Variation in sand composition at the individual beach level is an important factor for hatching success and hatchling phenotype that does not appear to have been previously investigated. We studied variation in intrabeach substrate composition in an important loggerhead turtle (Caretta caretta) nesting colony on the island of Maio, Cabo Verde, and examined its relationship with embryonic development success, hatchling phenotype, and hatchling vitality. Thirty-two nests from different females were studied under experimental conditions, controlling for beach position, depth, humidity, and temperature in a randomized block design. Two sand treatments corresponding to 2 types of sand from the same beach were used. While nesting females selected nesting sites indiscriminately between substrate types, their nests differed significantly in all variables measured for reproductive success (hatching success, hatchling size, and hatchling agility) between the 2 sand types. Therefore, the intrabeach observations of substrate phenotype of progeny found here could differentially affect offspring survival. The effects of choosing different nesting sites will generally act to spread the probability of selective pressures on embryos. Variation in reproductive success was due to differences between substrate types within the beach rather than the location of nests within the beach. The importance of determining sand types with the highest hatching success, even within the same beach, should be greatest in colonies or populations highly threatened with extinction, where the hatching success of each nest becomes of utmost importance.