What type of sand do turtles dig?

laura sand research

Hello, my name is Laura and I was a volunteer at Wildlife Sense for 9 weeks during the summer of 2013. I am currently studying for a degree in Environmental Science at the University of Southampton. I was lucky enough to be able to spend my time on the project collecting the data required for my dissertation. I aim to see whether beach sand characteristics have an effect on nest site selection and subsequent hatch success rates of Loggerhead sea turtles in Kefalonia.

The quality and stability of the nesting environment is vital to the reproductive success of marine turtles, and therefore much research has been carried out into the optimum sand types. It is widely agreed that coarser sand is less suitable for nesting as it is more prone to sand cave-ins and a collapsing of the egg chamber both during initial egg chamber construction and throughout the embryos’ incubation. However, very fine sand is also unfavourable due to its limited potential for gas and water exchange; something which is vital for the development of the embryos within the egg chamber. Some studies have reported an average sand grain diameter of 1.18-2mm as an optimum for hatch success rates as it allows a sufficient gas exchange whilst maintaining the structural integrity of the egg chamber.

Laura and her assistant

To collect my data I took 7 of the 11 local beaches monitored by Wildlife sense (Makris Gialos, Platis Gialos, Ammes, Megali Ammos, Ai Chelis, Avithos and Megali Petra) and divided them into sections that were 25 metres in length. Within each section I took five, 250g samples of sand from a depth of 30 cm, dried them to remove all moisture content and then sorted them into different diameter sizes using scientific sieves. By calculating the average diameter size of each section I hope distinguish between sections of the beach that did host nests, from those that did not.

There has been some research into the optimal level of moisture within the nests, with evidence suggesting that both very high and very low levels of moisture have damaging effects during incubation that lead to lower hatch success rates. By weighing the sand from my samples before and after drying them I was able to calculate the percentage moisture content for each sample in order to see what moisture levels any eggs in that section would have been incubated at.

Laura relocating a nest

During my time on the project I also participated in the daily morning patrols across the 11 study beaches in order to monitor the frequency of emergences onto the beach. My aim was to see whether there was a higher proportion of unsuccessful emergences on specific parts of the beaches and then to determine whether the sand quality in those locations would be considered less favourable for hatch success. In doing this I hope to see whether female loggerheads use sand quality as an important factor in nest site selection.

The hatch success rates of each nest were determined by performing excavations on nests approximately 7-10 days after hatching has begun. Excavations were also performed after 70 days if a nest failed to hatch. The eggs from all the excavated nests were removed and counted with a ratio of un-hatched to hatched eggs being calculated. There a different opinions as to what counts as a “successful” nest, but for the purposes of my study I decided that any nest where more than 80% of the eggs hatched was a successful one.

Hopefully I will be able to correlate the emergence and excavation data with the sand data and find some conclusive results regarding the importance of sand. As hatchling season is still ongoing, I haven’t been able to fully analyse my data sets yet, but I would like to take this opportunity to thank Nikos, Chanel and all the volunteers at Wildlife sense for being so helpful and accommodating with my research project, for without their support I don’t know how I could have done this. I would strongly recommend this project to everyone, volunteers and researchers alike and am incredibly proud to have taken part in it myself. Fingers crossed I get a good mark at the end of this!

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Tags: research, loggerhead, sea turtle nest