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Abstract During the cultivation of Ulva fenestrata in a land-based aquaculture system, the colonisation of the water tanks’ surfaces and eventually the macroalgal biomass by the biofouling diatom Fragilariopsis oceanica compromises the production process. Since germanium dioxide (GeO 2 ) is an effective growth inhibitor of diatoms, this study aimed to understand how it affects the presence of F. oceanica and the photosynthesis and growth of U. fenestrata as a primary parameter contribution to the biomass production. A toxicological dose-response experiment showed that the diatom’s growth was inhibited at the low GeO 2 concentration of 0.014 mg l −1 . In contrast, the photosynthetic performances and growth rates of U. fenestrata remained unaffected under a wide GeO 2 concentration range (0.022–2.235 mg l −1 ) in small- and large-scale experiments in 1-l glass beakers and 100-l Plexiglass water tanks, respectively. In the latter, the diatom density in the tanks was reduced by 40 %. The costs arising from the use of GeO 2 can range between €2.35 and €8.35 kg −1 fresh weight of produced U. fenestrata biomass under growth conditions resulting in growth rates of 20 and 11.5 % d −1 , respectively. GeO 2 is an effective agent to control biofouling diatoms such as F. oceanica during the land-based biomass production of U. fenestrata .
Ralf Rautenberger (Fri,) studied this question.