Temperature and pH fluctuations in the intertidal rock pool habitat of juvenile Heliocidaris erythrogramma were monitored in situ during the time that the larvae settle out of the plankton and when the early post-metamorphic juveniles reside in the pools (summer to early-autumn). Temperatures varied up to 8˚C between diel cycles, with a minimum of 15.5˚C during night time low tides and a maximum of 27˚C during daytime low tides. pH varied by 0.36 pHNIST units, with extremes of pH 8.38 pre-sunset and 7.95 pre-dawn. These data were used to place the investigation on the effects of temperature and pH on juvenile H. erythrogramma in context with current and near-future (2100: +4˚C/25˚C, -0.3 pH units/pH 7.8) environmental conditions. Juveniles were exposed to two temperature (21 & 25˚C) and pHNIST (8.1 & 7.8). The extreme pH treatments 7.2 and 6.9 were used to assess tolerance levels of juvenile growth. These treatments were used in cross-factorial experiments in all combinations. Negative effects on skeleton growth (test diameter, spine number, pore size) were largely restricted to the lowest pH treatments.