Published on March 4, 2014
1 Hawksbill Sea Turtle How does Climate Change affect Caribbean Sea Turtle populations? Federico Sotomayor 27 December 2013 Departamento de Recursos Naturales y Ambientales Culebra, Puerto Rico Leatherback Sea Turtle
2 Climate Change Climate change refers to the variability in climate features within the Earth’s atmosphere. Historically, this has been a natural process that has occurred for millions of years and has ultimately been responsible for macro and micro level fluctuations in the Earth’s temperature. The natural change in temperature has varied from mild to extreme and is primarily caused by orbital variations, tectonic and volcanic activity, solar variability, and periodic wind and ocean oscillations commonly referred to as ‘El Niño’ and ‘La Niña’ (ENSO) cycles. The planet’s temperature has been naturally changing over time, yet has found ways to ensure symbiotic balance able to sustain life. Only recently have we been able to conclude that the change in postindustrial climate has been linked to anthropogenic forces, or caused by humans. Modern human-induced global warming has come as a result of increased green house gas (GHG) emissions. The three most prevalent GHG’s are Methane, Nitrous Oxide, and Carbon Dioxide (which is the most significant of the three). The greatest sources of Methane and Nitrous Oxide are found in agricultural production processes (which include the use of fertilizers and livestock waste) and land-use changes (which include deforestation and the use of landfills). Carbon Dioxide on the other hand, is primarily emitted from the burning of coal and petroleum (and also natural gas to a lesser extent). Coal supplies over 41% of the global demand for electricity; it is one of the cheapest, most efficient, and most abundant natural resources which make it economically viable for electrical generation. Petroleum derivatives (oil, diesel, gasoline, etc.) are currently used to power 98% of the world’s total transportation, mostly due to its energy density and reliability. When these natural resources are burned, the chemical properties of carbon dioxide cause it to disperse and remain in our atmosphere as an all-encompassed preemptive layer of gas. When solar radiation reaches our planet as ultraviolet rays, it is absorbed by land, and then actually released back into space as infrared radiation, except in this case, the GHG’s preemptive layer causes the radiation to become trapped and thus has the effect of unnaturally warming the planet (the ‘greenhouse effect’). The overutilization of these fossil fuels has directly led to increased global mean temperatures via increased GHG’s which then leads to changes in weather patterns and seasonal variations, changes in regional precipitation, and increases in ocean acidification. All of these have monumental implications not only for humans, but all living species alike. One type of marine animal that is especially vulnerable to the negative effects of anthropogenic climate change is the sea turtle, and in particular those that inhabit the Caribbean Sea. Sea Turtles The two types of sea turtles primarily found in the Caribbean region are the Leatherback and Hawksbill sea turtles. Leatherbacks are the only sea turtle whose carapace is not made of skeletal and dermal bone, it is made mostly of flesh and tough skin comprised of seven equally spaced ridges, strikingly similar to leather, hence its name. Their unconventional shell structure
3 makes them easily identifiable, along with their mammoth size; they are the largest sea turtles with an average size of 3.5-6 ft. in length and weigh anywhere from 600-1,500 lbs. Their unique carapace design allows them to have two distinct advantages over other species of sea turtle. First, the hydrodynamic inverted teardrop formation allows them to swim at a much faster speed than most other sea turtles, and secondly the distinct biological composition of their carapace results in higher levels of insulation allowing them to travel in waters normally too cold for other species. These two characteristics make Leatherbacks one of the most migratory and wide ranging sea turtles, inhabiting all three major oceans – Atlantic, Pacific, and Indian. While mating tends to occur at sea, delivery of the offspring always takes place on the beaches of warm, tropical waters. A large proportion of nesting females actually return to the very same beaches they were born on to deliver their clutch of eggs. The nesting season occurs from February to July, with the last clutch of eggs hatching in September. Females lay anywhere from 1 to 11 clutches per nesting season with each clutch having 50-150 eggs. These clutches are laid 8 to 14 days apart from each other. It has also been observed that while the female Leatherback lays its eggs, a gentle flow of tears begins to fall from her eyes. Leatherbacks have a unique gland in their eyes that allow them to excrete excess salt, occurring both on shore and at sea. Local fables suggest the sea turtle is crying because she will likely never see her offspring again. The eggs hatch approximately 60 days after they are laid on the beach. Most clutches include an overwhelming share of either male or female hatchlings, depending on the temperature of the sand in which they were incubated; females tend to form in warmer temperatures, while the male in cooler sand temperatures. Once the eggs hatch and the offspring are born, they