FCP proteins are the major LH complexes of marine photosynthetic diatoms that contribute large amounts to the global biomass. Although the FCP complexes from diatoms belong to the same class of LH proteins as those of higher plants , their photophysical properties differ significantly because they contain different types and amounts of pigments. So far, FCP complexes have not been studied extensively from an atomistic point of view since the respective crystal structures from two different organisms (P. tricornutum 7 and C. gracilis ) have only been solved recently. FCP complexes contain Chl-a/c and the carotenoids Fx and Ddx. On one hand, the Chl network needs to control the excitation energy transfer from the peripherical entities towards the reaction centers of the PSII/PSI complexes. On the other hand, carotenoids participate in the regulation of the photoprotective mechanism in the diatoms and can release excess energy as heat upon excess illumination on the turbulent ocean surface.