14 páginas, 14 figurasThe tropical sponge Dysidea granulosa contains a number of symbiotic heterotrophicud bacteria and large quantities of the photosynthetic cyanobacterium Oscillatoria spongeliae, which areud reported to be responsible for the production of ecologically active polybrominated diphenyl ethersud (BDEs) in Dysidea spp. In order to better understand the relationship between these symbionts and theud production of BDEs, we looked at the variation in secondary chemistry in 3 populations of D. granulosaud and the relationship between cyanobacteria and secondary chemistry in the sponge, and experimentallyud assessed the role that depth and light play in this relationship by transplanting sponges in theud field. At a population scale, the concentration of BDEs is positively correlated with the concentration ofud chlorophyll a (chl a), both varying significantly between populations. Yet, in sponges experimentallyud transplanted to a deeper site, the concentration of chl a decreased significantly while BDE concentrationud remained stable. We specifically tested the importance of light in determining levels of symbiontsud and BDEs by placing sponges under transparent, UV-opaque, and black Plexiglas plates. After 5 wk,ud levels of BDEs and chl a had decreased significantly, although these trends differed between lightud treatment, suggesting a lack of direct correlation between BDEs and cyanobacterial populations. Thisud was also supported by a within-sponge analysis of chl a and BDEs, since high levels of compoundsud were found in the choanosome of the sponge, whereas chl a and cyanobacterial contents were minimal.ud Our data suggest that the relationship between the levels of BDEs in D. granulosa and its photosyntheticud symbionts is more complex than expected. Variation in the levels of secondary metabolitesud and symbionts seems to be related at a population scale, but unrelated at an individual scale.Peer reviewe