Symbiosis has been an important factor in evolution, and continues to drive speciation and allows organisms to fill new ecological niches. Symbiotic relationships in which both partners benefit from the association, or mutualisms, are ubiquitous in both terrestrial and aquatic ecosystems. Many of the symbionts in these associations are photosynthetic algae or cyanobacteria that fix carbon through photosynthesis and translocate a portion of this energy to their hosts. Host organisms utilize this fixed carbon for a variety of physiological processes, including growth and development, thus, photosynthetically-fixed carbon is vital for many hosts. The following chapters will describe carbon fixation and translocation in two algal symbioses: the freshwater association between the alga Oophila and the eggs of Ambystoma maculatum salmanders, and the relationship between the dinoflagellate Symbiodinium and marine zoanthids. These chapters will discuss carbon flux in symbiosis, and reveal some of the ways in which environmental factors alter photosynthesis in algal mutualisms. / Biology