On the pigment-protein complexes, antenna, of the photosynthetic membranes relies the capacity of the primary producers to collect solar radiation and to transfer the excitation energy to the reaction centre of the two photosystems, where takes place its transformation into chemical energy. In order to favour an efficient excitation transfer and a continuous flow of electrons, evolution has generated a large diversity of antenna collectors, which also must photoprotect the photosynthetic apparatus from the excess of energy absorbed through the formation of “quenchers”. Efficient excitation transfer has been achieved at expenses of reducing pigment ability to collect light. A phenomenon called “packaging effect” identified first for oceanographers while describing the variability in the inherent optical properties of phytoplankton, has found that photosynthetic pigments organized in alive structures are very inefficient to collect light due to self-shading. Multiple scattering of light has allowed counterbalancing the packaging effect, thanks to the enhancement in pigment absorption produced by the enlargement of the photon optical path. Multiple scattering, then, has mediated the design of a large biological diversity of solutions all of them led to the generation of efficient solar energy collectors. The establishment of mutualistic relationships with non-photosynthetic organisms able to supply scatting structures can also be explained by the capacity of multiple scattering to increase the photosynthetic performance of the new holobiont optimizing the use of the limiting resources. Here are presented a few examples of successful symbiotic relationships between invertebrates and algae, where the ability of (1) the highly reflective aragonite surfaces of the coral skeleton, or (2) the sponge silica spicula have allowed the appearance of the most efficient light collectors in nature, and explains the evolutionary and ecological success of these extremely efficient symbiotic relationships. This comparative study also highlights the capacity of multiple scattering to explain the origin itself of multicellularity in photosynthetic organisms.