One promising strategy to reduce climate-polluting methane emissions from livestock is the recent application of seaweed as feedstock in ruminant animals. Bromoform (CHBr3), is a relatively common chemical constituent of seaweeds and has been shown to be the likely active ingredient responsible for methanogen inhibition in cattle and sheep. Most notably this observation has been found in the red alga Asparagopsis taxiformis where bromoform concentration is relatively high compared to other seaweeds. However, Asparagopsis sp. has thus far proven difficult to culture due to some intrinsic traits of the genus. This study investigates an alternative seaweed Gracilaria parvispora as a viable option for scaled production of bromoform containing seaweed. Given the apparent importance of bormoform in seaweed for reducing methane emissions this study expanded on benchtop Asparagopsis experiments assessing bromoform emissions to G. parvispora. This pilot scale study uses twelve 350 liter conical bottom tanks with untreated flow-through seawater exposed to natural light. Independent variables of interest were irradiance, water temperature, culture time, and immersion time. The series of experiments lasted 6 weeks each with tissue samples taken throughout the experiment. Tissue samples were freeze dried and bromoform extracted using methanol quantified with gas chromatography.
We found that bromoform, a photosynthate, has a positive relationship with temperature and irradiance with a maximum of 503 μg/mg DWbiomass. However, growth (%/day) was negatively impacted by increased light and temperature. A principal finding in this study was the time needed to increase bromoform concentrations. We have shown that bromoform content can increase as much as 4X from sunrise to the irradiance maximum (< 5 hours). These findings will help inform seaweed culture efforts for the purpose of methane mitigation in ruminant livestock by outlining growth and harvesting conditions that maximize biomass and bromoform content intended for animal feed.