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Reproductive output (RO) is commonly used as a proxy for reproductive effort (RE) among Brachyuran crabs and other marine invertebrates, and so far no attempt has been made to incorporate the cost of brooding into RE to obtain a more reliable estimate of reproductive investment, nor to compare it along a temperature (latitudinal) gradient. We compared RO among 3 sites (ca. 20, 30 and 40 S, reflecting mean annual sea-surface temperatures of 18, 14 and 10 C, respectively), and the cost of brooding (oxygen provision) at those temperatures, in order to obtain a more reliable pattern of reproductive investment along an extended latitudinal gradient. A total of 187 brooding females of Cancer setosus were collected to estimate RO. Fecundity, volume and weight of the embryos, and embryo losses were also estimated. Laboratory experiments were carried out at the characteristic temperatures of those sites …