An aspect of climate change in California has been an increase in the intensity and frequency of winter storms. Disturbance from storms is a major source of variation in the standing biomass of the giant kelp Macrocystis pyrifera, a competitive dominant on shallow reefs that forms a dense overstory canopy at the sea surface. Climate induced changes in the standing biomass of Macrocystis are expected to have a profound effect on the assemblage of subordinate understory macroalgae. The extent to which the understory assemblage is able to compensate for the loss of production by Macrocystis due to increased storm disturbance is largely unknown. To assess this phenomenon we developed non-destructive methods for measuring understory algal biomass and a bio-optical model for measuring net primary production of the kelp forest understory that incorporates the biomass and photosynthetic efficiencies of understory species and bottom irradiance. These methodological tools are being used to compare short and long-term changes in the biomass and productivity of the algal understory in response to the experimental removal of Macrocystis designed to mimic losses of giant kelp due to winter storms.