P2.18 Thursday, Jan. 5 Beach characteristics affect the gas exchange environment for sea turtle nests SUSS, J.S.*; HONARVAR, S.; SPOTILA, J.R.; O'CONNOR, M.P.; Drexel Univ.; Drexel Univ.; Drexel Univ.; Drexel Univ. firstname.lastname@example.org
Sea turtles bury their eggs deeply on a variety of beaches worldwide. During incubation, the developing embryos exchange gases (oxygen and carbon dioxide) with the surrounding sand and atmosphere at a rate dependent on the properties of the sand. Movement of individual gases via diffusion through the sand is described by Fick’s Law and movement of bulk air via convection is described by Darcy’s Law. We tested the diffusivity and convective permeability of the sands from sea turtle nesting beaches in Greece, Equatorial Guinea, and both coasts of Costa Rica. Median sand grain size ranged from very fine (0.125mm) to coarse (1mm) sands. Permeability to bulk flow in coarser sands was an order of magnitude greater than that in finer sands. In all sand types, dry sands had a lower permeability than sands that were lightly wetted to 2-5% moisture by volume, similar to the field moisture at nest depth. This is due in part to an increase in porosity from the film adhesion of the wet sand particles creating incompressible aggregates and in part to a decrease in tortuosity from the film allowing for greater laminar flow than the rough, dry edges of particles. In monitored nests, oxygen decreased to 16% and carbon dioxide increased to 5% during incubation. Sand moisture on sea turtle nesting beaches can affect respiratory gas exchange of the developing eggs. Selective forces on sea turtle nests include protection from predators and development under optimal hydric, thermal, and respiratory conditions. Climate change models predict hotter, drier climates for many sea turtle nesting beaches that would increase the dry sand layer. It is imperative for conservation and hatchery practices to consider optimal gas exchange in the sand to improve future beach-monitoring efforts.