Meeting Abstract
Sea turtles hatch on oceanic beaches, enter the surf and then migrate to offshore nursery areas. Hatchlings are small and defenseless; predators take many. They reduce vulnerability by migrating at night, growing rapidly, and enhancing the protective function of the shell through changes in shape, spination, and sharp edges. We focus how those modifications differ among species during early growth. We compared changes in shape among loggerheads (Caretta caretta), Kemp’s ridleys (Lepidochelys kempii), green turtles (Chelonia mydas), and flatback turtles (Natator depressus). Flatbacks (F), which are closely related to green turtles (G), uniquely remain in predator-rich continental shelf waters; other species are oceanic as small juveniles. They return to coastal waters when larger/less vulnerable. Ridley (R) and loggerhead (L) turtles are more closely related to one another than to flatbacks and green turtles. These “R-L” and “G-F” groups have similarities and differences in development of defensive structures and behavior. All showed allometric shell growth, increasing in width faster than length, a modification that should decrease vulnerability to gape-limited predators. Shape change was more extreme in G-F (“hockey puck” shaped) than in the R-L, and most pronounced in flatbacks. Shell spination was pronounced in the R-L group. G-F shell surfaces remained smooth with sharp serrated margins that are more pronounced in flatbacks than in green turtles. Differences were correlated with behavioral contrasts in how the turtles avoid predators. R-L reduce detection by minimizing movement; G-F escape by fleeing rapidly. The two groups evolved different anti-predator strategies that are manifested by differences in how they grow, morphology and behavior.
