very difficult to properly assess each subpopulation of polar bears as they live in extreme environments. Therefore, no global assessment has been done and the status of some subpopulations is unknown. The study by Regehr et al. aimed to look at the effect of sea ice decline on polar bears by determining the generation length, forming a standardized sea ice metric, and then using statistical models and computer simulations.

Figure 2

Map of Ecoregions, Regehr et al.

In order to determine the generation length, the authors looked at the age of female polar bears with a cub and found the average to be 11.5 to 13.6 years. Live capture data was used to determine these numbers. The upper level is used to account for variations in generation length.

A sea ice metric was determined using satellite data from 1979 to 2014. This data was used to establish the carrying capacity, which is the maximum amount of organisms the habitat can support, for the polar bears. Then the value found for K (carrying capacity) was used in linear models. This analysis generated predicted future values of ice as well, as the effect these values had on subpopulations. The ice decline was shown to affect all subpopulations.

The statistical models and computer simulations looked at the relationship between polar bear populations and sea ice over three generations using three different methods. First they assumed that changes in sea ice are directly proportional to changes in subpopulation abundance. This method was useful for populations with limited data. Second they looked at a linear relationship between ice and subpopulation abundance for subpopulations, although data was only available for seven of the nineteen. There was not shown to be a significant change due to variations in the status subpopulations as well as uncertainty in estimates of abundance. Lastly they again looked at a linear relationship between ice and population but for each of the four ecoregions. Some ecoregions showed a significant change, whereas others did not, showing that dynamics and biological productivity varies between subpopulations.

Figure 3

Table of data found, Regehr et al.

This study looked at the IUCN Red List’s guidelines for risk tolerance. The culmination of these studies showed that the first generation’s mean global population size was to decrease by 30%, the second by 4%, and the third by 43% (Table 1). Since there was shown to be a high risk of the population decreasing by 30% and a low chance of the population decreasing by 50% (Table 1), polar bears are classified as vulnerable.

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: https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=132218&from=mn

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 https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

Smith, M. D. (2011, April 15). An ecological perspective on extreme climatic events: a synthetic definition and framework to guide future research. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01798.x/abstract

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 (https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature)

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 (https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature)

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.

 

References:

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.