move towards the water with the help of either the reflection of the sun or the stars on the surface of the ocean that guides them. It is theorized that only about 1% of all sea turtle hatchlings make it to adulthood. This occurs mostly due to the combination of both natural and unnatural forces such as carnivorous predators and/or human fishing nets, respectively. Juvenile and adult male sea turtles never return to shore, complicating the process of accurately identifying their population. Since it is almost impossible to track juveniles and adult males, total populations are often estimated using the information attained from nesting females. There are thought to be 20,000-30,000 nesting female Leatherback sea turtles left in the world, placing them in the vulnerable categorization of conservation status. The situation is even graver for the Hawksbill sea turtles which are classified as being critically endangered. Their natural habitat range is relatively smaller than the Leatherbacks’ and is primarily located in warmer, tropical waters. Hawksbill sea turtles are mostly found in lagoons or near coastal reefs, as opposed to Leatherbacks who are mostly found in open ocean waters. It is estimated that only 8,000 nesting females are left worldwide, making Hawksbill sea turtles the second least populous species, behind the Kemp’s ridley sea turtle. These sea turtles tend to reach 3ft. in length and weigh up to 250-300 lbs. as an adult. The Hawksbills have very unique structures to their carapace as well which allows them to change its color slightly, depending on the temperature of the water. This special feature of beautiful color design has unfortunately
4 made this particular species very sought after simply for its decorative utility. Another unique characteristic of this turtle’s physical structure is its beak-like mouth which resembles a bird, or a hawk, and thus explains the origins behind the name, ‘Hawksbill’. This turtle has similar mating and nesting habits as the Leatherback sea turtle. Hawksbill sea turtles primarily feed off of sea sponges while Leatherbacks mostly feed off of jellyfish, although the diets of both turtles consist of various sea anemones and jellyfish-like creatures such as cnidarians and hydrozoa. There have been numerous reported cases where sea turtles have died as a result of eating plastic bags, often mistaking them for jellyfish. Although there is a growing trend in declining sea turtle populations worldwide, one nation in the Caribbean that has been demonstrating significant conservation efforts is Puerto Rico and in particular two small islands off its east and west coasts, Culebra and Isla Mona, respectively (see figure 1.A). The island of Culebra is actually one of the few places on earth where the nesting population is on the rise. This data can be misleading for long term projections though, and unless we look at a macro level analysis of global trends, we cannot accurately forecast the future of these two sea turtles. Climate Change in the Caribbean As GHG emissions continue to rise and climate change becomes more ubiquitous, it will be important to understand the vast range of implications this will have on the Caribbean region in order to properly assess the negative effects to local sea turtle populations. To begin, global warming continues to melt frozen ice sheets at exponential rates in the northern and southern hemispheres which can have dire consequences on marine life, especially in the Mid-Atlantic. The Gulf Stream is an oceanic current of warm water that flows from Western Africa and runs along the eastern shore of Brazil and up through the Gulf of Mexico, eventually makings its way towards the North Atlantic. After reaching the North Atlantic, it becomes a current or flow of cool water that runs down south directly underneath the warm current, juxtaposing each other. It flows as a cycle that transfers the warm water from the Mid-Atlantic towards the north, and cool water from the north back down towards its original formation near the equatorial line. This cycle, otherwise known as the Gulf Stream, is extremely important in its ability to sustain marine life by delicately distributing water temperatures to match regional biodiversities, forming a natural balance of cool and warm water. Scientists have theorized that the contemporary melting of polar ice caps, ice sheets, and permafrost is jeopardizing this natural oceanic current and all of the marine life that depends on it for sustenance. If ice near the North Atlantic continues to melt, it will create a dynamic where the increased levels of cool water will decelerate the current and potentially shut down or completely stop the entire cycle of water flow from the Gulf Stream. This scenario will have major repercussions on the growth and distribution of plankton and microorganisms that sustain marine biodiversity, likely causing significant disturbances in natural food chains. Such rapid changes in biodiversity have often been characterized by massive losses of life, for both animals and humans. The breakdown of the Gulf Stream attributed to climate change is by far one of the
