The effects of nest environment on calcium mobilization by leatherback turtle embryos (Dermochelys coriacea) during development

We investigated the effect of sand moisture content and sand temperature on developmental success and the mobilization of calcium during development u sing laboratory incubated eggs (n = 251) collected from leatherbacks nestin g at Parque Nacional Marino Las Baulas, Costa Rica. Calcium concentrations of egg components [eggshell, yolk plus albumen (Y + A) and embryo] changed significantly through incubation for both viable and undeveloped eggs. In d eveloped eggs, eggshell calcium content decreased 42.9% by day 60 of incuba tion. The Y + A calcium decreased by 20.8% until the last quarter of incuba tion, and then increased to 0.99% above initial Y + A calcium concentration s just prior to hatching. In undeveloped eggs, eggshell calcium content dec reased by 25.7%, with the rate of decrease slowing significantly beyond day 30 of incubation. In contrast, Y + A calcium increased steadily through th e 60-day incubation period. Embryos incorporated a higher proportion of cal cium when incubated at a lower sand moisture content (5% H2O > 12% H2O) and at lower sand temperatures (28.5 degreesC, 29.5 degreesC > 31.0 degreesC). The total wet mass of freshly oviposited eggs was negatively correlated wi th calcium concentration per gram of eggshell (r = -0.569; P < 0.001). Thus , each yolked egg, regardless of initial wet mass, had an average of 1.23 g (+/-0.43 g) of calcium per egg (Mean egg mass: 76.24 +/- 1.21 g). Both dev elopmental success (24.1%) and hatching success (7.4%) of laboratory-incuba ted eggs were dependent to a greater extent on temperature than on moisture , with an increase in mortality as sand temperature increased. For natural nests on Playa Grande, developmental success (37.4%) and hatching success ( 19.8%) were similar in magnitude to the results obtained from the laborator y. The recent ENSO (El Nino Southern Oscillation) event and increased tidal activity may be responsible for the high embryonic mortality measured duri ng the 1997-1998 nesting season. (C) 2001 Elsevier Science Inc. All rights reserved.