Article: Patino-Martinez, J., et al. (2014). “The potential future influence of sea level rise on leatherback turtle nests.” Journal of Experimental Marine Biology and Ecology 461(0): 116-123.
Sea level rise is one of the most talked about aspects of global climate change and with about 40% of the world’s population living on or near a coast, this is no surprise. Sea level rise has also been discussed in terms of its impacts on coastal ecosystems and habitats; but few studies have looked at the effect of rising seas on mobile marine species or their use of coastal habitats. Currently, our oceans are rising about 3.2mm per year, and this has been attributed to human forces. On top of rising seas, we are seeing an increase in major storm frequency resulting in coastal erosion.
Many ecosystems that are threatened by sea level rise are home to sea turtle nesting sites. There are 7 species of sea turtles in the world, all of which spend the majority of their lives swimming in the ocean. Female sea turtles will trek to tropical beaches in order to make nests and lay their eggs (Fig 1). Of the 7 species of sea turtles, 4 are listed as endangered and 2 are listed as vulnerable. As a result, conservation and research groups have identified common nesting habitats for sea turtles and have worked to preserve and protect them (Fig 2). But conservation efforts look to be fighting even more of an uphill battle as oceans are on the rise. While sea turtle nesting habitat could disappear in the future, there is a more imminent threat resulting from sea level rise: environmental changes to turtle nests.
The environment of nests has a number of known impacts on reptile eggs and embryo development. Studies have shown nest temperature to influence the sex-ratios in new born turtles and high humidity led to longer incubation times in loggerhead turtles. It seems that the sand water content (or moisture) of nests influences embryonic development. Rising seas, erosion, and increased storms are likely to change the sand water content of nesting sites. Here, researchers investigate the effects of different percentages of nest moisture on the emergence of sea turtles from their nests.
In this study, researchers focused on one species of sea turtle, the leatherback turtle (Demochelys coriacea) (Fig 3). This species is listed as vulnerable by the World Conservation Union. Compared to other sea turtle species, leatherbacks have lower reproductive success, with successful hatchings averaging 40-50% of the original clutch. The goal of this study was to look at turtle emergence success and embryonic development under different levels of sand water content to figure out if rising seas and the resulting change in environment would impact turtle hatchings.
Researchers worked on the Caribbean coast of Colombia and used field, hatchery, and laboratory studies to investigate their question. For the field study, researchers chose to look at a section of beach that is known to host a large amount of nesting female leatherbacks. This beach was divided into 3 nesting zones all with different sand water content. Sand samples were taken from two depths at each zone to determine water content. For the hatchery phase, turtle eggs were removed from nests and brought to a protected part of the beach and placed in nests representing the 3 zones from the field study. This area was offered more protection and more monitoring. For the laboratory phase, researchers took recently laid turtle eggs from their nests and put them into mock nests at similar depths (Fig 4). Here they were able to manipulate the sand water content. Eggs were placed in one of 5 water content treatments: 1, 2, 6, 10, or 12%. Side note: the eggs used for the laboratory and hatchery phase were taken from nests which researchers determined were “doomed” based on their location.
For all 3 experiments, turtles hatchings were monitored and recorded. Each hatching represented a successful emergence. Once hatchings stopped, nests were excavated and the remaining eggs were removed. These embryos presumably all died and the stage at death was determined for each egg.
Overall, the researchers found strong correlations between sand water content and hatching success, increases in moisture lead to decreases in hatching success (Fig 5). The laboratory phase offered a glimpse into the moisture levels that triggered mortality. There was a jump between 2% and 6% continuing through 12%, where there was almost 100% mortality (Fig 6). All of the mortality at 12% happened in the first embryonic stage of the turtle.
The success of turtle eggs hatching is highly correlated with moisture content of the nests they are laid in. Nests with greater water content yield less turtles. This could be major problem for leatherbacks as sea levels continue to rise. Nesting sites are threatened from rising seas on one side and coastal development on the other. Suitable habitat is decreasing for many species and if the water content of their nests plays that big of a role in the viability of offspring, then turtles are likely to be impacted by this way before their habitat disappears. However, it is important to keep in mind that animals have the ability to adapt. Turtles may be able to change the structure or permeability of their eggs in order to get around this problem. But if the environment is changing too quickly, sea turtles may not have time to adapt.