The biochemistry of fatty acids (FA) can be affected by a number of factors, including environmental temperature, which may affect the way FAs are physiologically metabolized. In this study, we investigated FAs in Pachygrapsus crassipes, in relation to environmental temperatures in southern California. Although there was a trend toward differences in FA abundances in the hepatopancreas of females compared with those found in the hepatopancreas of males, these differences were not significant through most of the year. The sampling month influenced changes in the abundances of both individual FAs (identities) and FA saturation categories (saturated  =  SAFA, monounsaturated  =  MUFA, polyunsaturated  =  PUFA). The abundances of palmitoleic acid, palmitic acid, and docosahexaenoic acid were found to fluctuate significantly over time, although this fluctuation did not appear to be directly influenced by temperature since an increase in FA abundance between February and April preceded an increase in temperature. In all months except for June, PUFAs dominated the FA profile. Changes in FAs may be an acclimatory mechanism used by P. crassipes to take advantage of specific biochemical properties of FAs. We conclude that, while temperature may affect FA abundance and composition, other underlying factors, such as changes in day length, food availability, molting, mating and reproduction, may also influence FA abundances in P. crassipes from southern California.