Sea turtles test the sand before digging

Sophie takes a sand sample for analysis
Sophie collected sand samples from nests and random locations for moisture content and grain size analysis

During the 2014 nesting season, Sophie Mayes from the University of East Anglia conducted extensive research in Kefalonia to study the nesting sand preference of sea turtles, and the effect of sand conditions on the success rates of their nests. Sophie collected data on sand temperature, moisture, and grain size at a large number of nest and randomized locations on the nesting beaches. She found that the conditions on the surface matched those at nest depth, confirming that sea turtles use this characteristic to determine a location's suitability.

As they crawl towards the back of the beach to lay their eggs, sea turtles dip their lower jaw slightly into the sand. They sense the temperature, moisture, and texture of the sand to determine if the sand quality is good enough for them to make a nesting attempt. This ability to predict the suitability of a location before digging helps mother turtles conserve precious energy. Despite this ability, a turtle may still have to abandon the site after she begins to dig if the sand contains stones, plastic trash, clay, sea weed, or other debris.

Sea turtle on nesting beach
Sea turtles sense the sand with their lower jaw as they crawl towards the back of the beach looking for a suitable nesting location.

Moisture, temperature, and grain size of the sand around a sea turtle nest are important parameters for the successful incubation of the eggs. Sand temperature must remain between 26°C and 32°C, while the optimal moisture content is around 25%, meaning that 25% of the space between the sand grains is filled with water and the rest is filled with air. This moisture level is enough to keep the nest's temperature from becoming too hot during the day or too cold at night without blocking gas exchange, allowing the eggs and embryos to breathe while incubating.

A sea turtle egg immersed in sand
Moisture content, temperature, and grain size of the sand around a nest determine the hatching success of its eggs.

Many of Kefalonia's beaches are narrow and mostly backed by cliffs and hills. Wide beach sections with suitable sand moisture are limited, and many of those are used for beach bars and umbrellas. Light pollution and disturbance during the night scares sea turtles away, and pushes them to nest in narrower, less suitable parts of the beach. Continued research on sand characteristics and the success rates of nests is an important part of our conservation project, because the parts of the beach that are best for their nests must remain accessible to sea turtles and available for nesting.

Written by Nikos Vallianos | .

Tags: research, loggerhead, sea turtle nest, Caretta caretta, sea turtle