Environmental conditions within the intertidal environment are inherently variable, and this variability may prove stressful to intertidal residents. However, survival and reproductive success in the intertidal can be improved through the possession of behavioral, physiological, or morphological adaptations that minimize the impact of environmental stress. Encapsulated embryos deposited into the intertidal are at a high risk of mortality due to their sessile nature, and are therefore obliged to rely on their own physiological adaptations, protective characteristics of the egg mass in which they are contained, symbioses with other marine species, or maternal choices regarding deposition site, to keep stress at tolerable levels. Microscale environmental variability, as well as variability among habitats, can result in within- and among- population differences in egg mass characteristics. I investigated differences in aspects of egg mass morphology, as well as the impact of deposition site on algal growth on egg masses, using two species of cephalaspidean mollusc collected from three intertidal populations on San Juan Island, Washington. Numerous characteristics related to egg mass construction differed significantly among populations, presumably in response to differences in environmental conditions among habitats. Differences in the algal densities of egg masses were explained by differences in the biochemical composition of egg masses deposited by different adult populations. Differences in algal densities of egg masses collected from different deposition sites within a single habitat indicated that vertical placement in the water column when immersed played a larger role in influencing the algal densities of egg masses than the particular substrate on which they were deposited. Finally, attempts to investigate differences in heat-shock protein (Hsp70) induction temperature among populations were curtailed by the lack of a primary antibody capable of differentiation between the constitutive and inducible isoforms of the Hsps of interest; however, methodologically useful information regarding antibody suitability was obtained.