5 worst possible scenarios for humans, let alone sea turtles. Fortunately, this development is still many decades away, although if we continue with business as usual (BAU) in our emission of GHG’s, this situation will become inevitable. Another area where climate change will have an impact on sea turtle populations, albeit more immediate, is with the rise in sea-levels. The Caribbean is comprised of what the United Nations refers to as small island developing states, or SIDS. These small islands are characterized by their low elevations and limited resources. Since sea turtles primarily use beaches for nesting sites, the concern for heightened sea-levels is of major concern for them. A rise of just 1 meter (3.3 ft.) can have disastrous results for sea turtles that are looking to lay their eggs. This rise in sea-level from melting ice sheets will cause the beaches in this region to virtually disappear, thus eliminating the very nesting sites that are so crucial to the sustainability and longevity of these sea turtles. There is no exact timetable for this level of sea rise due to the extreme complexity involved in measuring global carbon dioxide and GHG emissions. The amount of GHG’s emitted on a daily basis are almost impossible to quantify and more difficult to predict due to the changing nature of supply and demand economics in business that are responsible for these emissions; although one trend is for certain, global levels of GHG emissions are on the rise. If BAU continues, sea-level rise will increase, potentially destroying the beaches and nesting sites of Caribbean sea turtles, causing them to migrate dangerously far distances or even worse, leading them towards extinction. Anthropogenic climate change is also leading to problems with ocean acidification. The ocean is the world’s largest carbon sink, essentially absorbing major levels of the carbon dioxide that is emitted into the atmosphere. The ocean is a natural absorber of carbon, but post-industrial levels of emissions have begun to facilitate potentially catastrophic levels of absorption. This is mostly due to the increase in GHG’s, but also comes as a result of increased deforestation (vegetation acts as the other major source of natural carbon sinks). Trees and plant life naturally absorb carbon dioxide and through the process of photosynthesis turn carbon dioxide into oxygen; though lately there has been a mass exploitation of forests for development purposes, thus increasing the oceanic absorption levels of carbon. This absorption has led to imbalances in the pH of regional bodies of water, leading to disturbances in marine ecosystems that affect all ranges of sea life. This acidification has led to the bleaching of coral reefs which are natural feeding habitats for sea turtles. The coral bleaching causes disintegration of entire reef ecosystems by dissolving the intracellular endosymbionts of the coral and thus extends to all marine life dependent on these tiny organisms for sustainable food chains. Similar to the effect that a collapsed Gulf Stream would have on plankton, the coral bleaching presents a domino effect where a disruption at the smallest organic level can lead to collapses of entire ecosystems. This can directly lead to the destruction of entire feeding areas for sea turtles, essentially eliminating regions that act as major sources of food. A less dramatic yet equally damaging scenario for Caribbean sea turtles is the effect that increased global temperatures will have on the gender of nesting eggs. If global mean temperatures continue to rise, it will likely result in the increased warming of the beaches and
6 sand, thus directly leading to a proliferation of female sea turtles, as opposed to a natural and sustainable balance of both male and female. Conclusion As you can see, the future of Caribbean sea turtle populations is significantly jeopardized if we cannot control our global levels of GHG emissions. The Leatherback sea turtle, as a more resilient and versatile species, holds hope in adapting to some of the milder negative effects of climate change, while the Hawksbill, already critically endangered, holds a very real possibility of not making it past the 21st century. The Caribbean region is especially vulnerable to climate change effects that could be devastating for sea turtles such as the dissolution of the Gulf Stream, the rise in sea-levels, acidification of the ocean and bleaching of coral reefs, and finally the increased temperatures of the beaches and sand. With the global demand for coal and petroleum products rising due to development, growth, and over population, it will become increasingly important to find alternative solutions to traditional environmentalist methods of changing the status quo. It will undoubtedly be an uphill battle to reduce global GHG emissions and transition towards sustainable models of development and growth, but that must not stop us from striving for these more environmentally friendly and ethical alternatives to business as usual, these majestic prehistoric sea turtles depend on it.
7 Figure 1.A Isla Mona and Culebra
8 Hawksbill Sea Turtle CR: Critically Endangered Major (Red) and Minor (Yellow) Nesting Sites Source: http://en.wikipedia.org/wiki/Hawksbill_sea_turtle Hawksbill Sea Turtle Habitat Range Source: http://en.wikipedia.org/wiki/Hawksbill_sea_turtle
9 Source: http://www.hawksbill.org/spanish/carey.html
10 Conventional Carapace
11 Leatherback Sea Turtle VU: Vulnerable Major (Red) and Minor (Yellow) Nesting Sites Source: http://en.wikipedia.org/wiki/File:Lieux_pontes_tortues_luth.png Source: http://www.gambassa.com/public/project/2770/SavannahSchwager'sSeaTurtleReport.html
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