Global climate change is increasing ocean temperature and pCO2 in coastal communities. Research in this field has largely focused on how these changes will impact early life stages of calcifying organisms, but effects on non-calcareous organisms are understudied despite their prevalence in many coastal ecosystems. In Chapter 1, I investigated how present-day and near-future levels of temperature (12 °C vs. 15 °C, respectively) and CO2 (400 _atm pCO2 vs. 1500 _atm pCO2, respectively) influence zoospore settlement, gametophyte survival and growth, and sporophyte production of the giant kelp, Macrocystis pyrifera. My results indicate that zoospore settlement was reduced in the elevated temperature and the combined elevated temperature and pCO2 treatments. Although elevated pCO2 and temperature cumulatively inhibited zoospore settlement, elevated pCO2 mitigated the effects of increased temperatures on gametophytes and sporophytes, and enhanced their overall survival under present-day temperatures. In Chapter 2, I examined how elevated pCO2, temperature, and ambient nitrate availability influence photosynthetic performance in rhodoliths (Experiment 1), three juvenile kelp species during a prolonged warming event (Experiment 2), and the mature canopy blades of two kelp species (Experiment 3). A combination of P-I curves and eCA activity assays were used to measure changes in photosynthetic performance. Elevated pCO2 doubled Pmax and IK in rhodoliths, but did not affect _. Elevated pCO2 also increased Pmax and eCA activity in all juvenile kelp species, however _ of juvenile kelps was greatest in 400 _atm seawater. IK did not differ among species or pCO2 treatments. In mature canopy blades, Pmax and _ of Egregia menziesii were two-fold and five-fold greater than in M. pyrifera, respectively. Conversely, IK and eCA activity were three-fold and 10% greater in M. pyrifera than in E. menziesii, respectively. NO3- enrichment facilitated HCO3- uptake in both species, but only E. menziesii exhibited inefficient HCO3- use relative to M. pyrifera. Although coastal ecosystems are regulated by the same suite of factors, these experiments demonstrate the range of responses we can expect among species and life stages in a changing ocean. However, further in situ, species-specific experiments are required to understand how global climate change will affect coastal ecosystems.