Green turtle

Climate change has the potential to expose sea turtle nests to higher temperatures, which may negatively impact sea turtle hatchling vigor. In this study, loggerhead and green hatchlings were sampled from the Boca Raton, Florida beach and via lab incubation, and hatchling vigor was determined. Elevated nest temperatures decreased loggerhead and green turtle hatchling performance and corticosterone levels, with the most significant effects found in hatchlings exposed to maximum incubation temperatures above 35°C during late development. Lab-incubated loggerhead post-hatchling corticosterone levels and growth rates were also determined. The differences seen in corticosterone levels with overall nest incubation temperatures, mean temperatures during early, middle or late stages of development, and its negative correlation with hatchling performance improves our understanding of the underlying physiological mechanisms linking elevated incubation temperatures and sub-lethal physiological effects that may significantly impact hatchling survival, a critical step for sea turtle conservation in south Florida and elsewhere.

Hatchling marine turtles use visual cues to orient from their nest to the sea at
night. However, the wavelengths of light that carry this information have not been
properly documented, nor do we understand why they are favored. I measured
wavelength irradiance at 20 nm intervals between 340 – 600 nm at a dark nesting beach
and then, in the laboratory, determined the thresholds of the hatchlings for each λ that
evoked a positive phototaxis. In this study, I show that green turtle hatchlings are (i) most
sensitive to the shorter (360 – 480 nm) light wavelengths. Those light energies (ii)
dominated the available natural lighting at the nesting beach. They also (iii) presented a
steep gradient in irradiance between a landward and seaward view, an important cue for
orientation. I attribute the phototactic responses to “stimulus filtering”, the outcome of
natural selection that optimizes behavioral responses (seafinding) according to their
function, as well as when and where they occur.

Sea turtle nests were compared to determine the effects of nest depth on hatchling anaerobic metabolism in Juno Beach, Florida, USA. In situ nests of 3 species (Caretta caretta, Chelonia mydas and Dermochelys coriacea) were compared. Relocated loggerhead nests were studied under an experimental regime. Nest temperatures and oxygen concentrations were monitored. On the night of first emergence, blood samples were taken from hatchlings resting at the nest chamber bottom and sand surface, and digging to the sand surface. Samples were analyzed for lactate concentrations. Blood lactate levels were high in hatchlings actively digging and low for those resting. Lactate levels differed among species and nest depths. Within in situ nests, actively digging green turtle hatchlings had the highest lactate, followed by loggerhead hatchlings and leatherbacks (lowest). Loggerhead hatchlings digging from deeper relocated nests had higher lactate than those digging from shallower depths.

The impact of coastline development on nesting sea turtles, nest contents,
and hatchlings was investigated in southeastern Florida. There were
95-128 loggerhead (Caretta caretta) nests per mile on six miles of beach.
Seventeen green turtle (Chelonia mydas) nests were found. Nesting females
did not avoid lighted, developed beaches in favor of undeveloped beaches.
Hatchling emergence bearings were measured at 397 nests, and ambient
light intensities were correlated with the incidence of misorientation. Most hatchlings emerging where artificial light sources were visible
were misoriented inland. From 0-96% of misoriented hatchlings were killed
by automobiles, ghost crabs, or dessication. Mortality was greatest
where hatchlings were able to enter roadways, and lowest where barriers
prevented this. Analysis of post-emergence contents of 422 nests
revealed that mortality within nests was greater on soft beaches with
large-grained sand than on fine-grained, firmer beaches, and was increased
by human footfalls and beach-cleaning machinery.

Hatchling sea turtles use visual cues to orient to the water. Streetlights placed on coastal roadways can attract the turtles inland. Filters were designed to be used with coastal roadway lighting to eliminate the more harmful wavelengths of light. I tested the General Electric 2422 and NLW filters in a laboratory setting with hatchling loggerhead and green turtles. Both species of turtles were attracted to the amber filtered lighting in arena experiments. Loggerhead hatchlings were used in T-maze experiments where they were given a choice between amber filtered and unfiltered lighting. The turtles preferred the unfiltered lighting to the filtered lighting, even when it was 100 to 1000 times dimmer. I conclude that amber filtered lighting does afford some protection to sea turtles, although it must be used in conjunction with other light management techniques to prevent the disruption of hatchling turtle orientation.