Year 0Nest 0 dTSP 0 °CHatchlings female 0 %Seagrass 0 %Turtles 0FPS 0

Drag to orbit, wheel or pinch to zoom. The number of turtles, the seagrass meadow, the coral colour and the fish follow the population model; the sex ratio comes from the nest temperature.

Sea Turtle Nest Heat, Sex Ratio and Reef Capacity Lab

Part 1: how warm is a nest and who hatches? Part 2: what a seagrass reef can feed over the decades.

Beach and nest

Turtle biology

Reef and time

Nest results

Sand temperature through the year (depth vs day)

Nest temperature during incubation

Sex ratio and hatch success across the season

Population and seagrass

Experiments

Independent numerical checks

Controls

Drag / one finger: orbit; wheel / pinch: zoom. Presets change several sliders together.
Nest sliders act at once (the nest panel updates instantly); the population panel replays from year 0 whenever the sex ratio, hatch success or reef health changes.
Time scale = simulated years per real second.

The science

Sand temperature. A buried clutch feels the damped, delayed annual temperature wave of the sand: T(z,t) = T̄ + A e^−z/δ cos(ω(t − t₀) − z/δ), δ = √(2α/ω) with α = 3×10⁻⁷ m²/s (about 1.7 m for the annual wave). Shade lowers the mean by 2.5 °C and the amplitude by 25 %, dark sand adds 1.5 °C, climate warming adds ΔT. Late in development the embryos warm the nest (metabolic heating, up to +1.5 °C).

Development and sex. Development speed dθ/dt = 2^(T−29)/10/55 d (55 d at 29 °C, Q₁₀ = 2). Sex is set by the mean temperature in the middle third of development (θ from 1/3 to 2/3): P(female) = 1/(1 + e^{−(T−T_piv)/s)}, s = TRT/(2 ln 19), so 5 % to 95 % female spans the transitional range. Hatch success falls with the peak nest temperature: 0.92/(1 + e^{(T_max−35)/0.7)}.

Population. Seven stages (first-year, juvenile, subadult, adult, split by sex). One year of food-limited reef: seagrass dS/dt = rS(1 − S/K) − cN S/(h + S), K = reef health; food satisfaction φ scales survival (φ^0.4). Females breed every 3 years, 4 clutches of 110 eggs; mating success 1 − e^{−3·males/females} (so extreme female bias lowers fertile eggs); first-year survival is Beverton-Holt crowded. The matrix eigenvalue λ is the growth rate in a healthy, uncrowded reef.

Honest simplifications. Sand heat is a one-dimensional analytic wave (no rain, no moisture, no daily cycle, no beach slope); a single temperature for sex and for hatching; all demographic rates are illustrative round numbers in the right order of magnitude, not a fit to a particular stock; migration, bycatch, predators and nest loss are not modelled. Results show how the pieces interact, not a forecast for any real beach.

Models built with Blender (turtle, corals, fish, seagrass, reef floor) and rendered with Three.js.