The effect of incubation conditions on leatherback (Dermochelys coriacea) and green (Chelonia mydas) sea turtle hatchling survival
This study was conducted at Parque Nacional Marino Las Baulas (PMLB) in Playa Grande, Costa Rica, looking at abiotic factors affecting the emergence success of leatherback turtle (Dermochelys coriacea) hatchlings. The proportion of leatherback turtle hatchlings that emerge decreases as sand temperatures and depth of the dry front above the nest increase throughout the nesting season. Ambient and sand temperature along with little to no rainfall impacted the depth of dry front in all seasons. The depth of the dry front in 2008-2009 and 2011-2012, and depth of dry front and temperature in 2012-2013 explained most of the variability in emergence rate for leatherbacks on this beach. ^ Depth of the dry front significantly affected the number of hatchlings that failed to emerge in all years and high temperature reduced emergence rate in 2008-2009 and 2012-2013, but was not significant in 2011-2012. Depth of the dry front and temperature significantly increased throughout the season. Likewise, emergence rate was significantly reduced, with the number of hatchlings (dead and live) that failed to emerge increasing. Additionally, the number of dead hatchlings found in the dry front significantly increased as the season progressed during the 2012-2013 season. By identifying factors that influence emergence rate we could potentially implement conservation strategies to improve environmental conditions within the nest to increase hatchling production and reproductive success. ^ These results led me to question what abiotic factors during development may be impacting hatchling survival and fitness. The second chapter of this thesis was designed to address this question by analysing the effect of temperature and substrate water content on green turtle (Chelonia mydas) eggs incubated in artificial laboratory conditions. The study investigated the water regulation of developing and non-developing green turtle eggs, measuring alterations of their total egg mass caused by the incubation conditions they were exposed to. The results indicated that non-developing eggs may play a role in modifying the hydric microenvironment of sea turtle nests. Incubation temperatures of 26°C and 29°C significantly impacted the emergence size of hatchlings produced and the duration of the incubation period of the eggs. Incubation temperature also had a significant effect on survival rate of hatchlings, with all fatalities occurring when hatchlings were still utilizing their yolk reserves. There was a significant increase in the instances of abnormalities of pigmented embryos and hatchlings with increasing temperatures, the greatest number of abnormalities being produced by the highest incubation temperature (32°C). Substrate water content during incubation did not have an impact on the number of deformed embryos or hatchlings produced.^
Frank V. Paladino, Purdue University.